Limited oil reserves together with an increasing effort to reduce the amount of CO ₂ emission not only cause a shift in electric energy production towards renewable forms of en ^¬ ergy, but also result in increasing research for alternative drive trains in the automotive industry. Moreover, an increasing demand for durable high power storage media within consumer electronics and telecommunication promotes both improvement of existing energy storage systems and de ^¬ velopment of new energy storage systems with the main focus on efficiency, cost reduction and safety. Due to its high gravimetric energy storage capability, the lithium ion bat- tery (LiB) is an established system, not only for today and future energy storage, but also for use in automobiles and in a large variety of other special fields of application.

The first commercialized LiB was based on L1C0O ₂ as posi- tive electrode and graphite as negative electrode. The

LiCo0 ₂ cathode delivers an average potential of 3.8 V vs. Li/Li ⁺ . However, since cobalt is both comparatively expen ^¬ sive and toxic, the search for alternative cathode materi ^¬ als is ongoing, and an increasing number of other material combinations are being tested and partially commercialized. One possibility to increase the energy density of the LiB is raising the operating voltage of the cells. This could be achieved by using cathode materials with higher elec ^¬ trode potential like the LiNio.5Mn1.5O4 spinel, delivering a voltage of 4.7 V vs. Li/Li ⁺ . A spinel means a crystal lattice where the oxide anions are arranged in a cubic close-packed lattice and the cations are occupying some or all of the octahedral and tetrahedral sites in the lattice. The symmetry of the spinel lattice is described by space groups of P4332 for the ordered phase and Fd-3m for the disordered phase. The spinel material may be a single disordered or ordered phase, or a mix of both (Adv. Mater. 24 (2012), pp 2109-2116).

Another important factor for the choice of materials in the LiB is the abundance of their components in the earth crust securing long term availability and cost reduction, due to which materials based on iron and manganese are of great interest. Especially manganese oxides constitute a promis ^¬ ing group of cathode materials, because manganese is a low priced and non-toxic element. In addition, manganese oxides have a rather high electronic conductivity together with a suitable electrode potential. Among the lithium manganese oxides, the layered LiMn0 ₂ and the spinel-type LiM^C^ (LMO) are the most prominent ternary phases. Advantages of the latter one in comparison to the layered phase are a higher potential of about 4.0 V against Li/Li ⁺ , whereas LiMn0 ₂ de ^¬ livers only 3.0 V on average. The LiM^C^ lattice offers a three-dimensional lithium diffusion, resulting in a faster uptake and release of this ion. The diffusion of Li ⁺ in doped LMO spinels is also equally fast in all three dimen ^¬ sions . Among the transition metal doped LiM^C^ spinel electrodes, Li _x i _y Mn ₂ -y0 ₄ , 0 ≤ y ≤ 0.5 is a very promising material: It operates partially at a relatively high voltage of 4.7 V vs. Li/Li ⁺ due to the electrochemical activity of the

Ni ²⁺ /Ni ⁴⁺ redox couple. LiNio. ₅ Mn ₁ . ₅ O ₄ has a theoretical spe ^¬ cific capacity of 147 mAh/g and therefore an attractive theoretical energy density of 4.7 V-147 Ah/kg = 691 Wh/kg active material, referring to lithium metal. By replacing 25% of the manganese ions with nickel, there is in theory no Mn ³⁺ left in the structure. For charge balance reasons, the Ni ²⁺ incorporation forces all manganese ions to their tetravalent state. If the less than 25% of the manganese is replaced by Ni, some Mn ³⁺ will be left in the structure. For Li i _y Mn ₂ -y0 ₄ the theoretical Mn ³⁺ :Mn ⁴⁺ ratio is equal to (0.5 - y) . It should be noticed that in practice there will often be small deviations from the theoretical composition and average oxidation states when synthesizing a material. This can occur because of deviation from the exact stoichi- ometry due to either the existence of defects and inhomoge- neity in the structure of Li i _y Mn2- _y 0 ₄ or the existence of impurity phases which alter the composition of the main phase. It is for instance well known that small amounts of a rock salt phase are present when synthesizing

LiNio. ₅ Mn ₁ . ₅ O ₄ , which affects the stoichiometry of the spinel phase and renders the total material oxygen deficient (J. Cabana et al . , Chemistry of Materials 24 (2012), 2952).

LNMO materials are lithium positive electrode active mate ^¬ rials dominated by Ni-doped LiMn ₂ 0 ₄ spinel phase, which more specifically may be characterised by the general for ^¬ mula Li _x Ni _y Mn ₂ -y0 ₄ with typical x and y values of 0.9 ≤ x ≤ 1.1 and 0 ≤ y ≤ 0.5, respectively. The formula represents the composition of the spinel phase of the material. Such materials may be used for e.g. portable electric equipment (US 8,404,381 B2), electric vehicles, energy storage sys ^¬ tems, auxiliary power units (APU) and uninterruptible power supplies (UPS) . Lithium positive electrode active materials based on LNMO are seen as prospective successors to current lithium secondary battery cathode materials such as LiCo0 ₂ due to their high voltage and high energy density, coupled with lower material costs.

Electrode active materials for lithium ion battery materials are described abundantly in the literature. Thus, US 5.631.104 describes insertion compounds having the formula Li _x+ iM _z Mn ₂ - _y - _z 0 ₄ wherein the crystal structure is spinel-like, that can reversibly insert significant amounts of Li at po ^¬ tentials greater than 4.5 V vs. Li/Li ⁺ . M is a transition metal, in particular Ni or Cr, 0 ≤ x ≤ 1 ; 0 ≤ y < 0.33 and 0 < z < 1. US 2015/0041710 Al relates to cathode active materials for lithium secondary batteries. More particularly it relates to a method for preparing 3V class spinel oxides with the composition Li _1+X [M _y Mn ₍₂ - _y) ] 0 ₄ - _z S _z (0 < x < 0.1; 0.01 < y < 0.5 and 0.01 ≤ z ≤ 0.5; M = Mn, Ni or Mg) by carbonate co-pre- cipitation.

In addition to the elemental composition and crystal struc ^¬ ture of the electrode materials, it is well known to those skilled in the art that control of the shape and micro- structure of the particles is vital, if batteries with good cycling behaviour and high performance are desired. For ex ^¬ ample, Zhu et al. (Solid State Ionics, 179 (2008) 1788) showed that powder morphology has a significant impact on the electrochemical performance of LMO spinel when tested in half cells where Li metal is used as the anode. In par ^¬ ticular, spherical LMO particles were found to have signif- icantly higher capacity retention after 100 charge-dis ^¬ charge cycles than irregularly shaped particles. According to the authors, increased performance was due to reduced stress on particles during cycling, because the local Jahn- Teller distortions on one side of the spherical particle were counteracted by identical distortions on the opposite side of the particle.

One way to quantify the size of particles in a suspension or a powder is to measure the size of a large number of particles and calculate the characteristic particle size as a weighted mean of all measurements. Another way to charac ^¬ terize the size of particles is to plot the entire particle size distribution, i.e. the volume fraction of particles with a certain size as a function of the particle size. In such a distribution, D10 is defined as the particle size where 10% of the population lies below the value of D10, D50 is defined as the particle size where 50% of the popu ^¬ lation lies below the value of D50 (i.e. the median), and D90 is defined as the particle size where 90% of the popu- lation lies below the value of D90. Commonly used methods for determining particle size distributions include dynamic light scattering measurements and scanning electron micros ^¬ copy measurements, coupled with image analysis. Similarly, there are several ways to characterize and quan ^¬ tify the sphericity and shape of particles. Almeida-Prieto et al . in J. Pharmaceutical Sci . , 93 (2004) 621, lists a number of form factors that have been proposed in the lit ^¬ erature for the evaluation of sphericity: Heywood factors, aspect ratio, roughness, pellips, rectang, modelx, elonga ^¬ tion, circularity, roundness, and the Vp and Vr factors proposed in the paper. Circularity of a particle is defined as 4 ·π · (Area) /( Perimeter) ² . An ideal spherical particle will thus have a circularity of 1, while particles with other shapes will have circularity values between 0 and 1. Particle shape can further be characterized using aspect ratio, defined as the ratio of particle length to particle breadth, where length is the maximum distance between two points on the perimeter and breadth is the maximum distance between two perimeter points linked by a line perpendicular to length.

For most battery applications, space is at a premium, and high energy density is desired. Powders of the electrode material with a high tap density tend to result in elec ^¬ trodes with higher active material loading (and thus higher energy density) than powders with a low tap density. It can be shown using geometry-based arguments that materials com ^¬ posed of spherical particles have a higher theoretical tap density than particles with irregular shapes. In addition to the shape of the spinel particles, the sur ^¬ face microstructure and roughness are thought to play a key role in determining the cycling behaviour and rate-capability of high-voltage electrode materials, such as LNMO, in batteries. The redox potential of the Ni ²⁺ /Ni ⁴⁺ redox couple in LNMO lies at approximately 4.7 V vs. Li/Li ⁺ , which is higher than the stability limit of common liquid carbonate- based electrolytes (typically between 4.0 to 4.3 V). This leads to the oxidation of the electrolyte on the positive electrode during battery operation and to the formation of a resistive cathode/electrolyte layer at the interface be ^¬ tween LNMO and the electrolyte. The rougher the surface of the active powder in the electrode (i.e. the higher its specific surface area) , the more of the electrolyte is lost due to oxidation and the formation of the cathode/electro ^¬ lyte interface layer. Therefore, positive electrode active materials with low specific surface area (i.e. smooth and non-porous surface morphology) are required to avoid capac ^¬ ity fading during long-term battery operation.

Lithium positive electrode active materials may be prepared from precursors obtained by mechanically mixing starting materials to form a homogenous mixture, followed by calci ^¬ nation. For example, in US 8,404,381 B2, an intimate mix ^¬ ture of nickel carbonate, manganese carbonate, and lithium carbonate is prepared by grinding in the presence of hex- ane . The mixture is dried and treated at 600°C (10 hours), and then at 900°C (15 hours) to form LNMO. Critically, LNMO materials prepared according to this method will not be spherical, which can have a significant negative effect on the cycling behaviour of the battery using such LNMO as positive electrode, as well as on the tap density of the LNMO powder.

A different way to prepare positive electrode active mate ^¬ rials for LiB is to use the method of precipitation, fol ^¬ lowed by calcination/lithiation . In precipitation, two or more solutions are mixed under controlled conditions and react to form an insoluble product, which can then be iso ^¬ lated from the rest of the mixture. When precipitation is used for battery material synthesis, the process typically starts with the precipitation of the transition metal species in the desired elemental ratio. Examples of such tran ^¬ sition metal species include, but are not limited to

Ni (OH) 2, NiC0 ₃ , Ni ₂ C0 ₃ (OH) ₂ , Ni( HC0 ₃ ) ₂ , Ni ₃ C0 ₃ (OH) ₄ , Mn(OH) ₂ , MnC0 ₃ , Ni ₀ . ₂₅ Mn ₀ .75 (OH) ₂ , Ni ₀ . ₂₅ Mn ₀ . ₇₅ C0 ₃ , Nio. ₅ Mn ₀ .5 (OH) ₂ ,

Nio. 5Mno . 5CO3 , ii/sMn!/sCoi/s (OH) 2 and i _{1 /} 3Mn ₁ /3Coi/3C0 ₃ . Such transition metal hydroxides, carbonates, or hydroxycar- bonates are often referred to as precursor materials. After precursor materials are obtained, they are typically mixed with a Li-containing material and calcined to elevated tem ^¬ peratures to ensure the formation of the correct crystallo- graphic phase. The Li-containing materials include, but are not limited to lithium hydroxide, lithium carbonate, and lithium nitrate. It is generally accepted that the shape and size of the powder particles of the final active mate ^¬ rial are to a great extent determined by the morphology and size of the precursor particles. Importantly, when reaction parameters are properly controlled, spherical precipitate particles can be obtained.

Precursor materials for LNMO-type LiB positive electrode materials can be prepared by precipitating the mixture of Ni and Mn as hydroxides, i.e. Ni _y Mn ₂ - _y (OH) ₄ , where 0 ≤ y ≤ 0.5. Such precipitation commonly uses the corresponding transition metal sulfates and NaOH as starting materials and ammonia (N¾, NH ₄ OH or N¾ · ¾0 ) as chelating agent. Ac ^¬ cording to this route, the reaction proceeds as: y NiS0 ₄ (aq) + 2-y MnS0 ₄ (aq) + 4 NaOH(aq) ->

2 Na ₂ S0 ₄ (aq) + Ni _y Mn ₂ - _y (OH) ₄ ( s ) (1) Similarly, precursor materials for LNMO-type LiB positive electrode materials can be prepared by precipitating the mixture of Ni and Mn as carbonates, i.e. i _y Mn2- _y (CO3) 2 , where 0 ≤ y ≤ 0.5. Such precipitation commonly uses the corresponding transition metal sulfates and a ₂ C03 as starting materials and ammonia (N¾, NH ₄ OH or N¾ ·¾0) as chelating agent: y NiS0 ₄ (aq) + 2-y MnS0 ₄ (aq) + 2 Na ₂ C0 ₃ (aq) ->

2 Na ₂ S0 ₄ (aq) + Ni _y Mn ₂ - _y (C0 ₃ ) 2 (s) (2)

Analyses of precipitated and intensively washed particles of io.5Mni.5 (OH) 4 have systematically revealed a high degree of sulfur impurities, typically 0.5 wt%, and a relatively low content of Na (below 500 ppmw) . The high level of sul ^¬ fur impurities in precipitated hydroxide precursors for battery materials is a well-known problem when sulfates are used in the precipitation process. For example, US 6274272 Bl mentions that the synthesis of the mixed hydroxide β- Nii- _x Co _x (OH) ₂ usually employs metal salts such as sulfates which cannot be eliminated entirely and which consume lith ^¬ ium in the subsequent calcination step. They report that the X-ray diffraction diagrams for the final cathode mate- rials obtained after Li addition and heat treatment can show the presence of L1 ₂ SO ₄ represented by an additional peak at around 29=22° (Cu Koii) if sulfates are used to make the hydroxide precursor.

In contrast, analysis of precipitated and intensively washed io. sMni . ₅ (CO ₃ ) ₂ particles systematically shows the op ^¬ posite picture, i.e. a high Na content and a relatively low sulfur content, typically 0.5 wt% Na and 500 ppmw sulfur.

There is no scientific consensus regarding the effect of these impurities on the electrochemical performance of Li- ion batteries. For example, X. Wang et al . ("Toward long- term performance stability in Li-ion batteries: Can evalua ^¬ tion of trace and ultra-trace level contaminants help?", presented at the TMS 2014 143 ^rd Annual Meeting and Exhibi ^¬ tion, Feb 16-20, 2014) demonstrate that the chemical purity of positive electrode materials can be important for the long-term cycling performance of Li-ion batteries. Specifi ^¬ cally, they compared LiBs made with LiFePC^ with various levels of impurities as the positive electrode material and observed significant differences in cycling behaviour be ^¬ tween the two cells. They assigned the different perfor ^¬ mance to differences in Mn and Mg content, but their analy ^¬ sis also revealed that Nb, Si, K, Zn, Na, Cr, Ti, Ca, Al and S content in the two materials was significantly dif ^¬ ferent. Thus, they propose that evaluating and controlling trace and ultra-trace level elemental contaminants in elec ^¬ trode materials should be exercised in LiB manufacturing.

It is very likely that calling some impurity elements "del ^¬ eterious" and some "beneficial" is a misnomer. For example, it is well known from the field of heterogeneous catalysis that some elements can act as promoters, enhancing the rate of desirable catalytic reactions, sometimes by several or- ders of magnitude. It is equally well known that the bene ^¬ ficial effect of these elements is highly dependent on the amount (concentration) of these promoters in the catalyst. In many cases, the same element can act as a promoter in low concentrations, but act as an inhibitor or a suppressor if present in high concentrations.

For example, some literature in the art, e.g. J. Wang et al., Electrochim. Acta 145 (2014) 245-253, reports that doping LiNio.5Mn1.5O4 with small amounts (up to 5% of the Li in the spinel) with Na has a positive effect on the proper ^¬ ties of the LiB material. When the Na-content is increased further, the authors report not only negative changes to the physical properties of the material, but electrochemi- cal performance that was poorer than that of undoped mate ^¬ rial .

In another paper, Sun et al . (J. of Power Sources, 161

(2006) 19-26, report that the substitution of small amounts of sulfur as LiNio.5Mn1.5O4-.xSx , where x = 0.05, changes the size and surface texture of the particles, which they be ^¬ lieve contributes to the improved capacity retention and rate-capability of the material in the 3-V region, compared to the Ni-only doped spinel material.

However, regardless of the impact of impurities, it is a clear advantage if the amount and type of impurities in the final product can be controlled. In fact, one of the best ways to understanding and quantifying the role of various impurities is to produce materials free of these impurities and then systematically add increasing amounts of these im ^¬ purities to the material. The prerequisite to such an ap ^¬ proach is a method capable of preparing LiB precursor mate- rials with low concentrations of the studied impurities.

Thus, according to the invention, a novel synthesis method has been developed, whereby LNMO precursors with a low con ^¬ tent in Na, K and S can be obtained. More specifically, the invention relates to a method for the precipitation of particles of a metal carbonate material comprising nickel and manganese in an atomic ratio of 0 ≤ Ni:Mn ≤ 1/3, in which the concentrations of sodium, potassium and sulfur in the precipitate after washing and drying are less than 0.2 wt%, wherein aqueous solutions comprising sulfates of nickel and manganese or aqueous solutions comprising nitrates of nickel and manganese are mixed with aqueous solutions of potassium hydroxide or potassium carbonate or mixtures of potassium hydroxide and potassium carbonate in a stirred reactor, wherein none of the aqueous solutions comprises ammonia .

Exclusion of these Na, K, and S impurities does not affect the powder properties (i.e. the morphology, the tap den- sity, the particle size distribution, the BET surface area and the powder transport properties) .

The "BET surface area", named after the Brunauer, Emmett and Teller (BET) theory, is a way of determining the specific surface area of a powder.

"Tap density" is the term used to describe the bulk density of a powder after consolidation/compression described in terms of ^x tapping' powder from the container a measured number of times, usually from a pre-determined height. The method of ^x tapping' is best described as ^x lifting and drop ^¬ ping' .

As used herein, a "precursor" is a composition prepared by mixing starting materials to obtain a homogeneous mixture (see, for example, Journal of Power Sources, 238 (2013) pp. 245-250) or by mixing a lithium source with a composition prepared by precipitation of starting materials (see, for example, Electrochim . Acta, 115 (2014) pp. 290-296).

It should be understood that product of the precipitation of the method of the invention is agglomerated particles. Throughout this specification, this product is also denoted "washed and dried agglomerated particles", "precipitate af ^¬ ter washing and drying", "washed and dried precipitate", "washed and dried precursor samples" and "washed and dried product", as those expressions are seen as synonyms.

In the precipitation methods known in the art, the product will either have a high content of sulfur impurity or a high content of sodium impurity, which the Applicant con ^¬ siders a problem. Now it has surprisingly turned out that it is possible to avoid this problem by using potassium species (including but limited to KOH, K ₂ CO ₃ or mixtures thereof) instead of sodium species (such as NaOH, a ₂ C0 ₃ or mixtures thereof) for the precipitation of iyMn2-y ( CO3 ) 2 _/ where 0 ≤ y ≤ 0.5.

Surprisingly and unexpectedly, using potassium species in- stead of sodium species does not result in high concentra ^¬ tions of K impurity in the thoroughly washed and dried pre ^¬ cipitate. In other words, when a potassium species is used for precipitation, precipitate particles that are simulta ^¬ neously low in sulfur, sodium, and potassium can be ob- tained. This is in clear contrast to i _y Mn ₂ - _y (CO ₃ ) ₂ precipi ^¬ tates obtained using sodium species, where the low concen ^¬ tration of S, Na, and K cannot be obtained simultaneously.

Thus, the present invention provides a method for the pre- cipitation of Ni _y Mn ₂ - _y (CO ₃ ) 2 , where 0 ≤ y ≤ 0.5, especially spherical Ni _y Mn ₂ - _y (CO ₃ ) 2 , by a synthesis, wherein aqueous so ^¬ lutions comprising sulfates of nickel and manganese or aqueous solutions comprising nitrates of nickel and manga ^¬ nese are mixed with aqueous solutions of potassium hydrox- ide or potassium carbonate or mixtures of potassium hydrox ^¬ ide and potassium carbonate in a stirred reactor, thereby forming agglomerated particles. None of the aqueous solu ^¬ tions comprises ammonia or other chelating agents. Some ox ^¬ idation of the precursor can occur in the process if there is access to oxygen. This does not alter the properties of the precursor with respect to subsequent process steps as long as the change in metal concentration (wt%) in the pre ^¬ cursor is taken into account.

In one embodiment of the present invention, the synthesis of precipitates of Ni _y Mn ₂ - _y (CO3) 2, where 0 ≤ y ≤ 0.5, pro ^¬ ceeds according to reaction scheme (3), given as:

y NiS0 ₄ (aq) + (2-y) MnS0 ₄ (aq) + 2 K ₂ C0 ₃ (aq) -> 2 K2SO4 (aq) + Ni _y Mn ₂ - _y (C0 ₃ )2 (s) . (3)

The invention has the important advantage that the sodium impurities are reduced to ppmw level instead of the wt% levels which are seen when precipitating with a sodium- based species. This allows for systematic investigations to elucidate the effect of sodium on the performance of LNMO- type materials. Furthermore, high amounts of Na lead to a P2-type impurity phase and thereby to a lower content of active material.

The invention has another advantage in that, when a K ₂ CO ₃ solution is used as the alkaline species in the precipita ^¬ tion, the alkaline solution is easier to handle during synthesis than an equimolar a ₂ C0 ₃ solution. It is well known (see, for example, A. Pabst, American Mineralogist, 15,

(1930), 69) that Na ₂ CC>3 solutions are not stable at temper ^¬ atures below approximately 36°C due to the slow precipita ^¬ tion of hydrates of a ₂ C03. As a result, the activity of the a ₂ C0 ₃ alkaline solution slowly decreases during the synthesis, unless the solution is constantly heated to keep it above 36°C. K ₂ CO ₃ solutions are substantially more sta ^¬ ble: according to the paper by A. Pabst, when solutions containing both 21.3 moles of a ₂ C0 ₃ and 21.3 moles of K ₂ CO ₃ per 1000 moles of water were prepared and let to stand at ca. 18°C, crystals of Na ₂ C0 ₃ -5/2 ¾0 formed, while no pre ^¬ cipitation of K ₂ CO ₃ was observed when the mixture was re ^¬ examined after 3 years of storage in loosely stoppered bot- ties. Furthermore, crystals of sodium carbonate hemi- pentahydrate, apparently without significant potassium car ^¬ bonate impurities, were obtained from a solution having the composition of 100.2 moles of K ₂ CO ₃ and 19.5 moles a ₂ C0 ₃ per 1000 moles of H ₂ 0.

In another embodiment of the invention, sulfur impurities are avoided by the use of metal nitrates instead of metal sulfates in the precipitation process, exemplified by reac ^¬ tion scheme ( 4 ) :

y Ni (N0 ₃ ) ₂ (aq) + (2-y) Mn(N0 ₃ ) ₂ (aq) + 2 K ₂ C0 ₃ (aq) -> 4 KNO3 (aq) + Ni _y Mn ₂ - _y (C0 ₃ )2 (s) (4)

Similarly, to the previous embodiment, by the use of a po- tassium-containing alkaline solution (K ₂ CO ₃ solution) , the concentration of Na in the precipitate can be kept low. As no sulfur-containing species are used in the synthesis, the concentration of S will also be low in the precipitate. However, compared to the previous embodiment, this embodi- ment has the disadvantage that the cost of the nitrates is generally higher compared to sulfates.

The precipitated materials comprising i _y Mn ₂ - _y (CO ₃ ) 2 , where 0 ≤ y ≤ 0.5, can be different from the exact chemical formula and still be used to produce LNMO material. One difference can occur because not all the Ni and Mn will be in oxida ^¬ tion state +2 which might be due to oxidation by oxygen originating from the atmosphere. Another difference might be caused by contamination of the raw materials. Yet an- other difference might be caused by intentional doping of the precursor material due to addition of other elements to the raw materials in the whole or part of the precipitation process that ends up in the precipitated precursor. Possi ^¬ ble elements include, but are not limited to Mg, Co, Cr, Fe, Al and Ti. As long as such differences do not prevent the production of a precursor material with low concentration of Na, K and S, they are included in the present in ^¬ vention .

According to an embodiment of the method of the invention, the washed and dried agglomerated particles are character ^¬ ized in that the concentration of sodium is less than 0.2 wt%, and preferably less than 0.06 wt%. According to an em ^¬ bodiment of the method of the invention, the washed and dried agglomerated particles are characterized in that the concentration of sulfur is less than 0.2 wt%, and preferably less than 0.02 wt%. According to an embodiment of the method of the invention, the washed and dried agglomerated particles are characterized in that the concentration of potassium is less than 0.2 wt%, and preferably less than 0.06 wt%. As mentioned above, the term "washed and dried agglomerated particles" are to be understood as the product of the method of the invention.

The invention is described further in the examples which follow .

Example 1 (comparative example)

A metal ion solution of N1SO ₄ and MnSC^ with a Ni:Mn atomic ratio of 1:3 was prepared by dissolving 281 g of NiS0 ₄ -7H ₂ 0 and 507 g of MnSC^ ·¾0 in 1756 g water. In a separate flask, a carbonate solution was prepared by dissolving 424 g of a ₂ C0 ₃ in 1937 g water. Then the metal ion solution and the carbonate solution were added separately into a reactor provided with vigorous stirring (450 rpm) and having a temperature of 35°C. In order to avoid the precipitation of hydrate species, the a ₂ C03 solution was continuously held at a temperature of around 45°C with the help of a hot- plate. The volume of the stirred reactor was 1 liter.

The product was continuously removed from the reactor, so that the residence time of the reactants in the reactor was 30 minutes. After 2 hours (4 residence times), the product in the reactor was collected and repeatedly and thoroughly washed on a Buchner funnel using room temperature deionized water (temperature approximately 20°C), until the electri ^¬ cal conductivity of the waste water was below 130 μΞ/ατι. Further washing did not result in any significant further decrease in conductivity.

The washed and dried precursor samples were analysed using inductively-coupled plasma atomic emission spectroscopy to determine the content of Ni, Mn, Na, and S species in the samples. The samples contained 11 wt% Ni, 32 wt% Mn, 0.559 wt% (5590 ppmw) Na and <200 ppmw S (below detection limit) .

It appears that despite the extensive amount of water used for washing the precursor samples, significant amounts of Na impurities remain in the dried product.

Example 2 (comparative example)

Precursor samples from exactly the same synthesis as de ^¬ scribed in Example 1 were washed precisely the same way as in Example 1, except that hot water (temperature approxi ^¬ mately 50°C) was used.

The washed and dried precursor samples were analysed using inductively-coupled plasma atomic emission spectroscopy to determine the content of Ni, Mn, Na, and S species in the samples. The samples contained 11 wt% Ni, 33 wt% Mn, 0.469 wt% (4690 ppmw) Na and <200 ppmw S (below detection limit) . It appears that despite the extensive amount of water used and the fact that hot water was used, significant amounts of Na impurities remain in the dried product. Example 3 (comparative example)

Precursor samples from exactly the same synthesis as de ^¬ scribed in Example 1 were washed precisely the same way as in Example 1, except that near-boiling water (close to 100°C) was used.

The washed and dried precursor samples were analysed using inductively-coupled plasma atomic emission spectroscopy to determine the content of Ni, Mn, Na, and S species in the samples. The samples contained 11 wt% Ni, 33 wt% Mn, 0.401 wt% (4010 ppmw) Na and <200 ppmw S (below detection limit) .

It appears that despite the extensive amount of water used and the fact that water close to its boiling point was used, significant amounts of Na impurities remain in the dried product.

Example 4 (comparative example)

Precursor samples were synthesized using metal ion and car ^¬ bonate solutions and an experimental procedure identical to those described in Example 1. After thorough washing and drying, 2 grams of precursor material was mixed with 328.7 milligrams of L1 ₂ CO ₃ and calcined in air at 900°C for 10 hours .

The phase composition of the calcined sample was determined using room temperature powder X-ray diffraction using Cu Koii radiation. The Rietveld refining of the obtained spec ^¬ trum results in the following phase composition: 90.1 wt% LNMO spinel, 2.3 wt% LiNio.5Mno.5O2 (03 phase), 2.6 wt% rock- salt phase, and 5 wt% Ni-rich P2 phase. The corresponding diffractogram is shown in Fig. 1.

The calcined sample was further analysed using inductively- coupled plasma atomic emission spectroscopy to determine the content of Ni, Mn, Na, and S species in the samples. The samples contained 15.4 wt% Ni, 44 wt% Mn, 1.7 wt%

(17000 ppmw) Na and 520 ppmw S. This shows that high con ^¬ centrations of Na-impurity in LNMO can lead to the for ^¬ mation of an additional crystallographic phase (the Na-rich P2 phase) .

Example 5

A metal ion solution of N1SO ₄ and MnS0 ₄ with a Ni:Mn atomic ratio of 1:3 was prepared by dissolving 281 g of NiS0 ₄ -7¾0 and 515 g of MnS0 ₄ ·¾0 in 1749 g water. In a separate flask, a carbonate solution was prepared by dissolving 552 g of K2CO ₃ in 1863 g water. The metal ion solution and the carbonate solution were added separately into a reactor provided with vigorous stirring (450 rpm) and a temperature of 35°C. The carbonate (K ₂ CO3) solution was held at room temperature without any heating. The volume of the stirred reactor was 1 liter.

After 5 hours of precipitation, the product in the reactor was collected and repeatedly and thoroughly washed on a Buchner funnel using hot deionized water (temperature ap- proximately 75°C) . Then the precipitation product was washed until the electrical conductivity of the waste water was below 130 μΞ/ατι. Further washing did not result in any significant further decrease in conductivity.

The washed and dried precursor samples were analysed using inductively-coupled plasma atomic emission spectroscopy to determine the content of Ni, Mn, K, and S species in the samples. The samples contained 12 wt% Ni, 35 wt% Mn, 470 ppmw K and 170 ppmw S. The Na content was not determined.

Example 6

The precipitation was carried out using solutions and reac ^¬ tion conditions similar to those used in Example 5. The re- actor was filled after 100 minutes, after which the product was removed from the reactor and divided into two parts. Precipitation was continued on half of the product for 60 minutes, after which it was again divided into two parts. This last step was repeated two more times. The shape and size of precipitate particles is shown in Fig. 2. The metal carbonate particles are essentially spherical, the few ir ^¬ regularly shaped species surrounding the spherical parti- cles in the scanning electron microscopy image is K ₂ SO ₄

(the sample used for imaging was not subjected to the same rigorous washing procedure as the rest of the sample) .

The final product in the reactor was collected, and then it was repeatedly and thoroughly washed on a Buchner funnel using deionized water (temperature varied between 20°C and 65°C) until the electrical conductivity of the waste water was below 130 μΞ/ατι.

The washed and dried precursor samples were analysed using inductively-coupled plasma atomic emission spectroscopy to determine the content of Ni, Mn, Na, K, and S species in the samples. The samples contained 12 wt% Ni, 35 wt% Mn, 370 ppmw Na, 440 ppmw K and 170 ppmw S. Compared to Exam- pies 1, 2, or 3, the product made according to the proce ^¬ dure in this example results in significantly lower Na con ^¬ tent in the washed and dried product.

Example 7

The precipitation was carried out using solutions and reac ^¬ tion conditions similar to those used in Example 5. The metal ion solution and the carbonate solution are added separately into a reactor provided with vigorous stirring (400 rpm) and a temperature of 35°C. The volume of the re ^¬ actor was 8 liters.

The product was removed from the reactor after 120 minutes and divided into two. Precipitation was continued on half of the product for 120 minutes, after which it was again divided into two. This last step was repeated two more times. The product thus obtained was collected and repeat- edly and thoroughly washed on a Buchner funnel using near- boiling deionized water, until the electrical conductivity of the waste water was below 130 μΞ/ατι. Further washing did not result in any significant further decrease in conduc ^¬ tivity.

The washed and dried precursor samples were analysed using a room-temperature powder X-ray diffraction using Cu Koii radiation. The Rietveld refining of the obtained spectrum results in the following phase composition: 100% rhodochro- site (a = 4.793 A, b = 15.549 A), i.e. a pure metal car ^¬ bonate. The corresponding diffractogram is shown in Fig. 3.

Example 8

A metal ion solution identical to that used in Example 5 was prepared. In a separate flask, 2 liters of a carbonate solution was prepared by dissolving 368 g K ₂ CO ₃ and 75 g KOH (corresponding to a molar ratio of K ₂ CO ₃ to KOH of 2:1) in deionized water. The metal ion solution and the car ^¬ bonate solution are added separately into a reactor pro ^¬ vided with vigorous stirring (650 rpm) and a temperature of 36°C. The volume of the reactor was 1 liter.

The product was removed from the reactor after 100 minutes and divided into two. Precipitation was continued on half of the product for 60 minutes. The product thus obtained was collected and repeatedly and thoroughly washed on a Buchner funnel using near-boiling deionized water, until the electrical conductivity of the waste water was below 130 μΞ/ατι. Further washing did not result in significant further decreases in conductivity.

The washed and dried precursor samples were analysed using a room-temperature powder X-ray diffraction using Cu Koii radiation. The Rietveld refining of the obtained spectrum results in the following phase composition: 100% rhodochro- site, i.e. a pure metal carbonate. The corresponding dif- fractogram is shown in Fig. 4. No peaks corresponding to hydroxides or hydroxycarbonates are present in the diffrac- togram. Therefore, pure metal carbonate material was ob ^¬ tained as product, even though the carbonate solution used during precipitation was a mixture of carbonate and hydrox- ide.

It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, and that it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.