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Title:
LITHIUM ION BATTERIES AND ELECTRODES THEREFOR
Document Type and Number:
WIPO Patent Application WO/2012/131321
Kind Code:
A1
Abstract:
A method of making a lithium ion battery electrode material, comprises incorporating lithium into a nano-structured carbon material formed by :- i) providing a porous carbon material having porosity; ii) impregnating a metallic material capable of catalyzing carbon nano structure growth within the porosity of the porous carbon material of step i) to provide an impregnated porous carbon material; or providing an impregnated porous carbon material produced by such an impregnating step; iii) heating the impregnated porous carbon material of step ii) to a temperature sufficient to promote carbon nano structure growth within the porosity of the carbon material to provide a nano-structured carbon material.

Inventors:
CLARK RICHARD (US)
BOFF JAMES (GB)
Application Number:
PCT/GB2012/050551
Publication Date:
October 04, 2012
Filing Date:
March 14, 2012
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
MORGAN CRUCIBLE CO (GB)
CLARK RICHARD (US)
BOFF JAMES (GB)
International Classes:
C01B31/02; H01M4/58; C04B35/83; D01F9/127; H01M4/04; H01M4/131; H01M4/505; H01M4/525; H01M4/62; H01M10/0525; H01M4/02; H01M4/86
Domestic Patent References:
WO2008070926A12008-06-19
WO2010113512A12010-10-07
Foreign References:
CN101872651A2010-10-27
EP2131422A12009-12-09
US20040111873A12004-06-17
CN101780952A2010-07-21
JP2002075364A2002-03-15
JP2003242974A2003-08-29
CN201010133489A2010-03-26
CN201010204539A2010-06-22
GB2399092A2004-09-08
Other References:
K. AMINE ET AL., ELECTROCHEMISTRY COMMUNICATIONS, vol. 7, 2005, pages 669 - 673, Retrieved from the Internet
Attorney, Agent or Firm:
PHILLIPS & LEIGH (London, London EC4A 3BA, GB)
Download PDF:
Claims:
Claims

1. A method of making a lithium ion battery electrode material, comprising of incorporating lithium into a nano- structured carbon material formed by:- i) providing a porous carbon material having porosity;

ii) impregnating a metallic material capable of catalyzing carbon nano structure growth within the porosity of the porous carbon material of step i) to provide an impregnated porous carbon material; or providing an impregnated porous carbon material produced by such an impregnating step;

iii) heating the impregnated porous carbon material of step ii) to a

temperature sufficient to promote carbon nano structure growth within the porosity of the carbon material to provide a nano- structured carbon material.

2. A method as claimed in Claim 1, in which the porous carbon material is activated carbon.

3. A method as claimed in Claim 1, in which the porous carbon material is produced by carbonising a biological precursor.

4. A method as claimed in any one of Claims 1 to 3, in which carbon nano

structure growth is catalysed from the carbon of the porous carbon material.

5. A method as claimed in any one of Claims 1 to 4, in which carbon nano

structure growth is catalysed from a carbon containing fluid.

6. A method as claimed in any one of Claims 1 to 5, in which the step of

incorporating lithium into the nano- structured carbon material occurs when an electrode made from the nano-structured carbon material of step iii) is in a lithium ion battery.

7. An electrode material for use in a lithium ion battery, the electrode material including a nano-structured carbon material comprising a porous carbon material having nano-structured carbon within the porosity.

8. An electrode material as claimed in Claim 7, further comprising:

a binder.

An electrode material as claimed in Claim 7 or Claim 8, further comprising :- • a conductive additive.

An electrode material as claimed in any one of Claims 7 to 9, further comprising:

• lithium.

An electrode material as claimed in any one of Claims 7 to 10, further comprising:-

• active materials capable of receiving and releasing lithium.

An electrode material as claimed in any one of Claims 7 to 11, further comprising:- active materials capable of modifying the electrical and/or physicochemical properties of the electrode material.

13. A lithium ion battery comprising an anode comprising an electrode material as claimed in any one of Claims 7 to 12.

14. A battery as in Claim 13, further comprising a cathode comprising one or more compounds of lithium.

15. A battery as claimed in Claim 14, in which the one or more compounds of lithium is or includes one or more olivine-type lithium phosphates.

16. A battery as claimed in Claim 14, in which the one or more compounds of lithium is or includes lithium iron phosphate.

17. A battery as claimed in Claim 14, in which the one or more compounds of lithium is or includes lithium nickel manganese cobalt oxide.

18. A battery as claimed in any one of Claims 14 to 17, in which one or more of the one or more compounds of lithium comprises one or more metals the same as a metal of the metallic material capable of catalyzing carbon nano structure growth.

Description:
LITHIUM ION BATTERIES AND ELECTRODES THEREFOR

This invention was made pursuant to a development agreement dated 6th April 2009 between The Morgan Crucible Company pic and Shanghai Jiao Tong University.

This invention relates to lithium-ion batteries and electrodes therefore.

Background

Lithium-ion batteries of various sorts have achieved widespread use in a number of applications. Whilst most regularly seen in electronic products such as mobile phones, laptops, cameras and other handheld devices, they have also seen use in power tools and are increasingly used in more demanding applications such as in vehicles ranging from electric cars and planes to tugboats and yachts.

There are many desirable aspects to the use of lithium-ion batteries in more varied applications, not least the environmental impact; if electric vehicles or hybrid electric vehicles utilising lithium-ion batteries are used in preference to vehicles powered by fossil fuels then harmful atmospheric emissions causing air pollution, smog, and climate change can be limited. However, if such batteries are to see widespread use they must deliver power efficiently whilst keeping the cost of manufacturing them low. There is therefore a need for methods of enhancing the properties of a lithium- ion battery which may be put into effect using low-cost materials and simple techniques which can be easily applied in industry. Such improvements must also take into consideration safety concerns, both in terms of the design of the battery and any risks posed to users by the materials used to make the battery.

Bearing in mind these considerations, a range of lithium-ion based batteries have been produced in which the negative electrode in discharge [referred to in the following as the anode], comprises carbon, and in particular graphite particles, since graphitic species are both safe, have a high capacity for the storage of lithium ions, and are conductive. Typically, anodes are made from a mixture of carbon materials with an electrically conductive additive [typically carbon black] and a binder. [Other anode materials have been proposed]. The positive electrode in discharge [referred to in the following as the cathode] may be of a variety of materials. Particular research has taken place recently with the use of olivine-type lithium phosphates such as LiFeP0 4 [known as LFP] as a cathode to replace the more conventionally used LiCo0 2 (see JP2002075364A and

JP2003242974A). Olivine-type lithium phosphates have the general formula LiMP0 4 , where M is at least one metal element, for example a transition metal element, and typically selected from the group of Co, Ni, Mn and Fe. When used in a lithium-ion battery the working voltage delivered varies depending on the type of the metal element M, permitting battery voltage to be selected simply by selecting the appropriate element for M. The olivines additionally deliver a large battery capacity per unit mass. The fact that suitable olivines can be produced from iron and phosphorus is also helpful, since iron and phosphorus are cheap and plentiful and so the manufacturing cost of batteries can be reduced. Additionally, lithium iron phosphate has less environmental impact than lithium-cobalt composite oxides, so there are also safety advantages. Other electrode materials proposed or in use include :-

• Lithium nickel manganese cobalt oxide (WO2010113512).

LiNio.sCoo.isAlo.osO, (NCA)

• LiMn 2 0 4 (LMO)

[see for example Advanced Lithium- Ion Batteries for Plug-in Hybrid-Electric

Vehicles, http://www.transportation.anl.gov/pdfs/HV/461.pdf] .

The present invention is not limited to any particular cathode material.

However, the cathode material is not the only factor contributing to the effectiveness of a lithium-ion battery. There is a need for anode materials which are safe, cheaply produced, have a low environmental impact, have a high capacity for absorbing lithium ions, and are able to retain their effectiveness in the event of accidental dissolution of cathode material into the electrolyte, as can happen with lithium iron phosphate batteries when cycles run at elevated temperatures (see abstract K. Amine et al. Electrochemistry Communications 7 (2005) pp. 669-673 at http://cat.inist.fr/?aModele=afficheN&cpsidt=16872369).

The applicant has realised that carbon materials with a sufficiently high electrical conductivity and high absorption capacity for lithium can be provided using relatively inexpensive raw materials and by a relatively inexpensive manufacturing route by incorporating lithium into high porosity carbon materials [e.g. activated carbon or biologically derived carbon materials] which have been treated to provide nano- structured carbon within the porosity of the material. Accordingly, the present invention provides a method of making a lithium ion battery electrode material, comprising of incorporating lithium into a nano- structured carbon material formed by:- i) providing a porous carbon material;

ii) impregnating a metallic material capable of catalyzing carbon nano structure growth within the carbon material into the porosity of the porous carbon material of step i) to provide an impregnated porous carbon material; or providing an impregnated porous carbon material produced by such an impregnating step;

iii) heating the impregnated porous carbon material of step ii) to a

temperature sufficient to promote carbon nano structure growth within the porosity of the carbon material to provide a nano- structured carbon material.

Further features of the invention are set out in the appended claims and are illustrated in the following description.

Chinese patent application 201010133489.1 discloses:-

1) Carbonising a biological precursor under vacuum or an inert atmosphere at temperatures between 400-1000°C.

2) Activating the carbonized material via an appropriate physical or chemical activation process to adjust its porous structure;

3) Impregnating the porous carbons made in step 2) with an element M precursor solution, and filtering and desiccating the mixture; 4) Calcining the resulting mixture between 300-1000°C under a vacuum or inert atmosphere to get porous carbons loaded with a functional oxide M x O y , where M is one or two of Ti, Fe, Ni,Co, Zn, Cu, Mn, Zr, Cr, Al, Sn, Y, Ce, La, Pb, Pd, Ru, Sr, In, Ga, Bi or Si, X is one of the 1,2 or 3, Y is one of 1,2,3 or 4.

The activation step 2) comprises either:

• heating samples at 300-1000°C for 1-12 h under a C0 2 , steam or air

atmosphere;

or

• mixing an activator KOH, ZnCl 2 or Fe(N0 3 ) 2 with the carbonised material and heating the mixture 300-1000°C for 1-12 h under a vacuum or inert atmosphere.

Chinese patent application 201010204539.0 (Shanghai Jiao Tong University) discloses carbon materials produced by a process comprising the steps of:- a) The preparation of in-situ self growth nano carbon matrix material;

b) The surface treatment of the carbon matrix material;

c) The preparation of metal oxide precursor;

d) Placing the carbon material of step (b) into the precursor of step (c), and

treating ultrasonically to make the material.

In detail:

Step a) comprised:

i) a porous carbon material having porosity [e.g. activated carbon] is provided; ii) a metallic material capable of catalyzing carbon nano structure growth from the carbon of the carbon material is impregnated into the porosity of the porous carbon material [e.g. Fe(N0 3 )3-9H 2 0];

iii) the impregnated porous carbon material is heated to a temperature sufficient to promote carbon nano structure growth within the porosity of the carbon material to provide a nano-structured carbon material.

Step b) comprised treating the resultant material with concentrated nitric acid to oxidise the carbon surface

Step c) comprised making a metal salt solution.

Step d) comprised ultrasonically treating a suspension of the material of step b) in the solution of step c). It will be evident that steps 1) and 2) of Chinese patent application 201010133489.1 and steps a) and b) of Chinese patent application 201010204539.0 are of immediate relevance to the present invention as providing a nano- structured carbon material. By nano-structured carbon material is meant a material in which a porous matrix carbon comprises carbon nano structures within the porosity of the material. By carbon nano structures is meant carbon structures different in form from the porous carbon matrix and having nanometric scale [e.g. less than ΙΟμιη, or less than Ιμιη, or even less than Ο.ΐμπι].

Nano-structures may comprise graphitic structures and/or nanofibres and/or nanotubes and/or fullerenes.

As stated above, the present invention involves incorporating lithium into a nano- structured carbon material formed by:- i) providing a porous carbon material;

ii) impregnating a metallic material capable of catalyzing carbon nano structure growth within the carbon material into the porosity of the porous carbon material of step i) to provide an impregnated porous carbon material; or providing an impregnated porous carbon material produced by such an impregnating step;

iii) heating the impregnated porous carbon material of step ii) to a

temperature sufficient to promote carbon nano structure growth within the porosity of the carbon material to provide a nano-structured carbon material.

In detail :-

Porous carbon material

The porous carbon material may comprise activated carbon and may comprise carbon produced by carbonisation of a biological material.

Activated carbon is a form of carbon that has been processed to make it extremely porous and so has a very large surface area. A typical specific surface area might be of the order of 500m 2.g- " 1 to 1500 m 2.g- " 1 although the present invention is not limited to this range.

Activated carbon is produced from carbonaceous source materials, for example nutshells, peat, wood, coir, lignite, coal and petroleum pitch. Activated carbon is not understood to bond well to lithium 1 .

The biological materials may comprise for example agricultural wastes or aquatic plants. The agricultural wastes may for example comprise straw, rice husk, coconut shell, husk shell, cotton fiber, fruit stone, wheat straw, corn cob, sawdust, bamboo or water bamboo; and the aquatic plants may for example be algae or hyacinth.

Impregnation of metallic material capable of catalyzing carbon nano structure growth in the porosity of the porous carbon material

Various metals may promote growth of carbon nano structures from the carbon of the carbon material. As examples, iron, nickel and cobalt are known to have some reactivity with carbon and indeed are used in both diamond synthesis and the synthesis of nanotubes. Chinese patent application 201010204539.0 observed nano structure growth at temperatures as low as 700°C with use of iron as the promoter of nano structure growth. The following are four examples of processes disclosed in that application as showing nano structured carbon

(1) Add l.Og carbon to 2.2 ml water and 0.55 g Fe(NO 3 ) 3 -9H 2 0, mix uniformly and then dry. Put above mixture into sintering furnace under vacuum, raise temperature to 450 °C, preserve for half hour, raise temperature to 700 °C, preserve for one hour, and cool to room temperature naturally. Then, put above material into 10-15% hydrochloric acid solution, at 50 °C, mix for 5hours, filter, and dry at 80 °C.

(2) Add 5g carbon material to 50 ml water and 5 g Fe(NO 3 ) 3 -9H 2 0, mix

uniformly and then dry. Put above mixture into sintering furnace under vacuum, raise temperature to 450°C, preserve half hour, then raise temperature

1 [http : //en . wikipedia. org/ wiki/ Acti vated_carbon#Properties] to 850 °C, preserve one hour, cool to room temperature naturally. Then, put above material into 10-15% hydrochloric acid solution, at 50 °C, mix for 5 hours, filter, and dry at 80 °C.

(3) Add lOg carbon material into 100 ml water and 10 g Fe(NO 3 ) 3 -9H 2 0, mix uniformly and then dry. Put above mixture into sintering furnace under vacuum, raise temperature to 450 °C, preserve half hour, then raise

temperature to 1000 °C, preserve one hour, cool to room temperature naturally. Then, put above material into 10-15% hydrochloric acid solution, at 50 °C, mix for 5 hours, filter, dry at 80 °C dry.

(4) Add l.Og carbon material into 50 ml water and 0.55 g Fe(NO 3 ) 3 -9H 2 0, mix uniformly and then dry. Put above mixture into sintering furnace under vacuum, raise temperature to 450 °C, preserve half hour, then raise

temperature to 700 °C, preserve one hour, cool to room temperature naturally. Then, put above material into 10-15% hydrochloric acid solution, at 50 °C, mix for 5 hours, filter, dry at 80 °C.

In addition or as an alternative to promoting nano structure growth from the carbon of the porous carbon material, it is possible to provide carbon nano structure growth by decomposition of a carbon containing fluid [e.g. a hydrocarbon/hydrogen mixture].

The fluid may be a vapour, a supercritical fluid, or a liquid, but production from a vapour has been demonstrated.

For example GB2399092 disclosed the production of nanofibres in the porosity of a fibrous material having pore sizes of the order of 10μιη-50μιη. Accordingly the applicant believes that a similar process would result in nanostructure growth from the vapour in the porosity of a porous carbon as described above.

Heating the impregnated porous carbon material of step ii) to a temperature sufficient to promote carbon nano structure growth Chinese patent application 201010204539.0 disclosed temperatures in the range 400- 1000°C. GB2399092 disclosed temperatures of the order of 650°C. The applicants expect that nano structure growth will be promoted both within and outside this range [e.g. up to 1200°C or more], but the range 400 - 1000°C is convenient.

Further treatment steps

The present invention does not require, but also does not preclude, treatment of the material to treat the surface of the material and/or to leach out the metal [e.g. by acid treatment] . As explained below, where the material is used as an electrode in a lithium ion battery and a counter electrode includes the same metal as used for catalysing carbon nano- structure growth, such treatment may not be necessary.

Incorporating lithium into the nano-structured carbon material

As mentioned above, activated carbon is not understood to bond well to lithium 1 above . However, the nano structured material is expected to accept lithium as both graphite and nanotubes are known to accept lithium.

The incorporation of lithium may be done before or after incorporation of the material into a battery.

The battery

A lithium ion battery comprises (among other things) at least one cathode and at least one anode. Typically the anode comprises carbon materials impregnated with lithium. The cathode may comprise a lithium compound which may also comprise a metal. If the metal in the lithium compound is the same as that used to catalyse the

nanostructure growth in the anode material the risk of adverse reaction is reduced.

As mentioned in the background above, typically anodes are made from a mixture of carbon materials with a conductive additive [typically carbon black] and a binder. The applicants have reason to believe that the presence of nano structured carbon, particularly graphitic structures and nanotubes, may raise the electrical conductivity of the carbon materials to a level that the amount of conductive additive required will be reduced; or even that a conductive additive may be dispensed with.

It will be readily understood that the anode and the cathode may comprise further active materials beyond those mentioned above. For example, the nano-structured carbon material may be blended with other components, capable of receiving and releasing lithium [e.g. other carbons, graphite, Li 4 Tis0 12 ]. Other active components for modifying the electrical and/or physicochemical properties of the electrode material may also be included.

The above description should be taken as illustrative only, and variants falling within the claimed scope will be evident to the skilled person.