A lithium cobalt oxide positive electrode material with a composite phase and its preparation method and application

Abstract

The embodiment of the present invention relates to a lithium cobalt oxide positive electrode material with a composite phase and its preparation method and application. The chemical formula of the lithium cobalt oxide positive electrode material with a composite phase is A X Co 1‑y M1 y O2; wherein 0.5≤x≤1, 0≤y≤0.03, A is Li or Li and Na, and M1 is one or more of Al, Zr, Ni, Mn, Y, Nb, La, Fe, Cu, Cr, Ti, W, Mg, Mo, or Yb; the composite phase of the lithium cobalt oxide positive electrode material includes an O2 phase, a T2 phase, and an O3 phase; wherein the sum of the molar proportions of the O2 phase and the T2 phase in the composite phase is greater than or equal to 90%, and the molar proportion of the O3 phase is less than or equal to 10%. The present invention can effectively improve the rate performance, structural stability under high voltage, thermodynamic structural stability, specific capacity, and discharge platform of the positive electrode material by regulating the composite phase ratio of the lithium cobalt oxide positive electrode material, thereby realizing a lithium cobalt oxide positive electrode material with both high energy density and high stability.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy materials, and in particular to a lithium cobalt oxide positive electrode material with a composite phase, a preparation method thereof, and applications thereof. Background Art

[0002] Lithium-ion batteries, with their high energy density, long cycle life, and excellent safety, are the preferred power source for portable electronic devices, electric vehicles, and energy storage systems. However, as devices become increasingly intelligent, their high-powered computing capabilities place higher demands on battery life. Therefore, the development of high-energy-density lithium-ion battery cathode materials is a key factor in promoting their further development.

[0003] Traditional lithium cobalt oxide positive electrode materials have an O3 phase structure and belong to the R-3m space group. Thanks to its advantages such as high compaction density and high energy density, it is widely used in energy storage fields such as 3C electronic devices. In actual use, the diffusion path of lithium ions in the bulk phase of lithium cobalt oxide with an O3 phase structure is single, and is affected by the electrostatic repulsion of the layered transition metal elements, which makes its diffusion rate relatively slow, and ultimately leads to poor rate performance of O3 phase lithium cobalt oxide. In addition, when charged to a high voltage (greater than 4.5V), a large number of lithium ions in the lithium cobalt oxide with an O3 phase structure will escape from the bulk structure, resulting in an irreversible phase change in the crystal structure and the generation of electrochemically inert Co3O4 on its surface, which will cause surface lithium ion conduction to be blocked and irreversible capacity attenuation.

[0004] In summary, current conventional lithium cobalt oxide cathode materials suffer from poor rate performance, poor cycling stability at high voltages, and low specific capacity. Therefore, there is an urgent need to develop a lithium-ion battery cathode material with high specific capacity, a high voltage platform, good structural reversibility, and structural stability at high voltages. Summary of the Invention

[0005] The present invention addresses the shortcomings of the prior art by providing a lithium cobalt oxide cathode material with a composite phase, a preparation method, and applications thereof. By regulating the composite phase ratio of the lithium cobalt oxide cathode material, the cathode material's rate performance, structural stability at high voltages, thermodynamic structural stability, specific capacity, and discharge plateau characteristics can be effectively improved, thereby achieving a lithium cobalt oxide cathode material with both high energy density and high stability.

[0006] To achieve the above object, the present invention provides a lithium cobalt oxide positive electrode material with a composite phase, the chemical formula of which is A X Co 1-y M1 y O2;

[0007] wherein 0.5≤x≤1, 0≤y≤0.03, A is Li or Li and Na, and M1 is one or more of Al, Zr, Ni, Mn, Y, Nb, La, Fe, Cu, Cr, Ti, W, Mg, Mo, or Yb;

[0008] The composite phase of the lithium cobalt oxide positive electrode material includes an O2 phase, a T2 phase and an O3 phase; wherein the sum of the molar proportions of the O2 phase and the T2 phase in the composite phase is greater than or equal to 90%, and the molar proportion of the O3 phase is greater than 0 and less than or equal to 10%.

[0009] Preferably, the chemical formula of the lithium cobalt oxide positive electrode material having a composite phase is Li x1 Na X2 Co 1-y M1 y O2, 0.5<x1<0.996, 0.0001≤x2≤0.004, 0≤y≤0.03, M1 is at least one of Al, Mg, and Ti.

[0010] Preferably, the molar ratio of the O2 phase in the composite phase is 1%-65%, the molar ratio of the T2 phase in the composite phase is 25%-98%, and the molar ratio of the O3 phase in the composite phase is 1%-10%.

[0011] Further preferably, the O2 phase, the T2 phase and the O3 phase are uniformly or unevenly distributed in the bulk structure of the lithium cobalt oxide positive electrode material;

[0012] The molar ratio of the O2 phase in the composite phase is 40%-65%, the molar ratio of the T2 phase in the composite phase is 30%-55%, and the molar ratio of the O3 phase in the composite phase is 5%-10%.

[0013] Preferably, M1 is uniformly distributed or gradiently distributed in the bulk phase of the lithium cobalt oxide positive electrode material having a composite phase.

[0014] Preferably, the lithium cobalt oxide of the T2 phase structure has a characteristic peak corresponding to the (002) crystal plane in the range of 17.00°≤2θ≤18.08°, a characteristic peak corresponding to the (112) crystal plane in the range of 40.7°≤2θ≤42.2°, and a characteristic peak corresponding to the (114) crystal plane in the range of 52.1°≤2θ≤53.9°;

[0015] Lithium cobalt oxide with O2 phase structure has a characteristic peak corresponding to the (002) crystal plane in the range of 18.08°<2θ≤18.32°, a characteristic peak corresponding to the (102) crystal plane in the range of 36.2°≤2θ≤37.7°, and a characteristic peak corresponding to the (105) crystal plane in the range of 56.7°≤2θ≤57.9°.

[0016] LiCoO2 with O3 phase structure has characteristic peaks corresponding to (003) crystal plane in the range of 18.51°≤2θ≤19.72°, and has characteristic peaks corresponding to (104) crystal plane in the range of 45.1°≤2θ≤45.9°.

[0017] Among them, the characteristic peak intensity of the T2 phase structure corresponding to the (002) crystal plane in the range of 17.00°≤2θ≤18.08° is I1, the characteristic peak intensity of the O2 phase structure corresponding to the (002) crystal plane in the range of 18.08°<2θ≤18.32° is I2, and the characteristic peak intensity of the O3 phase structure corresponding to the (003) crystal plane in the range of 18.51°≤2θ≤19.72° is I3, I1, I2, and I3 satisfy 0.5≤I2 / I1≤1.5, 0.1≤I3 / I2≤0.8; preferably, 0.8≤I2 / I1≤1.1, 0.2≤I3 / I2≤0.5.

[0018] Preferably, the lithium cobalt oxide positive electrode material with a composite phase is a spherical particle composed of primary particles and / or secondary particles;

[0019] The primary particles are composed of one or more crystal grains, the primary particles are flaky in shape, and have an average particle size of 4 μm-50 μm, preferably 5 μm-30 μm; the secondary particles are composed of agglomerates of multiple primary particles.

[0020] In a second aspect, an embodiment of the present invention provides a method for preparing the lithium cobalt oxide positive electrode material having a composite phase as described in the first aspect, comprising:

[0021] A sodium source and a cobalt source doped or undoped with the M1 element are weighed, mixed, and subjected to a first sintering in a stoichiometric ratio to obtain a P2 phase sodium cobaltate material; wherein the molar ratio of sodium in the sodium source to cobalt in the cobalt source is greater than or equal to 0.8; the first sintering has a heating rate of 3-20°C / min, a sintering temperature of 700-1000°C, and a sintering time of 10-36 hours;

[0022] The P2 phase sodium cobaltate material is mixed with a lithium source in a molar ratio of n(Na):n(Li)=1:1.5-1:10, and a second sintering is performed in an air atmosphere or an oxygen atmosphere to carry out a molten salt ion exchange reaction. The second sintered product is washed with water to obtain a lithium cobaltate positive electrode material with a composite phase; wherein the heating rate of the second sintering is 3-20°C / min, the sintering temperature is 250°C to 300°C, and the sintering time is 12-36 hours.

[0023] Preferably, the cobalt source includes: one or more of cobalt tetroxide, cobalt hydroxide, cobalt chloride, cobalt acetate, cobalt sulfate, and cobalt nitrate;

[0024] The sodium source includes: one or more of sodium carbonate, sodium hydroxide, sodium chloride, sodium nitrate, and sodium sulfate;

[0025] M1 is one or more of Al, Zr, Ni, Mn, Y, Nb, La, Fe, Cu, Cr, Ti, W, Mg, Mo or Yb;

[0026] The weighing according to the stoichiometric ratio is specifically: weighing according to the molar ratio of Na, Co, and M1 of [0.8-1]: [0.97-1]: [0-0.03];

[0027] The lithium source includes: one or more of lithium hydroxide, lithium nitrate, lithium chloride, lithium bromide, lithium sulfate, and lithium carbonate;

[0028] The second sintering has a heating rate of 3-15° C. / min, a sintering temperature of 255° C.-265° C., and a sintering time of 12-14 hours.

[0029] In a third aspect, an embodiment of the present invention provides a lithium battery, comprising the lithium cobalt oxide positive electrode material having a composite phase as described in the first aspect above, or the lithium cobalt oxide positive electrode material having a composite phase prepared by the preparation method as described in the second aspect above;

[0030] The lithium battery includes any one of a liquid lithium ion battery, a liquid metal lithium battery, a hybrid solid-liquid lithium ion battery, a hybrid solid-liquid metal lithium battery, a solid lithium ion battery or a solid metal lithium battery.

[0031] The lithium cobalt oxide positive electrode material with a composite phase provided by an embodiment of the present invention has a composite phase structure of O2, T2, and O3 phases. The sum of the molar proportions of the O2 and T2 phases in the composite phase is greater than or equal to 90%. The lithium cobalt oxide with the O2 phase structure has excellent rate performance, and the unique lithium-oxygen tetrahedral configuration of the T2 phase structure improves the structural stability of the lithium cobalt oxide material at high voltages, enabling the lithium cobalt oxide positive electrode material to have both excellent rate performance and high-voltage cycling stability. Furthermore, during the charging process of the lithium cobalt oxide positive electrode material, the O2 phase structure will also transform into the T2 phase lithium cobalt oxide with a Cmca crystal structure, thereby allowing sufficient lithium-oxygen tetrahedral configuration to exist between the layers as interlayer "pillars", which can further significantly improve the structural stability of the lithium cobalt oxide at high voltages and ensure that the composite phase lithium cobalt oxide material has excellent high-voltage stability. The composite phase also contains an O3 phase with a molar proportion of less than or equal to 10%, which can improve the overall discharge platform and energy density of the positive electrode material. Furthermore, by introducing M1 doping, the cycle stability of the lithium cobalt oxide positive electrode material can be further improved. At the same time, the irreversible structural phase change and surface structure reconstruction of the positive electrode material under high voltage can be inhibited, thereby further improving the electrochemical performance of the positive electrode material under high voltage.

[0032] The lithium cobalt oxide positive electrode material with a composite phase proposed in the present invention can effectively improve the rate performance, structural stability under high voltage, thermodynamic structural stability, specific capacity and discharge platform of the positive electrode material, thereby realizing a lithium cobalt oxide positive electrode material with both high energy density and high stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 X-ray diffraction (XRD) pattern of the lithium cobalt oxide positive electrode material with a composite phase provided in Example 2 of the present invention;

[0034] Figure 2 XRD pattern of the lithium cobalt oxide positive electrode material with a composite phase provided in Example 3 of the present invention;

[0035] Figure 3 XRD pattern of the lithium cobalt oxide positive electrode material with a composite phase provided in Comparative Example 1 of the present invention;

[0036] Figure 4 XRD pattern of the lithium cobalt oxide positive electrode material with a composite phase provided in Comparative Example 2 of the present invention;

[0037] Figure 5 XRD patterns of pure-phase lithium cobalt oxide positive electrode materials provided in Comparative Examples 3 and 4 of the present invention;

[0038] Figure 6 A scanning electron microscope (SEM) image of the lithium cobalt oxide positive electrode material with a composite phase provided in Example 1 of the present invention;

[0039] Figure 7 This is an SEM image of the lithium cobalt oxide positive electrode material with a composite phase provided in Example 2 of the present invention;

[0040] Figure 8 This is an SEM image of the lithium cobalt oxide positive electrode material with a composite phase provided in Example 3 of the present invention;

[0041] Figure 9 This is an SEM image of the lithium cobalt oxide positive electrode material with a composite phase provided in Example 4 of the present invention;

[0042] Figure 10 This is an SEM image of the lithium cobalt oxide positive electrode material with a composite phase provided in Comparative Example 1 of the present invention;

[0043] Figure 11 This is an SEM image of the lithium cobalt oxide positive electrode material with a composite phase provided in Comparative Example 2 of the present invention;

[0044] Figure 12 This is an SEM image of the pure phase lithium cobalt oxide positive electrode material provided in Comparative Example 3 of the present invention;

[0045] Figure 13This is an SEM image of the pure phase lithium cobalt oxide positive electrode material provided in Comparative Example 4 of the present invention;

[0046] Figure 14 This is a charge and discharge cycle curve diagram of Example 1 of the present invention;

[0047] Figure 15 This is a charge and discharge cycle curve diagram of Example 2 of the present invention;

[0048] Figure 16 This is a charge and discharge cycle curve diagram of Example 3 of the present invention;

[0049] Figure 17 This is a charge and discharge cycle curve diagram of Example 4 of the present invention;

[0050] Figure 18 This is a charge and discharge cycle curve diagram of Comparative Example 1 of the present invention;

[0051] Figure 19 This is a charge and discharge cycle curve diagram of Comparative Example 2 of the present invention;

[0052] Figure 20 This is a charge and discharge cycle curve diagram of Comparative Example 3 of the present invention;

[0053] Figure 21 This is a charge and discharge cycle curve diagram of Comparative Example 4 of the present invention;

[0054] Figure 22 This is a comparison of the energy densities of lithium-ion batteries assembled with the positive electrode materials of Examples 2-3 and Comparative Examples 1-4 after 100 cycles at a current density of 0.5C;

[0055] Figure 23 This is a rate performance diagram of lithium-ion batteries assembled with the positive electrode materials of Examples 1-4 and Comparative Examples 1-4 at current densities of 0.1C, 0.5C, 1C, 2C, 3C, and 5C. DETAILED DESCRIPTION

[0056] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments.

[0057] The embodiment of the present invention provides a lithium cobalt oxide positive electrode material with a composite phase, the chemical formula of which is A X Co 1- y M1 y O2; wherein 0.5≤x≤1, 0≤y≤0.03, A is Li or Li and Na, and M1 is one or more of Al, Zr, Ni, Mn, Y, Nb, La, Fe, Cu, Cr, Ti, W, Mg, Mo, or Yb;

[0058] In the case where A is Li and Na, the chemical formula of the lithium cobalt oxide positive electrode material with a composite phase is Li x1 Na X2 Co 1- y M1 y O2, 0.5<x1<0.996, 0.0001≤x2≤0.004, 0≤y≤0.03. When lithium cobalt oxide contains a small amount of Na ions, the presence of Na ions will make the interlayer spacing of lithium cobalt oxide larger, which is conducive to storing more Li and facilitating the rapid diffusion of Li ions. In addition, the presence of Na ions can also act as interlayer pillars (also known as intercalation pillars, pilling) to prevent the collapse of the layered structure, which can stabilize the positive electrode layered structure in the system and improve the cycle performance of the material. x1, x2, and y can be any value within the above range, for example, x1 can be 0.6, 0.7, 0.8, 0.9, 0.995; x2 can be 0.0001, 0.0005, 0.001, 0.002, 0.003, 0.004; y can be 0, 0.001, 0.002, 0.005, 0.007, 0.01, 0.02, 0.03, but are not limited to the above values.

[0059] When y≠0, M1 exists in the bulk phase of the lithium cobalt oxide positive electrode material with a composite phase, and is uniformly distributed or distributed in a gradient. The gradient distribution is a gradual increase in the M1 content from the inside to the outside, which can be specifically regulated by the sintering temperature and time during the preparation. Within the process range, the higher the temperature and the longer the time, the more uniform the resulting M1 distribution. M1 is preferably at least one of Al, Mg, and Ti. Introducing a small amount of doping element M1 into the system can inhibit the irreversible structural phase change and surface structure reconstruction of the positive electrode material at high voltage, thereby further improving the electrochemical performance of the positive electrode material at high voltage and improving the cycle stability of the lithium cobalt oxide positive electrode material.

[0060] The composite phase of the lithium cobalt oxide positive electrode material includes an O2 phase, a T2 phase, and an O3 phase. The sum of the molar proportions of the O2 and T2 phases in the composite phase is greater than or equal to 90%, and can be any value within the aforementioned range, such as, but not limited to, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%. The molar proportion of the O3 phase is greater than 0 and less than or equal to 10%, and can be any value within the aforementioned range, such as, but not limited to, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. The O2, T2, and O3 phases are uniformly or unevenly distributed within the bulk structure of the lithium cobalt oxide positive electrode material.

[0061] Preferably, the molar proportion of the O2 phase in the composite phase is 1%-65%, the molar proportion of the T2 phase in the composite phase is 25%-98%, and the molar proportion of the O3 phase in the composite phase is 1%-10%. More preferably, the molar proportion of the O2 phase in the composite phase is 40%-65%, the molar proportion of the T2 phase in the composite phase is 30%-55%, and the molar proportion of the O3 phase in the composite phase is 5%-10%.

[0062] The lithium cobalt oxide cathode material with a composite phase of the present invention is a spherical particle composed of primary particles and / or secondary particles. The primary particles are composed of one or more crystal grains, have a flaky morphology, and an average particle size of 4 μm to 50 μm, such as 4 μm, 6 μm, 8 μm, 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm, but are not limited to these values ​​and can be any value within the above range. Preferably, the particle size is 5 μm to 30 μm. The secondary particles are composed of multiple agglomerated primary particles.

[0063] The lithium cobalt oxide positive electrode material with a composite phase of the present invention meets the following characteristics:

[0064] LiCoO2 with T2 phase structure has characteristic peaks corresponding to (002) crystal plane in the range of 17.00°≤2θ≤18.08°, characteristic peaks corresponding to (112) crystal plane in the range of 40.7°≤2θ≤42.2°, and characteristic peaks corresponding to (114) crystal plane in the range of 52.1°≤2θ≤53.9°.

[0065] Lithium cobalt oxide with O2 phase structure has a characteristic peak corresponding to the (002) crystal plane in the range of 18.08°<2θ≤18.32°, a characteristic peak corresponding to the (102) crystal plane in the range of 36.2°≤2θ≤37.7°, and a characteristic peak corresponding to the (105) crystal plane in the range of 56.7°≤2θ≤57.9°.

[0066] LiCoO2 with O3 phase structure has characteristic peaks corresponding to (003) crystal plane in the range of 18.51°≤2θ≤19.72°, and has characteristic peaks corresponding to (104) crystal plane in the range of 45.1°≤2θ≤45.9°.

[0067] Among them, the characteristic peak intensity of the T2 phase structure corresponding to the (002) crystal plane in the range of 17.00°≤2θ≤18.08° is I1, the characteristic peak intensity of the O2 phase structure corresponding to the (002) crystal plane in the range of 18.08°<2θ≤18.32° is I2, and the characteristic peak intensity of the O3 phase structure corresponding to the (003) crystal plane in the range of 18.51°≤2θ≤19.72° is I3, I1, I2, and I3 satisfy 0.5≤I2 / I1≤1.5, 0.1≤I3 / I2≤0.8; preferably, 0.8≤I2 / I1≤1.1, 0.2≤I3 / I2≤0.5.

[0068] The space group of the O2 phase structure is P63mc, and the space group of the T2 phase structure is Cmca. Since the lithium cobalt oxide with the O2 phase (P63mc space group) structure has a unique layer stacking structure, the diffusion path of lithium ions in the positive electrode material layer is diversified and the diffusion energy barrier is small. The main phase structure of the composite phase of the present invention contains the O2 phase, which can enrich the ion diffusion channels in the lithium cobalt oxide bulk structure, which is beneficial to improving the diffusion dynamics of lithium ions in the positive electrode material structure, and thus has excellent rate performance. The unique lithium oxygen tetrahedron configuration in the T2 phase structure can improve the structural stability of the material at high voltage. Although the rate performance of the O2 phase lithium cobalt oxide is excellent and the specific capacity of the pure phase lithium cobalt oxide is high, the discharge platform of the O2 phase lithium cobalt oxide with relatively poor thermodynamic stability is low, which leads to the lower energy density of the O2 phase lithium cobalt oxide than the O3 phase lithium cobalt oxide with better thermodynamic stability, which limits the application of the O2 phase lithium cobalt oxide to a certain extent. The present invention simultaneously obtains better cycle stability and rate performance by making O2 phase and T2 phase the main phase structure of the lithium cobalt oxide positive electrode material. This is because when the lithium cobalt oxide material of the present invention is charged to a high voltage of 4.6V, the O2 phase will further transform into the T2 phase, which not only improves the structural stability of the lithium cobalt oxide positive electrode material at a high charging voltage, but also unexpectedly increases the interlayer spacing of the lithium cobalt oxide material, thereby making the lithium cobalt oxide positive electrode material of the present invention have high rate performance. The total content of O2 phase and T2 phase in the composite phase and the ratio of their respective contents in the lithium cobalt oxide positive electrode material of the present invention are limited within the scope of the present invention, which can synergistically play the advantages of the two, so that the lithium cobalt oxide positive electrode material can have both excellent rate performance and high voltage cycle stability. The composite phase of the lithium cobalt oxide positive electrode material of the present invention also contains an O3 phase, the space group of the O3 structural phase is R-3m, and the molar ratio of the O3 phase is greater than 0 and less than or equal to 10 mol%. Specific values ​​can be 1 mol%, 2 mol%, 3 mol%, 4 mol%, 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 10 mol%, but are not limited to these. The molar ratio of the O3 phase is preferably greater than or equal to 5 mol%. The O3 phase itself is a thermodynamically stable phase structure. The inclusion of a small amount of O3 phase in the composite phase of the lithium cobalt oxide positive electrode material can improve the thermodynamic stability of the lithium cobalt oxide positive electrode material and achieve an improvement in the discharge platform of the positive electrode, thereby enabling the lithium cobalt oxide positive electrode material of the present invention to have high energy density, high thermodynamic stability, and a high discharge platform. The lithium cobalt oxide material of the present invention has a three-phase composite phase of O2 phase, T2 phase, and O3 phase, which can obtain a higher energy density than the O3 phase.On the one hand, the O3 phase of lithium cobalt oxide is a thermodynamically stable phase with a higher discharge voltage platform, which can synergistically improve the performance of the composite phase cathode material, thereby increasing the energy density of the cathode material. On the other hand, the composite phase contains a T2 phase structure. The introduction of the T2 phase can form a localized LiO4 structure between the layers of the lithium cobalt oxide cathode material, and as an interlayer "pillar", it can greatly improve the structural stability of the layered lithium cobalt oxide, especially the structural stability under high voltage. At the same time, by controlling the proportion of the O3 phase, the probability of irreversible phase transition of the O3 phase at high charging voltage is reduced, solving the problem of material structural instability and rapid capacity decay of the O3 phase at high charging voltage. In addition, the introduction of the O3 phase into the O2 phase and T2 phase as the main phase structure to form a multi-phase composite lithium cobalt oxide cathode material can enrich the ion diffusion channels in the lithium cobalt oxide bulk structure, which is beneficial to improve the diffusion kinetics of lithium ions in the cathode material structure, and is beneficial to further improve the cycle stability and energy density of the lithium cobalt oxide cathode material at high voltage.

[0069] The present invention, through the above-mentioned three-phase composite and the limitation of the content of the three phases O2, T2 and O3, can synergistically bring into play the maximum advantages of each phase structure: the O3 phase has high thermodynamic stability, the T2 phase can improve the intrinsic structural stability of the material due to the presence of localized LiO4 stabilized layered materials, the O2 phase has multiple ion transport paths, which can improve the material dynamics, and under high charging voltage, the transformation of the O2 phase to the T2 phase further enhances the structural stability of the lithium cobalt oxide material. By limiting the molar ratio of the three-phase structure and regulating the proportion of the composite phase in the structure, it is possible to effectively improve the rate performance of lithium ions in the positive electrode material, the structural stability at high voltage, the stability of the thermodynamic structure, the specific capacity and the discharge platform, thereby realizing a lithium cobalt oxide positive electrode material with excellent performance such as high energy density and high stability.

[0070] The lithium cobalt oxide positive electrode material with a composite phase of the present invention can be obtained by the following preparation method. The main steps include:

[0071] Step 110 , weighing, mixing, and first sintering a sodium source and a cobalt source doped or not doped with the M1 element according to a stoichiometric ratio to obtain a P2 phase sodium cobaltate material.

[0072] The molar ratio of sodium in the sodium source to cobalt in the cobalt source is greater than or equal to 0.8; the materials are weighed according to the stoichiometric ratio: the materials are weighed according to the molar ratio of Na, Co, and M1 of [0.8-0.1]:[0.97-1]:[0-0.03].

[0073] The first sintering has a heating rate of 3-20° C. / min, a sintering temperature of 700-1000° C., and a sintering time of 10-36 hours.

[0074] The cobalt source includes one or more of cobalt tetroxide, cobalt hydroxide, cobalt chloride, cobalt acetate, cobalt sulfate, and cobalt nitrate;

[0075] The sodium source includes one or more of sodium carbonate, sodium hydroxide, sodium chloride, sodium nitrate, and sodium sulfate;

[0076] M1 is one or more of Al, Zr, Ni, Mn, Y, Nb, La, Fe, Cu, Cr, Ti, W, Mg, Mo or Yb.

[0077] The cobalt source doped with the M1 element can be purchased commercially or prepared by methods disclosed in the prior art, such as the method of doping Co3O4 with metal atoms that has been publicly reported in the industry.

[0078] Step 120: Mix the P2 phase sodium cobalt oxide material with a lithium source in a molar ratio of Na to Li of 1:1.5-1:10, perform a second sintering in an air atmosphere or an oxygen atmosphere to perform a molten salt ion exchange reaction, and wash the second sintered product with water to obtain a lithium cobalt oxide positive electrode material having a composite phase.

[0079] The molar ratio of Na to Li is 1:1.5-1:10, which can be written as n(Na):n(Li)=1:1.5-1:10.

[0080] The second sintering temperature is 250°C to 300°C at a heating rate of 3-20°C / min, and the sintering time is 12-36 hours. Preferably, the second sintering temperature is 255°C to 265°C at a heating rate of 3-15°C / min, and the sintering time is 12-14 hours.

[0081] The lithium source includes one or more of lithium hydroxide, lithium nitrate, lithium chloride, lithium bromide, lithium sulfate, and lithium carbonate.

[0082] In this step, the lithium source is added in excess. Through molten salt ion exchange during the reaction, lithium ions are exchanged for sodium ions. Some lithium ions may also occupy certain vacancies. The exchanged sodium ions precipitate on the material surface in the form of sodium salts and are removed by water washing, thereby obtaining a lithium cobalt oxide positive electrode material with a composite phase.

[0083] By adjusting the sodium content in the precursor, the P2 phase sodium cobaltate, and using a molten salt ion exchange method, the present invention precisely and directionally regulates the bulk structure of lithium cobaltate. This effectively controls the lithium content in the lithium cobaltate, allowing the T2 phase to appear and remain within a specific range. This results in a composite lithium cobaltate structure primarily composed of the O2 and T2 phases, with the O3 phase also present. Because the ion exchange process may be incomplete, a small amount of Na ions may remain in the bulk lithium cobaltate.

[0084] The lithium cobalt oxide positive electrode material proposed in the present invention has high energy density, structural stability and excellent cycle performance. It can be applied to lithium batteries such as liquid lithium ion batteries, liquid metal lithium batteries, hybrid solid-liquid lithium ion batteries, hybrid solid-liquid metal lithium batteries, solid-state lithium ion batteries or solid-state metal lithium batteries. It can also be applied to lithium battery packs or lithium battery modules, and can be widely used in consumer electronics, electric vehicles, large-scale energy storage and other fields. It also has good application prospects in large-scale energy storage systems.

[0085] To make the objectives, technical solutions, and advantages of the present invention more apparent, the present invention will be further described in detail below with reference to the accompanying drawings. It is apparent that the embodiments described are only some, not all, of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0086] Example 1

[0087] This embodiment provides a lithium cobalt oxide positive electrode material with a composite phase and a preparation process thereof.

[0088] The preparation process includes:

[0089] Step (1), Na2CO3 and Al element-doped Co3O4 are mixed in a molar ratio of n(Na):n(Co):n(Al)=0.8:1:0.02 to obtain a precursor raw material mixed powder sample; the precursor raw material mixed powder sample is pressed into a disc with a diameter of 12 cm using a tablet press at 16 MPa, and then the disc is heated to 900°C at a heating rate of 5°C / min, and sintered at a high temperature for 12 hours in an oxygen atmosphere. After the reaction is completed and cooled to room temperature, an Al element-doped NaCoO2 precursor containing a P2 phase structure is obtained;

[0090] Step (2) lithium nitrate and the Al element-doped NaCoO2 precursor prepared in step (1) are fully mixed in a molar ratio of n(Li):n(Na)=10:1, and the mixture is heated to 260°C at a heating rate of 5°C / min, and a molten salt ion exchange reaction is carried out in an air atmosphere for 4 hours. After the reaction is completed, it is cooled to room temperature, the product is taken out, washed with water, and dried to obtain a lithium cobalt oxide positive electrode material with a composite phase.

[0091] After inductively coupled plasma (ICP) testing, the obtained lithium cobalt oxide cathode material with a composite phase is composed of Na 0.001 Li 0.81 A1 0.02 Co 0.98 02 positive electrode material.

[0092] Example 2

[0093] This embodiment provides a lithium cobalt oxide positive electrode material with a composite phase and a preparation process thereof.

[0094] In step (1), the raw materials for preparing the precursor raw material mixed powder sample have a molar ratio of n(Na):n(Co):n(Al)=0.85:1:0.02, and the remaining steps are the same as in Example 1.

[0095] After inductively coupled plasma (ICP) testing, the obtained lithium cobalt oxide cathode material with a composite phase is composed of Na 0.001 Li 0.85 A l 0.02 Co 0.98 O2 positive electrode material.

[0096] Example 3

[0097] This embodiment provides a lithium cobalt oxide positive electrode material with a composite phase and a preparation process thereof.

[0098] In step (1), the raw materials for preparing the precursor raw material mixed powder sample have a molar ratio of n(Na):n(Co):n(Al)=0.90:1:0.02, and the remaining steps are the same as in Example 1.

[0099] After inductively coupled plasma (ICP) testing, the obtained lithium cobalt oxide cathode material with a composite phase is composed of Na 0.001 Li 0.87 A l 0.02 Co 0.98 O2 positive electrode material.

[0100] Example 4

[0101] This embodiment provides a lithium cobalt oxide positive electrode material with a composite phase and a preparation process thereof.

[0102] In step (1), the raw materials for preparing the precursor raw material mixed powder sample have a molar ratio of n(Na):n(Co):n(Al)=1:1:0.02, and the remaining steps are the same as in Example 1.

[0103] After inductively coupled plasma (ICP) testing, the obtained lithium cobalt oxide cathode material with a composite phase is composed of Na 0.001 Li 0.91 A l 0.02 Co 0.98 O2 positive electrode material.

[0104] Comparative Example 1

[0105] This comparative example provides a lithium cobalt oxide positive electrode material with a composite phase and a preparation process thereof.

[0106] In step (1), the raw materials for preparing the precursor raw material mixed powder sample have a molar ratio of n(Na):n(Co):n(Al)=0.6:1:0.02, and the remaining steps are the same as in Example 1.

[0107] After inductively coupled plasma (ICP) testing, the obtained lithium cobalt oxide cathode material with a composite phase is composed of Na 0.0009 Li 0.65 A l 0.02 Co 0.98 O2 positive electrode material.

[0108] Comparative Example 2

[0109] This comparative example provides a lithium cobalt oxide positive electrode material with a composite phase and a preparation process thereof.

[0110] In step (1), the raw materials for preparing the precursor raw material mixed powder sample have a molar ratio of n(Na):n(Co):n(Al)=0.7:1:0.02, and the remaining steps are the same as in Example 1.

[0111] After inductively coupled plasma (ICP) testing, the obtained lithium cobalt oxide cathode material with a composite phase is composed of Na 0.0009 Li 0.75 A l 0.02 Co 0.98 O2 positive electrode material.

[0112] Comparative Example 3

[0113] This comparative example provides a pure O2 phase lithium cobalt oxide positive electrode material and its preparation process.

[0114] (1) Na2CO3 and Al-doped Co3O4 were mixed in a molar ratio of n(Na):n(Co):n(M1)=60:90:2 to obtain a precursor raw material mixed powder sample; the precursor raw material mixed powder sample was pressed into a disc with a diameter of 12 cm using a tablet press at 16 MPa, and then the disc was heated to 900°C at a heating rate of 5°C / min and sintered at a high temperature for 12 hours in an oxygen atmosphere. After the reaction was completed and the temperature was cooled to room temperature, Al-doped Na-doped P2 phase was obtained. 0.7 CoO2 precursor;

[0115] Step (2) the Na prepared in step (1) 0.7The CoO2 precursor powder is placed in an aqueous solution containing lithium salt at a molar ratio of n(Li):n(Na)=10:1 and fully mixed at 100°C for 24 hours to carry out hydrothermal ion exchange. After the reaction is completed, the temperature is cooled to room temperature to obtain a pure O2 phase LiCoO2 positive electrode material.

[0116] Comparative Example 4

[0117] This comparative example provides a pure O3 phase lithium cobalt oxide positive electrode material and its preparation process.

[0118] A pure O2 phase LiCoO2 positive electrode material was prepared by the same preparation method as in Comparative Example 3, and used as a precursor, and calcined in a muffle furnace at 600°C for 12 hours to obtain a pure O3 phase LiCoO2 positive electrode material.

[0119] The performance parameters of the positive electrode materials prepared in the above embodiments and comparative examples are characterized through a series of tests.

[0120] (1) Structural characterization:

[0121] The lithium cobalt oxide positive electrode materials prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to XRD diffraction to calculate the phase composition thereof. Figure 1-2 They are the XRD test patterns of Examples 2-3 respectively. The XRD test patterns of Examples 1 and 4 are similar thereto, with only slight differences in characteristic peak intensities. Figure 3-4 They are the XRD test patterns of comparative examples 1-2, Figure 5 The XRD test diagrams of comparative examples 3 and 4 are shown in Table 1. The phase compositions of the positive electrode materials in the various embodiments and comparative examples obtained through XRD testing are shown in Table 1.

[0122] Chemical formula Phase composition Molar ratio of each phase Example 1 <![CDATA[Na 0.001 If 0.81 A1 0.02 What 0.98 02]]> O2 phase, T2 phase, O3 phase O2:T2:O3=72.28:25.9:1.82 Example 2 <h2 style=";text-align:left;direction:ltr"><![CDATA[Na <h2 style=";text-align:left;direction:ltr"> 0.001 <h2 style=";text-align:left;direction:ltr"> Li<h2 style=";text-align:left;direction:ltr"> 0.85 <h2 style=";text-align:left;direction:ltr"> Al<h2 style=";text-align:left;direction:ltr"> 0.02 <h2 style=";text-align:left;direction:ltr"> Co<h2 style=";text-align:left;direction:ltr"> 0.98 <h2 style=";text-align:left;direction:ltr"> O2]]><h2 style=";text-align:left;direction:ltr"> O2 phase, T2 phase, O3 phase O2:T2:O3=46.64:47.64:5.72 Example 3 <h2 style=";text-align:left;direction:ltr"><![CDATA[Na <h2 style=";text-align:left;direction:ltr"> 0.001 <h2 style=";text-align:left;direction:ltr"> Li<h2 style=";text-align:left;direction:ltr"> 0.87 <h2 style=";text-align:left;direction:ltr"> Al<h2 style=";text-align:left;direction:ltr"> 0.02 <h2 style=";text-align:left;direction:ltr"> Co<h2 style=";text-align:left;direction:ltr"> 0.98 <h2 style=";text-align:left;direction:ltr"> O2]]><h2 style=";text-align:left;direction:ltr"> O2 phase, T2 phase, O3 phase O2:T2:O3=61.58:31.71:6.71 Example 4 <h2 style=";text-align:left;direction:ltr"><![CDATA[Na <h2 style=";text-align:left;direction:ltr"> 0.001 <h2 style=";text-align:left;direction:ltr"> Li<h2 style=";text-align:left;direction:ltr"> 0.91 <h2 style=";text-align:left;direction:ltr"> Al<h2 style=";text-align:left;direction:ltr"> 0.02 <h2 style=";text-align:left;direction:ltr"> Co<h2 style=";text-align:left;direction:ltr"> 0.98 <h2 style=";text-align:left;direction:ltr"> O2]]><h2 style=";text-align:left;direction:ltr"> O2 phase, T2 phase, O3 phase O2:T2:O3=42.94:47.23:9.803 Comparative Example 1 <h2 style=";text-align:left;direction:ltr"><![CDATA[Na <h2 style=";text-align:left;direction:ltr"> 0.0009 <h2 style=";text-align:left;direction:ltr"> Li<h2 style=";text-align:left;direction:ltr"> 0.65 <h2 style=";text-align:left;direction:ltr"> Al<h2 style=";text-align:left;direction:ltr"> 0.02 <h2 style=";text-align:left;direction:ltr"> Co<h2 style=";text-align:left;direction:ltr"> 0.98 <h2 style=";text-align:left;direction:ltr"> O2]]><h2 style=";text-align:left;direction:ltr"> O2 phase, T2 phase O2:T2=1.56:98.44 Comparative Example 2 <h2 style=";text-align:left;direction:ltr"><![CDATA[Na <h2 style=";text-align:left;direction:ltr"> 0.0009 <h2 style=";text-align:left;direction:ltr"> Li<h2 style=";text-align:left;direction:ltr"> 0.75 <h2 style=";text-align:left;direction:ltr"> Al<h2 style=";text-align:left;direction:ltr"> 0.02 <h2 style=";text-align:left;direction:ltr"> Co<h2 style=";text-align:left;direction:ltr"> 0.98 <h2 style=";text-align:left;direction:ltr"> O2]]><h2 style=";text-align:left;direction:ltr"> O2 phase, T2 phase O2:T2=19.35:80.65 Comparative Example 3 <![CDATA[LiCoO2]]> Pure O2 phase 100％ Comparative Example 4 <![CDATA[LiCoO2]]> Pure O3 phase 100％

[0123] Table 1

[0124] from Figure 1 and Figure 2It can be seen that the XRD patterns of the lithium cobalt oxide cathode materials with composite phases obtained in Examples 2-3 simultaneously have characteristic peaks of O2, T2, and O3 phase structures. The structural characteristics include crystal plane characteristics, that is, the prepared modified cathode material simultaneously has the crystal plane characteristics of lithium cobalt oxide with O2 phase structure, the crystal plane characteristics of lithium cobalt oxide with T2 phase structure, and the crystal plane characteristics of lithium cobalt oxide with O3 phase structure. The lithium cobalt oxide cathode material has two (002) characteristic diffraction peaks, one (003) characteristic peak, (112) characteristic peak and (114) characteristic peak, as well as one (102) characteristic peak, (105) and (104) characteristic peaks. The analysis shows that there are two (002) characteristic diffraction peaks in the O2 / T2 / O3 composite phase of lithium cobalt oxide. The first (002) characteristic diffraction peak belongs to the T2 phase, with an angle of 17.00° to 18.08°; the second (002) characteristic diffraction peak belongs to the O2 phase, with an angle of 18.08° to 18.32°; the angle of the (003) characteristic diffraction peak of the O2 / T2 / O3 composite phase of lithium cobalt oxide is 18.51° to 19.72°; the (112) characteristic diffraction peak of the O2 / T2 / O3 composite phase of lithium cobalt oxide belongs to the T2 phase, with an angle of 40.7° to 42.2°; the (114) characteristic diffraction peak of the O2 / T2 / O3 composite phase of lithium cobalt oxide belongs to the T2 phase, with an angle of The angles of the two (002) characteristic diffraction peaks in the O2 / T2 / O3 composite phase lithium cobalt oxide (102) are smaller than the angles of the characteristic diffraction peaks of the O2 single phase lithium cobalt oxide (002) and the angles of the characteristic diffraction peaks of the O3 single phase lithium cobalt oxide (003).

[0125] exist Figure 1 and Figure 2In the XRD spectrum, the angles of the characteristic peaks (002), (003), (102), and (105) are all smaller than the angle of the characteristic diffraction peak (002) of the O2 single-phase structure lithium cobalt oxide, the angle of the characteristic diffraction peak (003) of the O3 single-phase structure lithium cobalt oxide, and the characteristic diffraction peaks (112) and (114) of the T2 phase lithium cobalt oxide. In the XRD spectrum of lithium cobalt oxide of the O2 / T2 / O3 composite phase, the peak intensity of the (002) characteristic peak defined in the range of 17.00°≤2θ≤18.08° is defined as I1, the peak intensity of the (002) characteristic peak defined in the range of 18.08°≤2θ≤18.32° is defined as I2, and the peak intensity of the (003) characteristic peak defined in the range of 18.51°≤2θ≤19.72° is defined as I3, satisfying 0.5≤I2 / I1≤1.5, 0.1≤I3 / I2≤0.8, wherein, in Example 1, I2 / I1 is 0.95, and I3 / I2 is 0.34. According to an embodiment of the present invention, two (002), one (003), one (102), one (105) and one (104) as well as (114) and (112) characteristic peaks are the most important characteristic peaks of the lithium cobalt oxide positive electrode material containing the O2 / T2 / O3 composite phase. The applicant has found that by regulating the peak intensity ratio and angle of the (002) characteristic peak and the (003) characteristic peak, so that the angles of the (002) and (003) characteristic peaks are both smaller than the angle of the characteristic diffraction peak of the O2 phase lithium cobalt oxide (002) and the angle of the characteristic diffraction peak of the O3 single-phase structure lithium cobalt oxide (003), and the ratio of the (002) and (003) characteristic diffraction peak intensities is within the range of 0.8≤I 2 / I 1≤1.1 and 0.2≤I 3 / I 2≤0.5, a positive electrode material with high capacity, high rate and high cycle life can be obtained.

[0126] from Figure 3 It can be seen that the XRD pattern of the lithium cobalt oxide positive electrode material obtained in Comparative Example 1 has a (002) characteristic peak corresponding to an angle of 17.00° to 18.08°, a (112) characteristic peak corresponding to an angle of 40.7° to 42.2°, and a (114) characteristic peak corresponding to an angle of 52.1° to 53.9°. The above three characteristic peaks belong to the T2 phase. In addition, there is a (002) characteristic peak corresponding to an angle of 18.08° to 18.32°, a (102) characteristic peak at an angle of 36.2° to 37.7°, and a (105) characteristic peak at an angle of 56.7° to 57.9°. The above characteristic peaks correspond to the O2 phase. Therefore, the composite phase of the positive electrode material of Comparative Example 1 is an O2 phase and a T2 phase structure. In addition, after structural analysis and fitting by Full prof software, it can be seen that the molar ratio of O2:T2 is 1.56:98.44. From Figure 4It can be seen that the XRD pattern of the lithium cobalt oxide positive electrode material obtained in Comparative Example 2 has a (002) characteristic peak corresponding to an angle of 17.00° to 18.08°, a (112) characteristic peak corresponding to an angle of 40.7° to 42.2°, and a (114) characteristic peak corresponding to an angle of 52.1° to 53.9°. The above three characteristic peaks belong to the T2 phase. In addition, there is a (002) characteristic peak corresponding to an angle of 18.08° to 18.32°, a (102) characteristic peak at an angle of 36.2° to 37.7°, and a (105) characteristic peak at an angle of 56.7° to 57.9°. The above characteristic peaks correspond to the O2 phase. Therefore, the composite phase of the positive electrode material of Comparative Example 2 is an O2 phase and a T2 phase structure. In addition, after structural analysis and fitting by Full prof software, it can be seen that the molar ratio of O2:T2 is 19.35:80.65.

[0127] It can be seen from Table 1 that when the molar ratio of sodium to cobalt in the precursor is less than 0.8, there is no O3 phase in the composite phase, and when the molar ratio of sodium to cobalt is greater than or equal to 0.8, there will be a certain proportion of O3 phase. It can be seen from Comparative Examples 1-2 that as the sodium content in the precursor increases, the proportion of T2 phase structure in the composite phase structure decreases, while the proportion of O2 phase increases. When the ratio of sodium to cobalt increases from 0.6 to 0.7, the molar proportion of T2 phase structure decreases by about 18%. This is because when the sodium atom content in the precursor is high, lithium ions can replace interlayer sodium sites during the ion exchange process to form O2 phase. As the Na content in the precursor increases, it can be replaced by more Li ions during the ion exchange process, which helps Li occupy the octahedral site of the alkali metal layer to form more O2 phase. It can be seen from Examples 2-3 that as the sodium content in the precursor increases, the proportion of O2 and O3 phase structures in the composite phase structure increases, while the proportion of T2 phase decreases. This is because a small amount of metastable phase may exist in the sodium-rich precursor, and the phase transformation to O3 phase may be promoted during the ion exchange process.

[0128] like Figure 5 As shown, by heating, the O2 phase lithium cobalt oxide (P63mc) in Comparative Example 3 is transformed into the O3 phase lithium cobalt oxide of the R-3m space group shown in Comparative Example 4, and it can be seen that O3 has a (003) characteristic peak and a (104) characteristic peak with an angle of 45.1° to 45.9°, as well as characteristic diffraction peaks after 50 degrees, such as a (105) characteristic peak with an angle of 49.0° to 50.3°, a (110) characteristic peak with an angle of 66.1° to 67.3°, and a (113) characteristic peak with an angle of 69.1° to 70.6°.

[0129] (2) Morphological characterization:

[0130] The morphology of the materials obtained in the examples and comparative examples was characterized by SEM testing:

[0131] Figures 6 to 13 The SEM images of the positive electrode materials prepared in Examples 1-4 and Comparative Examples 1-4 respectively. It can be seen that the positive electrode materials in Examples 1-4 and Comparative Examples 1-4 all present a flake-like morphology with a particle size of 5-30 μm. Figure 12 and Figure 13 By comparison, it can be seen that after calcination, the O2 phase material is transformed into the O3 phase material, and its morphological characteristics do not change, only the structural phase change occurs.

[0132] (3) Electrochemical performance test:

[0133] Electrochemical tests were performed on each embodiment and comparative example. Coin-type half-cells for testing were made using the positive electrode materials prepared in each embodiment and comparative example. The specific production steps are as follows.

[0134] The positive electrode materials of each embodiment and comparative example were used to prepare positive electrode sheets for lithium-ion batteries:

[0135] The positive electrode material was mixed with the conductive additive Super P and the binder polyvinylidene fluoride in a mass ratio of 8:1:1. An appropriate amount of organic solvent N-methylpyrrolidone was added to form a uniformly dispersed slurry. The slurry was then evenly coated on the aluminum foil current collector using a scraper and placed in an oven for drying. The dried electrode sheet was punched to obtain an active material loading of approximately 2.5 mg / cm 2 positive electrode sheet.

[0136] Assemble the lithium-ion button cell battery:

[0137] The prepared positive electrode sheet and the metal lithium negative electrode sheet were assembled into a lithium-ion button battery in a glove box filled with argon gas and with a water and oxygen content of less than 0.1 ppm.

[0138] The assembled button cells were subjected to electrochemical charge and discharge tests at a test voltage range of 3-4.6 V. The cycle performance test was performed by first activating the cells at a current density of 0.1 C (1 C = 270 mA / g) for two weeks and then performing a charge and discharge cycle test at 0.5 C. The test results are shown in Table 2. The charge and discharge cycle curves of Examples 1-4 and Comparative Examples 1-4 are shown in Table 2. Figure 14-21 shown.

[0139]

[0140]

[0141] Table 2

[0142] The first discharge specific capacity at 0.1C and 0.5C, the energy density at 0.5C, and the energy density after 100 cycles at 0.5C of the batteries assembled with the positive electrode materials of Examples 1-4 and the positive electrode materials of Comparative Examples 1-4 are recorded in Table 2, respectively.

[0143] From the perspective of the first discharge specific capacity at 0.1C and 0.5C and the energy density at 0.5C, Examples 1-4 are all superior to Comparative Examples 1-4. Since Examples 1-4 are composite phases of O2, T2, and O3 phases, they can synergistically maximize the advantages of each phase structure. The O3 phase has high thermodynamic stability. The T2 phase can improve the intrinsic structural stability of the material due to the presence of localized LiO4 stabilizing layered materials. The O2 phase has multiple ion transport paths, which can improve the material dynamics. At high charging voltages, the O2 phase transforms into the T2 phase to improve the material structural stability. The discharge platform of the positive electrode material can be improved through the synergistic effect of the three phases, thereby improving the energy density of the composite material.

[0144] Based on the performance test results, Examples 2-4 outperform Example 1 due to the increased ratio of the T2 phase to the O3 phase in the bulk structure. The increased O3 phase ratio ensures higher specific capacity and energy density for the battery, while the increased T2 phase ratio improves structural stability at high voltages.

[0145] Among them, the positive electrode materials of Examples 3 and 4 have the highest specific capacity at 0.5C and possess very high energy density. The O3 ratio in Example 3 reaches 6.71%, while that in Example 4 reaches 9.803%. This shows that the introduction of a certain amount of O3 phase can improve the energy density of the positive electrode material. The positive electrode material of Example 2 also has a three-phase composite structure, with O2:T2:O3 = 46.64:47.64:5.72. The O3 phase ratio is reduced by 0.99% compared to Example 3, resulting in an energy density of 894Wh / kg, a slight decrease compared to Example 3 (898Wh / kg). However, after 100 cycles at 0.5C, the energy density of the positive electrode material of Example 2 is 24Wh / kg higher than that of Example 3, demonstrating better performance at high voltage. The difference between Examples 2 and 3 lies in the relatively higher presence of O3 structures in the bulk structure of Example 3, which can cause greater structural stress on the overall structure of the material at high voltage, resulting in slightly less stable material during cycling. Therefore, an appropriate content of O3 phase structure can improve the overall capacity and energy density of the positive electrode material. Even when cycling at high voltage, the structural stress in some local structures caused by the phase change of the appropriate amount of O3 phase structure in the positive electrode material at high voltage will not cause irreversible effects on the overall structural stability of the positive electrode material.

[0146] The composite phase of the positive electrode material of Comparative Example 1-2 is an O2 phase and a T2 phase. The O2 phase content in Comparative Example 2 is higher than that in Comparative Example 1, while the T2 phase content is lower than that in Comparative Example 1. From the perspective of the initial discharge specific capacity at 0.1C and 0.5C, the energy density at 0.5C, and the energy density after 100 cycles at 0.5C, Comparative Example 2 is higher than that of Comparative Example 1. This is because the sodium content in the precursor used in Comparative Example 2 is higher than that in the precursor in Comparative Example 1, resulting in the positive electrode material of Comparative Example 2 having a higher lithium content after ion exchange. Therefore, during the initial discharge process, Comparative Example 2 has a higher discharge capacity than Comparative Example 1, but both cannot reach the performance of Examples 1-4.

[0147] From the perspective of the initial discharge specific capacity at 0.1C, Comparative Examples 1-2 are lower than Comparative Examples 3-4. However, from the perspective of the initial discharge specific capacity at 0.5C and the energy density after 100 cycles at 0.5C, Comparative Examples 1-2 are higher than Comparative Examples 3-4. In terms of the energy density at 0.5C, Comparative Examples 1-2 are higher than Comparative Example 3 and similar to Comparative Example 4. Since Comparative Examples 1-2 are a composite phase of O2 and T2 phases, Comparative Example 3 is pure O2 phase Li i CoO2, and Comparative Example 4 is pure O3 phase Li CoO2. Since Comparative Examples 1-2 are in a lithium-deficient state in their initial structure, the initial discharge capacity of Comparative Examples 1-2 at 0.1C is lower than that of the fully lithium-rich O2 phase Li CoO2. After activation at 0.1C, Comparative Examples 1-2 exhibited higher energy density and capacity retention than pure O3-phase Li-CoO2. This is due to the presence of the T2 phase with a larger interlayer spacing in the initial structure of Comparative Examples 1-2, which can store more lithium ions. This, combined with the structural stability of the O2 phase, enhances the structural reversibility of the composite structure during charge and discharge. Notably, after complete lithium replenishment through initial activation, the lithium-deficient state in Comparative Examples 1-2 disappears, and its electrochemical behavior is consistent with that of the pure O2-phase Li-CoO2 in Comparative Example 3.

[0148] Figure 22The energy density comparison chart of lithium-ion batteries assembled from the positive electrode materials of Examples 2-3 and Comparative Examples 1-4 after 100 cycles at a current density of 0.5C is shown. By converting the corresponding energy density from the discharge voltage platform and the discharge specific capacity after 100 cycles, it can be seen that after 100 cycles, Examples 2-3 have higher energy density and better performance than Comparative Examples 1-4. In Examples 2-3, the specific capacity of the material is improved as the O3 phase structure in the composite phase structure increases, so the examples have higher energy density after 100 cycles at a current density of 0.5C. The embodiments of the present invention have better cycle performance. This is because the O2 and T2 phases in the composite phase transform into each other as the interlayer Li ion concentration changes during the charge and discharge process. Due to the presence of LiO4 localized configuration in the T2 phase, LiO4 can serve as an interlayer pillar to stabilize the laminate structure. The presence of two lithium ion diffusion channels in the O2 phase structure can improve the material dynamics. It is worth noting that the cycle stability of the composite phase structure positive electrode material is higher than that of the pure O2 and O3 phase positive electrode materials. However, the thermodynamic metastability of the O2 and T2 phases determines that their electrode reaction potential is lower than that of the structurally thermodynamically stable O3 phase. Therefore, by comparing the examples and comparative examples, introducing an appropriate amount of O3 phase structure into the lithium cobalt oxide positive electrode material composed of the O2 and T2 phases can effectively improve the energy density of the positive electrode material.

[0149] Tables 3 and 4 show the rate performance tests of constant current and constant voltage charge and constant current discharge of Examples 1-4 and Comparative Examples 1-4 at 25°C, in the range of 3-4.6V, at currents of 0.1C, 0.5C, 1C, 2C, and 5C, respectively, for 5 cycles. Figure 23 This is a rate performance diagram of lithium-ion batteries assembled with the positive electrode materials of Examples 1-4 and Comparative Examples 1-4 at current densities of 0.1C, 0.5C, 1C, 2C, 3C, and 5C.

[0150] The test results of Examples 1-4 are shown in Table 3.

[0151]

[0152] Table 3

[0153] The test results of Comparative Examples 1-4 are shown in Table 4.

[0154]

[0155]

[0156] Table 4

[0157] By comparison, it can be seen that when the current density is increased, the difference in discharge specific capacity between the embodiment and the comparative example gradually becomes apparent. In particular, compared with the pure O2 phase and the pure O3 phase, it has better rate performance. Especially at a current density of 10C, Examples 1-4 still maintain good performance, with specific capacities all exceeding 160mAh / g, but the capacity retention rates of Comparative Examples 1-4 all drop below 80%, especially the positive electrode materials of Comparative Examples 3-4, with specific capacities below 100mAh / g, almost completely attenuated, and the specific capacity of Comparative Example 1-2 is also relatively low.

[0158] Because there is a local structural environment of tetrahedral interstitial sites formed by the coplanarity of LiO6 octahedrons and CoO6 octahedrons in the T2 phase of the composite phase structure, Li ions can quickly diffuse between the layers through the tetrahedral interstitial sites, ensuring a high ion diffusion rate of the positive electrode material at high current density. The special oxygen stacking mode of the O2 phase improves the mechanical stability of the material. Under high current density, the presence of a moderate O3 phase can improve the overall discharge platform and energy density of the positive electrode material, while excessive O3 phase content, such as pure O3 phase, may cause structural failure under high voltage and high rate conditions, such as irreversible structural phase change and lattice oxygen escape, which will eventually lead to a decrease in the material capacity retention rate. Therefore, the proportion of the O3 phase needs to be reasonably regulated. Under 10C high current density test conditions, the discharge specific capacity and capacity retention rate of the positive electrode materials of Examples 1-4 are higher than those of the positive electrode materials of Comparative Examples 1-4. It can be seen from this that the positive electrode material with a composite phase structure of the present invention has excellent rate performance.

[0159] From the above electrochemical test results, it can be seen that the lithium cobalt oxide positive electrode material containing a composite structure of O2, T2 and O3 phases prepared by the molten salt ion exchange method in this application is not only simple to prepare and easy to scale up, but also has obvious advantages in electrochemical performance compared with pure phase lithium cobalt oxide and lithium cobalt oxide with only a composite structure of O2 and T2 phases.

[0160] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A lithium cobalt oxide positive electrode material having a composite phase, characterized in that: The chemical formula of the lithium cobalt oxide positive electrode material with a composite phase is A X Co 1-y M1 y O2; wherein 0.5≤x≤1, 0≤y≤0.03, A is Li or Li and Na, and M1 is one or more of Al, Zr, Ni, Mn, Y, Nb, La, Fe, Cu, Cr, Ti, W, Mg, Mo, or Yb; The composite phase of the lithium cobalt oxide positive electrode material includes an O2 phase, a T2 phase and an O3 phase; wherein the sum of the molar proportions of the O2 phase and the T2 phase in the composite phase is greater than or equal to 90%, and the molar proportion of the O3 phase is greater than 0 and less than or equal to 10%.

2. The lithium cobalt oxide positive electrode material having a composite phase according to claim 1, characterized in that The chemical formula of the lithium cobalt oxide positive electrode material with a composite phase is Li x1 Na X2 Co 1-y M1 y O2, 0.5<x1<0.996, 0.0001≤x2≤0.004, 0≤y≤0.03, M1 is at least one of Al, Mg, and Ti.

3. The lithium cobalt oxide positive electrode material having a composite phase according to claim 1, characterized in that: The molar ratio of the O2 phase in the composite phase is 1%-65%, the molar ratio of the T2 phase in the composite phase is 25%-98%, and the molar ratio of the O3 phase in the composite phase is 1%-10%.

4. The lithium cobalt oxide positive electrode material having a composite phase according to claim 3, characterized in that The O2 phase, T2 phase and O3 phase are uniformly or unevenly distributed in the bulk structure of the lithium cobalt oxide positive electrode material; The molar ratio of the O2 phase in the composite phase is 40%-65%, the molar ratio of the T2 phase in the composite phase is 30%-55%, and the molar ratio of the O3 phase in the composite phase is 5%-10%.

5. The lithium cobalt oxide positive electrode material having a composite phase according to claim 1, characterized in that: M1 is evenly distributed or gradiently distributed in the bulk phase of the lithium cobalt oxide positive electrode material having a composite phase.

6. The lithium cobalt oxide positive electrode material having a composite phase according to claim 1, characterized in that: LiCoO2 with T2 phase structure has characteristic peaks corresponding to (002) crystal plane in the range of 17.00°≤2θ≤18.08°, characteristic peaks corresponding to (112) crystal plane in the range of 40.7°≤2θ≤42.2°, and characteristic peaks corresponding to (114) crystal plane in the range of 52.1°≤2θ≤53.9°. Lithium cobalt oxide with O2 phase structure has a characteristic peak corresponding to the (002) crystal plane in the range of 18.08°<2θ≤18.32°, a characteristic peak corresponding to the (102) crystal plane in the range of 36.2°≤2θ≤37.7°, and a characteristic peak corresponding to the (105) crystal plane in the range of 56.7°≤2θ≤57.9°. LiCoO2 with O3 phase structure has characteristic peaks corresponding to (003) crystal plane in the range of 18.51°≤2θ≤19.72°, and has characteristic peaks corresponding to (104) crystal plane in the range of 45.1°≤2θ≤45.9°. Among them, the characteristic peak intensity of the T2 phase structure corresponding to the (002) crystal plane in the range of 17.00°≤2θ≤18.08° is I1, the characteristic peak intensity of the O2 phase structure corresponding to the (002) crystal plane in the range of 18.08°<2θ≤18.32° is I2, and the characteristic peak intensity of the O3 phase structure corresponding to the (003) crystal plane in the range of 18.51°≤2θ≤19.72° is I3. I1, I2, and I3 satisfy 0.5≤I2 / I1≤1.5 and 0.1≤I3 / I2≤0.

8.

7. The lithium cobalt oxide positive electrode material having a composite phase according to claim 6, characterized in that: The I1, I2, and I3 satisfy 0.8≤I2 / I1≤1.1, 0.2≤I3 / I2≤0.

5.

8. The lithium cobalt oxide positive electrode material having a composite phase according to claim 1, characterized in that: The lithium cobalt oxide positive electrode material with a composite phase is a spherical particle composed of primary particles and / or secondary particles; The primary particles are composed of one or more crystal grains, the primary particles are flaky in shape, and have an average particle size of 4 μm-50 μm; the secondary particles are composed of agglomerates of multiple primary particles.

9. The lithium cobalt oxide positive electrode material having a composite phase according to claim 8, characterized in that: The average particle size of the primary particles is 5 μm to 30 μm.

10. A method for preparing a lithium cobalt oxide positive electrode material having a composite phase according to any one of claims 1 to 9, characterized in that: The method comprises: A sodium source and a cobalt source doped or undoped with the M1 element are weighed, mixed, and subjected to a first sintering in a stoichiometric ratio to obtain a P2 phase sodium cobaltate material; wherein the molar ratio of sodium in the sodium source to cobalt in the cobalt source is greater than or equal to 0.8; the first sintering has a heating rate of 3-20°C / min, a sintering temperature of 700-1000°C, and a sintering time of 10-36 hours; The P2 phase sodium cobaltate material is mixed with a lithium source in a molar ratio of n(Na):n(Li)=1:1.5-1:10, and a second sintering is performed in an air atmosphere or an oxygen atmosphere to carry out a molten salt ion exchange reaction. The second sintered product is washed with water to obtain a lithium cobaltate positive electrode material with a composite phase; wherein the heating rate of the second sintering is 3-20°C / min, the sintering temperature is 250°C to 300°C, and the sintering time is 12-36 hours.

11. The preparation method according to claim 10, characterized in that: The cobalt source includes: one or more of cobalt tetroxide, cobalt hydroxide, cobalt chloride, cobalt acetate, cobalt sulfate, and cobalt nitrate; The sodium source includes: one or more of sodium carbonate, sodium hydroxide, sodium chloride, sodium nitrate, and sodium sulfate; M1 is one or more of Al, Zr, Ni, Mn, Y, Nb, La, Fe, Cu, Cr, Ti, W, Mg, Mo or Yb; The weighing according to the stoichiometric ratio is specifically: weighing according to the molar ratio of Na, Co, and M1 of [0.8-1]: [0.97-1]: [0-0.03]; The lithium source includes: one or more of lithium hydroxide, lithium nitrate, lithium chloride, lithium bromide, lithium sulfate, and lithium carbonate; The second sintering has a heating rate of 3-15° C. / min, a sintering temperature of 255° C.-265° C., and a sintering time of 12-14 hours.

12. A lithium battery, characterized in that: The lithium battery comprises the lithium cobalt oxide positive electrode material having a composite phase according to any one of claims 1 to 9, or comprises the lithium cobalt oxide positive electrode material having a composite phase prepared by the preparation method according to claim 10 or 11; The lithium battery includes any one of a liquid lithium ion battery, a liquid metal lithium battery, a hybrid solid-liquid lithium ion battery, a hybrid solid-liquid metal lithium battery, a solid lithium ion battery or a solid metal lithium battery.

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