Cathode materials for ion batteries

Abstract

Doped layered cathode materials for an electrochemical device are disclosed, which comprises a layered cathode material and a dopant, wherein the dopant is selected and added so that the electrochemical device delivers a capacity retention of about 78% to about 88% after 500 cycles at 1 C.

Description

CATHODE MATERIALS FOR ION BATTERIES PRIORITY DOCUMENT

[0001] The present application claims priority from Australian Provisional Patent Application No.2023903504 titled “CATHODE MATERIALS FOR ION BATTERIES” and filed on 1 November 2023, the content of which is hereby incorporated by reference in its entirety. TECHNICAL FIELD

[0002] The present disclosure relates generally to cathode materials for electrochemical devices. In a particular form, the present disclosure relates to layered cathode materials comprising a dopant and methods for preparing layered cathode materials comprising a dopant. BACKGROUND

[0003] As a vital energy supply system for portable devices, ion batteries have become ubiquitous in everyday life over the past three decades[1]. Their successful commercialisation has led to widespread use in electric vehicles and other equipment with high energy requirements. In addition to lithium ion batteries (LIB), rechargeable sodium ion batteries (NIB) and potassium ion batteries (KIB) have attracted considerable attention due to the abundance and accessibility of sodium and potassium resources. Among the various rechargeable battery components, the cathode is the most expensive and heaviest, and cathode materials are considered as pivotal components for achieving higher energy density and longer cycle life[2-3]. Therefore, the development of cathode materials is critical to the success of ion batteries. Among various candidates, layered oxides (especially Ni-rich layered oxides) are regarded as the most promising cathode materials due to their high energy density and relatively low toxicity[4]. However, the practical application of Ni-rich cathodes still faces challenges associated with the rapid capacity decay caused by the increased Ni content[5].

[0004] Extensive research has been undertaken to explore the mechanisms behind the poor capacity retention in Ni-rich cathode based ion batteries. Lattice strains are recognized as a significant threat to the cycle stability of Ni-rich cathodes[6-7]. The insertion / extraction of Li+ions during cycling causes a dramatic structural change with anisotropic lattice distortions, which is unavoidably associated with the generation of lattice strains in the layered oxides[8]. The lattice distortion of layered cathode materials is found to result from anisotropic lattice variations along the c-axis and the a(b)-axis during the delithiation / lithiation, which ultimately causes severe lattice strain and leads to the failure of Ni-rich cathode materials. Lattice distortion also hinders Li+diffusion during charging and discharging and makesthe lattice unable to expand or contract freely, which in turn leads to insufficient Li+insertion / extraction during cycling[9].

[0005] However, eliminating lattice strain in layered cathodes remains challenging due to the influence of continuous Li+insertion / extraction during cycling. Considerable efforts have been made so far to protect layered cathodes from harmful lattice strains. Approaches to date include single crystallisation

[0010] , high-entropy material design

[0011] , and secondary phase introduction

[0012] . For instance, intergranular strains in the secondary particles can severely damage the cycle stability of Ni-rich cathode materials. By eliminating the grain boundaries, single-crystal Ni-rich oxides have been developed to prevent intergranular microcracks and material structure degradation

[0010] . Moreover, high-entropy strategies have also been employed by introducing a variety of cations in the layered structure. The synergy of various cations successfully reduces the lattice expansion and enables high cycle stability of Ni-rich cathodes

[0011] . Additionally, introducing a more stable perovskite phase in the layered lattice structure also prevents the generation of lattice strains. By acting as a “rivet”, the lattice strain evolution is mitigated

[0012] . However, the single crystallisation limits the Li+diffusivity due to the longer Li+diffusion pathway, which unavoidably sacrifices the rate capability of the Ni-rich cathodes. Meanwhile, high entropy strategy and secondary phase introduction are usually associated with the involvement of noble elements and electrochemical inactive components in Ni-rich cathodes, reducing the cost-effectiveness and capacity competitiveness of Ni-rich cathodes.

[0006] It has been argued that lattice distortion of the octahedrons in the Ni-rich layered structure induces lattice strain[13-15]. Meanwhile, the severe Jahn-Teller (JT) distortion of the transition metal containing octahedrons can compromise the structural stability by generating lattice strain

[0016] , and the cooperative JT distortion leads to strain transfer and accumulation throughout the layered lattice structure

[0017] , finally resulting in the failure of the Ni-rich cathodes.

[0007] Accordingly, there is a need for new or improved cathode materials that can be used to mitigate or address one or more issues outlined above. Alternatively, or in addition, there is a need for an alternative to known cathode material and processes that can have satisfactory structural stability and / or deliver desirable electrochemical performance. SUMMARY

[0008] According to a first aspect, there is provided a doped layered cathode material for an electrochemical device, which comprises a dopant and a layered cathode material, wherein the dopant is selected and added so that the electrochemical device delivers a capacity retention of about 78% to about 88% after 500 cycles at 1 C.

[0009] In some embodiments of the first aspect, the dopant is selected and added so that the electrochemical device delivers a capacity retention of about 80% to about 88% after 500 cycles at 1 C. In some embodiments, the dopant is selected and added so that the electrochemical device delivers a capacity retention of about 82% to about 88% (for example about 86.7%) after 500 cycles at 1 C. In some further embodiments, the dopant is selected and added so that the electrochemical device delivers a capacity retention of about 85% to about 87% after 500 cycles at 1 C.

[0010] In some embodiments of the first aspect, the dopant is selected and added so that the electrochemical device delivers an initial discharge capacity of at least about 200.0 mAh g-1at 0.1 C current density (1C = 200 mA g-1), for example at least 205.0 mAh g-1at 0.1 C, at least about 208.2 mAh g-1at 0.1 C, or at least about 215.1 mAh g-1at 0.1 C.

[0011] In some embodiments of the first aspect, the dopant is selected and added so that the electrochemical device delivers a rate capability of at least about 150 mAh g-1at 10 C, for example at least about 155 mAh g-1at 10 C, or at least about 160 mAh g-1at 10 C.

[0012] In some embodiments of the first aspect, the dopant ions occupy octahedral sites in the crystal structure of the layered cathode material. In some embodiments, the layered cathode material is a layered cathode oxide. In further embodiments, the dopant (D) forms a DO6octahedron in the crystal structure of the layered cathode material.

[0013] In some embodiments of the first aspect, the electrochemical device is selected from ion batteries. In some further embodiments, the electrochemical device is selected from lithium ion batteries, sodium ion batteries and potassium ion batteries.

[0014] In some embodiments of the first aspect, the layered cathode material comprises an intercalating metal ion and a bulk metal ion. In some embodiments, the layered cathode material comprises more than one intercalating metal ion, for example lithium ion and sodium ion. In some embodiments, the layered cathode material comprises more than one bulk metal ion.

[0015] In some embodiments of the first aspect, the layered cathode material comprises or consists of a layered cathode oxide. In some further embodiments, the layered cathode material comprises or consists of a layered cathode oxide which has a formula of AxMO2, wherein A is an alkali metal cation, M is metal cation, and O is oxygen anion. In some further embodiments, the oxide is fully alkaliated and x=1. In some further embodiments, A is selected from lithium cation, sodium cation and potassium cation. In even further embodiments, M is an ion of a transition metal, for example an inactive transition metal. In even further embodiments, M is a translation metal cation, and the transition metal is one or more selectedfrom the group consisting of Ni, Co, Mn, Cr, V, Fe, Ti, Sc, Zr, Pd, Mo, Ru, Pt, Nb, and Ta. In even further embodiments, the layered cathode oxide is an O3-type layered oxide.

[0016] In some embodiments of the first aspect, the layered cathode material comprises or consists of a Ni-rich layered oxide.

[0017] In some embodiments of the first aspect, the layered cathode material comprises or consists of a lithium layered oxide. In some further embodiments, the layered cathode material comprises or consists of a Ni-rich lithium layered oxide. In even further embodiments, the layered cathode material comprises or consists of an O3-type Ni-rich lithium layered oxide.

[0018] In some embodiments of the first aspect, the Ni-rich lithium layered oxide has a chemical formula of LiNi1-x-yCoxMnyO2 (1-x-y ≥ 0.5, 0.5 > x > 0, 0.5 > y > 0), for example LiNi0.9Co0.05Mn0.05O2 (NCM90), LiNi0.85Co0.10Mn0.05O2 (NCM851005), LiNi0.84Co0.10Mn0.06O2, LiNi0.8Co0.1Mn0.1O2 (NCM811), LiNi0.7Co0.2 Mn0.1 O2 (NCM721), LiNi0.6Co0.2 Mn0.2 O2 (NCM622), LiNi0.5Co0.2Mn0.3O2 (NCM523). In some further embodiments, the Ni-rich lithium layered oxide has a chemical formula of LiNi1-x-yCoxMnyO2(1-x-y ≥ 0.6, 0.4 > x > 0, 0.4 > y > 0). In even further embodiments, the Ni-rich lithium layered oxide has a chemical formula of LiNi1-x-yCoxMnyO2(1-x-y ≥ 0.7, 0.3 > x > 0, 0.3 > y > 0). In even further embodiments, the Ni-rich lithium layered oxide has a chemical formula of LiNi1-x-yCoxMnyO2(1- x-y ≥ 0.8, 0.2 > x > 0, 0.2 > y > 0).

[0019] In some embodiments of the first aspect, the Ni-rich lithium layered oxide has a chemical formula of LiNi1-xCoxO2(1-x ≥ 0.5, 0.5 > x > 0) or LiNi1-xMnxO2(1-x ≥ 0.5, 0.5 > x > 0), for example LiNi0.91Co0.09O2(NC90), LiNi0.5Mn0.5O2, LiNi0.98Mn0.02O2, and LiNi0.95Mn0.05O2.

[0020] In some further embodiments, the layered cathode material comprises or consists of a sodium layered oxide. In some further embodiments, the layered cathode material comprises or consists of a Ni- rich sodium layered oxide. In even further embodiments, the layered cathode material comprises or consists of an O3 type Ni-rich sodium layered oxide.

[0021] In some embodiments of the first aspect, the layered cathode material comprises or consists of a layered sulfide.

[0022] In some embodiments of the first aspect, the dopant (D) is capable of forming a DO6octahedron in the crystal structure of the layered cathode material. In some further embodiments, the dopant (D) is one or more selected from the group consisting of Ti, V, Cu, Cr, Ta, Ga, W, Zr, Mn, and Nb. In some specific embodiments, the dopant (D) is one or more selected from the group consisting of Ti, Nb, and W.In some further embodiments, the dopant (D) is Ti. In even further embodiments, the dopant precursor is tetrabutyltitanate or titanium tetrachloride (TiCl4).

[0023] In some embodiments of the first aspect, the amount of the dopant is about 0.25% to about 1.5% by moles based on the total amount of the dopant and the metal(s) originated from the doped layered cathode material. In some further embodiments, the amount of the dopant is about 0.3% to about 1.0% by moles based on the total amount of the dopant and the metal(s) originated from the doped layered cathode material. In even further embodiments, the amount of the dopant is about 0.3% to about 0.8% by moles, for example about 0.3% to about 0.5% by moles, based on the total amount of the dopant and the metal(s) originated from the doped layered cathode material.

[0024] In some embodiments of the first aspect, metal cations of the dopant (D) are homogenously distributed with metal cations of the layered cathode material. In some further embodiments, the layered cathode oxide which has a formula of AxMO2is an O3-type layered oxide and the metal cations of the dopant fill the vacancy of the A and M octahedral sites. In even further embodiments, the layered cathode oxide which has a formula of AxMO2 is an O3-type layered oxide and the metal cations of the dopant (D) within the layered cathode material assume a DO6octahedron. In even further embodiments, the layered cathode oxide which has a formula of AxMO2is an O3-type layered oxide and doping Ti cations within the layered cathode material assume a TiO6octahedron.

[0025] In some embodiments of the first aspect, when the layered cathode material is a layered cathode oxide which has a formula of AxMO2, wherein A is an alkali metal cation, M is a metal cation, and O is oxygen anion, the amount of the dopant is about 0.3% to about 1.0% by moles based on the total amount of the dopant and the A and M originated from the doped layered cathode material. In some further embodiments, the amount of the dopant is about 0.3% to about 0.8% by moles, about 0.5% by moles based on the total amount of the dopant and the A and M originated from the doped layered cathode material.

[0026] In some embodiments of the first aspect, the doped layered cathode material comprises or consists of LiNi0.8Co0.1Mn0.1O2(NCM811) as the layered cathode material and Ti as the dopant. In some further embodiments, the doped layered cathode material is selected from Li1-xNi0.8-yMn0.1Co0.1Tix+yO2(x + y = 0.02, 2.0-TNCM) and Li1-xNi0.8-yMn0.1Co0.1Tix+yO2(x + y = 0.01, 1.0-TNCM).

[0027] According to a second aspect, there is provided a method for preparing a doped layered cathode material comprising a dopant and a layered cathode material, wherein the layered cathode material comprises an intercalating metal ion and a bulk metal ion, the method comprises: (i) obtaining (a) a doped precursor comprising the dopant and a source of the bulk metal ion, (ii) obtaining a composition comprising (a) and (b) a source of the intercalating metal ion, and(iii) heating the composition.

[0028] In some embodiments of the second aspect, the method comprises obtaining (c) a precursor comprising a source of the bulk metal ion and, optionally, the dopant, and then step (ii) is to obtain a composition comprising (a), (b), and (c).

[0029] In some embodiments of the second aspect, the amount and the composition of each of (a) and (b) are selected so that the stoichiometric composition of the doped layered cathode material to be prepared is met.

[0030] In some embodiments of the second aspect, the source of the bulk metal ion within (a) and optionally (c) has the same stoichiometric ratio in terms of the metal(s) as that for the layered cathode material comprised by the doped layered cathode material to be prepared.

[0031] In some embodiments of the second aspect, the step (iii) is a staged heating under oxygen atmosphere. In some further embodiments, the staged heating under oxygen atmosphere consists of heating at about 450 °C to about 550 °C for a period and then heating at about 750 °C to about 850 °C for a period. In some further embodiments, the staged heating under oxygen atmosphere consists of heating at about 450 °C to about 550 °C for about 4 hours to about 5 hours and then heating at about 750 °C to about 850 °C for about 10 hours to about 15 hours.

[0032] In some embodiments of the second aspect, the doped layered cathode material consists of the layered cathode material of AxMO2and the dopant (doping metal=D), and the method may include: (i) obtaining (a) D-doped M(OH)2or M(CO3)2, (ii) obtaining a composition comprising (a) and (b) a hydrated hydroxide of A, a chloride of A or a carbonate of A, and (iii) heating the composition.

[0033] In some embodiments, the doping metal is Ti and the layered cathode material has a chemical formula LiNi1-x-yCoxMnyO2. In some further embodiments, the doped layered cathode material has a chemical formula Li1-xNi0.8-yMn0.1Co0.1Tix+yO2(x + y = 0.01, 1.0-TNCM) or Li1-xNi0.8-yMn0.1Co0.1Tix+yO2(x + y = 0.02, 2.0-TNCM).

[0034] According to a third aspect, there is provided an electrochemical device comprising the doped layered cathode material according to the first aspect or obtained according to the second aspect.

[0035] According to a fourth aspect, there is provided use of the doped layered cathode material according to the first aspect or obtained according to the second aspect in a cathode of an electrochemical device.

[0036] In some embodiments of the third or fourth aspect, the electrochemical device is selected from lithium ion batteries, sodium ion batteries and potassium ion batteries. BRIEF DESCRIPTION OF FIGURES

[0037] Embodiments of the present disclosure will be discussed with reference to the accompanying figures wherein:

[0038] Figure 1 shows (a) high-angle annular dark-field (HADDF) mode transmission electron microscopy (TEM) image of the 1.0-TNCM sample; (b) elemental distribution of Ni, Co, Mn, and Ti in the 1.0-TNCM sample; (c) the HAADF-STEM (scanning transmission electron microscopy) image corresponding to the regions highlighted with a box in (a); (d) the HAADF-STEM image of NCM811 corresponding to the region highlighted with a gray box in Figure 8; (e) line profile analysis along

[0003] plane of the green box and

[0104] plane of yellow box in (c) and (d); and (f) Ti 2p X-ray photoelectron spectroscopy (XPS) spectra of the 1.0-TNCM sample.

[0039] Figure 2 shows (a) DFT calculation of the formation energy for Ti substitution into the layered NCM811; Rietveld refinement against NPD data for (b) NCM811 with Rwp= 4.14% and GOF = 2.19; and (c) 1.0-TNCM with Rwp= 3.89% and GOF = 1.84.

[0040] Figure 3 shows (a) initial charge and discharge curves at 0.1 C of NCM811 and Ti-modified samples; (b) the rate capability of NCM811 and Ti-modified samples; (c) lithium diffusion coefficient of the NCM811 and Ti-modified samples; (d) cycling performance of NCM811, Ti-modified samples; (e) output voltage curves of NCM811, Ti-modified samples; (f) dQ / dV curves at different cycles of NCM811 and 1.0-TNCM; and (g) voltage variation of different peaks for NCM811 and 1.0-TNCM; (h) energy capacity and cycle performance comparison of 1.0-TNCM with other NCM811 in previous studies.[28-35]

[0041] Figure 4 shows a contour plot of in-operando synchrotron-based X-ray powder diffraction (XRPD) results and charge / discharge curves of the first cycle of (a) NCM811 and (b) 1.0-TNCM at 0.1C; lattice parameter (c) c; (d) a; (e) cell volume change as a function of voltage during the initial charging process of NCM811 and 1.0-TNCM; (f) shear strain changes of NCM811 and 1.0-TNCM during the initial charge process; and (g) evolution of the lattice strain along with the

[0003] planes as a function of voltage at the initial charging process.

[0042] Figure 5 shows Ni Extended X-Ray Absorption Fina Structure (EXFAS) spectra at different state of charge (SOC) of (a) NCM811 and (b) 1.0-TNCM; (c) FWHM of Ni-O and Ni-TM variations at different SOC of both samples; (d) Ti EXFAS spectra at different SOC of 1.0-TNCM; (e) schematic illustration of the Ti-O octahedron addressing the lattice strain issue; Mn EXFAS spectra at different SOCof (f) NCM811and (g)1.0-TNCM; (h) FWHM of Mn-O and Mn-TM variations at different SOC of both samples.

[0043] Figure 6 shows XRPD data of NCM811, 1.0-TNCM and 2.0-TNCM.

[0044] Figure 7 shows scanning electron microscopy (SEM) images of (a) NCM811 and (b) 1.0- TNCM.

[0045] Figure 8 shows TEM image of NCM811, wherein the grey box refers to the Figure 1(d).

[0046] Figure 9 shows rietveld refinement against neutron powder diffraction (NPD) data for 2.0- TCNM with Rwp= 3.90% and GOF = 1.98.

[0047] Figure 10 shows rietveld refinement against NPD data for 1.0-TNCM with (a) Ti fully occupying the Li sites with Rwp = 3.93% and GOF = 1.99 and (b) fully occupying the TM sites with Rwp = 3.93% and goodness-of-fit (GOF) = 2.00.

[0048] Figure 11 shows galvanostatic intermittent titration technique (GITT) curves of the (a) NCM811; (b) 1.0-TNCM and (c) 2.0-TNCM.

[0049] Figure 12 shows discharge curves of (a) NCM811 and (b) 1.0-TNCM at different cycles.

[0050] Figure 13 shows lattice parameters (a) c and (b) a of NCM811 and 1.0-TNCM during discharge.

[0051] Figure 14 shows (a) Ni-K edge and (b) Mn-K edge of the NCM811 and 1.0-TNCM at different states of charge.

[0052] Figure 15 shows Ni-L edge of the NCM811 and 1.0-TNCM at different states of charge.

[0053] Figure 16 shows NCM811 supercell for Density functional theory (DFT) calculation. DESCRIPTION OF EMBODIMENTS

[0054] The present disclosure arises from the inventors’ finding that the undesirable lattice strain within the local domain

[0018] can be relieved by introducing a flexible metal dopant octahedron (for example TiO6octahedron) into the structure of a layered cathode material (for example the LiNi0.8Co0.1Mn0.1O2(NCM811)) while minimizing the influence on the capacity of a electrochemical device. By preventing the JT distortion from transferring and accumulating via the flexible octahedrons, the lattice changes,especially along the c-direction, are significantly reduced. The design strategy is also illustrated in Figure 5(e). In some circumstances, the lattice variation along the c-axis was successfully suppressed by 95.2% (0.13% compared to 2.74% of the pristine). This approach enables high battery capacities (for example an initial discharge capacity of 215.1 mAh g-1at 0.1 C) and long battery durability (for example 86.7% capacity retention after 500 cycles at 1 C) of a cathode (for example a Ni-rich cathode). The strategy of relieving lattice strain in the local domain to stabilize layered cathode materials can be generally applied to address performance issues due to the similarity between many layered-structured cathode materials. It has also been found by the present inventors that a preparation method featuring a particular combination of steps can be helpful in introducing the flexible metal dopant octahedron into the structure of a layered cathode material (for example Ni-rich layered cathode material) to improve structure stability.

[0055] The term “electrochemical device” used herein refers to a device that can convert chemical energy into electrical energy through an electrochemical reaction. Examples of the electrochemical device are electrochemical cells, and batteries.

[0056] The term “layered cathode material” used herein denotes a layered material that can be used as a cathode active material for an electrochemical device. The layered cathode material may be combined with other components like conductive material and a binder to form a cathode.

[0057] The term “capacity” used in relation to an electrode refers to the total amount of electricity generated due to an electrochemical reaction at an electrode. It may be determined by the usable amount (e.g. mass) of active material of an electrode that participates in redox reactions.

[0058] The term “intercalating metal ion” used in relation to a layered cathode material refers to the metal ion contained by the layered cathode material that will be extracted from the cathode and be intercalated within the anode of an electrochemical device. The term “bulk metal ion” used in relation to a layered cathode material refers to the metal ion contained by the layered cathode material that will remain within the cathode during charging and discharging of an electrochemical device. For example, for the common layered cathode material LiNi0.8Co0.1Mn0.1O2, Li ion is the intercalating metal ion, Ni, Co and Mn ions are the bulk metal ions. For a Li-Na-mixed intercalation compound with the stoichiometry Li0.5Na0.4CoO2, Li and Na ions are the intercalating metal ions, Co ion is the bulk metal ion.

[0059] Disclosed herein is a doped layered cathode material for an electrochemical device, which comprises a layered cathode material and a dopant, wherein the dopant is selected and added so that the electrochemical device delivers a capacity retention of about 78% to about 88% after 500 cycles at 1 C.

[0060] The doped layered cathode material disclosed herein may find use in rechargeable ion batteries, for example, alkali ion batteries. The doped layered cathode material disclosed herein may be particularlyuseful for lithium ion batteries, sodium ion batteries, or potassium ion batteries. Various factors such as specific capacity, standard redox potential, structure integrity during cycling, ion diffusion coefficient, thermal stability and safety may be considered in designing a layered cathode material.

[0061] Layered cathode material

[0062] Layered intercalation compounds have become a dominant cathode material for rechargeable batteries at least because of their superior capacity. The layered cathode material used herein may comprise an intercalating metal ion and a bulk metal ion. In some circumstances, the layered cathode material comprises more than one intercalating metal ion, for example lithium ion and sodium ion. In some circumstances, the layered cathode material comprises more than one bulk metal ion, for example, transition metal ions like manganese, cobalt, iron and vanadium ions.

[0063] The layered cathode material may comprise or be a layered cathode oxide. In a particular form, the layered cathode material is a layered cathode oxide which adopts the general formula AxMO2 (A: alkali cation, M: metal cation, O: oxygen anion). A corresponds to the intercalating metal ion, and M corresponds to the bulk metal ion. In some embodiments, A may be one or more selected from lithium cation, sodium cation and potassium cation. In some embodiments, M may be an ion of a transition metal, for example, an ion of a single transition metal or ions of a combination of transition metals. Examples of the transition metal include, but are not limited to, Ni, Co, Mn, Cr, V, Fe, Ti, Sc, Zr, Pd, Mo, Ru, Pt, Nb, and Ta. In terms of oxygen stacking, the layered cathode oxide can be in the form of O3 type, O2 type, P2 type, P3 type, or a combination thereof, and it may be typical to have O3-type, P3-type, or P2-type. The O3-type layered material is stacked in an ABCABC mode, while the P3-type and P2-type are in ABBCCA and ABACAB modes, respectively.

[0064] A layered rocksalt cathode oxide is commonly referred to as an O3 type (R-3m space group) layered oxide, wherein O denotes the octahedral alkali ion environment (not to be confused with O for oxygen) and 3 denotes the number of MO2slabs in a repeat unit. O3 structure is equivalent to the structure of α-NaFeO2and the cation ordering is also known in metallic alloys as L11(CuPt prototype). For a layered rocksalt cathode oxide, the O anions form a face-centered cubic (FCC) framework with octahedral and tetrahedral sites. These two environments are face sharing and form a topologically connected network. When fully alkaliated such that x ~ 1, the oxide consists of AO2and MO2edge- sharing octahedra. The layered structure is aptly named because AO2 / MO2octahedra form alternating (111) planes of the FCC oxygen lattice when fully alkaliated (for example lithiated). The A and M cations alternate in the abc repeat unit of the oxygen framework to form a-b_c-a_b-c_ stacking where the minus sign indicates the location of M and the underscore “_” gives the position of the A ions. Because the oxygen stacking has a repeat unit of three and the metal layering repeats every two layers, periodicity is achieved after six oxygen layers.

[0042]

[0065] In the crystal structure of the O3 type layered oxides, alternating layers of alkali cation and M cation occupy the octahedral sites in a cubic close packed lattice of oxide ions. It is believed that the ordering of AO2 and MO2 in alternating layers is not the most favoured cation ordering from an electrostatic perspective, and the size difference between A and M atoms might be beneficial to the stability of the O3-type layered cathode material.

[0066] Similarly, the layered cathode material may be also a layered sulfide, for example an O3-type or P2-type layered sulfide. Suitable O3-type layered sulfides may include, but are not limited to, layered lithium- and sodium-sulfides. Illustrative examples thereof are Li2TiS3, NaCrS2, K0.8CrS2, and NaCr2 / 3Ti1 / 3S2.

[0067] It may be desirable to use an O3-type layered cathode material in the layered cathode material. To this end, it is possible for the O3-type layered cathode material with the general formula AxMO2 (A: alkali cation, M: metal cation, O: oxygen anion) to have a single metal cation, binary metal cations, ternary metal cations. That is, M can be ions of a blend of metals. For the purpose of illustration, the metal for the metal cation M may include, but is not limited to, Al, Mg, Zn, Cu, Ni, Co, Mn, Cr, V, Fe, and Ti. In some circumstances, M is a transition metal (for example, an inactive transition metal) and may be selected from one or more of Ni, Co, Mn, Cr, V, Fe, Nb, Ta, and Ti. In a particular embodiment, the transition metal for M may be selected from one or more of Ni, Co and Mn. An O3-type structure can be investigated through a suitable method known in the art, for example High Resolution Powder Diffraction (HRPD), X-ray diffraction (XRD) and Rietveld refinement.

[0068] It may also be desirable for the layered cathode material to be rich in Ni content. Taking AxMO2as an example, the Ni content within M is ≥ 1 / 3, ≥ 0.5, ≥ 0.6, ≥ 0.7, or ≥ 0.8. The Ni-rich layered compounds (for example oxides) have attracted considerable attention in the fabrication of cathodes due to their low cost, high theoretical capacity and energy density. Some Ni-rich layered cathodes have been commercially applied. For example, Tesla Motors adopted the LiNi0.8Co0.15Al0.05O2cathode in its Model S, which had a driving range of 270 miles. Furthermore, a LiNi0.8Co0.1Mn0.1O2cathode was used by Contemporary Amperex Technology to achieve the 300 Wh kg−1cell-level energy milestone.

[0069] When the layered cathode material is a lithium layered oxide, the lithium layered oxide may be a ternary oxide and have a chemical formula of LiNi1-x-yCoxMnyO2. It may be preferable that the lithium layered oxide is rich in Ni. In some embodiments, it suggests that, for the formula LiNi1-x-yCoxMnyO2, 1- x-y ≥ 0.5, 0.5 > x > 0, 0.5 > y > 0. Accordingly, examples of the Ni-rich lithium layered oxide include, but are not limited to, LiNi0.90Co0.07Mg0.03O2, LiNi0.9Co0.05Mn0.05O2, LiNi0.85Co0.10Mn0.05O2(NCM851005), LiNi0.84Co0.10Mn0.06O2, LiNi0.8Co0.1Mn0.1O2 (NCM811), LiNi0.7Co0.2 Mn0.1 O2 (NCM721), LiNi0.70Mn0.15Co0.15O2 (NMC71515), LiNi0.6Co0.2 Mn0.2 O2 (NCM622), and LiNi0.5Co0.2Mn0.3O2 (NCM523). For the chemical formula of LiNi1-x-yCoxMnyO2, it may be further preferable that 1-x-y ≥ 0.6,≥ 0.7 or even ≥ 0.8. Among the oxides represented by the formula of LiNi1-x-yCoxMnyO2, it may also be preferable to use an O3-type layered cathode material in the layered cathode material disclosed herein.

[0070] When the layered cathode material comprises or consists of a lithium layered oxide, the lithium layered oxide may be a binary oxide and have a chemical formula of LiNi1-xCoxO2 or LiNi1-xMnxO2. It may be preferable that the lithium layered oxide is rich in Ni. In some embodiments, it suggests that, for the formula LiNi1-xCoxO2 or LiNi1-xMnxO2, 1-x ≥ 0.5, 0.5 > x >0. Accordingly, examples of the Ni-rich lithium layered oxide include, but are not limited to, LiNi0.91Co0.09O2 (NC90), LiNi0.5Mn0.5O2, LiNi0.98Mn0.02O2, and LiNi0.95Mn0.05O2. For the chemical formula of LiNi1-xCoxO2 or LiNi1-xMnxO2, it may be further preferable that 1-x ≥ 0.6, ≥ 0.7 or even ≥ 0.8, and 0.4 > x >0, 0.3 > x >0, or even 0.2 > x > 0 respectively. Among the oxides represented by the formula of LiNi1-xCoxO2 or LiNi1-xMnxO2, it may also be preferable to use an O3-type layered cathode material in the layered cathode material disclosed herein.

[0071] As elements of the same main group, sodium and potassium have abundant reserves. When the layered cathode material comprises or consists of a sodium layered oxide, the sodium layered oxide may be a singular oxide, a ternary oxide, a quaternary oxide, a pentanary oxide or a more complex oxide. Examples of the sodium layered oxide include, but are not limited to, NaCrO2, NaFeO2, Na (Ni1 / 3Mn1 / 3Fe1 / 3)O2, NaNi1 / 3Co1 / 3Mn1 / 3O2, NaNi0.2Fe0.35Mn0.45O2, Na[NixFeyMn1-x-y]O2(x = 0.6, 0.7 and 0.8), Na(Mn0.25Fe0.25Co0.25Ni0.25)O2, NaNi0.2Fe0.35Mn0.4Zn0.05O2, and Na0.94Ni0.29Cu0.1Fe0.16Mn0.3Ti0.15O2. It may be preferable that the sodium layered oxide is an O3-type layered cathode material.

[0072] The standard electrode potential for K+ / K (-2.94 V, relative to a standard hydrogen electrode (SHE)) is lower than the standard electrode potential for Li+ / Li (-3.04 V, relative to a standard hydrogen electrode (SHE)), resulting in higher working voltage. Besides, compared to Na+, K+can reversibly insert into graphite, which satisfies the anode demand to a certain extent. Moreover, K will not alloy with aluminium foil (which means that aluminium foil can replace the more costly copper foil as a current collector) and take the place of aluminium foil, thereby saving costs. When the layered cathode material is a potassium layered oxide, the potassium layered oxide may be a singular oxide, a binary oxide, a ternary oxide or a more complex oxide. Examples of the potassium layered oxide include, but are not limited to, K0.45MnO2, K0.3MnO2, KCrO2, K0.5V2O5, K0.6CoO2, K0.44Ni0.22Mn0.78O2, K0.48Mn0.4Co0.6O2, K0.75[Ni1 / 3Mn2 / 3]O2, K0.75[Mn0.8Ni0.1Fe0.1]O2, K0.67Ni0.17Co0.17Mn0.66O2, and K0.5[Mn0.8Fe0.1Ni0.1]O2. It may be preferable that the potassium layered oxide is an O3-type layered cathode material.

[0073] The layered cathode materials may be commercially available. For example, LiNi0.85Co0.10Mn0.05O2and LiNi0.6Co0.2Mn0.2O2are commercially available from BASF SE. In addition, or alternatively, a suitable method known in the art may be employed to obtain the layered cathode materials, for example, solid state synthesis and sol-gel synthesis. The reaction temperature may be selected to obtain different layered cathode oxides. Co-precipitation is a common method for preparingternary cathode materials. Taking the LiNi0.8Co0.1Mn0.1O2 cathode material as an example, it can be synthesised through a co-precipitation method by use of, for example, sulphate, nitrate, hydroxide, chloride and acetate as starting materials. Specifically, the starting materials may be NiCl2·6H2O, MnCl2·4H2O, CoCl2·6H2O, Ni(CH3COO)2·4H2O, Co(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O.

[0074] Dopant

[0075] As used herein, the term “dopant” refers to any impurity deliberately added to a layered cathode material for the purpose of modifying an electrochemical performance when comprised in a cathode.

[0076] For the present disclosure, the dopant is selected and added to stabilise the structure of the layered cathode material, especially through relieving undesirable lattice strain in a local domain. After being introduced into the layered cathode material, the dopant should have no obvious impact on the size and shape of secondary crystal particles. It has been surprisingly found by the present inventors that the introduction of a flexible DO6 octahedron (wherein D represents doping metal cation) may facilitate reduction of lattice strains and thus enhance the structural stability of the doped cathode material. In some cases that a dopant is introduced into the structure of the layered cathode material, the lattice variation along the c-axis of the layered cathode material during charging is successfully suppressed by 95.2% compared to the undoped layered cathode material. The lattice distortion is alleviated so that the lattice could be able to expand or contract more freely, and ion diffusion during charging and discharging will be promoted.

[0077] It is beneficial that the dopant is homogenously distributed with the metal cation(s). In some embodiments, the layered cathode oxide which has a formula of AxMO2is an O3-type layered oxide, and the doping metal cation (for example Ti) may advantageously fill the vacancy of the A and M octahedral sites, or the dopants substitute the A and M ions.

[0078] The doping metal (D) originated from the dopant is capable of forming a flexible DO6octahedron in the crystal structure of the layered cathode material. The dopant (D) may be a single metal or a blend of metals. For the purpose of illustration, the doping metal for the present disclosure may be one or more selected from Ti, V, Cu, Cr, Ta, Ga, W, Zr, Mn and Nb, among which Ti, Nb and W might be preferable. In a preferable embodiment, especially for a Ni-rich layered cathode material, the doping metal (D) is Ti. Ti4+is electrochemically inert within the electrochemical window of Ni-rich layered oxides, even at high voltage. A Ti dopant precursor used to prepare the layered cathode material may be titanium tetrachloride (TiCl4), tetrabutyltitanate (TBOT) and anatase-type titanium dioxide (TiO2). An example of a Ta dopant precursor is Ta ethoxide. For example, when the layered cathode material has a formula of AxMO2and is an O3-type layered oxide, the dopant (D) may be Ti or Ta, which assumes a TiO6octahedron or a TaO6octahedron within the layered cathode material.

[0079] The ratio of the dopant and the layered cathode material should be carefully chosen to achieve desirable electrochemical performance of the cathode. Generally, it is suggested that the amount of the dopant does not exceed 1.5% by moles based on the total amount of the dopant and the metal(s) originated from the doped layered cathode material. If there is too much dopant, the sites exchange between the intercalation metal ions and the bulk metal ions will become intensified, which could destroy the electrochemical performance of the layered cathode material.

[0080] The dopant may be present in an amount of about 0.25% to about 1.5% by moles based on the total amount of the dopant and the metal(s) originated from the doped layered cathode material. In some embodiments, the amount of the dopant is about 0.3% to about 1.0% by moles based on the total amount of the dopant and the metal(s) originated from the doped layered cathode material. In a preferable embodiment, the amount of the dopant is about 0.3% to about 0.8% by moles, for example about 0.3% to about 0.5% by moles, based on the total amount of the dopant and the metal(s) originated from the doped layered cathode material.

[0081] When the layered cathode material comprises or consists of a layered cathode oxide which has a formula of AxMO2, wherein A is an alkali metal cation, M is a metal cation, and O is oxygen anion, the amount of the dopant may be about 0.25% to about 1.5% by moles, about 0.3% to about 1.0% by moles, about 0.3% to about 0.8% by moles, or about 0.5% by moles, based on the total amount of the dopant and the A and M originated from the doped layered cathode material. For example, when the layered cathode material is LiNi0.8Mn0.1Co0.1O2(NCM811) and the dopant is Ti, it may be preferable to have the dopant in an amount of about 0.5% by moles based on the total amount of the dopant and the A and M originated from the doped layered cathode material, which corresponds to a doped layered cathode material of Li1-xNi0.8-yMn0.1Co0.1Tix+yO2(x + y = 0.01, 1.0-TNCM).

[0082] Doped layered cathode material

[0083] The doped layered cathode material disclosed herein may comprise (or consist of) the layered cathode material and the dopant. For example, if LiNi0.8Co0.1Mn0.1O2(NCM811) is employed as the layered cathode material and Ti is used as the dopant, the doped layered cathode material may be Li1-xNi0.8-yMn0.1Co0.1Tix+yO2(x + y = 0.02, 2.0-TNCM), Li1-xNi0.8-yMn0.1Co0.1Tix+yO2(x + y = 0.015, 1.5- TNCM) or Li1-xNi0.8-yMn0.1Co0.1Tix+yO2(x + y = 0.01, 1.0-TNCM).

[0084] The doped layered cathode material can be used as a cathode active material, which may be combined with other components to form a cathode. Other components include, but are not limited to, a conductive material and a binder. Conductive materials and binders known in the art can be used in the cathode disclosed herein. Examples for the conductive material are conductive carbon additives, such as carbon black. Examples for a binder are polyvinylidene fluoride (PVDF) and carboxymethyl cellulose.For instance, a cathode is formed in the following way: mixing the Li1-xNi0.8-yMn0.1Co0.1Tix+yO2 (x + y = 0.01, 1.0-TNCM), super p and the polyvinylidene fluoride, and then mixing them in N-methyl pyrrolidinone, the mixed slurry is then spread uniformly on a thin aluminium foil and dried under vacuum.

[0085] In the presence of an appropriate dopant, the layered cathode material can be structurally stabilised and a cathode prepared from the layered cathode material can allow an electrochemical device to deliver outstanding electrochemical performances. Specifically, the electrochemical device comprising a cathode prepared from the doped layered cathode material disclosed herein may exhibit a high capacity retention, which may be in the range of about 78% to about 88%, about 80% to about 88%, about 82% to about 88%, or about 85% to about 87% (for example about 86.7%) after 500 cycles at 1 C. This is significantly higher than what is achieved with an electrochemical device using the un-doped layered cathode material. Capacity retention is a measure of the ability of an electrochemical device to retain stored energy during an extended open-circuit rest period. The term “capacity retention” used herein is defined in relation to the initial discharge capacity: CDch(n) / CDch(1), wherein CDch(n)represents the retained capacity of cycle n, and CDch(1)represents the initial discharge capacity. It is used as a predictor of long- term cycle life of an electrochemical device.

[0086] In addition, or alternatively, the electrochemical device comprising a cathode prepared from the doped layered cathode material disclosed herein may deliver an excellent initial discharge capacity, which may be at least about 205.0 mAh g-1at 0.1 C current density (1C = 200 mA g-1), for example at least about 208.2 mAh g-1at 0.1 C, or at least about 215.1 mAh g-1at 0.1 C. The term “initial discharge capacity” used herein refers to the amount of charge passing during discharge to the cut-off potential at a given discharge current density after the first cycle.

[0087] In addition, or alternatively, the electrochemical device comprising a cathode prepared from the doped layered cathode material disclosed herein may demonstrate a rate capability of at least about 150 mAh g-1at 10 C, for example at least about 155 mAh g-1at 10 C, or at least about 160 mAh g-1at 10 C. The term “rate capability” used herein means discharge capacity of the electrochemical device at a certain current rate. An electrochemical device (such as a battery) with higher rate capability suffers from less polarisation at a high current load.

[0088] Preparation of the doped layered cathode material

[0089] A suitable method known in the art may be adapted to prepare the doped layered cathode materials disclosed herein, for example a co-precipitation method.

[0090] Also disclosed herein is a method for preparing a doped layered cathode material comprising a dopant and a layered cathode material, wherein the layered cathode material comprises an intercalating metal ion and a bulk metal ion, the method comprises: (i) obtaining (a) a doped precursor comprising the dopant and a source of the bulk metal ion, (ii) obtaining a composition comprising (a) and (b) a source of the intercalating metal ion, and (iii) heating the composition.

[0091] It has been surprisingly found by the present inventors that the method might be particularly useful in preparing the layered cathode material disclosed herein. It is suggested that, instead of mixing a source of the bulk metal ion with a source of dopant and a source of the intercalating metal ion, mixing a doped precursor comprising the dopant and a source of the bulk metal ion with a source of the intercalating metal ion could be beneficial for the dopant (such as Ti) to occupy octahedral sites in the crystal structure of a layered cathode material and obtain a layered cathode material with improved structural stability. In an embodiment, the method disclosed herein may further comprise obtaining (c) a precursor comprising a source of the bulk metal ion and, optionally, the dopant. Then step (ii) is to obtain a composition comprising (a), (b) and (c).

[0092] The amount and the composition of each of (a), (b) and optional (c) are selected in accordance with the stoichiometric composition of the doped layered cathode material to be prepared. If the dopant is present in the optional precursor (c), the dopant content within (a) is recommended to be significantly different from that within (c), for example the dopant content within (a) is much higher than the dopant content within (c).

[0093] As mentioned hereabove, it is possible that the doped layered cathode material comprises more than one intercalating metal. It is also possible that the layered cathode material comprises more than one bulk metal.

[0094] In some circumstances, it is desirable for the source of the bulk metal ion within (a) and optional (c) has the same stoichiometric ratio in terms of the metal(s) as that for the doped layered cathode material comprised by the layered cathode material to be prepared. For instance, if the layered cathode material is LiNi0.8Co0.1Mn0.1O2, the source of the bulk metal ion within (a) and optional (c) may be Ni0.8Co0.1Mn0.1(OH)2and the source of the intercalating metal ion (b) may be LiOH·H2O. In a particular form that the dopant is Ti and the layered cathode material is Li1-xNi0.8-yMn0.1Co0.1Tix+yO2(x + y = 0.01, 1.0-TNCM), the amount of each of (a), (b) and optional (c) would be chosen so as to produce the doped layered cathode material. Similarly, if the layered cathode material is LiNi0.8Co0.2O2, the source of the bulk metal ion within (a) and optional (c) may be Ni0.8Co0.2(OH)2, and the source of the intercalating metal ion (b) may be LiOH·H2O.

[0095] When the doped precursor (a) consists of the dopant and a source of the bulk metal ion, it can be prepared by a method known in the art, for example, a co-precipitation method. Starting materials suitable for the present disclosure may be, for example, sulphates, nitrates, acetates, chlorides, and hydrated forms thereof. It is possible to use different types of salts as the starting materials, for example some starting material(s) is(are) an acetate and the other starting material(s) is(are) a nitrate. However, it might be preferable to use the same type of salts as the starting materials. The sulphates include, but are not limited to NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O. The nitrates include, but are not limited to, nickel nitrate (Ni(NO3)2∙6H2O), cobalt nitrate (Co(NO3)2∙6H2O), cobalt nitrate (Co(NO3)3∙9H2O), iron(III) nitrate (Fe(NO3)3·9H2O), and manganese(II) nitrate tetrahydrate (Mn(NO3)2·4H2O). The chlorides include, but are not limited to, NiCl2·6H2O, MnCl2·4H2O and CoCl2·6H2O. Furthermore, the source of the bulk metal ion in the precursor (a) can be identical to or be different from the source of the bulk metal ion in the optional precursor (c), which may be selected from, for example, hydroxide and carbonate. The source of the intercalating metal ion (b) can be selected from, for example, chlorides, hydroxides, carbonates and hydrated forms thereof. If needed, the pH of a solution comprising starting materials can be adjusted and controlled during preparation by adding an inorganic base like NaOH, KOH and ammonia. When Mn is present in the preparation process, an increased pH (for example, pH= about 10.8 to about 11.5) is favoured so as to reduce or avoid precipitation of manganese hydroxide. A complexing agent may also be added for the purpose of preparation and examples thereof are ammonia and NH4OH. The complexing agent may serve to promote the uniform distribution of elements and help control the nucleation and growth rate of crystals during the co-precipitation process. When the doped precursor (a) is Ti doped Ni0.6Co0.2Mn0.2(OH)2, it may be obtained by a co-precipitation method. For example, under Ar atmosphere, aqueous solutions of NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O (molar ratio of Ni / Co / Mn= 6:2:2) and TiCl4are introduced into a reactor together with a NaOH aqueous solution and an NH3·H2O aqueous solution, the mixture solution is stirred at a suitable speed (for example about 600 to about 1000 rpm) while maintaining a suitable reaction temperature (for example about 50 °C to about 60 °C) and controlling the pH value at about 11.0, after reaction for a period of time, the obtained Ti doped Ni0.6Co0.2Mn0.2(OH)2is washed for several times to remove the residual ions (Na+, SO42−or other ions) and dried in an oven (for example at 80 °C) overnight. The stirring speed, the pH and the temperature in the reactor can be adjusted and controlled as needed. For the optional precursor (c) comprising a source of the bulk metal ion and, optionally, the dopant, it can be prepared in a similar way to that used for the doped precursor (a).

[0096] The temperature of the heating step (iii) may be selected in light of the temperatures that have been used in the art to prepare the layered cathode material comprised by the doped layered cathode material and, if necessary, adjusted to suit the present disclosure. As for a layered cathode material comprising LiNi1-x-yCoxMnyO2 as the layered cathode material and Ti as the dopant, a composition comprising (a), (b) and optional (c) may be subjected to staged heating under oxygen atmosphere. Insome circumstances, the staged heating may comprise heating at about 450 °C to about 550 °C for a period and then heating at about 750 °C to about 850 °C for a period. For example, the staged heating may be first heated at about 450 °C to about 550 °C for about 4 hours to about 5 hours and then heated at about 750 °C to about 850 °C for about 10 hours to about 15 hours.

[0097] In a particular embodiment, the doped layered cathode material consists of the layered cathode material of AxMO2 and the dopant (doping metal=D), and the method may include: (i) obtaining (a) D-doped M(OH)2 and / or D-doped MCO3, (ii) obtaining a composition comprising (a) and (b) a hydrated hydroxide of A, a chloride and / or a carbonate of A, and (iii) heating the composition.

[0098] As stated above, M may be ions of a blend of metals. For example, if the layered cathode material AxMO2has a chemical formula of LiNi1-x-yCoxMnyO2, the M(OH)2within (a) and / or optional (c) can be [Ni1-x-yCoxMny](OH)2, or the MCO3within (a) and / or optional (c) can be [Ni1-x-yCoxMny] CO3. In the case that the layered cathode material is LiNi0.8Co0.1Mn0.1O2, the M(OH)2 within (a) and / or optional (c) can be [Ni0.8Co0.1Mn0.1](OH)2, or the MCO3within (a) and / or optional (c) can be [Ni0.8Co0.1Mn0.1] CO3.

[0099] For the purpose of illustration, a Ti-doped LiNi1-x-yCoxMnyO2may be prepared as follows. To prepare a Ti-doped precursor (a) having Ni1-x-yCoxMny(OH)2and Ti, NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O and TiCl4may be used as starting materials. NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O (Ni: Co: Mn = 1-x-y: x: y in molar ratios) and TiCl4are dissolved into deionized water and the solution is continuously pumped into a reactor. Simultaneously, a mixture of NaOH and NH4OH is pumped into the reactor at the same flow rate and the pH value is carefully controlled, for example at a pH of about 10.5 to about 12.0, preferably about 10.8 to about 11.5. Then the solution is maintained at about 50 °C to about 60 °C and magnetically stirred for about 24 to about 48 hours. Then the precursor obtained is washed with deionized water and dried. To prepare an optional precursor (c) having Ni1-x-yCoxMny(OH)2, NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O (Ni: Co: Mn = 1-x-y: x: y in molar ratios) are dissolved in deionized water and the subsequent steps are the same as those for the Ti-doped precursor. The obtained precursors (a) and optional (c) are mixed with an excess amount of LiOH·H2O (c) and then transferred to be subjected to calcination. The mixture was pre-heated at about 450 °C for about 5 hours and then heated at about 750 °C for about 10 hours under oxygen atmosphere to obtain the Ti-doped LiNi1-x-yCoxMnyO2.

[0100] Electrochemical device

[0101] A cathode can be prepared using the doped layered cathode material disclosed herein by means of a process known in the art. For example, a cathode can be made by mixing the doped layered cathodematerial disclosed herein, a conductive material and a binder, then mixing them in a solvent or a dispersing agent, applying the mixed slurry uniformly on a current collector, and drying the assembled cathode under vacuum at a suitable temperature.

[0102] A material for example a metal such as metal lithium, graphite, porous carbon or porous silicon can be used to prepare the anode. An electrolyte may be selected from, but is not limited to, LiPF6 (1M) dissolved in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) with a volume ratio of 1:1:1, and NaPF6 in ethylene carbonate (EC) / propylene carbonate (PC) / dimethyl carbonate (DMC) with a volume ratio of 1:1:1.

[0103] In fabricating the electrochemical device, other components such as a separator, a binder, a conductive agent, and a current collector may be employed. A separator serves to provide a barrier with no electrical conductivity between the negative electrode (anode) and the positive electrode (cathode) while allowing ion transport from one electrode to the other electrode. The separator is expected to retain chemical stability in the electrolyte while also having a high affinity for the electrolyte. It is also desirable for the separator to have good mechanical stability. Non-limiting examples of the separator include glass fibre separators, ceramic separators, polyolefin separators (e.g. polyolefin porous membrane), nonwoven separators, and porous polymer separators.

[0104] When powdered materials are used for the electrodes, a binder may be added to the electrodes to bring various components together and provide consistent mixing of electrode components so as to allow the electrodes to conduct the requisite amount of electrons and guarantee electronic contact during cycling of the electrochemical device. Non-limiting examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and carboxymethyl cellulose (CMC).

[0105] The primary role of a conductive material is to enhance conductivity of the electrodes. In some circumstances, the conductive agent used can be identical to that used for the functional carbohydrate, such as cyclodextrins. Non-limiting examples of the conductive agent include carbon black, Ketjen black, graphene, conductive nano carbon fiber (VGCF), carbon nanotubes (CNTs), and multi-walled carbon nanotubes (MWCNTs). In some embodiments, a conductive agent may be introduced into the solid positive electrode in addition to the conductive substrate combined with the functional carbohydrate.

[0106] A current collector is a bridging component that collects electrical current generated at the electrodes and connects with external circuits. It can have a great influence on the capacity, rate capability and long-term stability of the electrochemical device. Non-limiting examples of the current collector include aluminium (Al) foil, copper (Cu) foil, carbon-coated aluminium, carbon-coated titanium (Ti) foil, and carbonaceous materials.

[0107] The above description can be better understood with reference to the following examples. EXAMPLES

[0108] Material synthesis

[0109] LiNi0.8Co0.1Mn0.1O2 (NCM811) was synthesized by solid-state sintering of Ni0.8Mn0.1Co0.1 (OH)2 precursor and LiOH·H2O. To prepare the Ni0.8 Co0.1Mn0.1(OH)2 precursor, NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O (Ni: Co: Mn = 8:1:1, molar ratio) were dissolved in deionized water and the solution was continuously pumped into the reactor. Simultaneously, NaOH and NH4OH mixture was pumped into the reactor at the same flow rate and the pH value was carefully controlled between about pH 10.8 to about pH 11.5. Then the solution was maintained at 50 °C and magnetically stirred for 48 hours. After the reaction, the mixture was washed with deionized water and dried for 10 hours at 110 °C. The obtained precursor was mixed with excess LiOH·H2O (for example, 5% molar ratio). The mixture was then transferred into a tube furnace for calcination. The mixture was pre-heated at 450 °C for 5 hours and then heated at 750 °C for 10 hours under an oxygen atmosphere.

[0110] The Ti-modified samples were prepared as follows. To prepare the Ti-doped Ni0.8Co0.1Mn0.1(OH)2precursor, NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O and TiCl4(Ni: Co: Mn: Ti = 0.8-a: 0.1: 0.1: a, molar ratio) were dissolved into deionized water and the solution was continuously pumped into the reactor. Simultaneously, NaOH and NH4OH mixture was pumped into the reactor at the same flow rate and the pH value was carefully controlled between about pH 10.8 to about pH 11.5. Then the solution was maintained at 50 °C and magnetically stirred for 48 hours. After the reaction, the mixture was washed with deionized water and dried for 10 hours at 110 °C. According to the molar ratio defined by Li1-xNi0.8-yMn0.1Co0.1Tix+yO2(x + y = 0.02, 2.0-TNCM) or Li1-xNi0.8-yMn0.1Co0.1Tix+yO2(x + y = 0.01, 1.0-TNCM), the obtained precursor was mixed with excess LiOH·H2O (for example, 5% molar ratio). The mixture was then transferred into a tube furnace for calcination. The mixture was pre-heated at 450 °C for 5 hours and then heated at 750 °C for 10 hours under an oxygen atmosphere. A sample of Li1-xNi0.8-yMn0.1Co0.1Tix+yO2(x + y = 0.02, 2.0-TNCM) or Li1-xNi0.8-yMn0.1Co0.1Tix+yO2(x + y = 0.01, 1.0- TNCM) was obtained.

[0111] Computational methods

[0112] The DFT calculations were implemented using the Vienna ab-initio simulation package (VASP) with the core and valence electronic interactions modelled using the projector augmented wave (PAW) method[43-46]. The Perdew-Burke-Ernzerhof (PBE) exchange-correlation function was employed

[0047] . The wavefunctions were expanded with a kinetic energy cut-off of 500 eV, and a Monkhorst-Pack k-points of 9×9×5 was used. Geometrical optimizations were achieved by relaxing all ionic positions and supercell(Figure 16) vectors until the Hellman-Feynman forces were less than 0.01 eV Å-1. The dispersion correction was performed in this study using the DFT-D3 method

[0048] . Ti was considered as interstitial and substitutional dopants in a fully lithiated NCM811 structure. The doping energies (Edoping) of interstitial and substitutional Ti are calculated using the following equation: Edoping (Substitutional) = E(Ti-doped NCM811-xNi-yLi) + xE(Ni) + yE(Li) – E(NCM811) – E(Ti) where E(Ti-doped NCM811) and E(Ti-doped NCM811-xNi-yLi) are the energies of NCM811 supercell with interstitial Ti dopant and NCM811 supercell with substitutional Ti dopant replacing Ni or Li atom in its octahedral site. E(NCM811) is the energy of a fully lithiated NCM811 supercell. E(Ti), E(Ni), and E(Li) are the energies of Ti, Ni, and Li atoms from their unit cells of P6 / mmm, Fm-3m, and Fm-3m.

[0113] Electrochemical characterization

[0114] The cathode electrodes were prepared with 80% active materials, 10% super-P and 10% poly (vinylidene fluoride) (PVDF) mixed with N-methyl-2-pyrrolidone (NMP). The slurry was coated on the aluminium current collector. After desiccating for 12 hours under 110℃ the electrodes were cut into round pieces and pressed. The electrochemical performance of all samples was measured based on CR2032-type coin cells. The half-cell batteries were assembled in the Ar-filled glovebox. The Li metal was used as the anode, Celgard® 2400 polypropylene film was used as a separator, and 1M LiPF6in the mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC, volume ratio: 1:1, Gotion®) was used as electrolyte, respectively. Galvanostatic charge and discharge testing were performed at room temperature between 2.7V to 4.3V (vs. Li / Li+) on the Neware battery testing system. The batteries were activated in the first two cycles under 0.1C (1C = 200 mA g-1), and then long-termly cycled under 1C charging and discharging rate at room temperature. The Li+diffusion coefficient was measured using the galvanostatic intermittent titration technique (GITT) on the Neware battery testing system by charging at the current density of 0.1C for 10 minutes, followed by a 60 minute open-circuit relaxation.

[0115] Physical characterization

[0116] Scanning electron microscopy was performed on JEOL 7500 equipment. High-resolution transmission electron microscopy was acquired on JEOL ARM-200F equipment. The active materials were thinned with a cross-sectional focused ion beam (FIB) on an FEI Helios Nanolab instrument with a Ga+ion beam. Energy dispersive spectroscopy (EDS) was also performed on the JEOL ARM-200F.

[0117] To study the crystal structure of the as-prepared samples, the lab-based X-ray powder diffraction characterization was performed on the Rigaku MiniFlex 600 instrument in Bragg-Brentano reflection geometry with Cu K ^^ radiation ( ^ = 0.1540593 nm). The diffraction data were measuredbetween 10° to 90° with a 1° / minute scan rate. Neutron powder diffraction (NPD) data was collected at the Australian Nuclear Science and Technology Organisation (ANSTO) on the high-resolution neutron powder diffractometer Echidna. The data was recorded between 4° to 164° at a step size of 0.05° with a wavelength of 1.6215(7) Å (determined by La11B6National Institute of Standards and Technology (NIST) standard reference material 660b). The Rietveld refinement of all powder data was performed via GSAS- II software

[0049] . The refined parameters included background coefficients, zero shift, peak shape coefficients, lattice parameters, scale factors, oxygen positional parameters, site occupancy factors, and isotropic atomic displacement parameters.

[0118] The surface chemical composition was analyzed by X-ray photoelectron spectroscopy (XPS) based on a Thermo Scientific Nexsa X-ray photoelectron spectrometer system. The data was collected after 300s etching with an Ar ion gun. The data was analyzed on the CasaXPS software for data calibration and fitting.

[0119] In operando and ex situ measurements by synchrotron techniques

[0120] The customized CR2032 half-cell battery with 4 mm holes on each side of the caps was utilized to perform the in-situ synchrotron-based powder diffraction. To prevent exposure to the air, the holes were covered with aluminium and copper conductive tape on the positive and negative sides, respectively

[0050] . The data was collected on the powder diffraction beamline at the Australian Synchrotron. The batteries were tested between 2.7V to 4.3V (vs. Li / Li+) under 0.1C charge and discharge rate. The wavelength of the synchrotron X-ray beam is 0.68880(1) Å (determined by La11B6 NIST standard reference material 660b). The data was collected using MYTHEN microstrip detector with 3 minutes of exploring and an 828s collection window. The single peak fitting of the acquired data was performed on LAMP software

[0051] using R-3m structure to calculate the average lattice parameters of the active materials.

[0121] Williamson-Hall’s method

[0052] was employed to calculate the lattice strain with the following equation: ^^ ^^ =^^ ^^ ^^^^ ^^ ^^ ^^ ^^ Where ^^^^ ^^ ^^is the broadening of the diffraction peak measured at full-width at half-maximum, ^^ is the corresponding Bragg diffraction angle.

[0122] The ex situ X-ray absorption (XAS) characterizations of the electrodes at different states of charge were performed at the Australian Synchrotron. The electrodes were extracted from the half-cell batteries and then washed with DMC in the Ar-filled glove box. The Near-edge X-ray absorption fine structure (NEXAFS) data were acquired at the soft X-ray beamline and processed with QANT procedurebased on Igor pro software

[0053] . The XAS measurement was conducted at the XAS beamline of the Australian Synchrotron, and the data was performed on the Athena software

[0054] .

[0123] Morphology and crystal structure characterizations

[0124] Different NCM811 samples all developed the layered structure with R-3m space group symmetries, as evidenced by the X-ray powder diffraction data (Figure 6). Regular spherical secondary particles of NCM811 and Li1-xNi0.8-yMn0.1Co0.1Tix+yO2 (x + y = 0.01, 1.0-TNCM) samples are clearly observed in the scanning electron microscopy (SEM) images (Figure 7), confirming that the introduction of Ti does not have an obvious influence on the size and shape of the secondary particles. We focus on the optimal1.0-TNCM material in the following characterizations. Figure 1a and Figure 8 show the typical transmission electron microscopy (TEM) images of 1.0-TNCM and NCM811, respectively. The homogeneous distribution of all TM elements, including Ni, Co, Mn, and Ti, is verified by energy- dispersive X-ray (EDS) analysis based on scanning transmission electron microscopy (STEM) images (Figure 1b).

[0125] STEM was employed in high-angle annular dark-field (HADDF) mode to investigate the details of atomic crystal structures of materials of interest. It is known that light elements, such as Li and O, are invisible in the HADDF mode; however, the heavy atoms, including Ni, Co Mn and Ti, can be observed as bright columns[19-20]. Figure 1c displays the crystal structure of 1.0-TNCM along the rhombohedral

[0003] direction (d

[0003] =0.4782nm), which corresponds to the highlighted area in Figure 1a, with the equivalents of NCM811 shown in Figure 1d (d

[0003] =0.4736nm) and Figure 8, respectively. Notably, the layer spacing between

[0003] planes is slightly enlarged in 1.0-TNCM compared to NCM811, with the distance increasing from 0.4736 to 0.4782 nm. As displayed in Figures 1e and 1f, line-profile analysis was performed along the

[0003] (green) and

[0104] (yellow) crystal planes for both samples. The line- profile analysis shows a distinct peak between the characteristic peaks of TM octahedral sites in 1.0- TNCM (Figure 1e), which results from the occupation of lithium sites by the Ti dopants. X-ray photoelectron spectroscopy (XPS) is used to investigate the valance state of the Ti dopant in 1.0-TNCM. Two characteristic peaks at 458.9 eV (Ti 2p3 / 2) and 464.5^eV (Ti 2p1 / 2) are identified in the Ti 2p spectrum, which confirms the tetra-valance of the Ti dopant

[0021] .

[0126] Density functional theory (DFT) calculation was employed to calculate the formation energy of different types of Ti occupation in the NCM811 structure. As displayed in Figure 2a, the thermodynamic stability of the Ti dopant in the NCM811 structure was investigated. The substitution of Ti dopant fills the vacancy in TM octahedral sites, leading to the most favorable doping mechanism with Edopingof -6.22 eV. Alternatively, Ti dopant also occupies the Li octahedral sites indicated by the negative formation energy (Edoping of -1.83 and -1.70 eV).

[0127] As shown in Figures 2b, 2c, Tables 1, 2 and 3, neutron powder diffraction (NPD) data at neutron wavelengths of 1.6215(7) Å of both samples were used in the Rietveld refinement to analyze their detailed structure information

[0022] . Based on the line profile analysis and DFT calculation results

[0023] , three different Ti occupation situations have been taken into consideration during the Rietveld refinement analysis, namely total Ti occupying the Li site, total Ti occupying the TM site, and Ti occupying both Li and TM sites, respectively (Figure 9 and Figure 2d). When Ti was allocated at both TM and Li sites, the refinement results show the lowest weighted profile R-factor (Rwp = 3.89%) and combined goodness of fit (GOF = 1.84), in comparison to those of Ti totally occupying the Li (Rwp = 3.93%, GOF = 1.99) or TM sites (Rwp = 3.93%, GOF = 2.00), which is consistent with the results of previous STEM line profile analysis and DFT calculation, further confirming Ti occupying both Li and TM sites in the layered structure.

[0128] The degree of cation mixing in the Ni-rich layered cathode materials can considerably influence their electrochemical performance

[0024] . As shown in Table 1 and 2, the Li / Ni cation mixing in both NCM811 and 1.0-TNCM are 2.67% and 2.11%, respectively. The lattice parameter c of NCM811 is 14.1789(7) Å with the cell volume of 101.213(2) Å3. In comparison, the cell parameters of 1.0-TNCM are enlarged to 14.1952(3) Å (c) and 101.249(2) Å3(cell volume) upon the Ti introduction. These findings validate the success of Ti introduction in the bulk of the layered structure and highlight the modification on lattice parameters of NCM811 caused by Ti doping, especially along the c axis. In addition, NCM811 with higher Ti doping concentration (Li1-xNi0.8-yMn0.1Co0.1Tix+yO2(x + y = 0.02, 2.0-TNCM)) are also examined. As expected, 2.0-TNCM shows the largest lattice parameters (a = 2.87105(5) Å, c = 14.2006(17) Å and cell volume = 101.334(2) Å3). Meanwhile, the 2.0-TNCM also features the highest Li / Ni cation mixing (3.11%) in the R-3m structure.

[0129] Table 1 Crystallography details of undoped NCM811 obtained from the Rietveld refinement against NPD data.aConstrained to be 1,bconstrained to be 1.

[0130] Table 2 Crystallography details of 1.0-TNCM obtained from the Rietveld refinement against NPD data with Ti occupy both Li and TM sites.aConstrained to be 1,bconstrained to be 1.

[0131] Table 3 Crystallography details of 2.0-TNCM obtained from the Rietveld refinement against NPD data with Ti occupy both Li and TM sites.aConstrained to be 1,bconstrained to be 1.

[0132] Electrochemical performance

[0133] Figure 3a shows the initial charge and discharge curves of all samples at 0.1C (1C = 200 mA g-1) current density. The highest discharge-specific capacity is observed for 1.0-TNCM at 215.1 mAh g-1, followed by 2.0-TNCM at 208.2 mAh g-1, and NCM811 at 199.3 mAh g-1. Notably, 1.0-TNCM achieved a specific discharge capacity of 160 mAh g-1at 10C, which is 75.6% of the discharge capacity at 0.1C, outperforming both NCM811 (126.0 mAh g-1, 61.7%) and 2.0-TNCM (151.7 mAh g-1, 74.7%) in terms of rate capability (Figure 3b). As commonly acknowledged, a higher cation mixing degree in the structure limits the capacity of the active materials[25-26], which coincides with the observation that the 1.0-TNCMwith the lowest cation mixing degree (2.11%) delivers the highest battery capacity as well as the reduced capacity in the 2.0-TNCM caused by more cation mixing (3.11%). Further, to evaluate the influence of the Ti modification on Li+diffusion, the galvanostatic intermittent titration technique (GITT) was utilized (Figure 10)

[0027] . As illustrated in Figure 3c, during charging and discharging, the Li+diffusivities within NCM811 are not obviously influenced by the Ti introduction, which indicates that the Ti dopants barely block the Li+diffusion in the modified samples.

[0134] As shown in Figure 3d, the 1.0-TNCM shows extraordinary cycle stability with high reversible capacities of 163.5 mAh g-1after 500 cycles, corresponding to a high-capacity retention of 86.7%. In comparison, the NCM811 and 2.0-TNCM only maintain 36.5% and 78.7% of their initial capacities after 500 cycles. Meanwhile, the noticeable discharge voltage decay occurs in NCM811, which significantly lowers the battery output power and leads to eventual battery failure. In sharp contrast, the discharge voltage of the 1.0-TNCM is well maintained (Figure 3e), confirming the effects of the flexible TiO6 in enhancing the structural stability of the NCM811.

[0135] The discharge curves of both samples from 5thto 500thcycles are displayed in Figure 12, where the 1.0-TNCM sample experiences smaller voltage polarization than NCM811. The dQ / dV curves from the 5thto 500thcycles of both samples are displayed in Figure 3f. During the electrochemical reactions, the active materials undergo complicated phase evolutions, as the distinct peaks showed up in the dQ / dV curves. As displayed, from the 5thto the 500thcycles, the peaks almost overlap in the 1.0-TNCM sample, however, those in NCM811 dramatically shift in both charging and discharging processes. As displayed in Figure 3g, the voltage shifts of reactions during charging process from the hexagonal 1 (H1) to monoclinic (M) phases in NCM811 is 0.0850V from the 5thcycle to the 500thcycle, with the one corresponding to the hexagonal 2 (H2) to hexagonal 3 (H3) phase being 0.1345V. In comparison, minor voltage shifts of both H1 to M and H2 to H3 evolutions in 1.0-TNCM are observed (0.0685V and 0.0508V, respectively). To our knowledge, the electrochemical performance of 1.0-TNCM is remarkably high and comparable to other reported NCM811 materials (Figure 3h).

[0136] Structure stabilization analysis

[0137] The structure evolution of the NCM811 and 1.0-TNCM was investigated by in operando synchrotron-based X-ray powder diffraction (SXRPD) to gain further insight into the relationship between electrochemical performance enhancement and Ti introduction. Typically, the Ni-rich layered cathode materials experience a hexagonal to monoclinic transition (denoted H1 to M) occurring at the initial charging stage, followed by a transformation to a hexagonal phase 2 (H2) and final phase 3 (H3)

[0036] at high voltage. The corresponding diffraction data of NCM811 and 1.0-TNCM are displayed as a contour plot with intensity in the colour (Figure 4a and 4b), which is consistent with previous observations of Ni- rich layered cathodes

[0037] . During delithiation, the lattice parameter c experiences a gradual increase duringthe initial delithiation followed by a rapid decrease at a highly delithiated state. On the contrary, the lattice parameter a decrease monotonically during the whole delithiation procedure. The structure evolution and lattice parameter variations are accompanied by the generation of the lattice strain, which results in the undesirable structure instability

[0038] .

[0138] The reflection peaks located around 8.3° and 16.1° are indexed to the

[0003] and

[0101] reflections, respectively, of the R-3m phase. We performed single-peak fitting against the in operando XRPD data to analyze the lattice parameter changes. As displayed in Figure 4d, the lattice parameter a changes from 2.868 to 2.810Å and 2.871 to 2.816Å in NCM811 and 1.0-TNCM, respectively, where no obvious differences are observed after Ti introduction (2.02% and 1.91% of changes). Notably, as calculated, during delithiation, the lattice parameter c and the cell volume of the NCM811 change from 14.174 to 14.455Å and 101.030 to 96.138Å3, respectively. However, minor lattice variations in the 1.0- TNCM samples are observed, where the lattice parameter c change from 14.188 to 14.395Å and cell volume change from 101.303 to 98.731 Å3(Figures 4e and 4f) when charged to 4.0V. Surprisingly, at the highly delithiated states, the dramatic collapse of the layered structure along the c axis is observed in NCM811, which refers to the lattice parameter c dropping from 14.455 to 14.055Å (2.74%) when charged to 4.3V. On the contrary, at the highly delithiated state, the lattice parameter c of 1.0-TNCM only drops from 14.394 to 14.370Å (0.13%). This indicates that the lattice distortion of Ni-rich cathode materials at highly delithiated states is effectively mitigated. During the discharging process, the lattice parameter change was also displayed in Figure 13. On the contrary of delithiation process, the c value of the both samples increase at the initial lithiation state followed by a subsequent decrease at low voltage, and the a value increases during the lithiation process. As expected, 1.0-TNCM also suffers from less lattice change than NCM811during charging.

[0139] It is well-explained that lattice structure collapse and phase transformation always occur in conjunction with the generation of severe lattice strain

[0012] . Therefore, we quantitively analyze the anisotropic shear strain of both samples, as shown in Figure 4f. The obvious suppressed shear strain accumulation during the charging process has been noted, where the slope of the shear strain c / a was slowed down by nearly 67% in 1.0-TNCM. Meanwhile, a qualitative lattice strain within the

[0003] plane was also conducted to demonstrate the lattice stabilization by TiO6introduction. As displayed in Figure 4g, the NCM811 suffers from dramatic lattice strain variation, with the lattice strain increasing / decreasing irregularly. Although the lattice strain still exists in the 1.0-TNCM, the strain evolves smoothly without any violent changes. Therefore, it is clear that the TiO6 octahedron introduction can dramatically prohibit the lattice distortion along the c axis, which ultimately relief the lattice strain to stabilize the layered structure of the Ni-rich cathodes.

[0140] Local strain relief mechanism

[0141] The detailed redox behaviour of different TM ions was investigated via ex situ X-ray absorption spectroscopy (XAS) characterizations. As displayed in Figure 14a, from the open-circuit voltage (OCV) to the fully charged state, the Ni-K edges significantly shift to higher energy region in both NCM811 and 1.0-TNCM. During discharge, the Ni-K edges migrate back to their original positions. The obvious energy shift indicates the electrochemical activities of Ni during charge / discharge

[0016] . The corresponding extended X-ray absorption fine structure (EXAFS) spectra (Fourier transform of k2|χ(k)|) (Figure 5a and 5b) are employed to investigate the internal structure changes. The two major shells located at ~1.5 and ∼2.5 Å correspond to the Ni-O and Ni-TM bonds in the layered structure

[0039] .

[0142] As displayed in Figure 5a and 5b, we performed the peak fitting analysis against the corresponding Ni-O and Ni-TM at different SOC of NCM811 and 1.0-TNCM. The full-width at half- maximum (FWHM) of Ni-O / Ni-TM peak variation during the charging and discharging results from the JT effect of Ni3+([Ar] 3d7) in the NiO6 octahedron (Figure 5c)[13, 16, 40]. Quantitively, during the charging of NCM811, the Ni-O peak FWHM changes from 0.4895 to 0.5280 Å. However, in the 1.0-TNCM, the Ni-O peak FWHM only changes from 0.4891 to 0.5091 Å, where the distortion of the Ni-O octahedron successfully suppressed by 48%. During discharging, the Ni-O peak FWHM of 1.0-TNCM also decreases less than NCM811, indicating the Ni-O octahedron suffers from less distortion. Similar trends are observed in the Ni-TM peaks of the NCM811 and 1.0-TNCM. The slightly changed FWHM of Ni-TM peak in 1.0-TNCM indicates that the unit distortion is regulated by the TiO6 octahedron. Ni L-edge spectra were also measured via ex situ near edge X-ray absorption fine structure (NEXAFS), as displayed in Figure 15, comparing with the NCM811, the higher reversibility of the Ni-L edge of 1.0-TNCM also supports a more stable Ni-O octahedron structure

[0041] . Meanwhile, the EXFAS spectra of the Ti in 1.0- TNCM is also displayed in Figure 5d. The red area represents the shorter Ti-O coordination bond and yellow area represents the longer Ti-O coordination bond. [Flexibility] The area ratio (Sred:Syellow) change could reflect the coordination variations of TiO6 during the charging and discharging. The area ratio of 1.0-TNCM changes from 0.75 at the OCV state to 0.61 at charged state, indicating Ti-O bonds becoming more inequivalent. At the discharged state, the area ratio returns back to 0.76. The Ti-O octahedrons persist during charging / discharging with the changes of bond lengthens, benefiting from their structural flexibility (Figure 5e)

[0018] .

[0143] We show that the distortion of the octahedron structure unit occurs during the functioning of the Ni-rich cathode materials. Meanwhile, due to the existence of cooperative JT distortion, the octahedron distortion is continuously accumulated and aggravated, which finally results in the material structure distortion and severe lattice strain

[0017] . Benefiting from the introduction of the flexible TiO6octahedron (Figure 5e), the JT distortion of the structure units is prevented from transferring and accumulation, thereby, the lattice strain is successfully mitigated within the localized region. Further evidence of the local strain relief is provided by the Mn EXFAS structure

[0025] . Obvious FWHM expansion of Mn-O variation from 0.4360 to 0.5910 Å is observed in NCM811 (Figures 5f), which is induced by thecooperative JT distortion. In comparison, only a minor Mn-O peak FWHM shift is observed in the 1.0- TNCM sample (0.4951 to 0.5543 Å). Similarly, the FWHM of Mn-TM peak of 1.0-TNCM experienced 54% less variations compared with the NCM811(Figure 5h). Therefore, the success and necessity of the flexible TiO6 octahedron to prevent the structure unit distortion to be transferred and accumulated to relief the lattice strain is highlighted.

[0144] Regulating lattice strain is an effective method to improve the structural stability and electrochemical performance of Ni-rich layered cathode materials. In this work, we successfully accommodate the lattice strain in the local domain via the introduction of flexible TiO6 octahedron in the layered structure of NCM811. Characterized by in operando SXRPD, the lattice variation along the c direction in Ti modified NCM811 is suppressed by 95.3% compared to the pristine sample. The lattice strain is also successfully prevented from accumulation and violent variation by TiO6 introduction. The significantly reduced lattice change and strain accumulation upon cycling contributes to the excellent performance of NCM811 that deliver superior initial discharge capacities of 215.1 mAh g-1, together with extraordinary capacity retentions of 86.7% after 500 cycles. In conclusion, the introduction of flexible octahedrons in the material structure provides a prospective method for relieving hazardous lattice strain, enriches the optimization strategies for cathode materials, and advances the practical application of LIBs for high-energy requirement devices and long-lasting electric vehicles.

[0145] It will be understood that the terms “comprise” and “include” and any of their derivatives (e.g. comprises, comprising, includes, including) as used in this specification is to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.

[0146] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

[0147] It will be appreciated by those skilled in the art that the disclosure is not restricted in its use to the particular application or applications described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and / or features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope as set forth and defined by the following claims.REFERENCES

[0148] [1] M. Li, J. Lu, Z. Chen, K. Amine, Adv. Mater.2018, 30, 1800561.

[0149] [2] Y. Lyu, X. Wu, K. Wang, Z. Feng, T. Cheng, Y. Liu, M. Wang, R. Chen, L. Xu, J. Zhou, Adv. Energy Mater.2021, 11, 2000982.

[0150] [3] G. Liang, E. Olsson, J. Zou, Z. Wu, J. Li, C. Z. Lu, A. M. D'Angelo, B. Johannessen, L. Thomsen, B. Cowie, Angew. Chem.2022, 134, e202201969.

[0151] [4] L. Ni, S. Zhang, A. Di, W. Deng, G. Zou, H. Hou, X. Ji, Adv. Energy Mater.2022, 12, 2201510.

[0152] [5] Y. Xia, J. Zheng, C. Wang, M. Gu, Nano Energy 2018, 49, 434.

[0153] [6] C. Xu, K. Märker, J. Lee, A. Mahadevegowda, P. J. Reeves, S. J. Day, M. F. Groh, S. P. Emge, C. Ducati, B. Layla Mehdi, C. C. Tang, C. P. Grey, Nature Mater.2021, 20, 84.

[0154] [7] S. S. Zhang, Energy Storage Mater.2020, 24, 247.

[0155] [8] T. Liu, L. Yu, J. Lu, T. Zhou, X. Huang, Z. Cai, A. Dai, J. Gim, Y. Ren, X. Xiao, Nature communications 2021, 12, 6024.

[0156] [9] H. Zhang, X. He, Z. Chen, Y. Yang, H. Xu, L. Wang, X. He, Adv. Energy Mater.2022, 12, 2202022.

[0157]

[0010] X. Ou, T. Liu, W. Zhong, X. Fan, X. Guo, X. Huang, L. Cao, J. Hu, B. Zhang, Y. S. Chu, G. Hu, Z. Lin, M. Dahbi, J. Alami, K. Amine, C. Yang, J. Lu, Nat. Commun.2022, 13, 2319.

[0158]

[0011] R. Zhang, C. Wang, P. Zou, R. Lin, L. Ma, L. Yin, T. Li, W. Xu, H. Jia, Q. Li, S. Sainio, K. Kisslinger, S. E. Trask, S. N. Ehrlich, Y. Yang, A. M. Kiss, M. Ge, B. J. Polzin, S. J. Lee, W. Xu, Y. Ren, H. L. Xin, Nature 2022, 610, 67.

[0159]

[0012] L. Wang, T. Liu, T. Wu, J. Lu, Nature 2022, 611, 61.

[0160]

[0013] X. Xu, H. Zhu, Y. Tang, L. Wang, Q. Zhang, Y. Ren, S. Lan, L. Xiang, J. Jian, H. Huo, G.-X. Chen, L. Gu, G. Yin, X.-L. Wang, X. Sun, C. Du, Q. Liu, Nano Energy 2022, 100, 107502.

[0161]

[0014] H. Zhu, Y. Tang, K. M. Wiaderek, O. J. Borkiewicz, Y. Ren, J. Zhang, J. Ren, L. Fan, C. C. Li, D. Li, X.-L. Wang, Q. Liu, Nano Letters 2021, 21, 9997.

[0162]

[0015] X. Rong, E. Hu, Y. Lu, F. Meng, C. Zhao, X. Wang, Q. Zhang, X. Yu, L. Gu, Y.-S. Hu, H. Li, X. Huang, X.-Q. Yang, C. Delmas, L. Chen, Joule 2019, 3, 503.

[0163]

[0016] K. R. Tallman, G. P. Wheeler, C. J. Kern, E. Stavitski, X. Tong, K. J. Takeuchi, A. C. Marschilok, D. C. Bock, E. S. Takeuchi, J. Phys. Chem. C 2021, 125, 58.

[0164]

[0017] C. Zuo, Z. Hu, R. Qi, J. Liu, Z. Li, J. Lu, C. Dong, K. Yang, W. Huang, C. Chen, Z. Song, S. Song, Y. Yu, J. Zheng, F. Pan, Adv. Energy Mater.2020, 10, 2000363.

[0165]

[0018] H. Su, G. Guo, Y. Ren, X. Yu, X. Zhang, T. Ma, Y. Lu, Z. Zhang, H. Ma, M. Sui, H. Li, C. Sun, Z. Chen, G. Xu, R. Wang, K. Amine, H. Yu, Energy Environ. Sci 2020, 13, 4371.

[0166]

[0019] J.-Y. Piao, Y.-G. Sun, S.-Y. Duan, A.-M. Cao, X.-L. Wang, R.-J. Xiao, X.-Q. Yu, Y. Gong, L. Gu, Y. Li, Chem 2018, 4, 1685.

[0167]

[0020] B. Xiao, H. Liu, J. Liu, Q. Sun, B. Wang, K. Kaliyappan, Y. Zhao, M. N. Banis, Y. Liu, R. Li, Adv. Mater.2017, 29, 1703764.

[0168]

[0021] D. Zhang, Y. Liu, L. Wu, L. Feng, S. Jin, R. Zhang, M. Jin, Electrochim. Acta 2019, 328, 135086.

[0169]

[0022] L. B. McCusker, R. B. Von Dreele, D. E. Cox, D. Louer, P. Scardi, Journal of Applied Crystallography 1999, 32, 36.

[0170]

[0023] T. Weigel, F. Schipper, E. M. Erickson, F. A. Susai, B. Markovsky, D. Aurbach, ACS Energy Lett.2019, 4, 508.

[0171]

[0024] J. Li, G. Liang, W. Zheng, S. Zhang, K. Davey, W. K. Pang, Z. Guo, Nano Materials Science 2022.

[0172]

[0025] T. Liu, L. Yu, J. Liu, J. Lu, X. Bi, A. Dai, M. Li, M. Li, Z. Hu, L. Ma, Nat. Energy.2021, 6, 277.

[0173]

[0026] H. Yu, Y. Cao, L. Chen, Y. Hu, X. Duan, S. Dai, C. Li, H. Jiang, Nature Communications 2021, 12, 4564.

[0174]

[0027] Y. Zhu, C. Wang, J. Phys. Chem. C 2010, 114, 2830.

[0175]

[0028] Y.-G. Zou, H. Mao, X.-H. Meng, Y.-H. Du, H. Sheng, X. Yu, J.-L. Shi, Y.-G. Guo, Angewandte Chemie International Edition 2021, 60, 26535.

[0176]

[0029] X. Xu, H. Huo, J. Jian, L. Wang, H. Zhu, S. Xu, X. He, G. Yin, C. Du, X. Sun, Advanced Energy Materials 2019, 9, 1803963.

[0177]

[0030] Z. Feng, R. Rajagopalan, S. Zhang, D. Sun, Y. Tang, Y. Ren, H. Wang, Advanced Science 2021, 8, 2001809.

[0178]

[0031] X. Liu, J. Shi, B. Zheng, Z. Chen, Y. Su, M. Zhang, C. Xie, M. Su, Y. Yang, ACS Applied Materials & Interfaces 2021, 13, 41669.

[0179]

[0032] Y. Liu, T. Zeng, G. Li, T. Wan, M. Li, X. Zhang, M. Li, M. Su, A. Dou, W. Zeng, Y. Zhou, R. Guo, D. Chu, Energy Storage Materials 2022, 52, 534.

[0180]

[0033] M. Mao, B. Huang, Q. Li, C. Wang, Y.-B. He, F. Kang, Nano Energy 2020, 78, 105282.

[0181]

[0034] W. Liu, X. Li, Y. Hao, D. Xiong, H. Shan, J. Wang, W. Xiao, H. Yang, H. Yang, L. Kou, Z. Tian, L. Shao, C. Zhang, Advanced Functional Materials 2021, 31, 2008301.

[0182]

[0035] Y. Qiao, R. Hao, X. Shi, Y. Li, Y. Wang, Y. Zhang, C. Tang, G. Li, G. Wang, J. Liu, H. Liu, Y. Chen, Q. Li, L. Li, ACS Applied Energy Materials 2022, 5, 4885.

[0183]

[0036] S. Jamil, G. Wang, L. Yang, X. Xie, S. Cao, H. Liu, B. Chang, X. Wang, Journal of Materials Chemistry A 2020, 8, 21306.

[0184]

[0037] K.-W. Nam, S.-M. Bak, E. Hu, X. Yu, Y. Zhou, X. Wang, L. Wu, Y. Zhu, K.-Y. Chung, X.-Q. Yang, Adv. Funct. Mater.2013, 23, 1047.

[0185]

[0038] P. Yan, J. Zheng, J. Liu, B. Wang, X. Cheng, Y. Zhang, X. Sun, C. Wang, J.-G. Zhang, Nat. Energy.2018, 3, 600.

[0186]

[0039] L. Ma, L. Wang, T. Liu, T. Wu, J. Lu, Small Methods 2023, 7, 2201173.

[0187]

[0040] S. Yoon, G. Choi, J. Lee, J. Hwang, D. Kim, Chem. Eng. J.2023, 458, 141472.

[0188]

[0041] Y. Fan, E. Olsson, G. Liang, Z. Wang, A. M. D'Angelo, B. Johannessen, L. Thomsen, B. Cowie, J. Li, F. Zhang, Angew. Chem.2023, 135, e202213806.

[0189]

[0042] J. H. Yang, H. Kim, G. Ceder, Molecules 2021, 26, 3173.

[0190]

[0043] G. Kresse, J. Furthmüller, Computational Materials Science 1996, 6, 15.

[0191]

[0044] G. Kresse, J. Furthmüller, Physical Review B 1996, 54, 11169.

[0192]

[0045] P. E. Blöchl, Physical Review B 1994, 50, 17953.

[0193]

[0046] G. Kresse, D. Joubert, Physical Review B 1999, 59, 1758.

[0194]

[0047] J. P. Perdew, K. Burke, M. Ernzerhof, Physical Review Letters 1996, 77, 3865.

[0195]

[0048] S. Grimme, J. Antony, S. Ehrlich, H. Krieg, The Journal of Chemical Physics 2010, 132, 154104.

[0196]

[0049] B. H. Toby, R. B. Von Dreele, Journal of Applied Crystallography 2013, 46, 544.

[0197]

[0050] G. Liang, J. Hao, A. M. D'Angelo, V. K. Peterson, Z. Guo, W. K. Pang, Batteries & Supercaps 2021, 4, 380.

[0198]

[0051] D. Richard, M. Ferrand, G. J. Kearley, Journal of Neutron Research 1996, 4, 33.

[0199]

[0052] P. Bindu, S. Thomas, Journal of Theoretical and Applied Physics 2014, 8, 123.

[0200]

[0053] E. Gann, C. R. McNeill, A. Tadich, B. C. C. Cowie, L. Thomsen, Journal of Synchrotron Radiation 2016, 23, 374.

[0201]

[0054] B. Ravel, M. Newville, Journal of Synchrotron Radiation 2005, 12, 537.

Claims

CLAIMS 1. A doped layered cathode material for an electrochemical device, which comprises a dopant and a layered cathode material, wherein the dopant is selected and added so that the electrochemical device delivers a capacity retention of about 78% to about 88% after 500 cycles at 1 C.

2. The doped layered cathode material according to claim 1, wherein the dopant is selected and added so that the electrochemical device delivers an initial discharge capacity of at least about 200.0 mAh g-1at 0.1C.

3. The doped layered cathode material according to either claim 1 or claim 2, wherein the dopant is selected and added so that the electrochemical device delivers a rate capability of at least about 150 mAh g-1at 10 C.

4. The doped layered cathode material according to any one of claims 1 to 3, wherein the dopant ions occupy octahedral sites in the crystal structure of the layered cathode material.

5. The doped layered cathode material according to any one of claims 1 to 4, wherein the electrochemical device is selected from ion batteries.

6. The doped layered cathode material according to any one of claims 1 to 5, wherein the layered cathode material comprises an intercalating metal and a bulk metal.

7. The doped layered cathode material according to any one of claims 1 to 6, wherein the layered cathode material comprises or consists of a layered cathode oxide.

8. The doped layered cathode material according to claim 7, wherein the layered cathode material comprises or consists of a layered cathode oxide which has a formula of AxMO2, wherein A is an alkali metal cation, M is metal cation, and O is oxygen anion.

9. The doped layered cathode material according to any one of claims 1 to 8, wherein the layered cathode material is a Ni-rich lithium layered oxide.

10. The doped layered cathode material according to any one of claims 1 to 9, wherein the Ni-rich lithium layered oxide has a chemical formula of LiNi1-x-yCoxMnyO2(1-x-y ≥ 0.5, 0.5 > x > 0, 0.5 > y > 0).

11. The doped layered cathode material according to any one of claims 1 to 10, wherein the dopant (D) is capable of forming a DO6octahedron in the crystal structure of the layered cathode material.

12. The doped layered cathode material according to any one of claims 1 to 11, wherein the dopant (D) is one or more selected from the group consisting of Ti, V, Cu, Cr, Ta, Ga, W, Zr, Mn and Nb.

13. The doped layered cathode material according to any one of claims 1 to 12, wherein the doped layered cathode material is selected from Li1-xNi0.8-yMn0.1Co0.1Tix+yO2 (x + y = 0.02, 2.0-TNCM) and Li1- xNi0.8-yMn0.1Co0.1Tix+yO2 (x + y = 0.01, 1.0-TNCM).

14. A method for preparing a doped layered cathode material comprising a dopant and a layered cathode material, wherein the layered cathode material comprises an intercalating metal ion and a bulk metal ion, the method comprises: (i) obtaining (a) a doped precursor comprising the dopant and a source of the bulk metal ion, (ii) obtaining a composition comprising (a) and (b) a source of the intercalating metal ion, and (iii) heating the composition.

15. The method according to claim 14, wherein the method comprises obtaining (c) a precursor comprising a source of the bulk metal ion and, optionally, the dopant, step (ii) is to obtain a composition comprising (a), (b), and (c).

16. The method according to either claim 14 or claim 15, wherein the amount and the composition of each of (a), (b) and optional (c) are selected so that the stoichiometric composition of the doped layered cathode material to be prepared is met.

17. The method according to any one of claims 14 to 16, wherein the step (iii) is a staged heating under oxygen atmosphere of heating at about 450 °C to about 550 °C for a period and then heating at about 750 °C to about 850 °C for a period.

18. The method according to any one of claims 14 to 17, wherein the doped layered cathode material consists of the layered cathode material of AxMO2and the dopant (doping metal=D), A is an alkali metal cation, M is a metal cation, and O is oxygen anion, and the method includes: (i) obtaining (a) D-doped M(OH)2or M(CO3)2, (ii) obtaining a composition comprising (a) and (b) a hydrated hydroxide of A, a chloride of A or a carbonate of A, and (iii) heating the composition.

19. An electrochemical device comprising the doped layered cathode material according to any one of claims 1 to 13 or obtained according to any one of claims 14 to 18.

20. Use of the doped layered cathode material according to any one of claims 1 to 13 or obtained according to any one of claims 14 to 18 in a cathode of an electrochemical device.

Images