WO2023025941A1

WO2023025941A1 - Electrode Coating Method and Coated Electrode

Info

Publication number: WO2023025941A1
Application number: PCT/EP2022/073790
Authority: WO
Inventors: Jonathan SLAUGHTER; Victor Riesgo GONZALEZ; Dominic Wright; Clare GREY
Original assignee: Cambridge Enterprise Limited
Priority date: 2021-08-27
Filing date: 2022-08-26
Publication date: 2023-03-02
Also published as: GB202112283D0

Abstract

The invention relates to a method for coating an electrode active material with a metal oxide, a method for doping an electrode active material, and coated and doped electrode active materials produced by the methods. The coated and doped electrode active materials can be used in electrochemical cells. The method for coating an electrode active material comprises providing a coating composition comprising an organic solvent and a bimetallic alkoxide, depositing the coating composition to the surface of the electrode active material, and calcining the electrode active material to provide a coating of bimetallic oxide on the surface of the electrode active material. Compared to using two separate metal coating precursors, the bimetallic alkoxide acts as a single-source coating precursor, which provides a highly-uniform coating, accurate control of coating thickness and metal stoichiometry.

Description

Electrode Coating Method and Coated Electrode

Related Application

The present case claims priority to, and the benefit of, GB 2112283.3 filed on 27 August 2021 (27.08.2021), the contents of which are hereby incorporated by reference in their entirety.

Field of the Invention

The present invention relates to a method for coating an electrode active material with a metal oxide, a method for doping an electrode active material, and coated and doped electrode active materials produced by the process.

Background

Lithium-ion batteries have many of the desired properties for use in portable electronic applications like mobile phones, laptops, and power tools or in electric vehicles (EVs). They have good energy densities and can be recharged multiple times.

The earliest commercial lithium ion batteries used lithium cobalt oxide (LiCoCh) as a cathode material, due to its reasonable stability and energy density (Wang et al.). However, the high price and toxicity of cobalt has led to the development of alternative cathode materials with a mixture of transition metals such as lithium nickel manganese cobalt oxide (NMC), LiNixMn_yCoi-x-yO2, and lithium nickel cobalt aluminium oxide (NCA), LiNixCoyAh-x-yCh (Li et al.). In addition to reduced price and lower toxicity, these mixed transition metal cathodes also have improved electrochemical properties, with a higher nickel content typically providing a cathode with a higher specific capacity.

However, despite the benefits of NMC and NCA cathodes, they undergo faster degradation, particularly at high voltages and for greater amounts of nickel. This results in a reduced specific capacity of the cell following prolonged cycling.

This degradation has been attributed to several different chemical phenomena, such as the reaction of the electrode material with the electrolyte, secondary particle cracking due to the expansion and contraction of the electrode during cycling, lithium-nickel cation mixing, and transition metal dissolution occurring during cycling. All of these mechanisms decrease the capacity and shorten the useful lifetime of the cell, which is clearly undesirable.

Degradation phenomena are also observed in other cathode materials. For example, lithium cobalt oxide is unstable at high voltages, undergoing a layered structure collapse attributed to a large change in volume during charging and discharging. Lithium manganese oxide (LiMn2O4) undergoes degradation through the loss of active material by transition metal dissolution. Structural disorder is also introduced during prolonged cycling of lithium iron phosphate (LiFePCL) and lithium manganese phosphate cathodes (LiMnPCL).

Several different methods have been explored to mitigate these degradation pathways. Examples include coating the cathode material, doping the cathode material, using a single crystal cathode material, and making microstructure cathodes.

Several different coatings materials have been investigated, mainly focussing on monometallic oxides (e.g. AI2O3, MgO, TiC>2, ZrC>2), metal fluorides (e.g. AIF₃, FeF₃), and metal phosphates (e.g. U3PO4, FePCL). These coating materials typically provide increased discharge capacity retention. It is thought that this is due to a reduction in secondary particle cracking, preventing interaction of the cathode with the electrolyte, and forming a barrier to transition metal dissolution during cycling.

While the majority of reports have investigated the coating of the cathode material with a monometallic oxide, there are a few examples of bimetallic oxide coatings. These predominately include lithium metal oxides, such as Li₂ZrO3 (Song et a! , Zhan et al.) and UAIO2 (Liu et al.), which are thought to have better lithium transport kinetics, resulting in lower impedance than monometallic oxide coatings.

However, known methods for preparing bimetallic oxide coatings require two separate metal precursors to produce the coating material, which are combined in situ with the electrode. This typically results in an uneven distribution of different meal species over the surface of the electrode material. Moreover, it is difficult to accurately control the coating thickness and the stoichiometry of the two metal species using separate metal precursors. The use of separate species increases the complexity of the coating procedure, and high annealing temperatures are also needed to form the bimetallic oxide coating, increasing cost.

In addition, known methods for preparing bimetallic oxide coatings typically use an aqueous solvent. This limits the applicability of the coating methods, as many common electrode materials will react with water. In particular, aqueous coating methods are not suitable for preparing NMC and NCA electrodes having high amounts of nickel. High nickel content electrodes can also form LiOH surface species, resulting in lower discharge capacities.

Accordingly, there is a need to provide a method for coating an electrode active material with a bimetallic oxide which provides a highly-uniform coating, which provides accurate control of coating thickness and metal stoichiometry, and which can be applied to high nickel content electrodes without degradation.

Summary of the Invention

At its most general, the present invention provides a method for coating an electrode active material with a bimetallic oxide coating. The method uses a bimetallic alkoxide as a single- source precursor, which is deposited on the surface of the electrode active material. Calcination removes the organic groups to leave a bimetallic oxide coating on the electrode active material.

Accordingly, in a first aspect of the invention there is provided a method for coating an electrode active material with a bimetallic oxide, the method comprising:

(a) providing a coating composition comprising an organic solvent and a bimetallic alkoxide of formula (I):

(M¹)_a(M²)b(OR¹)c(R²OR³)d(R⁴C(=O)R⁵)_e (I) wherein:

M¹ and M² are different;

M¹ is selected from Li, Mg, Zr and Ti;

M² is selected from Al, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Li and Mg;

R¹ is C1-6 alkyl;

R² is H and R³ is C1-6 alkyl; or R² and R³ together with the oxygen atom to which they are bonded is a 5-7 membered heterocyclyl group;

R⁴ is C1-6 alkyl;

R⁵ is O or a group CH=C(O)R⁶, where R⁶ is C1-6 alkyl; a and b are independently from 1 to 4; c is from 8 to 16; d is from 0 to 6; and e is from 0 to 4,

(b) applying the coating composition to the surface of the electrode active material,

(c) evaporating the organic solvent to deposit the bimetallic alkoxide on the surface of the electrode active material, and

(d) calcining the electrode active material to provide a coating of bimetallic oxide on the surface of the electrode active material.

The use of a single-source precursor leads to a more uniform coating, with a more even distribution of metal species over the surface of the electrode active material. The singlesource precursor allows the coating thickness and the stoichiometry of the two metal species to be precisely controlled.

Moreover, the bimetallic alkoxide is soluble in organic solvents, allowing the process to be carried out in non-aqueous conditions. Thus, the coating method is applicable to a wide range of electrode active materials including electrode active materials having a high nickel content.

The alkoxide decomposition temperature is typically low, and so the coating method is more energy efficient than known aqueous coating methods.

In a second aspect of the invention, there is provided an electrode active material having a bimetallic oxide coating obtained or obtainable by the method of the first aspect. By using a single-source precursor in the preparation method, the bimetallic oxide coating is more uniform, having a more even distribution of metal species over the active material surface. The coating thickness and metal stoichiometry can also be specified with a high degree of precision.

In a third aspect of the invention, there is provided a coated electrode active material comprising a layer of a bimetallic oxide of formula (II) deposited on the surface of an electrode active material:

(M³)_f(M⁴)_gOh (II) wherein:

M³ is Zr;

M⁴ is selected from Al, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn and Mg; f and g are independently from 1 to 4; and h is from 4 to 8.

The bimetallic coating material reduces secondary particle cracking and is chemically inert, preventing chemical oxidation of common electrolyte solvents and forming a barrier to transition metal dissolution during cycling. Thus, the bimetallic coating provides increased discharge capacity retention.

In a fourth aspect of the invention, there is provided a method for doping an electrode active material, the method comprising:

(a) providing a coated electrode active material of the second aspect; and

(b) heating the coated electrode active material at a temperature of 600 °C to 1500 °C.

Further heating of the coated electrode active material is associated with the diffusion of some of the coating elements into the bulk electrode active material, providing a doped material. Preparing the doped electrode active material from the coated electrode active material concentrates the doped elements in the surface region of the electrode active material, rather than doping the entire bulk electrode active material. Moreover, the doping may occur in a gradient, with the quantity of doped elements decreasing with distance from the surface of the electrode active material.

In a fifth aspect of the invention, there is provided a doped electrode active material obtained or obtainable by the method of the method of the fourth aspect.

The doped electrode active materials undergo slower degradation. The doped atoms act to stabilise the delithiated structure, reducing particle cracking during cycling.

In a sixth aspect of the invention, there is provided a doped electrode active material comprising a layer of a bimetallic oxide deposited on the surface of an electrode active material, wherein: the bimetallic oxide comprises Zr; a second metal selected from Al, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, and Mg; and O, and the electrode active material comprises a surface region that is doped with Zr and a second metal selected from Al, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn and Mg.

In a seventh aspect of the invention, there is provided a working electrode comprising the coated electrode active material of the second or third aspects, or the doped electrode active material of the fifth or sixth aspects.

In an eight aspect of the invention, there is provided an electrochemical cell comprising the working electrode of the seventh aspect.

Using a working electrode comprising the coated or doped electrode active material reduces secondary particle cracking, reduces chemical oxidation of common electrolyte solvents, and reduces transition metal dissolution during cycling. Thus, the electrochemical cell has increased discharge capacity retention and an extended useful lifetime.

In a ninth aspect of the invention, there is provide a method for preparing a bimetallic alkoxide, the method comprising:

(a) providing a reaction mixture comprising: i) a compound of formula (III):

M⁵(OR⁷)j (III) wherein:

M⁵ is selected from Al, Sc, Ti, Zr, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, and Zn;

R⁷ is independently selected from C1-6 alkyl; and i is from 2 to 6, and ii) HOR⁸, wherein R⁸ is selected from C1-6 alkyl, and

(b) adding magnesium metal or Mg(R⁹)2, wherein R⁹ is selected from C1-6 alkyl.

Preparing the bimetallic alkoxide from a compound of formula (III) avoids the need to use expensive cyclopentadienyl (Cp) metal complexes.

These and other aspects and embodiments of the invention are described in further detail below.

Summary of the Figures

The present invention is described with reference to the figures listed below.

Figure 1 shows the X-ray crystal structure of Mg2Zr2(OⁿPr)i2(ⁿPrOH)4 (A), a molecular structure drawing of of Mg₂Zr2(OⁿPr)i₂(ⁿPrOH)4 (B) and a X-ray crystal structure of Li₂Zr₂(OⁿPr)io(THF)2 (C). Figure 2A is a thermogravimetric analysis (TGA) showing the weight change when Mg2Zr2(OⁿPr)i2(ⁿPrOH)4 is heated from 25 °C to 800 °C at a ramp rate of 10 “Omim¹ in air. A weight loss of 71 wt% was observed on heating to around 450 °C. Figure 2B is a thermogravimetric analysis (TGA) showing the weight change when Li2Zr2(OⁿPr) (THF)2 is heated from 25 °C to 800 °C at a ramp rate of 10 °Omin’¹ in air.

Figure 3A is a powder X-ray diffraction (XRD) pattern of Mg2Zr2(OⁿPr)i2(ⁿPrOH)4 heated to 450 °C (bottom) and 800 °C (top) in air. At 450 °C, a broad peak at 32° is observed and is attributable to the amorphous sample. At 800 °C, shaper peaks are observed, and are attributable to a mixture of crystalline ZrO2 and MgO. Figure 3B is a powder X-ray diffraction (XRD) pattern of Li2Zr2(OⁿPr) (THF)2 heated to 450 °C. Figure 3C is a powder X-ray diffraction (XRD) pattern of Li₂Zr₂(OⁿPr)io(THF)2 heated to 800 °C.

Figure 4 is an overview of a process for preparing a coated electrode active material according to an embodiment of the invention. NMC-811 is dip-coated in a coating composition comprising Mg₂Zr2(OⁿPr)i₂(ⁿPrOH)4 and an organic solvent at 50 °C, followed by evaporation of the solvent and calcination in air.

Figure 5 is an XRD pattern of pristine NMC-811 (bottom), NMC-811 coated with the bimetallic alkoxide Mg₂Zr2(OⁿPr)i₂(ⁿPrOH)4 and heated to 450 °C (top), and NMC-811 coated with Mg2Zr2(OⁿPr)i2(ⁿPrOH)4 and heated to 800 °C (middle). There is very little difference between the XRD pattern of the pristine material and the XRD pattern of the material heated to 450 °C. At 800 °C, some differences are observed in the XRD pattern, with a shift in some of the peaks to lower 20 values suggesting an increase in the unit cell size of the NMC.

Figure 6 provides scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) data for NMC-811 coated with the bimetallic alkoxide Mg2Zr2(OⁿPr)i2(ⁿPrOH)4 and heated to 450 °C. Both magnesium and zirconium are present on the surface of the NMC particles.

Figure 7 provides scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) data for NMC-811 coated with the bimetallic alkoxide Mg2Zr2(OⁿPr)i2(ⁿPrOH)4 and heated to 800 °C. Both magnesium and zirconium are present on the surface of the NMC particles, but at reduced amounts in comparison to the sample heated to 450 °C.

Figure 8A shows the discharge capacity retention in a hall-cell against lithium metal for an electrode comprising uncoated NMC-811 (bottom line at right) and an electrode comprising NMC-811 coated with the bimetallic alkoxide Mg₂Zr2(OⁿPr)i₂(ⁿPrOH)4 and heated to 450 °C (top line at right). The cells were cycled between 3.0 V and 4.4 V. Both materials display similar initial discharge capacity (cycles 0 to 20). After 150 cycles the coated material had a discharge capacity of 133 mAh*g'¹, compared to 108 mAh*g'¹ for the uncoated material. Figure 8B shows the discharge capacity retention in a hall-cell against lithium metal for an electrode comprising NMC-811 coated with the bimetallic alkoxide Mg2Zr2(OⁿPr)i2(ⁿPrOH)4 and heated to 450 °C (top line at right), coated with Li2Zr2(OⁿPr) (THF)2 and heated to 450 °C (bottom line at right) and coated with Zr(OⁿPr)4 and heated to 450 °C (middle line at right). The cells were cycled between 3.0 V and 4.4 V.

Figure 9A shows the discharge capacity retention in a hall-cell against lithium metal for an electrode comprising uncoated NMC-811 (bottom line at right) and an electrode comprising NMC-811 coated with the bimetallic alkoxide Mg₂Zr2(OⁿPr)i₂(ⁿPrOH)4 and heated to 450 °C (top line at right). The cells were cycled between 3.0 V and 4.6 V. The uncoated material has lower initial discharge capacity. After 20 cycles, the coated material had a discharge capacity of 190 mAh*g'¹, compared to 175 mAh*g'¹ for the uncoated material. After 100 cycles, the coated material had a discharge capacity of 160 mAh*g-¹, compared to only 100 mAh*g'¹ for the uncoated material. Figure 9B shows the discharge capacity retention in a hall-cell against lithium metal for an electrode comprising NMC-811 coated with the bimetallic alkoxide Mg2Zr2(OⁿPr)i2(ⁿPrOH)4 and heated to 450 °C (bottom line at right), coated with Li₂Zr₂(OⁿPr)io(THF)2 and heated to 450 °C (top line at right) and coated with Zr(OⁿPr)₄ and heated to 450 °C (middle line at right). The cells were cycled between 3.0 V and 4.6 V.

Figure 10 shows the discharge capacity retention in full-cell against a graphite anode for an electrode comprising uncoated NMC-811 (bottom line at right) and an electrode comprising NMC-811 coated with the bimetallic alkoxide Mg2Zr2(OⁿPr)i2(ⁿPrOH)4 and heated to 450 °C (top line at right). The cells were cycled between 2.5 V and 4.3 V. An increased discharge capacity is observed for the coated material after 120 cycles. After 250 cycles, the uncoated NMC had a discharge capacity of 133 mAh*g'¹, while the NMC-MgZr450 had a discharge capacity of 160 mAh*g-¹. The decrease in discharge capacity is more linear for the coated material in comparison to the uncoated NMC, which displayed a plateau for around 75 cycles and then a rapid decline.

Detailed Description of the Invention

The present invention provides a method for coating an electrode active material with a bimetallic oxide coating. The method uses a bimetallic alkoxide as a single-source precursor, which is deposited on the surface of the electrode active material. Calcination removes the organic groups to leave a bimetallic oxide coating.

Coating Composition

The coating method of the invention comprising providing a coating composition comprising an organic solvent and a bimetallic alkoxide. This may be referred to as the preparation step, step (a). The coating method of the invention uses a coating composition to coat the electrode active material. The coating composition comprises a bimetallic alkoxide of formula (I): (M¹)_a(M²)b(OR¹)c(R²OR³)d(R⁴C(=O)R⁵)e (I)

The groups M¹ and M² in formula (I) may be referred to as the metal centres.

The metal centres M¹ and M² are different. That is, M¹ and M² are not the same metal.

The metal M¹ is selected from Li, Mg, Zr and Ti. Preferably, M¹ is selected from Zr and Ti. More preferably, M¹ is Zr.

The metal M² is selected from Al, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Li and Mg. Preferable, the metal M² is selected from Al, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn and Mg. More preferably, M² is selected from Al, Ti, Mn, Fe, Co, Ni, Cu and Mg. Most preferably, M² is Mg.

The group (OR¹) in formula (I) may be referred to as the alkoxide ligand.

The group R¹ is a C1-6 alkyl group. Different alkoxide ligands may be present in a single compound formula (I). Thus, each R¹ is independently selected from C1-6 alkyl.

The group R¹ may be linear or branched. Examples of C1-6 linear alkyl groups include methyl (-Me), ethyl (-Et), n-propyl (-nPr), n-butyl (-nBu), n-pentyl (-Amyl) and n-hexyl. Examples of C1-6 branched alkyl groups include iso-propyl (-iPr), iso-butyl (-iBu), sec-butyl (-sBu), tert-butyl (-tBu), iso-pentyl, sec-pentyl, tert-pentyl, neo-pentyl, iso-hexyl, sec-hexyl, tert-hexyl and neohexyl. Preferably, R¹ is linear.

Preferably, R¹ is a C2-5 alkyl group. More preferably, R¹ is a C3-4 alkyl group. Most preferably, R¹ is a C3 alkyl group.

The group (R²OR³) may be referred to as the neutral ligand. Typically, the neutral ligand is an alcohol or ether.

Optionally, R² is H and R³ is a C1-6 alkyl group. Alternatively, R² and R³ together with the oxygen atom to which they are bonded form a 5-7 membered heterocyclyl group. Different neutral ligands may be present in a single compound of formula (I). Thus, each group (R²OR³) may be selected from these two alternative. Similarly, where R² is H, each R³ may be independently selected from a C1-6 alkyl group. Correspondingly, where R² and R³ together with the oxygen atom to which they are bonded is a 5-7 membered heterocyclyl group, each group (R²OR³) may be independently selected from a 5-7 membered heterocyclyl group.

Where R² is H, R³ may be linear or branched. Preferably, R³ is linear. Where R² is H, R³ is preferably a C2-5 alkyl group. More preferably, R³ is a C3-4 alkyl group. Even more preferably R¹ is a C3 alkyl group.

Where R² and R³ together with the oxygen atom to which they are bonded is a 5-7 membered heterocyclyl group, the group (R²OR³) is preferably a 5-6 membered heterocyclyl group.

More preferably, the group (R²OR³) is a 5-membered heterocyclyl group.

Examples of 5-7 membered heterocyclyl groups include oxolane (tetrahydrofuran), dioxolane, oxane (tetrahydropyran), dihydropyran, pyran, dioxane, trioxane, oxepane and dioxepane. Preferably, the 5-7 membered heterocyclyl group is oxolane, oxane or oxepane.

Preferably, R² is H and R³ is a C1-6 alkyl group.

The group (R⁴C(=O)R⁵) may be referred to as the carbonyl ligand. Typically, the carbonyl ligand is an acetate group or an acetylacetonate group.

R⁴ is a C1-6 alkyl group. Different carbonyl ligands may be present in a single compound formula (I). Thus, each R⁴ is independently selected from C1-6 alkyl.

The group R⁴ may be linear or branched. Examples of suitable linear and branched C1-6 alkyl groups are given above. Preferably, R⁴ is linear.

Preferably, R⁴ is a C1-4 alkyl group. More preferably, R⁴ is a C1-2 alkyl group. Most preferably, R⁴ is a methyl group.

Optionally, R⁵ is O. The oxygen atom is typically bound to the metal centre. In such cases, the ligand is a carboxylate ligand (e.g. an acetate ligand, AcO).

Alternatively, R⁵ is a group CH=C(O)R⁶, where R⁶ is C1-6 alkyl;

Where R⁵ is a group CH=C(O)R⁶, R⁶ may be linear or branched. Preferably, R⁶ is linear.

Where R⁵ is a group CH=C(O)R⁶, R⁶ is preferably a C1-4 alkyl group. More preferably, R⁶ is a C1-2 alkyl group. Most preferably, R⁶ is a methyl group (a 1 ,3-diketone ligand, e.g. an acetylacetonate ligand, acac).

The metal numbers a and b are independently from 1 to 4. Typically, a and b are integers. Preferably a and b are independently from 1 to 3. More preferably, a and b are independently 1 or 2. Most preferably, a and b are 2.

The alkoxide number c is from 8 to 16. Typically, c is an integer. Preferably, c is from 10 to 14. More preferably, c is from 10 to 12. The neutral ligand number d is from 0 to 6. Typically, d is n integer. Preferably, d is from 0 to 4.

The carbonyl ligand number e is from 0 to 4. Typically e is an integer. Preferably, e is from 0 to 2. More preferably, e is 2.

As noted above, M¹ is preferably Zr. Thus, the bimetallic alkoxide of formula (I) is preferably a bimetallic alkoxide of formula (la):

Zr_a(M²)b(OR¹)c(R²OR³)d(R⁴C(=O)R⁵)_e (la) where each of M², R¹, R², R³, R⁴, R⁵, a, b, c, d and e are as defined for formula (I), and the same preferences apply.

Specific examples of bimetallic alkoxides which are suitable for use in the coating method of the invention include Mg₂Zr2(OⁿPr)i₂(ⁿPrOH)4, Li₂Zr₂(OⁿPr) (THF)₂, Fe₂Zr₂(acac)₂(OEt) , Co₂Zr₂(acac)₂(OEt)w, Ni₂Zr₂(acac)₂(OEt) , and Cu₂Zr₂(acac)₂(OEt) .

Preferably, the bimetallic alkoxide is Mg₂Zr₂(OⁿPr)i₂(ⁿPrOH)4.

In one embodiment, M¹ is Li. In such case, the metal M² is selected from Mg, Al, Zr, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, and Zn. Preferable, the metal M² is selected from Al, Zr, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, and Zn. More preferably, M² is selected from Al, Zr, Ti, Mn, Fe, Co, Ni, and Cu.

In one embodiment, M¹ is Mg. In such case, the metal M² is selected from Li, Al, Zr, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, and Zn. Preferable, the metal M² is selected from Al, Zr, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, and Zn. More preferably, M² is selected from Al, Zr, Ti, Mn, Fe, Co, Ni, and Cu.

In one embodiment, M¹ is Ti. In such case, the metal M² is selected from Li, Mg, Al, Zr, Sc, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, and Zn. Preferable, the metal M² is selected from Al, Zr, Sc, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, and Zn. More preferably, M² is selected from Al, Zr, Mn, Fe, Co, Ni, and Cu.

Typically, the coating composition comprises a solvent. Preferably, the coating composition comprises an organic solvent.

Any suitable organic solvent may be used. Preferable, the organic solvent has a low boiling point, to permit easy removal. Typically, the boiling point of the organic solvent is 200 °C or lower. Preferably, the boiling point of the organic solvent is 180 °C or lower, more preferably 160 °C or lower, even more preferably 140 °C or lower and more preferably 120 °C or lower.

Preferably, the organic solvent is a hydrocarbon solvent. The hydrocarbon solvent may be an aliphatic or aromatic hydrocarbon solvent.

Examples of suitable aliphatic hydrocarbon solvents include linear alkanes such as pentane, hexane, heptane and octane; cycloalkanes such as cyclopentane, cyclohexane, cycloheptane and cyclooctane; and petroleum fractions such as kerosene and petroleum ether. Mixtures of these species may be used.

Examples of suitable aromatic hydrocarbon solvents include benzene, toluene and xylene.

Preferably, the organic solvent is an aromatic hydrocarbon solvent, more preferably the organic solvent is toluene.

Preferably, the coating composition is anhydrous. The quantity of water in the coating composition may be determined using standard techniques, such as Karl Fischer titration. Typically, the quantity of water in the coating composition may be less than 1000 ppm, preferably less than 500 ppm, more preferably less than 300 ppm, even more preferably less than 200 ppm and more preferably less than 100 ppm.

Coating Application

In the coating method of the invention, the coating composition is applied to the surface of the electrode active material. This may be referred to as the coating step, step (b).

Any suitable coating method may be used. Physical coating techniques such as dip and spin coating may be used. Similarly, spray coating and roll-to-roll coating techniques may be used. In the worked examples, a dip coating method is used.

Optionally, the coating step may comprise heating the coating composition on the surface of the electrode active material. Methods for providing heat are known and include, for example, using a heat lamp or using a reaction vessel having an external heating jacket.

Typically, the coating step comprises heating the coating composition on the surface of the electrode active material at a temperature of from 30 °C to 100 °C, preferably from 40 °C to 80 °C, more preferably from 40 °C to 60 °C.

The coating step may be carried out in the absence of water, for example in the absence of atmospheric moisture. This may be achieved by carrying out the coating step using dried air, or in the absence of air. For example, the coating may be applied under an inert atmosphere, such as under a shroud of nitrogen or argon. The coating method of the invention comprises evaporating the organic solvent to deposit the bimetallic alkoxide on the surface of the electrode active material. This may be referred to as the evaporation or drying step, step (c).

Any suitable evaporation method may be used and may be determined by the choice of coating method as is common in the art.

Typically, the evaporation method comprises heating the electrode active material having the coating composition on the surface to evaporate the organic solvent and deposit the bimetallic alkoxide on the surface of the electrode active material. Typically, the evaporation method comprises heating at a temperature of from 30 °C to 100 °C, preferably from 40 °C to 80 °C, more preferably from 40 °C to 60 °C.

Typically, the evaporation method comprises applying vacuum to the electrode active material having the coating composition on the surface. Alternatively, the evaporation method comprises applying a stream of gas, such as a stream of nitrogen, to the electrode active material having the coating composition on the surface.

Calcination

The coating method of the invention comprises calcining the electrode active material to provide a coating of bimetallic oxide on the surface of the electrode active material. This may be referred to as the calcination step, step (d).

During calcination, the bimetallic alkoxide decomposes and the organic components, the alkoxide and neutral ligands, are driven off to leave a bimetallic oxide. Method of calcination are known and include, for example, using a furnace.

Typically, the calcination step takes place at a temperature of from 300 °C to 600 °C, preferably from 350 °C to 550 °C, more preferably from 400 °C to 500 °C.

The calcination step may comprise gradually raising the temperature to the desired calcination temperature. Any suitable heating rate can be used. Typically, the calcination step comprising raising the temperature at a rate of from 5 °C per minute to 20 °C per minute, preferably about 10 °C per minute.

The calcination step may be performed for sufficient time to allow a desired quantity of the bimetallic alkoxide to decompose to bimetallic oxide. Typically, the calcination step is performed until substantially all the bimetallic alkoxide has decomposed to the bimetallic oxide. Optionally, the calcination step is performed until substantially all the organic components have been driven off. Typically, the calcination step comprises calcining the electrode active material for 1 hour to 24 hours. Preferably, the calcination step comprises calcining the electrode active material for 1 hour to 12 hours, more preferably 1 hour to 8 hours, even more preferably 2 hours to 6 hours.

The calcination step may be carried out in the absence of oxygen or atmospheric moisture. Typically, however, this is not necessary, and the calcination may be carried out in air.

Coated Electrode Active Material

The present invention also provides a coated electrode active material. The coated electrode active material has a layer of a bimetallic oxide deposited on the surface of an electrode active material. The bimetallic oxide has formula (II):

(M³)_f(M⁴)_gO_h (II)

The metal M³ is Zr.

The metal M⁴ is selected from Al, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn and Mg. Preferably, M⁴ is selected from Al, Ti, Mn, Fe, Co, Ni, Cu and Mg. More preferably, M⁴ is Mg.

The metal numbers f and g are independently from 1 to 4. Typically, f and g are integers. Preferably , f and g are independently from 1 to 3. More preferably, f and g are independently 1 or 2. Most preferably, f and g are 2.

The oxide number h is from 4 to 8. Preferably, h is 6.

As noted above, M³ is Zr. Thus, the bimetallic oxide of formula (II) may be referred to as a bimetallic oxide of formula (Ila):

Zr_f(M⁴)_gOh (Ila) where each of M⁴, f, g and h are as defined for formula (II), and the same preferences apply.

Specific examples of bimetallic oxides which are suitable for use in the coated electrode active material of the invention include Mg2Zr20e.

Preferably, the bimetallic oxide is Mg2Zr20e.

The coated electrode active material of the invention is obtained or obtainable by the coating method of the invention. For example, the coated electrode active material is obtained or obtainable by calcination of an electrode active material having the bimetallic alkoxide of formula (II) deposited on the surface. Doping

The present invention also provides a method for doping an electrode active material.

US 2019/341598 describes doping of a nickel-cobalt-manganese hydroxide cathode active material precursor. The nickel-cobalt-manganese hydroxide precursor is mixed with LiOH, ZrC>2 and AI(OH)₃ and then sintered at 480 °C for 5 hours followed by 700 to 750 °C for 16 hours.

US 2019/341598 does not describe a bimetallic alkoxide precursor, but instead uses separate mono-metallic precursors such as ZrO₂ and AI(OH)₃. US 2019/341598 also does not describe a step of providing a coated electrode active material and further heating the coated electrode active material to dope the electrode active material. Instead, US 2019/341598 describes heating the electrode active material to dope the material, without a coating step. Coating is only described in a separate subsequent step, and relates to a mono-metallic boron coating. Furthermore, US 2019/341598 describes lithiating the cathode active material precursor with LiOH simultaneously with doping the material with Zr and Al. In the present invention the electrode active material is preferably a pre-lithiated electrode active material.

The doping method of the invention comprises providing a coated electrode active material of the invention, such as a coated electrode active material comprising a layer of a bimetallic oxide of formula (II) deposited on the surface of an electrode active material. The coated electrode active material may be obtained or obtainable by the coating method of the invention. Typically, the doping method of the invention comprises, as a first step, coating an electrode active material with a bimetallic oxide according to the coating method of the invention.

The doping method of the invention comprises heating the coated electrode active material. This may be referred to as the doping step, step (e)

During doping, metal atoms from the bimetallic oxide coating layer move into the bulk of the electrode active material. Any of the metal components from bimetallic oxide layer may move into the bulk electrode active material.

The metal atoms move into the bulk electrode active material from the surface of the electrode active material (the interface between the electrode active material and the bimetallic oxide coating layer). Typically, the distribution of doped metal species in the electrode active material is non-uniform. Typically, the concentration of doped metal species is greater closer to the surface of the electrode active material. That is, the doping method provides a gradient of doped metals in the bulk electrode active material. Typically, the ratio of doped metals to bulk electrode active material decreases with distance from the surface of the electrode active material. Methods for heating the coated electrode active material are known and include, for example, using a furnace.

Typically, the doping step takes place at a temperature of from 600 °C to 1500 °C, preferably from 600 °C to 1200 °C, more preferably from 600 °C to 1000 °C.

The doping step may comprise gradually raising the temperature to the desired temperature. Any suitable heating rate can be used. Typically, the doping step comprising raising the temperature at a rate of from 5 °C per minute to 20 °C per minute, preferably about 10 °C per minute.

The doping step may be performed for sufficient time to allow a desired quantity of metal atoms from the coating layer to move into the bulk electrode active material.

Typically, the doping step comprises heating the coated electrode active material for 1 hour to 24 hours. Preferably, the doping step comprises heating the coated electrode active material for 1 hour to 12 hours, more preferably 1 hour to 8 hours, even more preferably 2 hours to 6 hours.

The doping step may be carried out in the absence of oxygen or atmospheric moisture. Typically, however, this is not necessary, and the doping may be carried out in air.

Doped Electrode Active Material

The present invention also provides a doped electrode active material. The doped electrode active material has a layer of a bimetallic oxide deposited on the surface of an electrode active material. The bimetallic oxide comprise Zr; a second metal selected from Al, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, and Mg; and oxygen. Preferably, the second metal is selected from Al, Ti, Mn, Fe, Co, Ni, Cu and Mg. More preferably, the second metal is Mg.

The doped electrode active material comprises a surface region that is doped with Zr and a second metal selected from Al, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, and Mg. The surface region is the region of the electrode active material that is in contact with the layer of bimetallic oxide.

Typically, the distribution of doped metal species in the surface region is non-uniform. The concentration of doped metal species is greater closer to the surface of the electrode active material. That is, the surface region comprises a gradient of doped metals. Typically, the ratio of doped metals to bulk electrode active material in the surface region decreases with distance from the surface of the electrode active material. Electrode Active Material

The present invention provides a method for coating an electrode active material, a coated electrode active material, and a doped electrode active material.

Any suitable electrode active material may be coated using the coating method of the invention, and in the coated and doped electrode active materials of the invention. Positive (cathode) and negative (anode) active materials may be used. Typically, the electrode active material is a metal oxide.

Suitable electrode active materials lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePOi) and lithium manganese phosphate (LiMnPOt).

Preferably, the electrode active material comprise nickel. The nickel content of the electrode active material is typically defined by the number of nickel atoms relative to the total number of transition metal atoms in the chemical formula, given in percent (%). For example, NMC- 811 (LiNi0.8Mn0.1Co0.1O2) would contain 80% nickel.

Typically, the electrode active material has a nickel content of 10% or more. Preferably, the electrode active material has a nickel content of 30% or more, more preferably 45% or more, even more preferably 55% or more and most preferably 75% or more.

Additionally, the electrode active material may comprise lithium. Preferably, the electrode active material comprises lithium before it is coated, for example using the coating method of the invention. Preferably the electrode active material comprises lithium before it is doped, for example using the doping method of the invention. In other words, the electrode active material may be pre-lithiated. The electrode active material may have a lithium content of 10% or more, more preferably 20% or more, even more preferably 25% or more. The lithium content may be calculated before the electrode active material is coated and/or doped.

Additionally, the electrode active material is preferably a metal oxide, more preferably a metal oxide comprising nickel, lithium or a combination thereof, even more preferably a metal oxide comprising nickel and lithium.

In some embodiments, the electrode active material is not a metal hydroxide.

Examples of suitable nickel-containing electrode active materials include lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminium oxide, (NCA), lithium nickel cobalt magnesium oxide (NCMg) and lithium nickel cobalt rare earth oxide (NCRE).

Preferably, the electrode active material is NMC (LiNixMnyCoi-x-yCh). Examples of suitable NMC materials include NMC-111 (LiNii/3Mni/₃Coi/₃O2), NMC-442 (LiNi0.4Mn0.4Co0.2O2), NMC-532 (LiNi0.5Mn0.sCo0.2O2), NMC-622 (LiNi0.6Mn0.2Co0.2O2), and NMC-811 (LiNi0.8Mn0.1Co0.1O2). Preferably, the electrode active material is NMC-622 or NMC-811 , more preferably the electrode active material is NMC-811.

Working Electrode

The present invention also provides a working electrode comprising the coated or doped electrode active material of the invention.

The working electrode may be a positive (cathode) or negative (anode) electrode, for example during a discharge step. Typically, the working electrode is the positive electrode.

The working electrode may consist essentially of the coated or doped electrode active material of the invention.

The working electrode typically comprises current collecting substrate. Any suitable current collecting substrate may be used. Examples of suitable current collecting substrates include a copper or aluminium plate or foil. The coated or doped electrode active material of the invention is typically disposed on the surface of the current collecting substrate.

Typically, the working electrode comprises from 80 wt% to 98 wt% of the coated or doped electrode active material. Here, wt% is relative to the total mass of the electrode excluding the mass of the current collecting substrate (for example, 100 wt% is the total mass of the coated electrode active material, doped electrode active material, conductive material and binder).

The working electrode typically comprises a conductive material to improve conductivity within the working electrode. Typically, the conductive material is a conductive carbon material. Any suitable conductive carbon material may be used. Examples of suitable conductive carbon materials include carbon black such as Super P (TIMCAL) carbon or Ketjen black.

Typically, the working electrode comprises from 1 wt% to 10 wt% of conductive material.

The working electrode of the invention typically comprises a binder to improve adhesion of the active material to a current collecting surface. Any suitable binder may be used. Examples of suitable binders include PVDF (e.g Kynar), PTFE, CMC, PAA, PMMA, PEO, SBR and co-polymers thereof.

Typically, the working electrode comprises from 1 wt% to 10 wt% of binder.

The inventors have assessed a working electrode comprising NMC-811 coated with Mg2Zr20e using a standard electrode configuration of 90:5:5 active material:carbon:binder (wt%), with an approximate loading of active material of 7.6 mg*cnr² and a diameter of 14 mm (an approximate electrode area of 1.54 cm²) against a lithium counter electrode in a 2032-type coin cell geometry and using 1.0 M LiPFe in ethylene carbonate/dimethyl carbonate (3:7 v/v) as electrolyte.

The inventors have found that, when the coated NMC-811 electrode was cycled for 150 cycles between 3.0 to 4.4 V at a rate of 1 C, with three cycles at 0.05C every 50 cycles, the working electrode maintained a discharge capacity of 133 mAh*g'¹. This compares to a discharge capacity of only 108 mAh*g-¹ for the corresponding uncoated material.

Electrochemical Cell

The present invention also provides an electrochemical cell comprising the working electrode of the invention.

The electrochemical cell typically comprises a counter electrode and an electrolyte. The electrochemical cell typically comprises terminals for connection to an external device or an external power supply.

Typically, the counter electrode is the negative electrode. A negative electrode comprising any suitable anode active material may be used. Examples of suitable anode active materials include graphite and lithium titanate (LTO, Li₄Ti₅0i2).

The electrochemical cell may be a lithium ion cell.

Typically, the electrolyte in the electrochemical cell is suitable for solubilising lithium ions. Typically, the electrolyte in a charged and discharged cell contains lithium ions.

Typically, the electrolyte comprises lithium salts, such as LiTFSI, (bis(trifluoromethane)sulfonimide lithium salt), LiPFe, LiBF₄, LiCIO₄, LiTF (lithium triflate) or lithium bis(oxalato) borate (Li BOB).

The electrolyte may be a liquid electrolyte, such as a liquid at ambient temperature, for example at 25 °C.

The electrolyte may be a non-aqueous electrolyte. The electrolyte may comprise a polar aprotic solvent. The electrolyte may comprise an organic solvent. Solvents for dissolving lithium ions are well known in the art. Suitable solvents include carbonate solvents. For example propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), chloroethylene carbonate, fluorocarbonate solvents (e.g., fluoroethylene carbonate and trifluoromethyl propylene carbonate), as well as the dialkylcarbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

Suitable solvents also include sulfone solvents. For example methyl sulfone, ethyl methyl sulfone, methyl phenyl sulfone, methyl isopropyl sulfone (MiPS), propyl sulfone, butyl sulfone, tetramethylene sulfone (sulfolane), phenyl vinyl sulfone, allyl methyl sulfone, methyl vinyl sulfone, divinyl sulfone (vinyl sulfone), di phenyl sulfone (phenyl sulfone), dibenzyl sulfone (benzyl sulfone), vinylene sulfone, butadiene sulfone, 4-methoxyphenyl methyl sulfone, 4-chlorophenyl methyl sulfone, 2-chlorophenyl methyl sulfone, 3,4-dichlorophenyl methyl sulfone, 4-(methylsulfonyl)toluene, 2-(methylsulfonyl) ethanol, 4-bromophenyl methyl sulfone, 2-bromophenyl methyl sulfone, 4-fluorophenyl methyl sulfone, 2-fluorophenyl methyl sulfone, 4-aminophenyl methyl sulfone, a sultone (e.g., 1,3-propanesultone), and sulfone solvents containing ether groups (e.g., 2-methoxyethyl(methyl)sulfone and 2- methoxyethoxyethyl(ethyl)sulfone).

Suitable solvents also include silicon-containing solvents such as a siloxane or silane. For example hexamethyldisiloxane (HMDS), 1 ,3-divinyltetramethyldisiloxane, the polysiloxanes, and polysiloxane-polyoxyalkylene derivatives. Some examples of silane solvents include methoxytrimethylsilane, ethoxytrimethy Isilane, dimethoxydimethylsilane, methyltrimethoxysilane, and 2-(ethoxy)ethoxytrimethylsilane.

Typically, an additive may be included in the electrolyte to improve performance. For example vinylene carbonate (VC), vinyl ethylene carbonate, allyl ethyl carbonate, t-butylene carbonate, vinyl acetate, divinyl adipate, acrylic acid nitrile, 2-vinyl pyridine, maleic anhydride, methyl cinnamate, ethylene carbonate, halogenated ethylene carbonate, a-bromo-y- butyrolactone, methyl chloroform ate, 1 ,3-propanesultone, ethylene sulfite (ES), propylene sulfite (PS), vinyl ethylene sulfite (VES), fluoroethylene sulfite (FES), 12-crown-4 ether, carbon dioxide (CO2), sulfur dioxide (SO2), and sulfur trioxide (SO3).

The electrochemical cell may also include a solid porous membrane positioned between the negative and positive electrodes. The solid porous membrane may partially or completely replace the liquid electrolyte. The solid porous membrane may comprise a polymer (e.g., polyethylene, polypropylene, or copolymer thereof) or an inorganic material, such as a transition metal oxide (e.g., titania, zirconia, yttria, hafnia, or niobia) or main group metal oxide, such as silicon oxide, which can be in the form of glass fibre.

The solid non-porous membrane may comprise a lithium-ion conductor. For example, LLZO (garnet family), LSPO (LISICON family), LGPS (thio-LISICON family), LATP/LAGP (NASICON family), LLTO (perovskite family) and phosphide/sulfide glass ceramics. Methods

The invention also provides a method of charging and/or discharging an electrochemical cell of the invention.

The method may be a method of charging and/or discharging an electrochemical cell at a current density of at least 150 mA*g-¹, such as at least 200 mA*g-¹.

The method may involve a cycle of charging and discharging or discharging and charging the electrochemical cell. The cycle may be repeated more than once. Thus, the method of charging/discharging comprises 2 cycles or more, 5 cycles or more, 10 cycles or more, 20 cycles or more or 50 cycles or more.

The electrochemical cell of the invention shows increased capacity retention over prolonged cycling. Thus, the method of charging/discharging preferably comprises 100 cycles or more, more preferably 150 cycles or more, even more preferably 200 cycles or more and most preferably 250 cycles or more.

Battery

The present invention also provides a battery comprising one or more electrochemical cells of the invention. The battery may be a lithium ion battery.

Where there are a plurality of cells, these may be provided in series or parallel.

A battery of the invention may be provided in a road vehicle, such as an automobile, moped or truck. Alternatively, a battery of the invention may be provided in a rail vehicle, such as a train or a tram. A battery of the invention may also be provided in an electric bicycle (e-bike).

A battery of the invention may be provided in a regenerative braking system.

A battery of the invention may be provided in a portable electronic device, such as a mobile phone, laptop or tablet. A battery of the invention may be provided in a power tool.

A battery of the invention may be provided in a power grid management system.

Preparation of Bimetallic Alkoxide

The present invention also provides a method for preparing a bimetallic alkoxide, such as a bimetallic oxide of formula (I).

The preparation method of the invention uses a reaction mixture comprising a metal alkoxide of formula (III): M⁵(OR⁷),(111)

The group M⁵ is a metal. The metal M⁵ is selected from Al, Sc, Zr, Ti, Zr, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, and Zn. Preferably, M⁵ is selected from Al, Zr, Ti, Mn, Fe, Co, Ni and Cu. More preferably, M⁵ is selected from Zr, Ti and Al. Even more preferably, M⁵ is selected from Zr and Ti. Most preferably, M⁵ is Zr.

The group (OR⁷) in formula (III) is an alkoxide ligand. The group R⁷ is an C1-6 alkyl group. Different alkoxide ligands may be present in a single compound formula (III). Thus, each R⁷ is independently selected from C1-6 alkyl.

The group R⁷ may be a linear or branched. Preferably, R⁷ is linear.

Preferably, R⁷ is a C2-5 alkyl group. More preferably, R⁷ is a C3-4 alkyl group. Most preferably, R⁷ is a C3 alkyl group.

The alkoxide number i is from 2 to 6. Preferably, i is 3 or 4. More preferably, i is 4.

Specific examples of metal alkoxides which are suitable for use in the preparation method of the invention include Zr(OⁿPr)4, Zr(O'Pr)4 and Zr(0Et)4.

Preferably, the metal alkoxide is Zr(OⁿPr)4.

The reaction mixture also comprises an alcohol, HOR⁸.

The group R⁸ is an C1-6 alkyl group.

The group R⁸ may be a linear or branched. Preferably, R⁸ is linear.

Preferably, R⁸ is a C2-5 alkyl group. More preferably, R⁸ is a C3-4 alkyl group. Most preferably, R⁸ is a C3 alkyl group.

The alcohol, HOR⁸, may be used as the solvent in the reaction mixture. Optionally, an additional solvent or co-solvent may be included. Any suitable organic solvent may be used.

The preparation method of the invention comprises adding a magnesium source to the reaction mixture. This may be referred to as the reaction step, step (b).

The magnesium source may be magnesium metal or an organomagnesium compound.

Preferably, the magnesium source is magnesium metal. This avoids the use of the expensive and highly reactive orangomagnesium compound, improving safety and reducing cost. In such cases, the alcohol, HOR⁸, is typically used as the solvent in the reaction mixture.

In such cases, the reaction step typically comprises heating the reaction mixture after addition of the magnesium metal. Methods for providing heat are known and include, for example, using a reaction vessel having an external heating jacket. In such cases, the reaction step typically comprises heating the reaction mixture under reflux. That is, heating the reaction mixture to the boiling point of the solvent. For example, were the solvent is 1-propanol, the reaction mixture is heated to around 98 °C.

Alternatively, the magnesium source is an organomagnesium compound. This typically avoids the need to heat the reaction mixture.

The organomagnesium compound has the formula Mg(R⁹)₂.

The group R⁹ is an C1-6 alkyl group.

The group R⁹ may be a linear or branched. Preferably, R⁹ is linear.

Preferably, R⁹ is a C2-5 alkyl group. More preferably, R⁹ is a C3-4 alkyl group. Most preferably, R⁹ is a C3 alkyl group.

In such cases, the reaction mixture typically comprises an additional solvent or co-solvent. Typically, the additional solvent is a hydrocarbon solvent or an ether solvent.

The additional solvent may be an aliphatic or aromatic hydrocarbon solvent.

Examples of suitable ether solvents include tetrahydrofuran (THF), tetrahydropyran (THP), diethyl ether, cyclopentyl methyl ether (CPME) and methyl tert-butyl ether (MTBE).

Preferably, the additional solvent is an aliphatic hydrocarbon solvent, more preferably the organic solvent is hexane or heptane.

In such cases, the reaction step typically comprises stirring the reaction mixture at ambient temperature (room temperature; approx. 20 °C). Optionally, the reaction step in such cases may be carried out at lower temperature, such as from -10 °C to 15 °C. In such cases, a solution of the organomagnesium compound in an organic solvent may be added to the reaction mixture. Suitable organic solvents include the hydrocarbon and ether additional solvents used in the reaction mixture.

In such cases, the organomagnesium compound may be added in a continuous-feed manner. For example, organomagnesium compound may be added in a drop-wise manner.

Alternatively, the organomagnesium compound may be added using a pump, for example a syringe pump.

The reaction step may be performed for sufficient time to allow a desired quantity of the bimetallic alkoxide to form. Typically, the reaction step is performed until substantially all the metal alkoxide is consumed. Typically, the reaction step is accompanied by release of gas and production of a suspension. The reaction step may be performed until release of gas has abated.

The reaction time may be from 30 minutes to 24 hours. Preferably, the reaction time is from 30 minutes to 12 hours, more preferably from 30 minutes for 8 hours, even more preferably from 1 hour to 6 hours and most preferably from 1 hour to 4 hours.

The method for preparing a bimetallic alkoxide may further comprise:

(c) isolating the bimetallic alkoxide.

This may be referred to as the isolation step, step (c).

Any suitable isolation method may be used.

The isolation step may comprise returning the reaction mixture to room temperature. The isolation step may comprise quenching the reaction mixture.

Typically, the isolation step comprises adding a hydrocarbon solvent to the reaction mixture. Suitable hydrocarbon solvents include the hydrocarbon additional solvents used in the reaction mixture.

Typically, the isolation step comprises filtering the reaction mixture. This filtration removes any suspension that is generated during the reaction. Any suitable filtration method may be used. In such cases, the filtration takes place after addition of the hydrocarbon solvent.

Typically, the isolation step comprises storing the filtrate. On storage, the bimetallic alkoxide precipitates or crystalises. Optionally, the isolation step comprises cooling the filtrate. The filtrate may be cooled to from -20 °C to 10 °C.

The solid bimetallic alkoxide (as precipitate or crystals) may be isolated by filtration. Definitions

The following common definitions are used herein, as determined by the relevant context.

A bimetallic compound is a compound containing two different metallic elements. Thus, each of Li2ZrC>3, UAIO2, Li2TiC>3 and Mg2Zr20e are bimetallic oxides, for example.

Elements are referred to using their chemical symbols. Thus, H is hydrogen, O is oxygen, Mg is magnesium and Zr is zirconium, for example.

An electrode active material is a component that stores and releases the charge-carrying ions, such as lithium, within an electrochemical cell. The electrode active material may be the positive (cathode) or negative (anode) active material.

Unless otherwise stated, the voltage values described herein are made with reference to Li⁺/Li.

An alkyl group is monovalent saturated hydrocarbon group. In this context, the prefix (e.g. C1-6) denotes the number or range of carbon atoms in the hydrocarbon backbone. Alkyl groups may be linear or branched.

A cycloalkyl group is a monovalent saturated hydrocarbon group which comprises a ring in which all of the ring atoms are carbon atoms. In this context, the prefix (e.g. C1-6) denotes the number or range of carbon atoms in the ring. Cycloalkyl groups may be monocyclic, or they may comprise two or more rings.

A heterocyclyl group is a cycloalkyl group in which one or more ring atoms are heteroatoms, for example N, O and S. In this context, the prefix (e.g. 5-7 membered) denotes the number or range of ring atoms, whether carbon atoms or heteroatoms. The heterocyclyl group may be monocyclic, or it may comprise two or more rings.

Other Preferences

Each and every compatible combination of the embodiments described above is explicitly disclosed herein, as if each and every combination was individually and explicitly recited.

Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure.

“and/or” where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example “A and/or B” is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein. Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments which are described.

Certain aspects and embodiments of the invention will now be illustrated by way of example and with reference to the figures described above.

Worked Examples

The following examples are provided to further illustrate the present invention and are not intended to limit the scope of the invention.

Experimental Methods

X-ray crystallography data were collected on a Bruker D8 Quest (Cu Ka, A = 1.54184 A), equipped with an Oxford Cryosystems low-temperature device. Structures were solved using SHELXT, with refinement, based on P, by full-matrix least-squares.

Nuclear magnetic resonance (NMR) data were collected on a Bruker Avance III HD 400 MHz Smart Probe FT NMR spectrometer (400.130 MHz for ¹H, 100.613 MHz for ¹³C). Spectra were obtained at 25 °C. ¹H and ¹³C chemical shifts are internally referenced to deuterated solvent and calculated relative to TMS. Chemical shifts are given in 5 ppm. Abbreviations used are br = broad, m = multiplet, sext = sextet, t = triplet.

Elemental analysis was carried out on a PerkinElmer 240 Elemental Analyzer.

Thermogravimetric analysis (TGA) was carried out using a Mettler Toledo TGA/DSC 2 under an air atmosphere, with heating from 25 °C to 800 °C at a ramp rate of 10 “Cornin'¹.

Powder X-ray diffraction (XRD) was carried out using an analytical Empyrean (Cu radiation) with a scan range of 5-80° and 4488 scans.

Scanning electron microscopy (SEM) was carried out using a TESCAN MIRA3 FEG-SEM.

Energy-dispersive X-ray spectroscopy (EDS) was carried out using Oxford Instruments Aztec Energy X-maxN 80 EDS system.

Example 1-1 - Synthesis of Mg₂Zr2(OⁿPr)i2(ⁿPrOH)₄

Zr(OⁿPr)4 in ⁿPrOH (3.6 ml, 8.0 mmol) was combined with ⁿPrOH (2.0 ml) and hexane (20 ml) under a nitrogen atmosphere. Mg(ⁿBu)2 (8.0 ml, 8.0 mmol, 1.0 M in heptane) was added dropwise and the solution was stirred at room temperature overnight. The solution was then stored at -20 °C, resulting in the formation of crystalline material.

The resulting material was confirmed to be Mg2Zr2(OⁿPr)i2(ⁿPrOH)4 following characterisation by NMR and X-ray diffraction. The crystal structure (Figure 1A) shows the M4O16 core structure which is characteristic of many zirconium alkoxide compounds. Both magnesium and zirconium have octahedral coordination geometries, with ₂- and ₃-propoxides bridging the metals. The magnesium ions occupy the central positions with coordination by two ^2- propoxides, two ₃-propoxides and two terminal propanols. The zirconium ions occupy the outer metal positions and are coordinated by two 2-propoxides, one ₃-propoxide and three terminal propoxides.

¹H NMR (400 MHz, benzene-d₆): 54.67 (br, 4H, OH), 4.20 (br, m, 24H, CH₂), 3.53 (t, J = 6.8 Hz, 8H, Me), 1.98 (br, m, 24H, CH₂), 1.55 (sext, J = 7.1 Hz, 8H, CH₂), 1.10 (m, 36H, CH₃), 0.85 (t, J = 7.4 Hz, 12H, CH₃). ¹³C NMR (400 MHz, benzene-d₆): 569.9, 64.9 (CH₂), 28.6, 26.8 (CH2), 10.8, 10.5, 10.4, 10.3 (CH₃). Elemental analysis calculated for C4sHn6Mg20i6Zr2 (%): C 48.84, H 9.90, Mg 4.12, O 21.68, Zr 15.46; found (%): C 49.42, H 10.14. X-ray crystal data: C4sHn6Mg20i6Zr2, M = 1180.46, orthorhombic, space group Cmca, a = 21.4340(6), b = 14.3039(4) c = 21.4961 (7) A, a = 90, = 90, y = 90, V = 6590.5(3) A³, Z = 4, Pcaicd = 1.190 g cm^-3, p = 3.221 mm^-1, T = 180(2) K. 3099 data (2345 unique, R_int = 0.1408, 0 < 66.623°) were collected. wR₂ = {Z[w(F₀ ² - F_c ²)²]/Z[w(F₀ ²)²]}^1/2 = 0.2922, conventional R = 0.1045 on F values of 2345 reflections with F² > 2o(F²), GoF = 1.035, 261 parameters. Max. peak/hole ±2.097 eA~³.

Example 1-2 - Alternative Synthesis of Mg₂Zr2(OⁿPr)i2(ⁿPrOH)₄

Zr(OⁿPr)4 in ⁿPrOH (1.8 ml, 4.0 mmol) was combined with ⁿPrOH (5.0 ml) and magnesium turnings (97 mg, 4.0 mmol) under a nitrogen atmosphere. The suspension was heated to reflux for 2 hours, resulting in the release of gas and a grey suspension. Hexane (10 ml) was added, and the resulting suspension was filtered to give a clear solution. Storage of the solution at room temperature resulted in the formation of crystalline material.

The resulting material was confirmed to be Mg2Zr2(OⁿPr)i2(ⁿPrOH)4 following characterisation by NMR and X-ray diffraction. The NMR spectra are identical to that synthesised above.

Example 1-3 - Characterisation of Mg2Zr2(OⁿPr)i2(ⁿPrOH)4

Thermogravimetric analysis (TGA) was performed on Mg2Zr2(OⁿPr)i2(ⁿPrOH)4 to understand the decomposition to bimetallic oxide (Figure 2A). A sample of the bimetallic alkoxide was gradually heated up to 800 °C in air. A weight loss of 71 wt% was observed, leaving the bimetallic oxide Mg2Zr20e. There is an initial weight loss of 20 wt% which occurred over 120-160 °C which is attributed to the loss of the four n-propanol ligands. There is another weight loss of 51 wt% at 320-450 °C which is attributed to the loss of the twelve propoxide ligands to give Mg2Zr₃O6 (Figure 2A). This suggests that Mg2Zr2(OⁿPr)i2(ⁿPrOH)4 is fully decomposed to Mg2Zr₃O6 by heating to 450 °C.

XRD was performed on the material heated to 450 °C and 800 °C in air (Figure 3A). The XRD pattern of the material heated to 450 °C showed a very broad peak at 32° due to the amorphous sample. The XRD pattern of the material heated to 800 °C revealed a pattern which was attributable to a mixture of crystalline ZrC>2 and MgO.

Example 1-4 - Synthesis of Li2Zr2(OⁿPr)io(THF)2

Zr(OⁿPr)4 in ⁿPrOH (0.90 ml, 2.0 mmol) was combined with hexane (5 ml) under a nitrogen atmosphere. ⁿBuLi (8.0 ml, 8.0 mmol, 1.6 M in hexane) was added dropwise at -78 °C and the solution was stirred at room temperature overnight. The solvent was removed under vacuo and redissolved in THF (0.5 ml). The solution was then stored at -20 °C, resulting in the formation of crystalline material.

The resulting material was confirmed to be Li2Zr2(OⁿPr) (THF)2 following characterisation by NMR and X-ray diffraction. The crystal structure (Figure 1C) shows the lithium has a tetrahedral geometry and zirconium has an octahedral coordination geometry, with ₃- and p₃- propoxides bridging the metals. The lithium ions occupy the peripheral positions with coordination by two 2-propoxides, one ₃-propoxide and one terminal THF. The zirconium ions occupy the inner metal positions and are coordinated by two ^-propoxides, two p₃- propoxides and two terminal propoxides.

¹H NMR (400 MHz, C₆D₆): 5 4.38-4.11 (20 H, m, OCH₂), 3.69 (7.5 H, m, THF), 2.12-1.69 (20 H, m, CH₂), 1.40 (7.5 H, m, THF), 1.22-0.98 (30 H, m, Me). ¹³C NMR (101 MHz, C₆D₆): 5 71.3, 70.0, 69.9 (OCH₂), 68.3 (THF), 29.0, 28.8, 26.7 (CH₂), 25.5 (THF), 11.2, 11.0, 10.4 (Me). ⁷Li NMR (155 MHz, CeDe): 5 0.6, 0.3. Elemental analysis calculated (%) for C₃8H86Li2Oi2Zr₂: C 49.0, H 9.3. Found: C 46.2, H 9.1.

Example 1-5 - Characterisation of Li2Zr2(OⁿPr)io(THF)2

Thermogravimetric analysis (TGA) was performed on Li2Zr2(OⁿPr) (THF)2 to understand the decomposition to bimetallic oxide (Figure 2B). A sample of the bimetallic alkoxide was gradually heated up to 800 °C in air. A weight loss of 73 wt% was observed, leaving the bimetallic oxide Li₃ZrO₃ and ZrO₃.

There is an initial weight loss of 18 wt% which occurred over 100-200 °C which is attributed to the loss of the THF ligands. There is another weight loss of 57 wt% at 200-380 °C which is attributed to the loss of the ten propoxide ligands to give Li₃ZrO₃ and ZrO₃ (Figure 2B). This suggests that Li2Zr2(OⁿPr) (THF)2 is fully decomposed to Li2ZrOa and ZrC>2 by heating to 450 °C.

XRD was performed on the Li2Zr2(OⁿPr) (THF)2 material heated to 450 °C (Figure 3B) and 800 °C (Figure 3C) in air. The XRD pattern of the material heated to 450 °C shows relatively broad peaks due to the amorphous nature of the sample. The XRD pattern of the material heated to 800 °C revealed a pattern which was attributable to a mixture of crystalline Li₂ZrO3 and ZrC>2.

Example 2-1 -Preparation of MgZr Coated NMC-811

Pristine NMC-811 was coated with the magnesium-zirconium alkoxide via a solution-based deposition by slowly evaporating the solvent to leave a thin layer of magnesium-zirconium alkoxide. The coated material was then annealed to the desired temperature in air (Figure 4).

NMC-811 (2.0 g), Mg₂Zr2(OⁿPr)i₂(ⁿPrOH)4 (72 mg) and n-propanol (5.0 ml) were combined under a nitrogen atmosphere and stirred for 1 hour at 50 °C. This was followed by removal of the solvent under vacuum at 50 °C to give NMC-811 coated with the bimetallic alkoxide (NMC-MgZr).

NMC-MgZr was then heated to the desired temperature for 4 hours in air with a heating rate of 10 °C*min'¹. The samples are labelled NMC-MgZr450 and NMC-MgZr800, which were heated to 450 °C and 800 °C respectively.

Example 2-2 - Characterisation of MgZr Coated and Doped NMC-811

XRD was performed on material heated to 450 °C (NMC-MgZr450) and 800 °C (NMC- MgZr800) in air to understand how the material changes during annealing.

The XRD patterns from NMC-MgZr450 reveals very little difference to the pristine NMC material (Figure 5). This suggests that the bulk NMC material has not undergone any significant structural rearrangement during the coating process.

The XRD patterns from NMC-MgZr800 does show some differences to the pristine NMC material (Figure 5), with a shift in some of the peaks to lower 20 values. This suggests an increase in the unit cell size of the NMC. It is thought this is associated with the diffusion some of the coating elements into the bulk NMC. There are no peaks that can be assigned to the coating material, due to the small amount of coating material (1 wt%) relative to bulk NMC.

SEM and EDS were performed on the particles to investigate their morphology (Figure 6).

SEM shows that NMC-MgZr450 is significantly different to the pristine material, with the particles covered with a thin coating. The EDS analysis reveals both magnesium and zirconium are present on the surface of NMC-MgZr450.

SEM and EDS of the NMC-MgZr800 sample show that magnesium and zirconium are present on the surface of the particles, but in reduced amounts in comparison to the sample heated to 450 °C (Figure 7). This suggests that both elements have doped into the bulk NMC material.

Example 2-3 -Preparation of LiZr Coated NMC-811

Pristine NMC-811 was coated with the lithium-zirconium alkoxide via a solution-based deposition by slowly evaporating the solvent to leave a thin layer of lithium-zirconium alkoxide. The coated material was then annealed to the desired temperature in air (Figure 4).

NMC-811 (2.0 g), Li₂Zr₂(OⁿPr)io(THF)2 (68 mg) and n-propanol (5.0 ml) were combined under a nitrogen atmosphere and stirred for 1 hour at 50 °C. This was followed by removal of the solvent under vacuum at 50 °C to give NMC-811 coated with the bimetallic alkoxide (NMC- LiZr).

NMC-LiZr was then heated to the desired temperature for 4 hours in air with a heating rate of 10 °C*min'¹. The samples are labelled NMC-LiZr450 and NMC-LiZr800, which were heated to 450 °C and 800 °C respectively.

Example 2-4 -Preparation of Comparative Zr Coated NMC-811

Pristine NMC-811 was coated with a zirconium n-propoxide via a solution-based deposition by slowly evaporating the solvent to leave a thin layer of zirconium oxide. The coated material was then annealed to the desired temperature in air.

NMC-811 (2.0 g), Zr(OⁿPr)4 in n-propanol (0.07 ml) and n-propanol (5.0 ml) were combined under a nitrogen atmosphere and stirred for 1 hour at 50 °C. This was followed by removal of the solvent under vacuum at 50 °C to give NMC-811 coated with the metallic alkoxide (NMC- Zr).

NMC-Zr was then heated to the desired temperature for 4 hours in air with a heating rate of 10 °C*min'¹. The samples are labelled NMC-Zr450 and NMC-Zr800, which were heated to 450 °C and 800 °C respectively.

Example 3-1 - Preparation of Coated and Doped NMC-811 Electrodes

A slurry of NMC-MgZr (900 mg), conductive carbon (Timcal Super P Li, 50 mg), and polyvinylidene fluoride binder (Kynar HSV900, 50 mg) was mixed with anhydrous N-methyl-2- pyrrolidone (NMP; 1.5 cm³) in a planetary centrifugal mixer (Thinky ARE-310 ) at 2000 rpm over 10 minutes (5 minutes per cycle, for two cycles). The slurry was casted with a doctor blade (slit size 200 pm) onto battery-grade aluminium foil (16 pm thick, MTI Corporation) then dried at 100 °C under flowing N2. Dried electrodes were punched out with a diameter of 14 mm (electrode area approx. 1.54 cm²; areal loading approx. 7.6 mg*cm^-2) and dried at 120 °C under dynamic vacuum (~10^-2 mBar) in a Buchi oven for 10 h. Once dry, the electrodes were cooled to room temperature and transferred into an argon-filled glovebox (H₂O < 1 ppm; O2 < 1 ppm) without air exposure for cell assembly. Commercial LP57 electrolyte (SoulBrain Ml) with a composition of 1 M LiPFe in ethylene carbonate/ethyl methyl carbonate (3:7 v/v) was used with glass fibre separators (GF/B, Whatman) dried under vacuum at 100 °C.

NMC-LiZr, NMC-Zr and NMC (uncoated) electrodes were prepared analogously, by replacing the NMC-MgZr with NMC-LiZr, NMC-Zr or uncoated NMC respectively.

Example 3-2 - Electrochemical Characterisation of Coated NMC-811 Electrode

Electrochemical cycling was performed in NMC/Li half-cells with 2032 coin cells (Cambridge Energy Solutions) where the cell stack consists of one 14 mm cathode, one 17 mm separator soaked with 150 pl LP57 electrolyte and one 16 mm Li metal disk (99.9 %, PI-KEM). Galvanostatic cycling on NMC/Li half-cells were conducted at room temperature (20 ± 2 °C) with a constant current constant voltage (CCCV) charging and constant current (CC) discharge protocol. For diagnostic cycles, a current density of 10 mA g^-1 (0.05 C rate, assuming NMC-811 has a practical specific capacity of 200 mAh g^-1) was applied between the 3.0 V and 4.4 V (or 4.6 V) potential window with the CV hold at the upper cut off voltage until a current limit of 0.025 C was reached. After two initial diagnostic cycles, ageing with current densities of 200 mA g^-1 (1 C rate) were used in the CCCV charge (current limit for CV was C/10 value) and CC discharge protocols. Subsequent diagnostic cycles (in sets of 3) are collected every 49 cycles.

The electrochemical performance of the coated NMC-MgZr450 and uncoated NMC was investigated using the electrochemical cycling method described above, with cycling between 3.0V and 4.4 V at a C rate of 1 C, with three 0.05 C cycles every 50 cycles (Figure 8A).

The NMC-MgZr450 coated material had a similar initial discharge capacity compared to the uncoated NMC, and the discharge capacity remained similar for around 20 cycles. Further cycling of the half cells, however, revealed better capacity retention of the coated NMC-MgZr450. After 150 cycles the coated material had a discharge capacity of 133 mAh*g-¹, compared to 108 mAh*g-¹ for the uncoated material.

The half-cell cycling was repeated at higher voltages, with cycling between 3.0V and 4.6 V (Figure 9A). At these higher voltages, the uncoated material shows much poorer initial discharge capacity, and discharge capacity retention was low. After 20 cycles, the coated material had a discharge capacity of 193 mAh*g'¹, compared to 177 mAh*g'¹ for the uncoated material. After 100 cycles, the coated material had a discharge capacity of 160 mAh*g-¹, compared to only 96 mAh*g'¹ for the uncoated material.

This significant difference in discharge capacity retention may be attributed to the chemical oxidation of the electrolytes by the cathode. The NMC-MgZr450 coated material prevents contact of the electrode active material with the electrolyte, because of the chemically inert MgZr coating, which may prevent the chemical oxidation.

Example 3-3 - Electrochemical Characterisation of Additional Coated NMC-811 Electrodes

Electrochemical cycling was performed in NMC/Li half-cells with 2032 coin cells (Cambridge Energy Solutions) where the cell stack consists of one 14 mm cathode, one 17 mm separator soaked with 150 pl LP57 electrolyte and one 16 mm Li metal disk (99.9 %, PI-KEM). Galvanostatic cycling on NMC/Li half-cells were conducted at room temperature (20 ± 2 °C) with a constant current constant voltage (CCCV) charging and constant current (CC) discharge protocol. For diagnostic cycles, a current density of 10 mA g^-1 (0.05 C rate, assuming NMC-811 has a practical specific capacity of 200 mAh g^-1) was applied between the 3.0 V and 4.4 V (or 4.6 V) potential window with the CV hold at the upper cut off voltage until a current limit of 0.025 C was reached. After two initial diagnostic cycles, ageing with current densities of 200 mA g^-1 (1 C rate) were used in the CCCV charge (current limit for CV was C/10 value) and CC discharge protocols. Subsequent diagnostic cycles (in sets of 2) are collected every 50 cycles. The capacity retention for cells in Example 3-3 is thought to be slightly higher compared to similar cells in Example 3-2 due to a new supply of NMC-811 electrode material.

The electrochemical performance of the coated NMC-MgZr450, NMC-LiZr450 and NMC- Zr450 was investigated using the electrochemical cycling method described above, with cycling between 3.0 V and 4.4 V at a C rate of 1 C, with two 0.05 C cycles every 50 cycles (Figure 8B).

The NMC-MgZr450 coated material has a similar initial discharge capacity compared to the NMC-Zr, while NMC-LiZr450 has a slightly higher initial discharge capacity. The discharge capacity of the NMC-MgZr450 and NMC-LiZr450 coated materials remain similar for around 25 cycles, while the capacity of the NMC-Zr450 coated material starts to decrease. After 50 cycles, the diagnostic cycles show a higher capacity for NMC-MgZr450 and NMC-LiZr450 coated materials compared to NMC-Zr450. Following further cycling the capacity retention for the coated NMC-MgZr450 is shown to be higher than both LiZr and Zr coated materials for this 3.0V to 4.3V cell cycling.

The half-cell cycling was repeated at higher voltages, with cycling between 3.0 V and 4.6 V (Figure 9B). At these higher voltages, the NMC-MgZr450 and NMC-LiZr450 materials shows better capacity retention than the NMC-Zr450 material. Despite similar capacities and capacity retention over the first 50 cycles, further cell cycling resulted in a more rapid decrease in capacity for NMC-Zr. In particular, the NMC-LiZr450 material shows excellent capacity retention after repeated cycling at 1C at higher voltages.

Example 4-1 - Full-Cell Cycling

To further test the coated material, full cell cycling of the coated NMC-MgZr450 and uncoated NMC was investigated (Figure 10). Full cell cycling was performed in using 2032 coin cells as for the half-cell experiments above. Graphite anodes were purchased from the Cell Analysis, Modelling, and Prototyping (CAMP) Facility at the Argonne National Laboratory. The graphite anodes comprised 91.83 wt% graphite powder(Hitachi MagE3), 2 wt% carbon black (Timcal C45), 6 wt% PVDF binder (Kureha 9300), and 0.17 wt% oxalic acid. The anodes had a thickness of 52 pm (including 10 pm Cu foil), a porosity of 30.3% and an areal loading of 6.35 mg*cnr². The same electrolyte was used.

A full-cell comprising the NMC-MgZr450 cathode revealed a marked improvement over a cell containing an uncoated NMC cathode, with an increased discharge capacity after 120 cycles. After 250 cycles, the uncoated NMC had a discharge capacity of 133 mAh g-¹, while the NMC-MgZr450 had a discharge capacity of 160 mAh g-¹. Thus, the coated material shows far greater discharge capacity retention, which is indicative of an improved cell lifetime.

Moreover, the discharge capacity retention is more linear, in comparison to the uncoated NMC, which displayed a plateau for around 75 cycles and then a rapid decline.

References

A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein.

Li et al., “High-nickel layered oxide cathodes for lithium-based automotive batteries”, Nature Energy, 2020, Vol. 5, pp. 26-34.

Liu et al., “Significantly improving cycling performance of cathodes in lithium ion batteries: The effect of AI2O3 and LiAICh coatings on LiNi0.6Co0.2Mn0.2O2”, Nano Energy, 2018, Vol. 44, pp. 111-120.

Song et al., “Thermoeletrochemical study on LiNi0.8Co0.1Mn0.1O2 with in situ modification of Li₂ZrO₃”, Ionics (Kiel), 2018, Vol. 24, pp. 3325-3335.

Wang et al., “Recent advances and historical developments of high voltage lithium cobalt oxide materials for rechargeable Li-ion batteries”, Journal of Power Sources, 2020, Vol. 460, pp. 228062. Zhan et al., “Influence of annealing atmosphere on Li2ZrO3-coated LiNi0.6Co0.2Mn0.2O2 and its high-voltage cycling performance”, Electrochimica Acta, 2019, Vol. 300, pp. 34-44.

Claims

- 34 -WO 2023/025941 PCT/EP2022/073790 Claims

1. A method for coating an electrode active material with a bimetallic oxide, the method comprising:

(M¹)_a(M²)b(OR¹)c(R²OR³)d(R⁴C(=O)R⁵)e (I) wherein: M¹ and M² are different;

M¹ is selected from Zr, Ti, Li and Mg;

M² is selected from Al, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Li and Mg; R¹ is C1-6 alkyl group;

R² is H and R³ is a C1-6 alkyl group, or R² and R³ together with the oxygen atom to which they are bonded is a 5-7 membered heterocyclyl group;

R⁴ is C1-6 alkyl;

2. The method of claim 1 , wherein M¹ is Zr.

3. The method of claim 1 or 2, wherein M² is Al, Ti, Mn, Fe, Co, Ni, Cu and Mg.

4. The method of any preceding claim, wherein R¹ is C3 alkyl.

5. The method of any preceding claim, wherein: i) R² and R³ together with the oxygen atom to which they are bonded is a 5-7 membered heterocyclyl group selected from is oxolane, oxane or oxepane; and/or ii) R⁴ is C1-2 alkyl and R⁵ is a group CH=C(O)R⁶, where R⁶ is C1-2 alkyl.

6. The method of any preceding claim, wherein the compound of formula (I) is:

Mg₂Zr₂(OⁿPr)i2-(ⁿPrOH)4

7. The method of any preceding claim, wherein the organic solvent is a hydrocarbon solvent, such as an aromatic hydrocarbon solvent, such as toluene. - 35 -

WO 2023/025941 PCT/EP2022/073790

8. The method of any preceding claim, wherein the coating composition is anhydrous.

9. The method of any preceding claim, wherein in step (d), the electrode active material is calcined at a temperature of 300 °C to 600 °C, such as 350 °C to 550 °C, such as 400 °C to 500 °C.

10. A coated electrode active material obtained or obtainable by the method of any preceding claim.

11. A coated electrode active material comprising a layer of a bimetallic oxide of formula (I I) deposited on the surface of an electrode active material:

(M³)_f(M⁴)_gO_h (II) wherein:

M³ is Zr;

M⁴ is selected from Al, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn and Mg; f and g are independently from 1 to 4; and h is from 4 to 8,

12. The coated electrode active material of claim 11 , wherein the bimetallic oxide is Mg₂Zr₂O6.

13. The coated electrode active material of claim 11 or 12, wherein the electrode active material: i) has a nickel content of 10% or greater; and/or ii) is selected from lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminium oxide, (NCA), lithium nickel cobalt magnesium oxide (NCMg) and lithium nickel cobalt rare earth oxide (NCRE).

14. The coated electrode active material of claim 13, wherein the electrode active material is selected from NMC-811 or NMC-622.

15. A method for doping an electrode active material, the method comprising:

(a) providing a coated electrode active material according claim 10; and

(b) heating the coated electrode active material at a temperature of from 600 °C to 1500 °C.

16. A doped electrode active material obtained or obtainable by the method of claim 15.

17. A doped electrode active material comprising a layer of a bimetallic oxide deposited on the surface of an electrode active material, wherein: i) the bimetallic oxide comprises Zr; a second metal selected from Al, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn and Mg; and O; and ii) the electrode active material comprises a surface region that is doped with Zr and a second metal selected from Al, Sc, Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn and Mg.

18. The doped electrode active material of claim 17, wherein the ratio of doped metals to bulk electrode active material decreases with distance from the surface of the electrode active material.

19. The doped electrode active material of claim 17 or 18, wherein the electrode active material: i) has a nickel content of 10% or greater; and/or ii) is selected from lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminium oxide, (NCA), lithium nickel cobalt magnesium oxide (NCMg) and lithium nickel cobalt rare earth oxide (NCRE).

20. The doped electrode active material of claim 19, wherein the electrode active material is selected from NMC-811 or NMC-622.

21. An electrochemical cell comprising a working electrode, wherein the working electrode comprises the coated electrode active material of claims 10 to 14 or the doped electrode active material of claims 16 to 20.

22. A method for preparing a bimetallic alkoxide, the method comprising:

(a) providing a reaction mixture comprising: i) a compound of formula (III):

M⁵(OR⁷)i (III) wherein:

R⁷ is independently selected from C1-6 alkyl; and i is from 2 to 6, and ii) HOR⁸, wherein R⁸ is selected from C1-6 alkyl; and

23. The method of claim 22, wherein: i) M⁵ is Zr; and/or ii) R⁷ is C3 alkyl.

24. The method of claim 22 or 23, wherein step (b) comprising adding magnesium metal.