WO2023110830A1

WO2023110830A1 - Cathode material

Info

Publication number: WO2023110830A1
Application number: PCT/EP2022/085549
Authority: WO
Inventors: James Alexander CORBIN; Carlos MARIN FLORIDO; Andreas Laumann; Anna PALACIOS PADROS; Cameron Jon WALLAR
Original assignee: Ev Metals Uk Limited
Priority date: 2021-12-17
Filing date: 2022-12-13
Publication date: 2023-06-22

Abstract

The invention relates to a surface-modified particulate lithium nickel composite oxide material comprising boron, wherein particles of the particulate material have an enriched surface layer comprising zirconium; and processes for preparing such material. The material is useful in an electrode within a lithium-ion electrochemical cell or secondary battery.

Description

CATHODE MATERIAL

Related applications

This application claims the priority of UK application GB 2118391.8 filed on 17 December 2021 , the contents of which are incorporated by reference herein in their entirety.

Field of the Invention

This invention relates to an improved particulate lithium nickel composite oxide material suitable for use as a cathode material in a lithium-ion electrochemical cell or secondary battery, and to an electrode and an electrochemical cell incorporating the lithium nickel composite oxide material. The invention further extends to an improved process for making the particulate lithium nickel composite oxide materials.

Background of the Invention

Lithium nickel composite oxide materials having a layered structure are useful as cathode materials in secondary lithium-ion batteries. Typically, lithium nickel composite oxide materials are produced by mixing metal precursors, such as nickel-based hydroxides or oxy hydroxi des, with a source of lithium, and then calcining the mixture. During the calcination process, the metal precursor is lithiated and oxidised and undergoes a crystal structure transformation via intermediate phases to form the desired layered LiNiCh structure.

Studies of LiNCh and similar materials have shown that there is a phase transition from one hexagonal phase (H2) to another hexagonal phase (H3) during delithiation which occurs at high voltages (around 4.2 V vs Li7Li) i.e. when the material has a significantly reduced lithium content. This phase transition is accompanied by a large and sudden reduction in volume of the unit cell caused by c-axis contraction. This c-axis contraction results in permanent structural damage to the material which has been linked to capacity fade upon cycling.

With increasing demand for lithium-ion batteries in applications such as electric vehicles (EVs), it is imperative to use cathode materials which provide not only high discharge capacity across a range of discharge rates, but which also retain structural stability, so that the range of the vehicle after each charge over its lifetime is as consistent as possible.

WO 2021/080901 A1 describes particles that may be used in the synthesis of final electrochemically active material employed in a cathode of a lithium-ion cell. The particles include a non-lithiated nickel oxide particle of the formula MOx wherein M comprises 80 at% Ni or greater and wherein x is 0.7 to 1.2, wherein M optionally excludes boron in the MOx crystal structure; and wherein boron oxide is intermixed with, coated on, present within, or combinations thereof, the non-lithiated nickel oxide particle.

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.

There remains a need for improved lithium nickel composite 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. It is hence an object of this invention to provide a particulate lithium nickel composite oxide material with increased capacity retention when used in a lithium-ion electrochemical cell or secondary battery.

Summary of the Invention

The present inventors have found that a combination of the presence of boron in a lithium nickel composite oxide particle and the presence of zirconium in an enriched surface layer at a surface of the particle, provides improved capacity retention when the material is used as a cathode material in a lithium secondary battery. Such materials provide a particularly excellent balance of capacity retention, discharge capacity at high discharge rates and low internal resistance.

According to a first aspect of the invention, there is provided a surface-modified particulate lithium nickel composite oxide material comprising boron, wherein particles of the particulate material have an enriched surface layer comprising zirconium.

Preferably, the surface-modified particulate lithium nickel composite oxide material in accordance with the first aspect of the invention, has a composition according to Formula I:

Li_aNixCOyMg_zBcZrpM_qO2+d

Formula I in which:

0.8 < a < 1.2

0.8 < x < 1

0 < y < 0.2

0 < z < 0.05

0 < c < 0.02

0.001 < p < 0.015

0 < q < 0.2; and

-0.2 < d < 0.2; wherein M is selected from Mn, V, Ti, Al, Sr, Ca, Cu, Sn, Cr, Fe, Ga, Si, W, Mo, Ta, Y, Sc, Nb, Pb, Ru, Rh, S, Ce, La, Sb and Zn and combinations thereof.

According to a second aspect of the invention, there is provided a process for preparing a particulate lithium nickel composite oxide material with a composition according to Formula I, the process comprising the steps of:

(i) mixing a lithium-containing compound with a nickel-containing compound, a cobalt- containing compound, optionally a boron-containing compound, optionally a magnesium-containing compound, and optionally an M-containing compound, wherein a single compound may optionally contain two or more of Ni, Co, B, Mg and M, to obtain a mixture;

(ii) calcining the mixture in a first calcination process step to obtain a first calcined material; and

(iii) contacting the first calcined material with a zirconium-containing compound and optionally a boron-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 optionally boron.

A third aspect of the invention provides a particulate lithium nickel composite oxide material 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 composite oxide material according to the first aspect.

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

The present invention relates to particulate lithium nickel composite oxide materials. The term “lithium nickel composite oxide” as used herein means a mixed metal oxide comprising lithium and nickel. Typically, the lithium nickel composite oxide comprises nickel in combination with cobalt and/or manganese. Typically, lithium nickel composite oxides have layered structure (such as an a-NaFeCh-type structure). Typically, the amount of Ni in the lithium nickel composite oxide material is at least 50 mol% of the total amount of non-lithium metals in the material, or at least 70 mol% of the total amount of non-lithium metals in the material, or at least 90 mol% of the total amount of non-lithium metals in the material, such as from about 50 mol% to about 98 mol%.

An overall particle of the surface-modified particulate lithium nickel composite oxide material may comprise from about 0.1 to about 2 at% boron. It may be preferable that the particle comprises from about 0.3 to about 0.7 at% boron. Preferably, the particulate lithium nickel composite 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 composite oxide material.

In Formula I, 0.8 < a < 1.2. It may be preferred that a is greater than or equal to 0.90, or greater than or equal to 0.95. It may be preferred that a is less than or equal to 1.10, or less than or equal to 1.05. It may be preferred that 0.90 < a < 1.10, for example 0.95 < a < 1.05 or 0.98 < a < 1 .02. It may be preferred that a is about 1.

In Formula I, 0.8 < x < 1. It may be preferred that 0.83 < x < 1 , 0.85 < x < 1 , or that 0.90 < x < 1. It may be preferred that x is less than or equal to 0.99, 0.98, 0.97, 0.96 or 0.95. It may be preferred that 0.83 < x < 1 , for example 0.83 < x < 0.99, 0.83 < x < 0.98, 0.83 < x < 0.97, 0.83 < x < 0.96.0.83 < x < 0.95 or 0.83 < x < 0.9. It may be preferred that 0.9 < x < 0.95, for example 0.92.

In Formula I, 0 < y < 0.2, for example 0 < y < 0.11. It may also be preferred that 0.01 < y < 0.2, 0.02 < y < 0.2, 0.03 < y < 0.2, 0.01 < y < 0.17, 0.01 < y < 0.15, or 0.01 < y < 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 < 0.05. It may be preferred that z is greater than or equal to 0.001 , 0.002, 0.003, 0.004, or 0.005. It may be preferred that z is less than or equal to 0.04, 0.03, 0.02, or 0.01. It may be preferred that 0 < z < 0.04, 0 < z < 0.03, or 0 < z < 0.02. It may be further preferred that 0.001 < z < 0.05, 0.002 < z < 0.05, 0.003 < z < 0.05, 0.004 < z < 0.05, 0.005 < z

< 0.05, 0.005 < z < 0.04, 0.005 < z < 0.03, 0.005 < z < 0.02, or 0.005 < z < 0.01 , for example 0.003 < z < 0.012. It may be further preferred that z = 0.

In Formula I, 0 < c < 0.02. It may be preferred that c is greater than or equal to 0.001 , 0.002, or 0.003. It may be preferred that c is less than or equal to 0.019, 0.018, 0.017, 0.016, or 0.015. It may be preferred that 0 < c < 0.019, 0 < c < 0.018, 0 < c < 0.017, 0 < c < 0.016, or 0

< c < 0.015. It may be further preferred that 0.001 < c < 0.019, 0.001 < c < 0.018, 0.001 < c < 0.017, 0.001 < c < 0.016, 0.001 < c < 0.015, 0.001 < c < 0.014, 0.001 < c < 0.013, 0.001 < c < 0.012, 0.001 < c < 0.011 , or 0.001 < c < 0.010. It may be particularly preferred that 0.001 < c < 0.02, preferably 0.003 < c < 0.007. It may be most preferred that c is about 0.005.

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, M is one or more selected from Mn, V, Ti, Al, Sr, Ca, Cu, Sn, Cr, Fe, Ga, Si, W, Mo, Ta, Y, Sc, Nb, Pb, Ru, Rh, S, Ce, La, Sb and Zn. In some embodiments, M is one or more selected from Mn, V, Ti, Al, Sr, Ca, Cu, Sn, Cr, Fe, Ga, Si and Zn. In some embodiments, M is Al, Mn or a combination thereof. In some embodiments, M represents a compound which is present within 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 Formula I, -0.2 < d < 0.2. It may be preferred that d is greater than or equal to -0.1. It may also be preferred that d is less than or equal to 0.1. It may be further preferred that - 0.1 < d < 0.1 , or that d is 0 or about 0.

In some embodiments, the particulate lithium nickel composite oxide material is a crystalline (or substantially crystalline) material. It may have the a-NaFeO2-type structure. It may be a polycrystalline material, meaning that each particle of lithium nickel composite oxide material is made up of multiple primary particles (also known as crystal grains) which are agglomerated together. The crystal grains are typically separated by grain boundaries. Where the particulate lithium nickel composite oxide is polycrystalline, it will be understood that the particles of lithium nickel composite oxide comprising multiple primary particles are secondary particles.

For clarity, the discussions of the particulate lithium nickel composite oxide material according to the present invention, relate to the overall particle of the particulate material, i.e. reference to “particle” may include a secondary particle (in the case of polycrystalline material), including an enriched surface layer at a surface of the secondary particle. If a boron-containing compound is added during mixing step (i) as described herein, boron may be present within the primary particle or at the grain boundaries between primary particles. The present inventors have found that boron may preferentially migrate to or near the surface of the secondary particles. In some embodiments, boron may form a generally continuous layer or region at the surface of the secondary particles. In other embodiments, the surface of the particles may include discontinuous regions of greater concentrations of boron. Accordingly, the concentration of boron in the lithium nickel composite oxide material may be higher at or near the surface of the particle and may decrease towards a general central internal region thereof.

Typically, if a boron-containing compound is added during the mixing step (i), the primary particles at or near the surface of the secondary particles may have an elongate shape. The primary particles may have an oval or stick shape (i.e. the primary particles at the surface of the secondary particles are not spherical). Typically, the primary particles located at or near the surface of the secondary particle, are arranged such that the longitudinal axes of said primary particles generally extend from the surface of the secondary particle towards a core or centre thereof, or towards a general central internal region or core region within the secondary particle. The length of the primary particles at or near the surface of the secondary particles may increase with an increase in the concentration of boron in the general central internal region of the lithium nickel composite oxide particles of the present invention.

An enriched surface layer is present at the surface of each particle of the particulate lithium nickel composite oxide material, such as a material of Formula I. The particles are subjected to a surface modification process, such as described in step (iii) herein, to form the enriched surface layer. In some embodiments the surface modification results from contacting the particles with a zirconium-containing compound, and then optionally carrying out a second calcination of the particulate material. The compound may be in solution, and in such context herein the term “compound” refers to the corresponding dissolved species. In some embodiments the surface modification results from contacting the particles with a zirconium- containing compound and optionally a boron-containing compound and/or a cobalt-containing compound, and then optionally carrying out a second calcination of the particulate material. The compounds may be in solution, and in such context herein the terms “compound” or “compounds” refer to the corresponding dissolved species.

Herein, the terms “surface modified”, “enriched surface” and “enriched surface layer” refer to a particulate material which has undergone a surface modification or surface enrichment process to increase the concentration of zirconium and optionally boron and/or cobalt 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 zirconium and optionally boron and/or cobalt than the remaining material of the particle, i.e. a core or a generally central internal region 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 zirconium and optionally boron and/or cobalt. The coating of the particulate lithium nickel composite oxide material of the present invention may therefore be discontinuous. The concentration of zirconium, and optionally the concentration of boron and/or cobalt, 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 zirconium and optionally of boron and/or cobalt in the lithium nickel composite 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 generally central internal region of the particle, the surface of a secondary particle and the enriched 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 overall particle excluding the enriched surface 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 overall particle excluding the enriched surface 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. 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 0.5 at% zirconium, this means that 0.5 at% of the zirconium is added in the surface enrichment step but does not preclude materials where some of the zirconium added in the surface enrichment step has migrated into the generally central internal region of the particle.

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 zirconium in the surface enriched layer refer to atoms of these metals at any suitable oxidation state, not just to these metals in elemental form.)

The surface enriched layer may comprise 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.

The surface enriched layer may optionally comprise boron, preferably 0.1 to 2 at% or 0.3 to 0.7 at% boron based on total metal content (excluding lithium). The surface enriched layer may include at least 0.2, 0.25 or 0.35, for example 4 at% boron. (For the avoidance of doubt, references to boron in the surface enriched layer refer to atoms of these metals at any suitable oxidation state, not just to these metals in elemental form.)

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.

The surface enriched layer may be obtainable by contacting lithium nickel composite oxide 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 first calcined material particles and the surface modification composition may be heated to the recited temperatures.

It may be preferred that the particles of the lithium nickel composite oxide material comprise enriched grain boundaries, i.e. the concentration of one or more elements (such as at least one of Co, Al, Mg and B) at the grain boundaries is greater than the concentration of the one or more elements in the crystal grains. It may be preferred that the concentration of cobalt at the grain boundaries between the crystal grains of the lithium nickel composite oxide material is greater than the concentration of cobalt in the crystal grains. Alternatively, or in addition, it may be further preferred that the concentration of aluminium at the grain boundaries between the crystal grains is greater than the concentration of aluminium in the crystal grains. Alternatively, or in addition, it may be further preferred that the concentration of boron at the grain boundaries between the crystal grains is greater than the concentration of boron on the crystal grain. The enrichment of grain boundaries with cobalt and/or aluminium and/or boron offers protection from particle degradation and improved electrode lifetime.

The concentration of a metal or compound, such as cobalt, aluminium or boron, at the grain boundaries and in the crystal grains may be determined by energy dispersive X-ray spectroscopy (EDX) analysis of the centre of a grain boundary and the centre of an adjacent crystal grain for a thinly sliced (e.g. 100-150 nm thick) section of a particle by a sectioning technique such as focused ion beam milling.

The particulate lithium nickel composite 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 composite 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 term D50 refers to the median particle diameter of the volume-weighted distribution. The D50 of the particles may be determined by using a laser diffraction method. For example, the D50 may be determined by suspending the particles in water and analysing 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 as described above.

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). The particulate lithium nickel composite oxide material 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 about 97 % after 50 cycles. 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 process for preparing the particulate lithium nickel composite oxide according to the present invention typically comprises the steps of:

(iii) contacting the first calcined material with a zirconium-containing compound and optionally a boron 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 optionally boron.

The process as described above may be used to prepare particulate lithium nickel composite oxide material of Formula I.

In some embodiments a boron-containing compound is added to step (i) such that the mixture obtained in step (i) comprises a boron-containing compound. It may be preferable to add a boron-containing compound in step (i) which constitutes the entire amount of boron present in the particulate lithium nickel composite oxide material of Formula I. It will be appreciated that, in such an instance, a boron-containing compound is not introduced in the surface modification step (step (iii)) described above. It will be appreciated by the skilled person that a boron-containing compound is added during the process in step (i) and / or step (iii).

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

Suitable lithium-containing compounds include lithium salts, such as inorganic lithium salts, for example lithium hydroxide (e.g. LiOH or UOH.H2O), lithium carbonate (U2CO3), and hydrated forms thereof. Lithium hydroxide may be particularly preferred.

Suitable nickel-containing compounds include 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.

Suitable cobalt-containing compounds include from cobalt hydroxide (Co(OH)2), cobalt oxide (CoO, CO2O3, CO3O4), cobalt oxyhydroxide (CoOOH), cobalt sulfate, cobalt nitrate, cobalt acetate and hydrated forms thereof. Cobalt hydroxide may be particularly preferred.

Suitable boron-containing compounds include boron trioxide (B2O3), boric acid (H3BO3), lithium tetraborate (U2B4O7), lithium metaborate (UBO2), lithium triborate (UB3O5), lithium borate (U2B4O7), boron nitride, boron carbide, boron trifluoride, boron phosphate, and sodium borate. Boron trioxide may be particularly preferred.

Suitable magnesium-containing compounds include lithium salts, such as inorganic magnesium salts, for example magnesium hydroxide (Mg(OH)2), magnesium oxide (MgO), magnesium sulfate, magnesium nitrate, magnesium acetate and hydrated forms thereof. Magnesium hydroxide may be particularly preferred.

Suitable M-containing compounds 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.

It may be preferred that the nickel-containing compound, the cobalt-containing compound and optionally the M-containing compound are in the form of a mixed metal 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 II: NixCo_yMg_zBcM_q [O_f(OH)_g]_a Formula II in which x, y, z, c and q are each independently as defined herein and wherein f is in the range 0 < f < 1 ; q is in the range 0 < g < 2; and a is selected such that the overall charge balance is 0.

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.

Typically, the mixed metal hydroxide materials have a volume-based particle size distribution such that the D50 is in the range of and including 2 to 20 pm. The term D50 as used herein refers to the median particle diameter of the volume-weighted distribution. The D50 may be determined by using a laser diffraction method. For example, the D50 may be determined by suspending the particles in water and analysing using a Malvern Mastersizer 3000. It may be preferred that the D50 is in the range of and including 3 to 18 pm. It may be further preferred that the D50 is in the range of and including 5 to 15 pm.

Typically, the particles of the mixed metal hydroxide are provided in the form of secondary particles comprising a plurality of primary particles.

It may be preferred that the mixed metal hydroxide does not include boron, i.e. in Formula II c = 0. In such cases a separate boron-containing compound may be added in step (i) of the process. It may be preferred that the ratio of the average size (D50) of the mixed metal hydroxide to the average size (D50) of the boron-containing compound is in the range of and including 10:1 to 2000:1. Control of the size of the boron-containing compound can lead to increased homogeneity of primary particle morphology and increases in discharge capacity.

It may be preferred that the boron-containing compound is milled prior to the mixing step (i). The milling may preferably be carried out under a moisture-free atmosphere, for example a moisture-free air or moisture-free inert atmosphere, such as nitrogen or argon. As used herein, the term “moisture-free” is intended to include atmospheres including less than 100 ppm H2O, e.g. less than 50 ppm H2O, less than 20 ppm H2O, or less than 10 ppm H2O. These moisture levels may be achieved by using commercial sources of dry gases or through the use of a desiccator.

The mixture is then calcined in a first calcination process to obtain a first calcined material. The first calcination step may be carried out at a temperature of 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 at least 600 °C or at least 650 °C for a period of at least 2 hours, at least 3 hours, at least 4 hours or at least 5 hours. The period may be less than 8 hours.

It may be preferred that the first calcination process comprises heating to a temperature in the range of and including 650 to 750 °C for a period of from 4 to 8 hours. It may be further preferred that the calcination comprises heating to a temperature in the range of and including 680 to 720 °C for a period of from 4 to 8 hours.

The first calcination process may be carried out under a CC>2-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. Preferably the CCh-atmosphere comprises at least 90 vol% oxygen, e.g. at least 93% % oxygen. The CCh-free atmosphere may be oxygen (e.g. pure oxygen). Preferably, the atmosphere is an oxidising atmosphere. As used herein, the term “CO2-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 CCh-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.

The calcination may be carried out in any suitable furnace known to the person skilled in the art, for example a static kiln (such as a tube furnace or a muffle furnace), a tunnel furnace (in which static beds of material are moved through the furnace, such as a roller hearth kiln or push-through furnace), or a rotary furnace (including a screw-fed or auger-fed rotary furnace). The furnace used for calcination is typically capable of being operated under a controlled gas atmosphere. It may be preferred to carry out the calcination step in a furnace with a static bed of material, such as a static furnace or tunnel furnace (e.g. roller hearth kiln or push-through furnace).

Where the calcination is carried out in a furnace with a static bed of material, the material is typically loaded into a calcination vessel (e.g. saggar or other suitable crucible) prior to calcination.

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

In some embodiments, the surface-modification step comprises contacting the particles of the first calcined material with additional metal selected from one or more of cobalt, 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 zirconium, boron, cobalt, aluminium, lithium and 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 ZrO(NOa)2. Other suitable compounds include Zr acetate, Zr chloride and Zr sulfate.

The lithium nickel composite oxide 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 composite oxide (first calcined material) 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 mixture (the first calcined material) may be dried, e.g. by evaporation of the solvent or by spray drying. The zirconium-containing compound and optionally the boron-containing compound, and/or the cobalt-containing compound and/or the one or more further metal-containing compounds may be provided as a composition, referred to herein as a “surface modification composition”.

The zirconium-containing compound and optionally the boron-containing compound, the cobalt-containing compound or the one and/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 mixture obtained in step (i) described herein. It may be particularly preferred that the zirconium-containing compound and/or the boron-containing compound and/or the cobalt-containing compound and/or each of the one or more further metalcontaining compounds is a metal-containing nitrate.

In some embodiments, the surface modification step comprises contacting the particles of the first calcined material with additional metal-containing compounds in an aqueous solution. The first calcined 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 first calcined material to water in the slurry after addition of the first calcined 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 process 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 process.

The second calcination step may be carried out under a CC>2-free atmosphere as described above with reference to the first calcination process. 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 reach the desired size. For example, the particles of lithium nickel composite oxide (e.g. secondary particles) are typically milled until they have a D50 particle size of 20 pm or less, e.g. 15 pm or less or 13 pm or less, for example a D50 particle size in the range of 2 to 20 pm, or of 5 to 15 pm.

The process of the present invention may further comprise the step of forming an electrode (typically a cathode) comprising the lithium nickel composite oxide material. Typically, this is carried out by forming a slurry of the particulate lithium nickel composite 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, at least 3 g/cm³, or at least 3.3 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 composite 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.

Brief description of the drawings

Figure 1 is a plot of capacity retention for full cell tests of Examples 1 , 3 and 4.

Figure 2 is a plot of discharge capacity of half-cell coin cells incorporating the materials of Examples 1 , 2 and 3. Figure 3 is a plot of capacity retention for half-cell coin cells incorporating the materials of Examples 1 , 2 and 3.

Examples

Example 1

A sample of the surface modified material according to the present invention was prepared as follows:

B2O3 (40g, Alfa Aesar) was loaded into a milling pot in a glove box and then sealed in a nitrogen atmosphere with zirconia beads. The B2O3 was milled for 25 minutes (5 minutes milling followed by 10 minutes resting) in a ball mill. A precursor material of formula Nio.9iCoo.o8Mgo.oi(OH)2 (D50 10pm, 115g) was mixed with 30.5 g LiOH and 0.224g B2O3 in a glove box under a nitrogen atmosphere. The sample was then further mixed using a shaker mixer (WAB Turbula type T2F) for 30 minutes. The sample was placed into a saggar and calcined under an oxygen atmosphere using the following profile: heating at a rate of 5 °C/min to a temperature of 450 °C, holding at a temperature of 450 °C for 2 hours, heating at a rate of 2 °C/min to a temperature of 700 °C, holding at a temperature of 700 °C for 6 hours. The sample was allowed to cool to 100 °C and then transferred to a glove box. The samples were ground using a pestle and mortar and then passed through a sieve (56 pm).

The sample was analysed 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.

ICP-OES analysis indicated the lithium nickel composite oxide material had the following compositional formulae:

Lil .01 N io.907COo.08oMgo.009Bo.00402

80g of the lithium nickel composite oxide material was slurried in 60 mL deionised water, using a further 10 mL deionised water to rinse residual material. The slurry was stirred at room temperature using a magnetic stirrer. Co(NO3)2.6H2O (2.38 g) was dissolved in deionised water (10 mL). ZrO(NOs)2 solution (ZrO(NOs)235wt% in dilute nitric acid (available from Sigma Aldrich as “dilute nitric acid”) (1.49 mL) was added to the 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 CCh-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 Sample 1 was determined by ICP analysis to be Lil.0lNi0.89CO0.088Mg0.0lB0.004Zr0.004O2.

Example 2

A comparative example was prepared by forming a lithium nickel composite oxide material having a composition determined by ICP analysis of Lio.gggNio916COo.079Mgo.00802.

The following protocol was used in preparing Comparative Example 1 :

100 g Nio.9iCoo.o8Mgo.oi(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 oxygen atmosphere. 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. Oxygen 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.

Example 3

A comparative example was prepared by forming a lithium nickel composite oxide material with milling of a boron precursor according to the following procedure.

Lil .01 N io.907COo.08oMgo.009Bo.00402

Example 4

A comparative surface modified lithium nickel composite oxide material was prepared using a surface modification composition of 0.64 at% Al and 4.0 at% Co.

A base material having a composition determined by ICP analysis of Lio.gggN io.9i6Coo.o79Mgo.oo8C>2 was first prepared according to the following protocol:

The powder mixture is loaded into 99%+ alumina crucibles and calcined under an artificial CO2-free air mix which is 80:20 N2:O2. 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 material is 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. The surface modified material was prepared from the base material according to the following procedure:

80g base material was slurried in 60m L 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(NC>3)2.6H20 (9.5g), AI(NC>3)3.9H2O (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 CC>2-free air mix which was 80:20 N2:O2. 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 hour 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 Example 4 was determined by ICP analysis to be Lio.988N io.878COo.115Mgo.008Alo.00602.

Electrochemical testing - Full Cell

Electrodes were prepared by blending 94%wt of lithium nickel metal oxide active material, 3%wt of Super-C as conductive additive and 3%wt of polyvinylidene fluoride (PVDF) as binder in N-methyl-2-pyrrolidine (NMP) as solvent. The slurry was added onto a reservoir and a 125 pm doctor blade coating (Erichsen) was applied to aluminium foil. The electrode was dried at 120 °C for 1 hour before being pressed to achieve a density of 3.0 g/cm³. Typically, loadings of active is 9 mg/cm². The pressed electrode was cut into 14 mm disks and further dried at 120 °C under vacuum for 12 hours.

Full cell electrochemical testing was performed with a CR2032 coin-cell type, which was assembled in an argon filled glove box (MBraun). Graphite electrodes in 90:5:5 (Graphite:C65:PVDF) were used as anode and balanced to reach a N/P ratio between 1.1- 1.3. A glass fibre F disk was used as separator and 1M LiPFe in 1 :1 :1 mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) with 1% of vinyl carbonate (VC) was used as electrolyte. The cells were tested on a MACCOR 4000 series using a conditioning step at slow rate, followed by C-rate and retention steps using a voltage range of between 2.7 and 4.2 V. The C-rate test charged cells at 0.5C and discharged cells at 0.1 C and 3 C (0.1C = 200 mAh/g). The capacity retention test was carried out by a 0.5C charge and 1C discharge over 240 cycles.

The capacity retention results for full cell tests of above Examples 1 , 3 and 4 are provided in Table 1 and shown in Figure 1. It can be seen that the material provides superior capacity retention over the cycling period.

Table 1 - Results of capacity retention after 400 cycles.

Electrochemical testing - Half-cell Coin Cells

Electrodes were made in a 94:3:3 active:carbon:binder formulation with an ink at 64 % solids. 0.30 g of SuperC65 carbon was mixed with 2.88 g of N-methyl pyrrolidone (NMP) on a Thinky® mixer. 9.40 g of active material was added and further mixed using the Thinky® mixer. Finally, 3.00 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 150 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 LiPFe 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, and DCIR using a 10s pulse and a 1s pulse.

The discharge capacity results of Examples 1 , 2 and 3 at different discharge rates are provided in Table 2. It can be seen that the material of Example 1 achieved the overall best discharge capacity results across a range of discharge rates. Table 2 - Discharge capacity results of half-cell coin cells.

The discharge capacity results are also shown in Figure 2.

The Direct Current Internal Resistance results of Examples 1, 2 and 3 were measured using a 10s pulse and a 1s pulse are provided in Table 3. The resistances measured for the material of Example 1 were lower than the corresponding resistance measurements for the comparative samples (Examples 2 and 3).

Table 3- Resistance results of half-cell coin cells.

The capacity retention results of half-cell coin cell tests of the above Examples are shown in Figure 3. The material of Example 1 provides superior capacity retention over the cycling period.

Claims

1. A surface-modified particulate lithium nickel composite oxide material comprising boron, wherein particles of the particulate material have an enriched surface layer comprising zirconium.

2. The surface-modified particulate lithium nickel composite oxide material according to claim 1 having a composition according to Formula I:

Li_aNixCOyMg_zBcZrpM_qO2+d Formula I in which:

0.8 < a < 1.2

0.8 < x < 1

0 < y < 0.2 0 < z < 0.05 0 < c < 0.02 0.001 < p < 0.015 0 < q < 0.2; and -0.2 < d < 0.2; wherein M is selected from Mn, V, Ti, 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 particle comprises an enriched surface layer at a surface of the particle, wherein the enriched surface layer comprises zirconium.

3. The surface-modified particulate lithium nickel composite oxide material according to claim 1 or claim 2 wherein 0.95 < a < 1.05, preferably 0.98 < a < 1.02.

4. The surface-modified particulate lithium nickel composite oxide material according to any one of claims 1 to 3, wherein 0.83 < x < 1 , preferably 0.9 < x < 1 .

5. The surface-modified particulate lithium nickel composite oxide material according to any one of claims 1 to 3, wherein 0 < y < 0.11 , preferably 0.08 < y < 0.11.

6. The surface-modified particulate lithium nickel composite oxide material according to any one of claims 1 to 5, wherein 0.001 < z < 0.05, preferably 0.005 < z < 0.01 .

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7. The surface-modified particulate lithium nickel composite oxide material according to any one of claims 1 to 6, wherein 0.001 < c < 0.02, preferably 0.003 < c < 0.007.

8. The surface-modified particulate lithium nickel composite oxide material according to claim 7, wherein c is about 0.005.

9. The surface-modified particulate lithium nickel composite oxide material according to any one of claims 1 to 8, wherein 0.002 < p < 0.01, preferably 0.003 < c < 0.007.

10. The surface-modified particulate lithium nickel composite oxide material according to claim 9, wherein p is about 0.005.

11. The surface-modified particulate lithium nickel composite oxide material according to any one of the preceding claims in the form of secondary particles comprising a plurality of primary particles, wherein the enriched surface layer is at or proximate a surface of the secondary particle.

12. The surface-modified particulate lithium nickel composite oxide material according to claim 11 , comprising elongate primary particles located at or near the surface of a secondary particle, and wherein the elongate primary particles are arranged such that their longitudinal axes extend from the surface of the secondary particle towards a general central internal region within the secondary particle.

13. The surface-modified particulate lithium nickel composite oxide material according to any one of claims 11 to 12, wherein the concentration of boron at or proximate the surface of the secondary particles is greater than the concentration of boron in the primary particles.

14. The surface-modified particulate lithium nickel composite oxide material according to any preceding claim, wherein the enriched surface layer comprises boron.

15. The surface-modified particulate lithium nickel composite oxide material according to any preceding claim, wherein the enriched surface layer comprises cobalt.

16. The surface-modified particulate lithium nickel composite oxide material according to claim 15, wherein the enriched surface layer comprises 0.1 to 5 at% cobalt.

17. A process for preparing the particulate lithium nickel composite oxide material claimed in any preceding claim, the process comprising the steps of: (i) mixing a lithium-containing compound with a nickel-containing compound, a cobalt-containing compound, optionally a boron-containing compound, optionally a magnesium-containing compound, and optionally an M-containing compound, wherein a single compound may optionally contain two or more of Ni, Co, B, Mg and M, to obtain a mixture;

(iii) contacting the first calcined material with a zirconium-containing compound and optionally a boron-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 optionally boron. The process according to claim 17, wherein the nickel composite oxide material has a composition according to Formula I. The process according to claim 17 or 18, wherein the mixture obtained in step (i) comprises a boron-containing compound. The process according to any one of claims 17 to claim 19, wherein in step (i) the nickel-containing compound and the cobalt-containing compound are in the form of a mixed metal hydroxide. The process according to any one of claims 17 to 20, wherein in step (i) the ratio of the average size of the mixed metal hydroxide to the average size of the boron-containing compound is 10:1 to 2000:1. The process according to any one of claims 17 to 21 , wherein the first calcination comprises heating to at least 650 °C, preferably for a period of between 4 and 8 hours. The process according to any one of claims 17 to 22, wherein the calcination in step (ii) is carried out under an atmosphere comprising at least 90 vol% oxygen. The process according to claim 23, wherein the calcination is carried out under an atmosphere comprising 93 vol% oxygen. The process according to any one of claims 17 to 24, wherein the surface modification step in step (iii) is carried out a temperature from 10 to 50°C.

26. The process according to any one of claims 17 to 25, wherein in step (iii) the surfacemodification step comprises a heat-treatment. 27. The process according to any one of claims 17 to 26 further comprising the step of forming an electrode comprising the particulate lithium nickel composite oxide material.

28. The process according to claim 27 further comprising the step of constructing a battery or electrochemical cell including the electrode comprising the lithium nickel composite oxide material.

29. An electrode comprising the particulate lithium nickel composite oxide material according to any one of claims 1 to 16, or a lithium nickel composite oxide material obtained or obtainable by the process according to any one of claims 17 to 28.

30. An electrochemical cell comprising the electrode according to claim 29.

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