Field of the invention The invention is especially related to lithium ion batteries and the coating of a separator film and/or electrodes, which are part of the structure of the batteries. The invention is further related to the coating of such separator films and/or electrodes using so-called pulse laser technology.

Background of the invention As the need for mobile devices, electrically operated cars and storing of energy grows, the need for the development of battery technology has increased. Li ion batteries have been successful in very many applications, due to their especially good energy density and recharging possibilities compared to, among others, Ni- CD and Ni-Mn batteries. Li ion battery technology is based on a positive cathode, in which active material is, for example, transition metal oxide, and a carbon-based negative anode. A mi- croporous polymeric separator is used between the anode and cathode to prevent the contact between the anode and cathode, but nevertheless allowing the ions to move through the separator film. In addition to ion permeability, the separator film also has to possess good mechanical strength and long-term thermal and chemical resistance.

It has been attempted to increase the thermal, chemical and mechanical resistance of the separator film by coating it using different methods. As a polymeric separator film melts, for example, due to local thermal overload or mechanical failure, a ce- ramie coating prevents or decelerates the contact between the anode and cathode and, as a consequence, the generation of a short circuit, fire or explosion. In addition, with coatings it has been attempted to contribute to the absorption and even distribution of electrolytes to the separator film and elsewhere into the structures of the battery in connection with the battery's manufacture. Alternatively, the coating of, for example, cathode surfaces can also be used to minimize detrimental electro-chemical and chemical reactions as well as damage of materials used in batteries during its use. Further, coating a cathode or anode surface with a ceramic film can prevent or decelerate the contact of cathode and anode and short circuit in cases of damage.

When coating a cathode, anode or separator film it must be ensured that the coating does not close the bus between the anode and cathode, considerably weakening or fully preventing the diffusion of ions and the operation of the battery.

Among others, slurry coating, i.e. the use of the combination of a polymeric binding agent and inorganic material has been used for coating separator films, in which the binding agent helps to bind the particles in the inorganic material with each other and also to the separator film. One restriction of this solution is its relatively large thickness, generally > 3 pm, which, especially in the case of thin polymeric separator films, increases the relative share of this inactive material in Li ion batteries and thus reduces the energy density. In addition, the binding agent may block the pores in the polymeric film, it may react with battery materials or weaken in use so that the coating may detach from the polymeric film. This method is suitable mainly for the manufacture of porous coatings with a thickness of 3 - 5 pm, and it is not suited for the manufacture of dense and thin coatings with a thickness of less than 100 pm.

The development of alternative, thin but reliable coating methods, which make possible the operation of a Li ion battery, would make possible the increase in the en- ergy density of batteries, compared to thick coatings, because the relative share of non-active materials can be reduced, compared to, for example, the slurry coating mentioned earlier.

Atomic Layer Deposition (ALD) has also been proposed especially for the coating of separator films and electrodes, which is a conformal method well suited for the manufacture of thin and dense coatings. A restriction with the method is its relatively poor productivity and relatively high coating temperature, which may restrict the coating of at least certain polymer types. The melting point of several polymer types used in separator films is in the range of 130 - 160 °C, and the temperature's increase to this range in the coating may melt or otherwise damage the polymer film and impair its functionality.

Because of the conformality of the ALD method, the coating is also generated onto the surface of pores in the polymer film or electrodes even in the interior of the membrane, which may block or narrow pores of the size of 30 - 100 nm. Conformal coating refers to a coating process, in which the coating penetrates into and forms a coating onto almost all surfaces of the base material in the coating chamber, including the pore surfaces where the coating material has room to penetrate. As the thickness of the coating is 10 - 30 nm, and as the coating is formed onto the pore surfaces even very deep inside the porous polymer film, the film permeability may weaken considerably, which prevents, for example, the even and fast absorption of the electrolyte into the film structure in connection with the manufacture of batteries.

For their functionality, it is important in the Li ion batteries that the electrode material and the separator film are porous and that the electrolyte is evenly distributed over the entire area. Even sufficient porosity is a prerequisite for the even distribution of the electrolyte in the separator film. If the coating method used reduces the porosity thus reducing permeability, this weakens the operation of the Li ion battery.

Other possible methods for the manufacture of thin film coatings to coat separator films or electrodes in Li ion batteries are e.g. several physical and chemical vapour deposition methods (PVD and CVD). Their use in the coating of polymer films is, nevertheless, restricted by e.g. high thermal load and particles generating into the coating. Further, chemical vapour deposition methods, like atomic layer methods, are conformal by their nature.

The manufacture of a dense, non-conformal very thin coating (typically 10 - 50 nm) suitable for the coating of a separator film or electrode (anode or cathode) used in Li ion batteries makes it possible to increase the thermal, mechanical and chemical resistance of Li ion batteries, which contributes to the improvement of the performance, safety and service life of current and future Li ion battery solutions. The coating can be used either in a separator film, electrodes, or both, and because of the thinness of the coating, the method makes possible, for example, better func- tionality and energy density of Li ion batteries, for example, compared to protective coatings with a thickness of several micrometres.

Summary of the invention

In the present invention, there is presented a method for the coating of separator films or electrodes in Li ion batteries with a thin and dense oxide coating, making use of so-called non-conformal pulsed laser deposition (PLD) technology and laser pulses with ultra-short duration. The coating improves the thermal, chemical and mechanical resistance of the structure without a substantial increase in the relative share of the non-active battery material (separator film and its coating). In addition, the coating reduces the shrinkage of the porous polymer membrane due to warming-up during use and contributes to the most efficient absorption and even distribution of the liquid electrolyte as possible. The coating is generated onto the surface of fibres in a porous polymer separator film, but leaves the areas between the fibres mainly uncoated, if the thickness of the coating is limited to less than 100 nm. An example of this is later illustrated in Figure 2. The manufacture of the coating does not considerably weaken the permeability or porosity of the polymer membrane nor does it cause considerable weakening of other functionality, for example, due to thermal or mechanical impacts. Metal oxides, such as aluminium oxide or silicon oxide are used as the coating material, the mechanical properties, temperature resistance and chemical resistance of which are suited for the coating of separator films in Li ion batteries or for example, for the coating of a cathode material layer. The price of many metal oxides is sufficiently low for mass production, and their availability as target materials and applica- bility for pulsed laser technology are good.

In pulsed laser technology, the thickness of the coating can be controlled sufficiently accurately on an area of < 100 nm so that it is possible to produce in a controlled manner a sufficiently thick coating onto the surface of a porous polymeric separator film to produce the above described functional features, but simultaneously avoiding the blocking of the porous structure.

The PLD method is non-conformal, i.e. coating is formed principally onto those surfaces, from which there is direct visibility to the target material, from which laser pulses detach material to be coated. In the PLD method, coating does not penetrate inside the pores to a considerable extent. The difference between the conformal and non-conformal coating when coating porous materials is illustrated later in Figure 5.

The coating can also be used together with coatings fabricated in another way; for example, with thicker porous coatings, with which, for example, even better resistance against shrinkage or mechanical damages can be achieved. In this case, for example, a thin dense coating material can be manufactured onto a separator film on the side of cathode material, and a porous thick coating can be manufactured onto the other surface of the separator film so that both coatings provide functional benefits to the separator film.

A thin coating can be produced with different process parametres, and thus the process can be adjusted to suit the manufacture of a thin dense coating. It is essential to avoid thermal damages in the polymer film by reducing the thermal load applied to it and thermal and mechanical load caused by the material flow and to produce an essentially atomised material flow to produce a thin dense metal oxide coating without extensive areas which contain too thick or too large particles. Thermal load causes the mechanical properties and permeability of the polymer film to weaken and macroscopic deformations. Too thick a coating containing many large particles reduces the porosity and permeability of the polymer film.

Alternative processing methods making use of short pulsed laser technology are e.g. thermal vapourisation, cold ablation and combinations of these. The material detachment mechanism of these and the thermal load caused by the generating material flow are different, which has to be taken into account in the process control and, for example, in the thickness of the coating produced at one time. Further, the quantity of energy required by the methods for a certain transferred material volume is different. An advantage of cold ablation is, among others, that the rise of temper- ature in the target material is smaller, which reduces the need to cool the target and the coating station and lowers the thermal load caused by radiation heat in the object to be coated. In all cases it is especially attempted to avoid forming molten or hot particles, which may damage the polymer film and decrease its permeability.

The method of the invention has the following advantages: i. A dense metal oxide coating can be manufactured onto the surface of a porous polymer firm without thermal or mechanical damage to the film. ii. A thin non-conformal metal oxide film with a thickness of less than 100 nm can be manufactured so that the pores of the porous polymer film do not close by the impact of the coating as the coating is principally formed onto the outer surface of the polymer fibres.

iii. The chemical resistance and service life of an Li ion battery can be improved, thus reducing the lifecycle costs of solutions utilising Li ion batteries.

iv. The absorption of the electrolyte into the separator film can be improved and thus ensure the distribution of the electrolyte in the Li ion battery as well and evenly as possible.

v. Benefits related to the chemical, mechanical and thermal resistance can be achieved with a considerably smaller amount of non-active material, compared, for example, to slurry coating, which improves the energy den- sity of batteries. vi. Better productivity can be achieved than, for example, with the ALD technology.

vii. Thin coatings with a thickness of < 100 nm can be achieved as thin and homogenous.

viii. With the same method (pulsed laser technology), it is possible to manufacture both dense thin films and thick porous films onto the surface of both a polymeric separator film and electrodes,

ix. The method can be utilised both in the manufacture of sheets and in a roll-to-roll type manufacture. Short description of the drawings

Figure 1 illustrates the principle of the coating process with different physical components in an example of the invention;

Figure 2 illustrates an exemplary structure of a coated separator film, i.e. a dense coating on the outer surface of a porous polymer film so that the coating is principally on the outer surface of polymer fibres;

Figure 3 illustrates an example of the so-called roll-to-roll method relating to the coating process;

Figure 4 illustrates a principle for forming a fan-shaped rectilinear laser pulse front with an apparatus arrangement of the invention;

Figure 5 illustrates the principled difference between a conformal and non-conformal coating;

Figure 6 illustrates an exemplary intensity distribution viewed one-dimensionally for an individual laser pulse;

Figure 7 illustrates an example of a possible flat-top distribution; and

Figure 8 illustrates an exemplary situation of the superposition of consecutive laser pulses on a laser scanning line.

Detailed description of the invention

In a method of the invention there is manufactured a polymeric separator film coated with thin dense oxide, in which the oxide coating protects mainly the outer surface of the polymeric separator film, but does not completely close the gaps between the polymeric fibres or the pores in the polymeric film, thus making possible the penetration of the electrolyte into the separator film and the diffusion of ions during the operation of the battery. The method can also be utilised in the coating of an electrode (cathode or anode) with a respective coating. The method can be utilised together with the manufacture of thick porous coatings. In this case, thick coatings can be fabricated, for example, with pulsed laser technology, other vapour deposition methods or slurry coating.

A dense metal oxide coating is fabricated by using ultra-short laser pulses produced with pulsed laser technology, the laser pulses detaching the material forming the coating from the target material in a desired manner. The pulsed laser technology is a so-called non-conformal method, i.e. the coating is generated mainly onto the surfaces, onto which the material flow generating from the target material can directly transfer. Deviating from the conformal methods, the material flow does not efficiently coat pores, notches or the back or side sections of the object to be coated. Some coating may indeed be generated into the cavities and notches of the surface directly impacted by the material flow as far as the material flow can directly transfer there from the target.

In the method of the invention, a fine-grained material flow is formed from the target material onto the surface of the material to be coated so that the coating forms essentially a dense, non-porous layer onto the outer surface of the substrate and onto the outer surface of the fibres or particles in the material. Because both the separator film and the electrode materials in Li ion batteries must be porous, filling of the pores with the coating must be prevented, which is typical in conformal methods, such as atomic layer coating and chemical vapour deposition.

In the coating solution of the invention, the objective is to coat only the outermost surface layer of a separator film and/or cathode, which surfaces without the coating would be in contact with each other after the manufacture of the Li ion battery. It is attempted to limit the generation of the coating inside the cavities and notches in the porous structure to the minimum, which is considerably easier in the pulsed laser deposition than, for example, in atomic layer coating or chemical vapour deposition.

An objective is that the particle content in the material flow from the target to the base is minimised in the coating, using the process parametres to attempt to promote the generation of atomic, possibly partly ionised material as the result of abla- tion achieved by the laser pulses. The material may also have some small particles, which are formed either in ablation or in the material flow from the target toward the object to be coated, but the generation of very small particles and their occasional transfer onto the surface of the membrane does not essentially impair the quality of the coating. In the invention, it is especially attempted to avoid the generation of large particles of over 1000 nm and molten drops with appropriately selected process parametres, such as sufficiently short laser pulse lengths and correct pulse energy density and total pulse energy. For the functionality of the coating, it can contain some particles, but essentially the material flow should be based on atom- ised material.

The process parametres of the pulsed laser source are adjusted so that a continuous and even material flow, however, with relatively low density is achieved from the target to the substrate without momentary high energy density, material density or thermal load. Owing to the sufficiently low and even material flow density and small particle quantity, the thickness of the coating can be adjusted relatively precisely even in the thickness range of 5 - 50 nm. In order to achieve a low material flow density, the laser pulse length and energy must be low and the repetition frequency of the laser pulses very high.

Especially when coating thermosensitive materials, such as polymers, and to be able to avoid the melting of the target material and the generation of molten particles, especially large molten particles, the pulse length must be limited to be as short as possible. The laser pulse length can be adjusted so that the laser pulse length would be shorter than the so-called electron-phonon-relaxation time so that the transfer of energy in the target material to the matrix can be minimised and circum- stances corresponding as closely as possible to the so-called cold ablation can be achieved or at least the generation of too large a molten area and the transfer of large molten particles to the material flux can be avoided. At the same time, it is possible to reduce the warming-up of the coating chamber caused by the heating of the target material and the extensive temperature rise of the chamber, target mate- rial and the components therein. The laser pulse length should be limited to under 20 ps, and in the case of aluminium and silicon oxide, preferably to under 2 ps.

The total energy density (J/cm ² ) generated by the laser pulses must be sufficiently high to exceed the so-called ablation threshold of the material used as the target material. If the ablation threshold is not exceeded, the laser pulses are not able to atomise the target material, and material detaches from it only through melting or micro exfoliation, which does not provide the desired thin, dense oxide layer. For example, with aluminium oxide, the energy density must be typically at least in the range of 1 .5 - 2 J/cm ² in the wavelength range of 1030 nm, if it is desired to ensure the atomisation of the material. The ablation threshold decreases along with the decrease in wavelength. It is often desired to clearly exceed the wavelength to ensure that the energy level of the material flow is sufficient after ablation, that the material flow stays atomised and that the formation of particles in the material flow is prevented.

Coating is performed under negative pressure in a coating chamber, in which the pressure of background gas is sufficiently low to prevent the material detached from the target from forming particles. As the gas pressure rises, the atoms and particles in the material flow collide with gas molecules, contributing to the formation of particles, which must be avoided in the case of thin coatings. Typically, a background gas pressure of under 10 ^"3 mbar is to be endeavoured, preferably under 10 ^"5 mbar, when the objective is to fabricate dense and essentially particle-free coatings. The lower the density of the material flow detaching from the target, the higher is the background gas pressure allowed without promoting the formation of particles and vice versa. By adjusting the density of oxide material in the material flow generating on the target, controlling the pulse length and pulse energy and adjusting the background pressure, the material flow can be kept as fine-grained as possible without particle formation in the material flow from the target to the base material.

In the method of the invention it is essential that the material detached from the target is as fine-grained as possible, i.e. its transfer occurs essentially as atomised, vapourised, very small particles or clusters, and a combination of these. Thus, it is possible to reliably fabricate dense, thin coatings with a thickness of less than 100 nm and to avoid the blocking of nano- and micropores in the separator films or cathode material. Simultaneously it is important that when coating porous polymer films, the thermal load produced by the coating does not cause damage, melting or excessive structural changes in the polymer film. Especially large molten particles may cause cavities and thermomechanical damages into the polymer films. Likewise, too large a material flow causing an energetic or large thermal load can damage especially a porous polymer membrane. In order to avoid thermal damages in the polymer membrane, the material flow must be made as even as possible, avoiding significant thermal load peaks in it or large quantities of hot or molten particles. This is contributed by quickly repeating laser pulsing and by limiting the pulse energy and pulse length. Further, increase in thermal load may cause excessive heating in the target material or coating chamber and its components, which can be minimised by adjusting the process.

In addition to atomisation and/or vapourisation created by individual, essentially non-superimposed laser pulses, a material flux from the target to the separator film or electrode to be coated can be achieved by focusing onto the same area of the target surface several lower-energy pulses with the same repetition frequency, the accumulation of energy of which induces the atomisation or vapourisation of the material. In this case, the energy and intensity of individual laser pulses used are so small that it would not cause material to detach from the target, but a cumulative energy accumulation caused by several low-energy laser pulses makes the material to detach, for example, by vapourisation.

This type of a process can be thermal, but if the generation of large drops can be avoided, this can be utilised in the fabrication of thin coatings. In this case it must be possible to prevent the generation of large molten drops by minimising the heat transfer to the target material and by limiting the growth of the molten area to the minimum by minimising pulse energy and pulse length and by controlling energy distribution on the target surface. When using very high repetition frequencies and several pulses focused onto the same area of the target surface, the pulse energy can be relatively low, even under 4 J, and the average energy density can be under 100 mJ/cm ² as several, even more than 500 laser pulses are focused on the same point of the target.

Intensity distributions of laser pulses are described later in connection with Figures 6 - 8.

The basic principle of the coating process is described in the basic image of Figure 1 , in which the structural parts and directions of travel of the material involved in the coating process are shown in the level of principle. In Figure 1 , the energy source for the ablation process is the laser source 1 1 , from which laser light is guided as short pulses 1 towards the target material 13. On the surface of the target material 13, the laser pulses 12 cause material to detach from the target as atoms or ions, and partly as very small particles, which have been mentioned above. This way plasma and/or other material flow 14 is created, which extends towards the material 15 to be coated. The correct orientation can be implemented by placing the direction of the surface plane of the target material 13 appropriately so that the direction of motion energy releasing from the material detaching from the material in the form of plasma and/or other shape is towards the material 15 to be coated. The laser source 1 1 can naturally be transferred in relation to the target 13, or the angle of orientation of the laser beams in relation to the surface of the target 13 can be modified.

In Figure 2, there is illustrated an exemplary structure of a coated separator film, i.e. a dense coating 21 on the outer surface of a porous polymer film 22 so that the coating 21 is located mainly on the outer surface of the polymer fibres. The porous points in the polymer film operating as the base (substrate) are the points 23. The coating 21 is created onto the surface of the fibres in the porous polymer separator film 22, but the method leaves the areas between the fibres mainly uncoated, if the thickness of the coating 21 is restricted to be less than 100 nm. This can be seen in the coating 21 as visible aperture points in an otherwise dense coating structure.

In addition, a separate arrangement can be placed between the laser source 1 1 and target 13, with which the direction of the laser pulse front hitting the target 13 can be made uniform. To improve uniform quality and productivity, it would be advantageous to provide as wide a material flow as possible from the target to the base material. This can be performed in one example of the invention by disintegrating the laser pulses by rotating mirrors to form a laser pulse front on the same plane. This exemplary arrangement is illustrated in Figure 3. Instead of the target, the laser pulses 12 of the laser source 1 1 are guided to the rotating mirrors 31 , which can be, for example, a hexagonal and rotatable mirror surface similar to that shown in Figure 3. From the rotating mirrors 31 , the laser pulses 12 are reflected as a fan-shaped laser pulse formation (or laser beam distribution), and said reflected pulses are guided to a telecentric lens 32. By means of the telecentric lens 32, the laser pulse front can be directed to form an essentially rectilinear laser pulse front 33 and focused essentially on the same plane so that the laser pulses hit the target 13 in the same angle and same-sized. The angle in question is 90° in this example of Figure 3.

The coating of the invention can be utilised separately or together with other coatings and/or coating methods. For example, it can be combined with thick porous coatings, which are fabricated with pulsed laser technology, other manufacturing methods of thin films, or slurry coating to provide optimal protection and correct functionality.

Broadly, in one example used in the invention the vapourisation or atomisation of the target surface, and the transfer of the material from the target onto the surface of a polymer film or cathode material as a dense essentially non-conformal layer is achieved by laser pulses focused on the target, in which the timely duration of an individual laser pulse can be in the range of 0.1 - 20 ps.

In an embodiment of the invention, laser pulses can be generated on a repetition frequency, which is in the range of 100 kHz - 100 MHz. In an example of the invention, the pulse energy used in pulsed laser technology is 1—3 μϋ, which is generated on the repetition frequency of 40 MHz so that at least 1000 laser pulses are almost simultaneously targeted at one point of the target material. The material of the polymer film used can be, for example, polyethylene or polypropylene, and its thickness can be 5 - 30 pm and porosity 40 - 65 percent by volume.

In an example of the invention, the material to be coated is cathode material containing lithium (LCO, LFP, LTO, NMC), which is coated in accordance with the invention with a thin, dense aluminium-oxide coating with a thickness of less than 50 nm by using pulsed laser technology.

In one example of the invention, a porous separator film made of polyethylene is coated with dense aluminium oxide coating with a thickness of 20 nm, and the surface of cathode material facing it is coated with porous aluminium oxide with a thickness of approximately 1 pm. In an application laser ablation and coating occur in a vacuum chamber, in which the pressure is at most 10 ^"3 mbar.

In an application example, a dense oxide coating with a thickness of at most 100 nm is fabricated onto the one side of a polymeric separator film, and a thicker coating with a thickness of at least 300 nm and with a porosity of at least 30% is fabri- cated onto the opposite side using pulsed laser technology or some other method.

In an application example, a dense oxide coating is first fabricated onto the side of the polymeric separator film facing the cathode material, and a coating with a thickness of at least 300 nm and with a porosity of at least 30% is fabricated onto the opposite side using pulsed laser technology or some other method. In an application example, a dense oxide coating layer with a thickness of at most 100 nm is first fabricated onto one surface of a polymer membrane, and after this an oxide coating layer with a porosity of at least 30% and a thickness of at least 300 nm is fabricated onto the dense coating using pulsed laser technology.

In an application example, the separator film is well suited to be coated so that ma- terial is discharged from a roll to be coated to a desired width in a coating chamber. A basic view of this application alternative is shown in Figure 4. Material is targeted to a desired coating width from one or several coating sources so that material is continuously discharged from the roll to the coating, and after having passed the coating zone, the material is reassembled to a second roll. This method can be called a roll-to-roll method. In other words, the separator film 42 to be coated is originally wound on the roll 41 a. An ablation apparatus with its laser sources 1 1 and target materials 13 are included in the same way as what has been described above. The laser pulses 12 cause the material to detach 14 (in other words, in the form of a material flux) towards the material 42 to be coated, and as the result of attachment there is created the coated polymer film 43. The coated separator film 43 is allowed to wind around the second roll 41 b, the direction of motion of the film being from left to right in the case in Figure 4. The roll structures 41 a, 41 b can be driven by motors. The separator film to be coated can comprise the whole surface area seen in the direction of depth in the figure, or only a part of the surface. Likewise, in the direction of motion of the film a desired part (length) of the film can be selected for coating or alternatively the entire roll from start to finish can be gone through so that the whole roll is coated.

In Figure 5 there is illustrated the difference between the earlier described conformal and non-conformal coating method. In the conformal method (upper picture), coating material travels to the even sections 51 of the base surface, but also to the pores

52 opening on the edge surface of the base or film and to the inner surfaces of the straight and meandering cavities 53. In the upper picture, a tubular L-shaped cavity

53 is outlined with dashed lines, the cross-section of which in the vertical direction is seen as a circle with black edges. Because the conformal method is based on the free travel of a gaseous substance onto the surfaces of a solid material, the coating material attaches also to the pore pits 52 visible on the upper surface in addition to the inner surfaces of cavities 53 of different lengths; i.e. all places the gaseous substance has access to. The closed pores 54 inside the base material do thus not receive a coating onto their surfaces. It is to be noted that a coating of the conformal method is formed to all places where coating material can travel, as a layer of uniform thickness. In a non-conformal coating method (lower picture) the coating travels only to those points on the outer surface of the base or film, which have a direct connection to the ablation point on the target. Because the relation of the ablation point of the target to the surface of the base to be coated moves so that the so-called angle of incidence of the arriving material varies in relation to the plane of the base surface, the thickness of coating layers generated in the non-conformal coating varies at different points of the base surface depending on the time, for which each base surface point "sees" the ablation point. No coating is formed to the end of the cavity 57, from which there is no direct visual connection to the moving ablation point at any stage of the coating process. Naturally, coating does not travel to the closed pores 58 in the interior of the base material in this method, either. Instead, a thick coating layer is formed to the even sections 55 of the outer surface of the base, because these parts see the ablation point for a long time. In addition, a thinner coating layer is formed to the pores 56 opening to the outer surface, i.e. to the small pits of the surface, depending on the forms and depth of the pit. For example, in the separator films of batteries there are many long cavities in accordance with the pore type 57, which have points that remain uncoated. In the case of battery separator films this is an important characteristic, because the pores must not be blocked entirely, and thus it is essential that the coating principle of the invention is expressly non-conformal, for example, as the PLD method is.

In Figures 6 - 8 there are illustrated different intensity distributions for laser pulses, in which the location on the scanning line on the surface of the target is on the x- axis and the intensity is on the y-axis. Typically, the regional intensity distribution for laser pulses in a plane perpendicular to the direction of travel of the pulse follows the normal distribution, on average. In Figure 6, there is illustrated an exemplary intensity distribution viewed one-dimensionally for an individual laser pulse. The pulse size is determined typically either as FWHM (Full Width at Half Maximum) or as width on the intensity plane, which is 1/e ² of the intensity peak value. The pulse energy is measured from the whole pulse, and the average energy density is obtained by dividing the pulse energy by the area of the laser pulse, determined typically on the basis of the full width at half maximum or the 1 /e ² width. The local energy density varies on the laser pulse area in accordance with the intensity distribution.

In some cases, especially when detaching material with individual laser pulses, it can be advantageous to use laser pulses, the energy density of which is as even as possible, i.e. the intensity follows then the so-called flat-top distribution. In Figure 7, there is an example of a possible flat-top distribution. The quantity of laser pulses hitting one point is obtained by multiplying the repetition frequency of laser pulses by the time, which is needed for one laser pulse width measure to travel on the surface of the target with a set laser scanning velocity. In Figure 8, there is illustrated the superposition of successive laser pulses one-dimensionally on the laser scanning line. The accumulative impact of laser pulses depends at least on the number of pulses, repetition frequency, size and intensity distribution. As it has emerged above in many connections, the inventive idea of the invention comprises, in addition to the manufacturing method, the manufactured product, i.e. the coated separator film, cathode and/or anode material. Both the cathode and anode material can be coated with a dense coating with a thickness of under 100 nm or a porous coating with a thickness of at least 300 nm, using the laser ablation method. In addition, the inventive idea comprises the system, i.e. the apparatus for executing the coating to be carried out by PLD.

In an application of the invention, the air permeability method used can be, for example, a measurement executed by the so-called Gurley method. In the invention, the homogeneous quality of the thickness of the coating refers to the variation of thickness within set limits. For example, if the nominal desired thickness were 100 nm and homogeneous quality is ± 30%, in practice the thickness varies between 70 nm and 130 nm.

In an application of the invention, one coating layer can be manufactured in several parts, when needed. In this case, part of the coating can first be produced as one very thin layer onto a desired surface area, and after this, the coating can be repeated onto the same area. The method can also be executed more than twice onto the same polymer film area, and this way it is possible to produce a coating with a desired thickness from thinner partial coating layers. Because with this method a new partial coating layer can be attached tightly to the lower material surface, it cannot be distinguished from the finished coating obtained as the final result, of how many partial coating layers it has been fabricated. The final result is thus, for example, similar to Figure 2, in which the coating layer can have been fabricated of several partial coating layers made at different stages. In an application of the invention, the resistivity of the coated polymer film does not exceed 50% compared to an uncoated polymer film. This characteristic must be tested in a battery or a finished electrical pair so that the separator film of the battery has been absorbed with an electrolyte, i.e. the battery has to be in normal working order so that the travel of ions over the separator film is possible. The resistivity of the coated separator film can then be measured, and on the other hand, the resistivity of an uncoated separator film according to the state of the art can be measured, when the electrolyte has been absorbed in it. In this measurement, the resistivity of the coated polymer film is determined to be at most 50% bigger compared to the respective resistivity measurement with an uncoated separator film. In a way of a summary, the above-mentioned parts, steps, features and other characteristics of the invention expressed in another way, the concept of the invention comprises the following facts.

The invention deals with a method for the manufacture of a separator film for a Li ion battery, in which method

- laser pulses with a maximum duration of 20 ps are transmitted from the laser source to the target, which target comprises oxide, and as a consequence of which material is detached from the target by means of pulsed laser technology:

- a thick porous polymer film with a maximum thickness of 50 pm is placed in relation to the target so that the material detached from the target travels onto at least one surface or part of surface of the porous polymer film so that

- oxide attaches as a dense oxide coating layer with a maximum thickness of 100 nm onto at least one surface or part of surface of the porous polymer film, thus forming a separator film, and a characteristic of the invention is that the method used is non-conformal so that the forming oxide coating layer is generated onto the outer surface of the polymer film in places, from which there essentially is a direct visual connection to the ablation point of the target at the moment of coating attachment. In an application of the invention, the target comprises metal oxide.

In an application of the invention, the oxide in the target is aluminium oxide or silicon oxide.

In an application of the invention, the thickness of the oxide coating layer on the surface of the polymer film is at most 50 nm. In an application of the invention, the thickness of the oxide coating layer on the surface of the polymer film is at most 25 nm.

In an application of the invention, the thickness of the oxide coating layer forming onto the inner surfaces of the pore pits is thinner than elsewhere on the outer surface of the porous polymer film. In an application of the invention, the length of laser pulses transmitted by the laser source is at most 5 ps. In an application of the invention, the length of laser pulses transmitted by the laser source is at most 1 ps.

In an application of the invention, the repetition frequency of laser pulses transmitted by the laser source is in the range of 100 kHz - 100 MHz. In an application of the invention, laser pulses are targeted at the surface of the target so that the superposition of successive laser pulses is at most 10%.

In an application of the invention, the average energy density generated by the laser pulses on the surface of the target is 0.4 - 12.0 J/cm ²

In an application of the invention, the average density generated by the laser pulses on the surface of the target is 1 .5 - 5.0 J/cm ² .

In an application of the invention, laser pulses are targeted at the surface of the target so that at least two laser pulses are focused on the same point of the target surface so that their superposition is at least 50%.

In an application of the invention, the average energy density generated by an indi- vidual laser pulse on the surface of the target is 10 - 500 mJ/cm ²

In an application of the invention, the average energy density generated by an individual laser pulse on the surface of the target is 10 - 50 mJ/cm ²

In an application of the invention, the pulse energy of an individual laser pulse is at most 10 pJ. In an application of the invention, the pulse energy of an individual laser pulse is at most 4 pJ.

In an application of the invention, the target and the porous polymer film are placed inside the coating chamber, in which the pressure is at most 10 ^"3 mbar.

In an application of the invention, the target and the porous polymer film are placed inside the coating chamber, in which the pressure is at most 10 ^"5 mbar.

In an application of the invention, the porosity of the porous polymer film is in the range of 20 - 70 percentages by volume.

In an application of the invention, the cathode material or in addition to the cathode material also the separator film is coated. In an application of the invention, the oxide coating layer has an amorphic structure of at least 35%.

In an application of the invention, determined by an air permeability method, the permeability of the coated polymer film decreases at most 50% compared with an uncoated polymer film.

In an application of the invention, the total porosity of the coated polymer film does not decrease over 40% compared to an uncoated polymer film.

In an application of the invention, the coating of the polymer film does not cause the resistivity measured over the polymer film to increase over 50% compared to an uncoated polymer film, when the polymer film is part of a battery or an electro-chemical cell.

In an application of the invention, a dense oxide coating layer with a thickness of at most 100 nm is fabricated onto the first surface of the porous polymer film, and an oxide coating layer with at least 30% porosity and the thickness of 300 nm is fabri- cated onto the second, opposite side of the polymer film, using pulsed laser technology.

In an application of the invention, a dense oxide coating layer with a thickness of at most 100 nm is fabricated onto the first surface of the porous polymer film, and an oxide coating layer with at least 30% porosity and the thickness of 300 nm is fabri- cated onto the second, opposite side of the polymer film, using slurry technology by making use of binding agents to bind the metal oxide particles together and attached to the polymer film.

In an application of the invention, a dense oxide coating layer with a thickness of at most 100 nm is fabricated onto both surfaces of the polymer film. In an application of the invention, a dense oxide coating layer with a thickness of at most 100 nm is fabricated onto at least one surface of a porous polymer film, and an oxide coating layer with 30% porosity and a thickness of at most 300 nm is fabricated on top of this layer, using pulsed laser technology.

In an application of the invention, a dense oxide coating layer with a thickness of at most 100 nm is fabricated on the separator film onto the surface facing the cathode material, and an oxide coating layer with 30% porosity and a thickness of at most 300 nm is fabricated on the surface of the cathode material. In an application of the invention, laser pulses are guided from the laser source to rotating mirrors, in which there is formed a laser beam distribution, which is targeted at different points on the target surface for detaching the material.

In an application of the invention, the coating is fabricated with a roll-to-roll method so that a porous polymer film is guided in a band-type manner from the first roll to the first coating area, from the coating area to a next coating area, when needed, and from the last coating area in a finished form further to the second roll, and in which application the width of the polymer film band is in the range of 60 mm - 3000 mm, and in which there can be one or several coating areas. In an application of the invention, the polymer film band moves through the coating area or coating areas with a velocity of 300 mm/min.

In an application of the invention, the coating is fabricated so that the polymer film band moves through at least two coating areas continuously in order to fabricate layer structures by pulsed laser technology. In an application of the invention, the variation in the thickness of the oxide coating layer for an oxide coating layer fabricated from roll to roll is at most +/- 30%.

Further, the inventive idea of the invention includes a separator film for a Li ion battery obtained as the result of the manufacturing method, the separator film comprising a porous polymer film with a thickness of at most 50 nm and a dense oxide coating layer with a thickness of at most 100 nm. A characteristic of the separator film is that the attachment of the dense oxide coating layer onto the surface of the porous polymer film has been carried out by pulsed laser technology so that the method used is non-conformal so that the forming oxide coating layer is generated onto the outer surface of the porous polymer film to places, from which there essen- tially is a direct visual connection to the ablation point of the target at the moment of attachment of the coating.

The inventive idea of the invention further comprises a coated cathode material for Li ion batteries obtained as the result of another type of the manufacturing method, the coated cathode material comprising cathode material on top of metallic material, and on top of the cathode material there is provided a dense oxide coating layer, the thickness of which is at most 100 nm. A characteristic of the coated cathode material is that the attachment of the dense oxide coating material onto the cathode material is carried out by means of pulsed laser technology so that the method used is non-conformal so that the forming oxide coating layer is generated onto the outer surface of the cathode material to places, from which there essentially is a direct visual connection to the ablation point of the target at the moment of attachment of the coating.

The inventive idea of the invention further comprises a method (i.e. apparatus ap- plying PLD technology) for manufacturing a separator film for a Li ion battery using pulsed laser technology. The system in question comprises

- a laser source for transmitting laser pulses with a duration of at most 20 ps;

- rotating mirrors for forming a laser pulse front from the laser pulses transmitted by the laser source and for guiding it to the surface of the target;

- a target, which comprises oxide, and in which system material is detached from the target as the laser pulse front hits the target;

- a porous polymer film with a thickness of at most 50 pm placed in relation to the target so that the material detached from the target travels through the porous polymer film onto at least one surface or part of surface, in which by the system

- oxide attaches as a dense oxide coating layer with a thickness of at most 100 nm onto at least one surface or part of surface of the porous polymer film, thus forming a separator film; and in addition a characteristic of the system is that the method used is non-conformal so that the forming oxide coating layer is generated onto the outer surface of the porous polymer film to places, from which there essentially is a direct visual connection to the ablation point of the target at the moment of attachment of the coating.

In the invention, it is possible to combine individual features mentioned above and in the dependent claims into new combinations, in which two or several individual features can have been included in the same embodiment.

The present invention is not limited to the illustrated examples, but many variations are possible within the scope determined by the claims.