WO2022195255A1

WO2022195255A1 - Cathode material and process

Info

Publication number: WO2022195255A1
Application number: PCT/GB2022/050605
Authority: WO
Inventors: Fiona Claire COOMER; James Alexander CORBIN; Cameron Jon WALLAR
Original assignee: Ev Metals Uk Limited
Priority date: 2021-03-19
Filing date: 2022-03-09
Publication date: 2022-09-22
Also published as: GB202103815D0

Abstract

The present invention relates to improved particulate lithium nickel oxide materials which are useful as cathode materials in lithium secondary batteries. The present invention also provides processes for preparing such lithium nickel oxide materials, and electrodes and cells comprising the materials.

Description

CATHODE MATERIAL AND PROCESS

Field of the Invention

Background of the Invention

Lithium transition metal oxide materials having the formula UMO2, where M typically includes one or more transition metals, find utility as cathode materials in lithium ion batteries. Examples include LiNiC>2 and UC0O2.

US 6921609 B2 describes a composition suitable for use as a cathode material of a lithium battery which includes a core composition having an empirical formula Li_xM’_zNii-yM”y0₂ and a coating on the core which has a greater ratio of Co to Ni than the core.

WO 2013/025328 A1 describes a particle including a plurality of crystallites including a first composition having a layered a-NaFe0₂-type structure. The particles include a grain boundary between adjacent crystallites, and the concentration of cobalt in the grain boundaries is greater than the concentration of cobalt in the crystallites. Cobalt enrichment is achieved by treatment of the particles with a solution of UNO₃ and Co(NOs)₂, followed by spray drying and calcining.

With demand increasing for lithium-ion batteries in high-end applications such as electric vehicles (EVs), it is imperative to use cathode materials which provide not only acceptable specific capacity but also excellent retention of that capacity over a large number of charging cycles, so that the range of the vehicle after each charge over its lifetime is as consistent as possible. Capacity retention is also commonly referred to simply as the “cyclability” of the battery.

There therefore remains a need for improved lithium transition metal oxide materials and processes for their manufacture. In particular, there remains a need for improvements in the capacity retention of lithium transition metal oxide materials when used as cathode materials in lithium secondary batteries. Summary of the Invention

The present inventors have found that providing surface enrichment comprising cobalt and zirconium to lithium nickel oxide particles can provide a particularly excellent balance of capacity, capacity retention, lithium surface impurities and DCIR. Particular quantities of cobalt and zirconium in the surface enrichment can provide particularly desirable properties as demonstrated in the Examples. For these surface enriched materials, controlling the temperature during surface enrichment can help to further supress lithium surface impurities.

Accordingly, a first aspect of the invention is a surface-modified particulate lithium nickel oxide material comprising particles having Formula I

LiaNixCOyMg_zZrpMq0_2+b Formula I in which:

0.8 £ a £ 1.2 0.8 £ x < 1 0.010 £ y £ 0.15 0 £ z £ 0.030 0.001 £ p £ 0.015 0 £ q £ 0.2; and -0.2 £ b £ 0.2; wherein M is selected from Mn, V, Ti, B, Al, Sr, Ca, Cu , Sn, Cr, Fe, Ga, Si, W, Mo, Ta, Y, Sc, Nb, Pb, Ru, Rh and Zn and combinations thereof; and wherein the particles comprise a core and an enriched surface layer at the surface of the core, and wherein the enriched surface layer includes zirconium and cobalt. It may be preferred that the enriched surface layer includes 0.1 to 1.5 or 1.0 at% zirconium and 0.1 to 5 at% cobalt.

A second aspect of the invention is a process for preparing particulate lithium nickel oxide material having Li_aNixCoyMg_zZrpMq02_+b

Formula I in which:

0.8 £ a £ 1.2 0.8 £ x < 1 0.010 £ y £ 0.15 0 £ z £ 0.030 0.001 £ p £ 0.015 0 £ q £ 0.2; and -0.2 £ b £ 0.2; wherein M is selected from Mn, V, Ti, B, Al, Sr, Ca, Cu , Sn, Cr, Fe, Ga, Si, W, Mo, Ta, Y, Sc, Nb, Pb, Ru, Rh and Zn and combinations thereof; and the process comprising the steps of: mixing lithium-containing compound with a nickel-containing compound, a cobalt- containing compound, optionally a magnesium-containing compound, and/or an M- containing compound, wherein a single compound may optionally contain two or more of Ni, Co, Mg, and M, to obtain a mixture; calcining the mixture to obtain a calcined material; and contacting the first calcined material with a cobalt-containing compound and a zirconium-containing compound in a surface modification step to form an enriched surface layer on the first calcined material, such that the enriched surface layer includes zirconium and cobalt. It may be preferred that the enriched surface layer includes 0.1 to 1.5 or 1.0 at% zirconium and 0.1 to 5 at% cobalt.

It may be preferred that the surface modification step is carried out at a temperature from 10 to 50°C.

A third aspect of the invention provides particulate lithium nickel oxide obtained or obtainable by a process described herein.

A fourth aspect of the invention provides a cathode material for a lithium secondary battery comprising the particulate lithium nickel oxide material according to the first aspect.

A fifth aspect of the invention provides a cathode comprising the particulate lithium nickel oxide material according to the first aspect.

A sixth aspect of the invention provides a lithium secondary cell or battery (e.g. a secondary lithium ion battery) comprising the cathode according to the fifth aspect. The battery typically further comprises an anode and an electrolyte. A seventh aspect of the invention provides use of the particulate lithium nickel oxide according to the first aspect for the preparation of a cathode of a secondary lithium battery (e.g. a secondary lithium ion battery).

An eighth aspect of the invention provides the use of the particulate lithium nickel oxide according to the first aspect as a cathode material to improve the capacity retention or cyclability of a lithium secondary cell or battery.

A ninth aspect is a method of improving the capacity retention or cyclability of a lithium secondary cell or battery, comprising the use of a cathode material in the cell or battery, wherein the cathode material comprises the particulate lithium nickel oxide material according to the first aspect.

Detailed Description

Preferred and/or optional features of the invention will now be set out. Any aspect of the invention may be combined with any other aspect of the invention unless the context demands otherwise. Any of the preferred and/or optional features of any aspect may be combined, either singly or in combination, with any aspect of the invention unless the context demands otherwise. It is intended that upper and lower limits of ranges are independently combinable, and that the various ranges and values given for a, b, x, y, z, p and q are combinable with each other and with the other features recited herein.

The particulate lithium nickel oxide material has a composition according to Formula I defined above. The compositions recited herein may be determined by Inductively Coupled Plasma (ICP) analysis as described in the Examples section below. It may be preferred that the compositions recited herein are ICP compositions. As used herein, the at% (atom %) content of the metals in the surface enriched layer is given with respect to the total metal content (excluding lithium) of the lithium nickel oxide material.

In Formula I, 0.8 £ a £ 1.2. In some embodiments a is greater than or equal to 0.9, 0.95,

0.99 or 1.0. In some embodiments, a is less than or equal to 1.1, or less than or equal to 1.05. In some embodiments, 0.90 £ a £ 1.10, for example 0.95 £ a £ 1.05. In some embodiments, 0.99 £ a £ 1.05 or 1.0 £ a £ 1.05. It may be particularly preferred that 0.95 £ a £ 1.05.

In Formula I, 0.8 £ x < 1. In some embodiments, 0.85 £ x < 1 or 0.88 £ x < 1. In some embodiments, x is less than or equal to 0.99, 0.98, 0.97, 0.96, 0.95, 0.94, 0.93, or 0.92. In some embodiments, x is greater than or equal to 0.85, 0.87, 0.88 or or 0.89. In some embodiments, 0.8 £ x £ 0.99, for example 0.85 £ x £ 0.98, 0.85 £ x £ 0.97, 0.85 £ x £ 0.96 or 0.87 £ x £ 0.93. It may be particularly preferred that 0.85 £ x £ 0.98.

In Formula I, 0.010 £ y £ 0.15. In some embodiments y is greater than or equal to 0.03,

0.05, 0.06, 0.065, 0.07, or 0.08. In some embodiments y is less than or equal to 0.14, 0.12, 0.11 or 0.10. In some embodiments, 0.05 £ y £ 0.13. In some embodiments,

0.07 £ y £ 0.12. In some embodiments, 0.08 £ y £ 0.11

In Formula I, 0 £ z £ 0.03. In some embodiments z is greater than or equal to 0.001 , 0.003, 0.006 or 0.007. In some embodiments, z is less than or equal to 0.025, 0.020, 0.015, 0.012 or 0.010. Avoiding too high a magnesium content can be advantageous as it can lead to higher specific capacity. Where the cobalt and zirconium content in the surface enriched layer is as provided in the present invention, excellent capacity retention can be obtained even with relatively low magnesium contents.

In Formula I, 0.001 £ p £ 0.015. In some embodiments, p is less than or equal to 0.013, 0.012, 0.010, 0.008, 0.007, 0.0065, 0.0060, 0.0055, 0.0050, or 0.0045. In some embodiments p is greater than or equal to 0.002, 0.0025 or 0.003. In some embodiments, 0.002 £ p £ 0.01, 0.002 £ p £ 0.009, 0.002 £ p £ 0.007, 0.002 £ p £ 0.005, 0.003 £ p £ 0.007 or 0.003 £ p £ 0.005.

In Formula I, -0.2 £ b £ 0.2. In some embodiments b is greater than or equal to -0.1. In some embodiments b is less than or equal to 0.1. In some embodiments, -0.1 £ b £ 0.1. In some embodiments, b is 0 or about 0. In some embodiments, b is 0.

In Formula I, M is one or more selected from Mn, V, Ti, B, Al, Sr, Ca, Cu , Sn, Cr, Fe, Ga, Si, W, Mo, Ta, Y, Sc, Nb, Pb, Ru, Rh and Zn. In some embodiments, M is one or more selected from Mn, V, Ti, B, Al, Sr, Ca, Cu , Sn, Cr, Fe, Ga, Si and Zn. In some embodiments, M is Mn. In some embodiments, M represents a dopant which is present within the core of the particle but not within the enriched surface layer.

In Formula I, 0 £ q £ 0.2. In some embodiments, 0 £ q £ 0.15. In some embodiments, 0 £ q £ 0.10. In some embodiments, 0 £ q £ 0.05. In some embodiments, q is 0.

In some embodiments:

0.95 £ a £ 1.05 0.85 £ x < 1 0.07 £y£ 0.12 0.003 £z£0.012

0.002 £ p £0.01

0 £ q £ 0.2, and -0.2 £ b £ 0.2.

In some embodiments:

0.95 £ a £ 1.05 0.85 £ x < 1 0.07 £y£ 0.12 0.003 £z£0.012

0.002 £ p £0.01 q = 0, and -0.2 £ b £ 0.2.

In some embodiments:

0.95 £ a £ 1.05 0.85 £ x < 1 0.07 £y£ 0.12 0.003 £z£0.012 0.002 £ p £ 0.007 0 £ q £ 0.2, and b = 0.

In some embodiments:

0.95 £ a £ 1.05 0.85 £ x < 1 0.07 £y£ 0.12 0.003 £z£0.012 0.002 £ p £ 0.007 q = 0 and b = 0.

In some embodiments, the particulate lithium nickel oxide material is a crystalline (or substantially crystalline) material. It may have the a-NaFeC>2-type structure. It may be a polycrystalline material, meaning that each particle of lithium nickel oxide material is made up of multiple crystallites (also known as crystal grains or primary particles) which are agglomerated together. The crystal grains are typically separated by grain boundaries. Where the particulate lithium nickel oxide is polycrystalline, it will be understood that the particles of lithium nickel oxide comprising multiple crystals are secondary particles.

The particulate lithium nickel oxide material of Formula I comprises an enriched surface, i.e. comprises a core material which has been surface modified (subjected to a surface modification process) to form an enriched surface layer. In some embodiments the surface modification results from contacting the core material with a Co-containing compound a zirconium-containing compound, and then optionally carrying out calcination of the material. The compounds may be in solution, and in such context herein the term “compound” refers to the corresponding dissolved species. For clarity, the discussions of the composition according to Formula I herein when in the context of surface-modified particles relate to the overall particle, i.e. the particle including the enriched surface layer.

Herein, the terms “surface modified”, “enriched surface” and “enriched surface layer” refer to a particulate material which comprises a core material which has undergone a surface modification or surface enrichment process to increase the concentration of cobalt and zirconium at or near to the surface of the particles. The term “enriched surface layer” therefore typically refers to a layer of material at or near to the surface of the particles which contains a greater concentration of cobalt and zirconium than the remaining material of the particle, i.e. the core of the particle. In some embodiments, the layer may be a continuous layer or region covering the surface of the particles. In other embodiments, the surface of the particles may include discontinuous regions of greater concentrations of cobalt and/or zirconium. The concentration of cobalt and / or zirconium may decrease from the surface of the particles in a direction towards the centre of the particles. The present inventors have found that elements added in a surface modification step may preferentially migrate to the grain boundaries between primary particles. Accordingly, the concentration of cobalt in lithium nickel oxide material may be higher in the grain boundaries than in the primary particles. The concentration of zirconium in lithium nickel oxide material may be higher in the grain boundaries than in the primary particles. The concentration of cobalt and zirconium in lithium nickel oxide material may be higher in the grain boundaries than in the primary particles.

As the skilled person will understand, elements may migrate between the core and the surface layer during preparation, storage or use of the material. Herein, where an element is stated to be present in (or absent from, or present in certain quantities in) the core, this is to be understood to refer to that element being intentionally added to, (or excluded from, or added in a particular quantity to) the core, and is not intended to exclude from the scope of protection materials where the distribution of elements is altered by migration during preparation, storage or use. Similarly, where an element is stated to be present in (or absent from, or present in certain quantities in) the surface enriched layer, this is to be understood to refer to that element being intentionally added to, (or excluded from, or added in a particular quantity to) the surface enriched layer, and is not intended to exclude from the scope of protection materials where the distribution of elements is altered by migration during preparation, storage or use. For example, where the surface enriched layer includes 1 at% cobalt, this means that 1 at% of the cobalt is added in the surface enrichment step, but does not preclude materials where some of the Co added in the surface enrichment step has migrated into the core.

The surface enriched layer comprises zirconium, preferably 0.1 to 1.5 at% or 0.1 to 1.0 at% zirconium based on total metal content (excluding lithium). The surface enriched layer may include at least 0.2, 0.25 or 0.35 at% zirconium. The surface enriched layer may include less than or equal to 0.95, 0.9, 0.8, 0.75, 0.7, 0.65, 0.6, 0.55, or 0.5 at% zirconium. For example, the surface enriched layer may include 0.1 to 0.9, 0.1 to 0.8, 0.1 to 0.7, 0.1 to 0.6, 0.2 to 0.6, 0.1 to 0.5 or 0.2 to 0.5 at% zirconium. (For the avoidance of doubt, references to cobalt and/or zirconium in the surface enriched layer refers to atoms of these metals at any suitable oxidation state, not just to these metals in elemental form.)

The surface enriched layer comprises cobalt, preferably 0.1 to 5 at % cobalt based on total metal content (excluding lithium). The surface enriched layer may include at least 0.2, 0.3, 0.5, 0.7 or 0.9 at% cobalt. The surface enriched layer may include less than or equal to 4, 3, 2.5, 2, 1.5 or 1.1 at% cobalt. For example, the surface enriched layer may include 0.5 to 3, 0.7 to 3, 0.5 to 1.5 or 0.7 to 1.5 at% cobalt.

Where the zirconium content in the surface enriched layer is at least 0.5 at% or 0.6 at% or more, it may be preferred that the cobalt content in the surface enriched layer is 1.8, 1.5 or 1.2 at% or less.

In some cases, it may be preferable to add additional lithium, e.g. during a surface enrichment step, to retain a suitable lithium to metal ratio. This may be preferred, e.g. where the total amount of Co and Zr in the surface enriched layer is particularly high (e.g. greater than or equal to 2 at%, 3 at% or 4 at%). The surface enriched layer may be obtainable by contacting lithium nickel oxide (core) particles with a surface modification composition at a temperature in the range from 10 to 80°C, for example at a temperature of at least 10, 15 or 20°C, for example at a temperature of less than or equal to 50, 40, 35 or 30°C. A temperature range of 10 to 50°C or 10 to 40°C may be particularly preferred. This may result in reduced surface lithium impurities, and reduced operational costs for running the process. Alternatively, a mixture of the lithium nickel oxide (core) particles and the surface modification composition may be heated to the recited temperatures.

The particulate lithium nickel oxide material typically has a D50 particle size of at least 4 pm, e.g. at least 5 pm, at least 5.5 pm, at least 6.0 pm or at least 6.5 pm. The particles of lithium nickel oxide (e.g. secondary particles) typically have a D50 particle size of 20 pm or less, e.g. 15 pm or less or 12 pm or less. In some embodiments, the D50 particle size is from about 5 pm to about 20 pm, for example about 5 pm to about 19 pm, for example about 5 pm to about 18 pm, for example about 5 pm to about 17 pm, for example about 5 pm to about 16 pm, for example about 5 pm to about 15 pm, for example about 5 pm to about 12 pm, for example about 5.5 pm to about 12 pm, for example about 6 pm to about 12 pm, for example about 6.5 pm to about 12 pm, for example about 7 pm to about 12 pm, for example about 7.5 pm to about 12 pm. Unless otherwise specified herein, the D50 particle size refers to Dv50 (volume median diameter) and may be determined by using the method set out in ASTM B822 of 2017 under the Mie scattering approximation, for example using a Malvern Mastersizer 3000.

In some embodiments, the D10 particle size of the material is from about 0.1 pm to about 10 pm, for example about 1 pm to about 10 pm, about 2 pm to about 8 pm, or from about 5 pm to about 7 pm. Unless otherwise specified herein, the D10 particle size refers to Dv10 (10% intercept in the cumulative volume distribution) and may be determined by using the method set out in ASTM B822 of 2017 under the Mie scattering approximation, for example using a Malvern Mastersizer 3000.

In some embodiments, the D90 particle size of the material is from about 10 pm to about 40 pm, for example from about 12 pm to about 35 pm, about 12 pm to about 30 pm, about 15 pm to about 25 pm or from about 16 pm to about 20 pm. Unless otherwise specified herein, the D90 particle size refers to Dv90 (90% intercept in the cumulative volume distribution) and may be determined by using the method set out in ASTM B822 of 2017 under the Mie scattering approximation, for example using a Malvern Mastersizer 3000. In some embodiments, the tapped density of the particulate lithium nickel oxide is from about 1.9 g/cm³ to about 2.8 g/cm³ , e.g. about 1.9 g/cm³ to about 2.4 g/cm³.

The tapped density of the material can suitably be measured by loading a graduated cylinder with 25 ml_ of powder. The mass of the powder is recorded. The loaded cylinder is transferred to a Copley Tapped Density Tester JV Series. The material is tapped 2000 times and the volume re-measured. The re-measured volume divided by the mass of material is the recorded tap density.

The particulate lithium nickel oxide typically comprises less than 0.1 wt% of surface U2CO3.

It may comprise less than 0.08 wt% of surface U2CO3, e.g. less than 0.07 wt%, less than 0.06 wt%, or less than 0.5 wt%. It may have 0 wt% surface U2CO3, but in some embodiments there may be at least 0.01 wt% or 0.02 wt% of surface U2CO3. It is preferred to minimise U2CO3 impurities since their presence leads to lower active mass, and a reduction in the amount of lithium available for charge and discharge capacity. Additionally, U2CO3 is known to cause problems with cell gassing.

The amount of surface U2CO3 may be determined by titration with HCI using bromophenol blue indicator. Typically, a first titration step with HCI and phenolphthalein indicator is carried out before titration with bromophenol blue indicator to remove any lithium hydroxide. The titration protocol may include the following steps:

Extract surface lithium carbonate from sample of particulate lithium nickel oxide material by agitating in deionised water for 5 minutes to provide an extractate solution, and separate extractate solution from residual solid;

- Add phenolphthalein indictor to the extractate solution, and titrate using HCI solution until extractate solution becomes clear (indicating the removal of any LiOH);

- Add bromophenol blue indictor to the extractate solution, and titrate using HCI solution until extractate solution turns yellow; (the amount of lithium carbonate in the extractate solution can be calculated from this titration step); and

Calculate wt% of surface lithium carbonate in the sample of particulate lithium nickel oxide material, assuming 100% extraction of surface lithium carbonate into the extractate solution. The particulate lithium nickel oxide typically comprises less than 0.1 wt% LiOH as Li, for example less than 0.09, less than 0.08, less than 0.07, less than 0.06, less than 0.05 less than 0.045 or less than 0.04wt%. It may have 0 wt% surface LiOH as Li, but in some embodiments there may be at least 0.005 wt% or 0.01 wt% of surface surface LiOH as Li. It is preferred to minimise LiOH impurities since their presence leads to lower active mass, and a reduction in the amount of lithium available for charge and discharge capacity.

Furthermore, LiOH readily reacts with atmospheric carbon dioxide to form U2CO3, which is known to cause problems with cell gassing.

The amount of LiOH as Li may be determined by titration with HCI using a phenolphthalein indicator. The titration protocol may include the following steps:

Extract surface lithium hydroxide from sample of particulate lithium nickel oxide material by sonication in methanol for ten minutes, and separate the methanol solution to provide an extractate solution.

- Add phenolphthalein indictor to the extractate solution, and titrate using HCI solution until extractate solution becomes clear.

Calculate wt% of surface LiOH in the sample of particulate lithium nickel oxide material, assuming 100% extraction of surface LiOH into the extractate solution.

The particulate lithium nickel oxide of the invention is characterised by an improved capacity retention for cells which incorporate the material as a cathode, in particular a high retention of capacity after 50 cycles. When determined at a temperature of 23 °C in a half cell coin cell vs lithium, under a charge/discharge rate of 1C and voltage window of 3.0-4.3V, with an electrode loading of 9.0 mg/cm² and an electrode density of 3.0 g/cm³, it has been found that materials according to the invention may provide a capacity retention of greater than 95% after 50 cycles, and in some cases as high as around 96%. The % capacity retention after 50 cycles is defined as the capacity of the cell after the 50^th cycle as a percentage of the initial capacity of the cell after its first charge. For clarity, one cycle includes a complete charge and discharge of the cell. For example, 90% capacity retention means that after the 50^th cycle the capacity of the cell is 90% of the initial capacity.

The material may have a capacity retention (after 50 cycles in a half cell coin cell vs Li, at an electrode loading of 9.0 mg/cm² and an electrode density of 3.0 g/cm³, tested at 23 °C and a 1C charge/discharge rate and voltage window of 3.0-4.3V) of at least 94%, at least 95% or at least 96%. The process for preparing the particulate lithium nickel oxide typically comprises the steps of: mixing lithium-containing compound with a nickel-containing compound, a cobalt- containing compound, optionally a magnesium-containing compound, and/or an M- containing compound, wherein a single compound may optionally contain two or more of Ni, Co, Mg, and M’, to obtain a mixture; calcining the mixture to obtain a calcined material; and contacting the first calcined material with a cobalt-containing compound and a zirconium-containing compound in a surface modification step to form an enriched surface layer on the first calcined material, such that the enriched surface layer includes 0.1 to 1.0 at% or more zirconium and 0.1 to 5 at% or more cobalt, wherein M’ is selected from Mn, V, Ti, B, Al, Zr, Sr, Ca, Cu , Sn, Cr, Fe, Ga, Si, W, Mo, Ta,

Y, Sc, Nb, Pb, Ru, Rh and Zn and combinations thereof. In some embodiments, M’ is one or more selected from Mn, V, Ti, B, Al, Sr, Ca, Cu , Sn, Cr, Fe, Ga, Si and Zn. In some embodiments, M’ is Mn.

In some embodiments, the first calcined material is a core material having Formula II:

I — la 1 Nίc1 COyl MQ 1 M ql 02+t>1

Formula II in which:

0.8 £ a1 £ 1.2 0.8 £ x1 < 1 0.008 £ y1 £ 0.14 0 £ z1 £ 0.03 0 £ q1 £ 0.2; and -0.2 £ b1 £ 0.2; wherein M’ is selected from Mn, V, Ti, B, Zr, Al, Sr, Ca, Cu , Sn, Cr, Fe, Ga, Si, W, Mo, Ta,

In some embodiments, the process includes a further calcination step after the surface modification step.

In some embodiments q1 = 0. The lithium-containing compound may be selected from lithium hydroxide (e.g. LiOH or UOH.H₂O), lithium carbonate (U₂CO₃), and hydrated forms thereof. Lithium hydroxide may be particularly preferred.

The nickel-containing compound may be selected from nickel hydroxide (Ni(OH)₂), nickel oxide (NiO), nickel oxyhydroxide (NiOOH), nickel sulfate, nickel nitrate, nickel acetate and hydrated forms thereof. Nickel hydroxide may be particularly preferred.

The cobalt-containing compound may be selected from cobalt hydroxide (Co(OH)₂), cobalt oxide (CoO, C0₂O₃, C0₃O₄), cobalt oxyhydroxide (CoOOH), cobalt sulfate, cobalt nitrate, cobalt acetate and hydrated forms thereof. Cobalt hydroxide may be particularly preferred.

The magnesium-containing compound may be selected from magnesium hydroxide (Mg(OH)₂), magnesium oxide (MgO), magnesium sulfate, magnesium nitrate, magnesium acetate and hydrated forms thereof. Magnesium hydroxide may be particularly preferred.

The M-containing compound may be selected from M hydroxide, M oxide, M nitrate, M sulfate, M carbonate or M acetate and hydrated forms thereof. M hydroxide may be particularly preferred.

Alternatively, two or more of nickel, cobalt, magnesium and optionally M may be provided as a mixed metal hydroxide, e.g. a mixed nickel cobalt hydroxide or a mixed nickel cobalt M hydroxide. The mixed metal hydroxide may be a coprecipitated hydroxide. It may be polycrystalline.

The mixed metal hydroxide may have a composition according to Formula III:

Ni_xCOyMg_zM’q(OH)2+b Formula III in which x, y, z, q, b and M’ are each independently as defined herein. As a cobalt enrichment step is carried out (as described below), it may be preferred that the value for y in Formula III is less than the value for y in Formula I.

Such mixed metal hydroxides may be prepared by co-precipitation methods well-known to the person skilled in the art. These methods may involve the co-precipitation of the mixed metal hydroxide from a solution of metal salts, such as metal sulfates, for example in the presence of ammonia and a base, such as NaOH. In some cases suitable mixed metal hydroxides may be obtainable from commercial suppliers known to the skilled person.

The calcination step may be carried out at a temperature of at least 400 °C, at least 500 °C, at least 600 °C or at least 650 °C. The calcination step may be carried out at a temperature of 1000 °C or less, 900 °C or less, 800 °C or less or 750 °C or less. The material to be calcined may be at a temperature of 400 °C, at least 500 °C, at least 600 °C or at least 650 °C for a period of at least 2 hours, at least 5 hours, at least 7 hours or at least 10 hours. The period may be less than 24 hours.

The calcination step may be carried out under a CC free atmosphere. For example, CC>2-free air may be flowed over the materials to be calcined during calcination and optionally during cooling. The CC>2-free air may, for example, be a mix of oxygen and nitrogen. The CC>2-free atmosphere may be oxygen (e.g. pure oxygen). Preferably, the atmosphere is an oxidising atmosphere. As used herein, the term “CC>2-free” is intended to include atmospheres including less than 100 ppm CO2, e.g. less than 50 ppm CO2, less than 20 ppm CO2 or less than 10 ppm CO2. These CO2 levels may be achieved by using a CO2 scrubber to remove CO2.

In some embodiments, the CC>2-free atmosphere comprises a mixture of O2 and N2. In some embodiments, the mixture comprises a greater amount of N2 than O2. In some embodiments, the mixture comprises N2 and O2 in a ratio of from 50:50 to 90:10, for example from 60:40 to 90:10, for example about 80:20.

In some embodiments, the particulate lithium nickel oxide material of Formula I comprises a surface-modified structure comprising a core and an enriched surface layer at the surface of the core, resulting from performing a surface-modification step on a core material having Formula II:

I — la 1 Nίc1 COyl MQ 1 M ql 02+t>1

Formula II in which:

The surface modification step may comprise contacting the core material with a cobalt- containing compound and a zirconium-containing compound, which may optionally be provided in solution, for example in aqueous solution.

In some embodiments q1 = 0.

The surface-modification step of the processes of the invention (also referred to herein as a surface enrichment step) comprises contacting the core material with cobalt, to increase the concentration of cobalt at or near to the surface of the particles and/or in the grain boundaries. The surface-modification step of the processes of the invention (also referred to herein as a surface enrichment step) comprises contacting the core material with zirconium, to increase the concentration of cobalt at or near to the surface of the particles and/or in the grain boundaries.

In some embodiments, the surface-modification step (also referred to herein as a surface enrichment step) comprises contacting the core material with additional metal selected from one or more of aluminium, lithium and M, to increase the concentration of such metal in the grain boundaries and/or at or near to the surface of the particles.

The cobalt, zirconium, aluminium, lithium and/or M may be independently selected from nitrates, sulfates or acetates. Nitrates may be particularly preferred. The compounds may be provided in solution (e.g. aqueous solution). The compounds may be soluble in water. The zirconium containing compound may suitably be ZG0(N0₃)₂. Other suitable compounds include Zr acetate, Zr chloride and Zr sulfate. The cobalt-containing compound may suitably be CO(N0₃)₂. Other suitable compounds include Co acetate, Co chloride and Co sulfate.

The lithium nickel oxide (core) particles with a surface modification composition at a temperature in the range from 10 to 80°C, for example at a temperature of at least 10, 15 or 20°C, for example at a temperature of less than or equal to 50, 40, 35 or 30°C. A temperature range of 10 to 50°C or 10 to 40°C may be particularly preferred. This may result in reduced surface lithium impurities, and reduced operational costs for running the process. Alternatively, a mixture of the lithium nickel oxide (core) particles and the surface modification composition may be heated to the recited temperatures.

Where the coating composition is a solution, the mixture of the solution with the intermediate may be dried, e.g. by evaporation of the solvent or by spray drying.

The cobalt-containing compound, zirconium-containing compound and optional one or more further metal-containing compounds may be provided as a composition, referred to herein as a “surface modification composition”. The surface modification composition may comprise a solution of the cobalt-containing compound and optional one or more further metal- containing compounds (e.g. aqueous solution).

The cobalt-containing compound, zirconium-containing compound and optional one or more further metal-containing compounds used in the surface modification step may be as defined above with reference to the compounds used in the formation of the intermediate (core) material. It may be particularly preferred that the cobalt-containing compound, zirconium- containing compound and/or each of the one or more further metal-containing compounds is a metal-containing nitrate.

In some embodiments, the surface modification step comprises contacting the core material with additional metal-containing compounds in an aqueous solution. The core material may be added to the aqueous solution to form a slurry or suspension. In some embodiments the slurry is agitated or stirred. In some embodiments, the weight ratio of core material to water in the slurry after addition of the core material to the aqueous solution is from about 1.5:1 to about 1:1.5, for example from about 1.4:1 to about 1:1.4, about 1.3:1 to about 1:1.3, about 1.2:1 to about 1:1.2 or about 1.1:1 to about 1:1.1. The weight ratio may be about 1:1.

Typically, the surface modification step is carried out after the first calcination step described above.

The surface modification step may be followed by a second calcination step. The second calcination step may be carried out at a temperature of at least 400 °C, at least 500 °C, at least 600 °C or at least 650 °C. The second calcination step may be carried out at a temperature of 1000 °C or less, 900 °C or less, 800 °C or less or 750 °C or less. The material to be calcined may be at a temperature of 400 °C, at least 500 °C, at least 600 °C or at least 650 °C for a period of at least 30 minutes, at least 1 hour or at least 2 hours. The period may be less than 24 hours. The second calcination step may be shorter than the first calcination step.

The second calcination step may be carried out under a CC free atmosphere as described above with reference to the first calcination step.

The process may include one or more milling steps, which may be carried out after the first and/or second calcination steps. The nature of the milling equipment is not particularly limited. For example, it may be a ball mill, a planetary ball mill or a rolling bed mill. Alternatively the materials may be manually ground, e.g. using a pestle and mortar. The milling may be carried out until the particles (e.g. secondary particles) reach the desired size. For example, the particles of lithium nickel oxide (e.g. secondary particles) are typically milled until they have a D50 particle size of at least 5 pm, e.g. at least 5.5 pm, at least 6 pm or at least 6.5 pm. The particles of lithium nickel oxide (e.g. secondary particles) are typically milled until they have a D50 particle size of 15 pm or less, e.g. 14 pm or less or 13 pm or less.

The process of the present invention may further comprise the step of forming an electrode (typically a cathode) comprising the lithium nickel oxide material. Typically, this is carried out by forming a slurry of the particulate lithium nickel oxide, applying the slurry to the surface of a current collector (e.g. an aluminium current collector), and optionally processing (e.g. calendaring) to increase the density of the electrode. The slurry may comprise one or more of a solvent, a binder, carbon material and further additives.

Typically, the electrode of the present invention will have an electrode density of at least

2.5 g/cm³, at least 2.8 g/cm³ or at least 3 g/cm³. It may have an electrode density of

4.5 g/cm³ or less, or 4 g/cm³ or less. The electrode density is the electrode density (mass/volume) of the electrode, not including the current collector the electrode is formed on. It therefore includes contributions from the active material, any additives, any additional carbon material, and any remaining binder.

The process of the present invention may further comprise constructing a battery or electrochemical cell including the electrode comprising the lithium nickel oxide. The battery or cell typically further comprises an anode and an electrolyte. The battery or cell may typically be a secondary (rechargeable) lithium (e.g. lithium ion) battery. The present invention will now be described with reference to the following examples, which are provided to assist with understanding the present invention, and are not intended to limit its scope.

Examples

Preparation of Base Material

Base material was provided having a composition determined by ICP analysis of

U0.999N io.916COo.079Mgo.00802.

Base material may be prepared according to the following protocol:

100 g Nio_.96oCoo_.o_3iMgo_.o₉₉(OH)₂ and 26.36 g LiOH are dry mixed in a poly-propylene bottle for 30 mins. The LiOH is pre-dried at 200 °C under vacuum for 24 hours and kept dry in a purged glovebox filled with dry N2.

The powder mixture is loaded into 99%+ alumina crucibles and calcined under an artificial C0₂-free air mix which is 80:20 I\l₂:0₂. Calcination is performed as follows: to 450 °C (5 °C/min) with 2 hours hold, ramp to 700 °C (2 °C/min) with a 6 hour hold and cooled naturally to 130 °C. The artificial air mix is flowed over the powder bed throughout the calcination and cooling.

The samples are then removed from the furnace at 130 °C and transferred to a high-alumina lined mill pot and milled on a rolling bed mill until D50 is between 9.5 and 12.5 pm.

D50 is measured according to ASTM B822 of 2017 using a Malvern Mastersizer 3000 under the Mie scattering approximation.

Preparation of Surface Modified Materials Comparative Example 1

A comparative surface modified material was prepared from the base material described above using a surface modification composition of 0.64 at% Al and 4.0 at% Co according to the following procedure.

80g base material was slurried in 60mL deionised water which had been pre heated to 60°C under reflux. A further 10 mL deionised water was used to rinse in residual base material. The slurry was stirred at room temperature using a magnetic stirrer. Co(NO₃)₂.6H₂0 (9.5g), AI(Nq₃)₃.9H₂q (1.95g) and UNO3 (2.08g) were dissolved in 10mL deionised water to form a mixed nitrate solution. This mixed nitrate solution was added to the base material slurry. The mixture was stirred for 1h 20 minutes at 60°C, and then spray dried. After spray drying, 80g of spray dried material was loaded into 99%+ alumina saggars under an artificial CO2- free air mix which was 80:20 N2:C>2. Calcination was performed as follows: ramp to 450 °C (5°C/min) with 1 hour hold, ramp to 700 °C (2°C/min) with a 2 hours hold and cooled naturally to a temperature below 200°C. The artificial air mix was flowing over the powder bed through the calcination and cooling. The sample was crushed in a pestle and mortar in an N2 glovebox and sieved through 56pm mesh.

The composition of the sample of Comparative Example 1 was determined by ICP analysis to be Lio.988Nio.878COo.115Mgo.008Alo.00602.

Example 1

The base material prepared above was surface modified with 0.8 at% Zr according to the following procedure.

80g base material was slurried in 60 ml_ deionised water, using a further 10 mL deionised water to rinse residual base material. The slurry was stirred at room temperature using a magnetic stirrer. ZrO(NC>3)2 solution (ZrO(NC>3)235wt% in dilute nitric acid (available from Sigma Aldrich as “dilute nitric acid”) (2.38 mL) was added to the base material slurry using a mechanical pipette. The mixture was stirred for 20 minutes at room temperature, and then spray dried. After spray drying, 80g of spray dried material was loaded into 99%+ alumina saggars under an artificial CC>2-free air mix which was 80:20 N2:C>2. Calcination was performed as follows: ramp to 450 °C (5°C/min) with 1 hour hold, ramp to 700 °C (2°C/min) with a 2 hours hold and cooled naturally to a temperature below 200°C. The artificial air mix was flowing over the powder bed through the calcination and cooling. The sample was crushed in a pestle and mortar in an N2 glovebox and sieved through 56pm mesh.

The composition of the sample of Example 1 was determined by ICP analysis to be

Lio.983Nio.91 lCOo.079Mgo.008Zro.00802.

Example 2

80g base material was slurried in 60mL deionised water at 60°C under reflux, using a further 20 mL deionised water to rinse residual base material. ZrO(NC>3)2 solution (ZrO(NC>3)2 35wt% in dilute nitric acid) (2.38 mL) was added to the base material slurry. The mixture was stirred for 20 minutes at 60°C, and then spray dried. After spray drying, 80g of spray dried material was loaded into 99%+ alumina saggars under an artificial CC free air mix which was 80:20 N2:C>2. Calcination was performed as follows: ramp to 450 °C (5°C/min) with 1 hour hold, ramp to 700 °C (2 °C/min) with a 2 hours hold and cooled naturally to a temperature below 200°C. The artificial air mix was flowing over the powder bed through the calcination and cooling. The sample was crushed in a pestle and mortar in an N2 glovebox and sieved through 56pm mesh.

The composition of the sample of Example 2 was determined by ICP analysis to be

Lio.984Nio.912COo.078Mgo.008Zro.00802.

Example 3

The base material prepared above was surface modified with 1.2 at% Zr and 2 at% Co according to the following procedure.

80g base material was slurried in 50ml_ deionised water heated to 60°C under reflux, using a further 10 mL deionised water to rinse residual base material. The slurry was stirred at 60°C using a magnetic stirrer. Co(NC>₃)₂.6H₂0 (4.75g) was dissolved in 10ml_ deionised water. ZrO(NC>3)2 solution (ZrO(NC>3)2 35wt% in dilute nitric acid) (4.46 mL) was added to the cobalt nitrate solution using a mechanical pipette. This mixed nitrate solution was added to the base material slurry, using a further 10 mL deionised water to wash in. The mixture was stirred for 20 minutes at 60°C, and then spray dried. After spray drying, 80g of spray dried material was loaded into 99%+ alumina saggars under an artificial CC>2-free air mix which was 80:20 N2:C>2. Calcination was performed as follows: ramp to 450 °C (5°C/min) with 1 hour hold, ramp to 700 °C (2 °C/min) with a 2 hours hold and cooled naturally to a temperature below 200°C. The artificial air mix was flowing over the powder bed through the calcination and cooling. The sample was crushed in a pestle and mortar in an N2 glovebox and sieved through 56pm mesh.

The composition of the sample of Example 3 was determined by ICP analysis to be

Lio.973Nio.89lCOo.097Mgo.008Zro.01202.

Example 4

The base material prepared above was surface modified with 0.64 at% Zr and 2 at% Co according to the following procedure.

80g base material was slurried in 50mL deionised water at 60°C under reflux, using a further 10 mL deionised water to rinse residual base material. The slurry was stirred at room temperature using a magnetic stirrer. Co(NC>3)2.6H20 (4.75g) and UNO3 (0.37g) were dissolved in 10ml_ deionised water. ZrO(NC>3)2 solution (ZrO(NC>3)235wt% in dilute nitric acid) (2.38 mL) was added to cobalt nitrate solution using a mechanical pipette. This mixed nitrate solution was added to the base material slurry, using a further 10 mL deionised water to wash in. The mixture was stirred for 20 minutes at 60°C, and then spray dried. After spray drying, 80g of spray dried material was loaded into 99%+ alumina saggars under an artificial CC>2-free air mix which was 80:20 N2:C>2. Calcination was performed as follows: ramp to 450 °C (5°C/min) with 1 hour hold, ramp to 700 °C (2°C/min) with a 2 hours hold and cooled naturally to a temperature below 200°C. The artificial air mix was flowing over the powder bed through the calcination and cooling. The sample was crushed in a pestle and mortar in an N2 glovebox and sieved through 56pm mesh.

The composition of the sample of Example 4 was determined by ICP analysis to be

Lio.965Nio.90l COo.097Mgo.008Zro.00602.

Example 5

80g base material was slurried in 50mL deionised water, using a further 10 mL deionised water to rinse residual base material. The slurry was stirred at room temperature using a magnetic stirrer. Co(NC>3)2.6H20 (4.75g) and LiNCh (0.37g) were dissolved in 10mL deionised water. ZrO(NC>3)2 solution (ZrO(NC>3)235wt% in dilute nitric acid) (2.38 mL) was added to cobalt nitrate solution using a mechanical pipette. This mixed nitrate solution was added to the base material slurry, using a further 10 mL deionised water to wash in. The mixture was stirred for 20 minutes at room temperature, and then spray dried. After spray drying, 80g of spray dried material was loaded into 99%+ alumina saggars under an artificial CC>2-free air mix which was 80:20 N2:C>2. Calcination was performed as follows: ramp to 450 °C (5°C/min) with 1 hour hold, ramp to 700 °C (2°C/min) with a 2 hours hold and cooled naturally to a temperature below 200°C. The artificial air mix was flowing over the powder bed through the calcination and cooling. The sample was crushed in a pestle and mortar in an N2 glovebox and sieved through 56pm mesh.

The composition of the sample of Example 5 was determined by ICP analysis to be

Lio.99oNio.893COo.097Mgo.008Zro.00602. Example 6

The base material prepared above was surface modified with 0.64 at% Zr and 1 at% Co according to the following procedure.

80g base material was slurried in 50ml_ deionised water, using a further 10 mL deionised water to rinse residual base material. The slurry was stirred at room temperature using a magnetic stirrer. Co(NC>3)2.6H20 (2.37g) was dissolved in 10ml_ deionised water. ZrO(NC>3)2 solution (ZrO(NC>3)235wt% in dilute nitric acid) (2.38 mL) was added to cobalt nitrate solution using a mechanical pipette. This mixed nitrate solution was added to the base material slurry, using a further 10 mL deionised water to wash in. The mixture was stirred for 20 minutes at room temperature, and then spray dried. After spray drying, 80g of spray dried material was loaded into 99%+ alumina saggars under an artificial CC>2-free air mix which was 80:20 N2:C>2. Calcination was performed as follows: ramp to 450 °C (5°C/min) with 1 hour hold, ramp to 700 °C (2 °C/min) with a 2 hours hold and cooled naturally to a temperature below 200°C. The artificial air mix was flowing over the powder bed through the calcination and cooling. The sample was crushed in a pestle and mortar in an N2 glovebox and sieved through 56pm mesh.

The composition of the sample of Example 6 was determined by ICP analysis to be

Lio.987 Nio.902COo.089 M go. OOdZTq.00602

Example 1

The base material prepared above was surface modified with 0.4 at% Zr and 2 at% Co according to the following procedure.

80g base material was slurried in 50mL deionised water, using a further 10 mL deionised water to rinse residual base material. The slurry was stirred at room temperature using a magnetic stirrer. Co(NC>3)2.6H20 (4.75g) and LiNCh (0.24g) were dissolved in 10mL deionised water. ZrO(NC>3)2 solution (ZrO(NC>3)235wt% in dilute nitric acid) (1.49 mL) was added to cobalt nitrate solution using a mechanical pipette. This mixed nitrate solution was added to the base material slurry, using a further 10 mL deionised water to wash in. The mixture was stirred for 20 minutes at room temperature, and then spray dried. After spray drying, 80g of spray dried material was loaded into 99%+ alumina saggars under an artificial CC>2-free air mix which was 80:20 N2:C>2. Calcination was performed as follows: ramp to 450 °C (5°C/min) with 1 hour hold, ramp to 700 °C (2°C/min) with a 2 hours hold and cooled naturally to a temperature below 200°C. The artificial air mix was flowing over the powder bed through the calcination and cooling. The sample was crushed in a pestle and mortar in an N2 glovebox and sieved through 56pm mesh.

The composition of the sample of Example 7 was determined by ICP analysis to be

Lio.983Nio.898COo.097Mgo.008Zro.00402.

Example 8

The base material prepared above was surface modified with 0.4 at% Zr according to the following procedure.

80g base material was slurried in 60ml_ deionised water, using a further 20 ml_ deionised water to rinse residual base material. The slurry was stirred at room temperature using a magnetic stirrer. ZrO(NC>3)2 solution (ZrO(NC>3)235wt% in dilute nitric acid) (1.49 ml_) was added to the base material slurry using a mechanical pipette. The mixture was stirred for 20 minutes at room temperature, and then spray dried. After spray drying, 80g of spray dried material was loaded into 99%+ alumina saggars under an artificial CC>2-free air mix which was 80:20 N2:C>2. Calcination was performed as follows: ramp to 450 °C (5°C/min) with 1 hour hold, ramp to 700 °C (2 °C/min) with a 2 hours hold and cooled naturally to a temperature below 200°C. The artificial air mix was flowing over the powder bed through the calcination and cooling. The sample was crushed in a pestle and mortar in an N2 glovebox and sieved through 56pm mesh.

The composition of the sample of Example 8 was determined by ICP analysis to be Lio.99l Nio.914COo.079Mgo.008Zro.00402.

Example 9

The base material prepared above was surface modified with 0.4 at% Zr and 1 at% Co according to the following procedure.

80g base material was slurried in 50ml_ deionised water, using a further 10 mL deionised water to rinse residual base material. The slurry was stirred at room temperature using a magnetic stirrer. Co(NC>₃)₂.6H₂0 (2.37g) were dissolved in 10ml_ deionised water.

ZrO(NC>3)2 solution (ZrO(NC>3)235wt% in dilute nitric acid) (1.49 mL) was added to cobalt nitrate solution using a mechanical pipette. This mixed nitrate solution was added to the base material slurry, using a further 10 mL deionised water to wash in. The mixture was stirred for 20 minutes at room temperature, and then spray dried. After spray drying, 80g of spray dried material was loaded into 99%+ alumina saggars under an artificial CC>2-free air mix which was 80:20 N₂:C>₂. Calcination was performed as follows: ramp to 450 °C (5 °C/min) with 1 hour hold, ramp to 700 °C (2°C/min) with a 2 hours hold and cooled naturally to a temperature below 200°C. The artificial air mix was flowing over the powder bed through the calcination and cooling. The sample was crushed in a pestle and mortar in an N2 glovebox and sieved through 56pm mesh.

The composition of the sample of Example 9 was determined by ICP analysis to be

Lio.992Nio.902COo.09()Mgo.008Zro.00402.

Example 10

200g base material was slurried in 140ml_ deionised water, using a further 20 ml_ deionised water to rinse residual base material. The slurry was stirred at room temperature using a magnetic stirrer. Co(NC>₃)₂.6H₂0 (5.93g) was dissolved in 20ml_ deionised water. ZrO(NC>₃)₂ solution (ZrO(NC>₃)₂35wt% in dilute nitric acid) (3.73 ml_) was added to cobalt nitrate solution using a mechanical pipette. This mixed nitrate solution was added to the base material slurry, using a further 20 ml_ deionised water to wash in. The mixture was stirred for 20 minutes at room temperature, and then spray dried. After spray drying, 150g of spray dried material was loaded into 99%+ alumina saggars under an artificial CC>₂-free air mix which was 80:20 N₂:C>₂. Calcination was performed as follows: ramp to 450 °C (5°C/min) with 1 hour hold, ramp to 700 °C (2 °C/min) with a 2 hours hold and cooled naturally to a temperature below 200°C. The artificial air mix was flowing over the powder bed through the calcination and cooling. The sample was crushed in a pestle and mortar in an N2 glovebox and sieved through 56pm mesh.

The composition of the sample of Example 10 was determined by ICP analysis to be

Lio.973Nio.908COo.09()Mgo.008Zro.00402.

Table 1 below summarises the metal content of the surface modification and the surface modification temperature. Table 1

The surface-modified materials were tested to determine their surface LiOH impurity levels and their surface U₂CO₃ impurity levels.

Surface U₂CO₃ content in samples was determined using a two-stage titration with phenolphthalein and bromophenol blue. For the titration, surface lithium carbonate was extracted from a sample of each material by agitating in deionised water for 5 minutes to provide an extractate solution, the extractate solution was separated from residual solid. Phenolphthalein indictor was added to the extractate solution, and the extracted solution was titrated using HCI solution until the extractate solution became clear (indicating the removal of any LiOH). Bromophenol blue indictor was added to the extractate solution, and the extracted solution titrated using HCI solution until the extractate solution turned yellow. The amount of lithium carbonate in the extractate solution was calculated from this bromophenol titration step, the wt% of surface lithium carbonate in each sample was calculated assuming 100% extraction of surface lithium carbonate into the extractate solution.

Surface LiOH content was determined by titration. For the titration, surface lithium hydroxide was extracted from a sample of each material by ultrasonication in methanol for 10 mintues, and separation of the methanol solution to provide an extractate solution. Phenolphthalein indicator was added to the extractate solution, and the extracted solution was titrated using HCI solution until the extractate solution became colourless. The amount of lithium hydroxide in the extractate solution was calculated from this titration, and the wt% f surface LiOH was calculated assuming 100% extraction of surface lithium hydroxide into the extractate solution.

The results for the materials tested were as set out in Table 2:

Table 2

ICP (Inductively Coupled Plasma )

The elemental composition of the compounds was measured by ICP-OES. For that, 0.1 g of material are digested with aqua regia (3:1 ratio of hydrochloric acid and nitric acid) at ~130°C and made up to 100 ml_. The ICP-OES analysis was carried out on an Agilent 5110 using matrix matched calibration standards and yttrium as an internal standard. The lines and calibration standards used were instrument-recommended.

Electrochemical Testing

Electrodes were made in a 94:3:3 active:carbon:binder formulation with an ink at 65 % solids. 0.6 g of SuperC65 carbon was mixed with 5.25 g of N-methyl pyrrolidone (NMP) on a Thinky® mixer. 18.80 g of active material was added and further mixed using the Thinky® mixer. Finally, 6.00 g of Solef® 5130 binder solution (10 wt% in NMP) was added and mixed in the Thinky mixer. The resulting ink was cast onto aluminium foils using a 125 pm fixed blade coater and dried at 120 °C for 60 minutes. Once dry, the electrode sheet was calendared in an MTI calendar to achieve a density of 3 g/cm³. Individual electrodes were cut and dried under vacuum overnight before transferring to an argon filled glovebox.

Coin cells were built using a lithium anode and 1M LiPF₆ in 1:1:1 EC (ethylene carbonate) : EMC (ethyl methyl carbonate) : DMC (dimethyl carbonate) + 1 wt% VC (vinylene carbonate) electrolyte. Electrodes selected had a loading of 9.0 mg/cm² and a density of 3 g/cm³.

Electrochemical measurements were taken from averages of three cells measured at 23 °C, and a voltage window of 3.0-4.3V.

Electrochemical characteristics evaluated include 1.0 C specific capacity at cycle 1 and cycle 50, capacity retention, first cycle efficiency (FCE) and DCIR growth using a 10s pulse and a

1s pulse. Capacity retention and DCIR growth were determined based on performance after 50 cycles at 1C.

The results are given in Table 3 below.

Table 3

Claims

1. A surface-modified particulate lithium nickel oxide material comprising particles having Formula I

Li_aNixCOyMg_zZrpMq02_+b Formula I in which:

0.8 £ a £ 1.2 0.8 £ x < 1 0.010 £ y £ 0.15 0 £ z £ 0.030 0.001 £ p £ 0.015 0 £ q £ 0.2; and -0.2 £ b £ 0.2; wherein M is selected from Mn, V, Ti, B, Al, Sr, Ca, Cu , Sn, Cr, Fe, Ga, Si, W, Mo, Ta, Y, Sc, Nb, Pb, Ru, Rh and Zn and combinations thereof; and wherein the particles comprise a core and an enriched surface layer at the surface of the core, and wherein the enriched surface layer includes cobalt and zirconium.

2. A surface-modified particulate lithium nickel oxide according to claim 1 wherein the surface enriched layer includes 0.1 to 1.0 at% zirconium and 0.1 to 5 at% cobalt.

3. A surface-modified particulate lithium nickel oxide according to claim 2 wherein the surface enriched layer includes 0.1 to 0.7 at% zirconium or 0.2 to 0.6 at% zirconium.

4. A surface-modified particulate lithium nickel oxide according to claim 3 wherein the surface enriched layer includes 0.2 to 0.5 at% zirconium.

5. A surface-modified particulate lithium nickel oxide according to any one of the preceding claims wherein the surface enriched layer includes 0.5 to 3 at% cobalt.

6. A surface-modified particulate lithium nickel oxide according to any one of the preceding claims wherein where the zirconium content in the surface enriched layer is at least 0.5 at%, the cobalt content in the surface enriched layer is 1.8 at% or less.

7. A surface-modified particulate lithium nickel oxide according to any one of the preceding claims which comprises less than 0.07 wt% of surface U₂CO₃.

8. A surface-modified particulate lithium nickel oxide according to any one of the preceding claims which comprises less than 0.07 wt% of surface LiOH as Li.

9. A process for preparing particulate lithium nickel oxide material having Li_aNixCOyMg_zZrpMq02_+b

Formula I in which:

0.8 £ a £ 1.2 0.8 £ x < 1 0.010 £ y £ 0.15 0 £ z £ 0.030 0.001 £ p £ 0.015 0 £ q £ 0.2; and -0.2 £ b £ 0.2; wherein M is selected from Mn, V, Ti, B, Al, Sr, Ca, Cu , Sn, Cr, Fe, Ga, Si, W, Mo, Ta, Y, Sc, Nb, Pb, Ru, Rh and Zn and combinations thereof; and the process comprising the steps of: mixing lithium-containing compound with a nickel-containing compound, a cobalt- containing compound, optionally a magnesium-containing compound, and/or an M- containing compound, wherein a single compound may optionally contain two or more of Ni, Co, Mg, and M, to obtain a mixture; calcining the mixture to obtain a calcined material; and contacting the first calcined material with a cobalt-containing compound and a zirconium-containing compound in a surface modification step to form an enriched surface layer on the first calcined material, such that the enriched surface layer includes 0.1 to 1.0 at% or more zirconium and 0.1 to 5 at% or more cobalt.

10. A process according to claim 9 wherein the surface modification step is carried out at a temperature from 10 to 50°C.

11. A cathode comprising the particulate lithium nickel oxide material of any one of claims 1 to 8.

12. A lithium secondary battery comprising the cathode according to claim 11.

13. Use of the particulate lithium nickel oxide material of any one of claims 1 to 8 to improve the capacity retention of a lithium secondary cell or battery.