Low-strain lithium cobalt oxide and preparation method and application thereof

Abstract

The embodiment of the invention relates to low-strain lithium cobalt oxide and a preparation method and application thereof.The preparation method comprises the steps that cobaltosic oxide, lithium carbonate and a sintering aid are mixed together, no doping reagent is added or no more than a certain mass of doping reagent is added, and blended powder is obtained; sintering the blended powder, firstly raising the temperature of the blended powder to 680-780 DEG C and preserving heat for 3-8 hours, then raising the temperature to 900-1100 DEG C and preserving heat for 8-24 hours, and finally cooling to 300 DEG C at the cooling rate of not more than 5 DEG C / min to obtain a sintered material; the sintering aid is alkali metal salt and / or alkaline earth metal salt which does not react with the lithium cobalt oxide and has the melting point lower than 900 DEG C and the boiling point higher than 1200 DEG C; in the sintering process, lithium carbonate and cobaltosic oxide react to generate L CoO < 2 >, and the L CoO < 2 > grows in a liquid phase formed by the sintering aid in a fusion manner; crushing, crushing, washing, drying and sieving the sintered material to obtain a lithium cobalt oxide matrix; the preparation method comprises the following steps: coating a lithium cobalt oxide matrix, and grinding and sieving an obtained material containing a coating layer to obtain the low-strain lithium cobalt oxide.

Description

Technical Field

[0001] This invention relates to the field of lithium battery cathode materials technology, and in particular to a low-strain lithium cobalt oxide, its preparation method, and its applications. Background Technology

[0002] In the field of lithium-ion battery technology, lithium cobalt oxide has the highest volumetric energy density among commercially available cathode materials, making it the best choice for consumer electronics. As the power consumption of consumer electronics increases, end-product manufacturers are placing higher demands on the energy density of lithium-ion batteries.

[0003] Currently, the most direct and effective way to improve the energy density of lithium cobalt oxide is to increase its charging cut-off voltage, which can lead to a dual improvement in voltage and specific capacity. However, it is generally believed in industry and academia that with the increase of charging voltage, lithium cobalt oxide undergoes an irreversible phase transition, namely, the transformation from the O3 phase to the H1-3 phase. This phase transition is not completely reversible. Furthermore, although increasing the charging cut-off voltage can extract more lithium ions, at high delithiation levels, the electrolyte is more prone to side reactions with the delithiated lithium cobalt oxide. This results in the formation of a Co3O4 passivation layer on the lithium cobalt oxide surface and a cathode-electrolyte-interphase (CEI) generated by electrolyte decomposition. Both the passivation layer and CEI are detrimental to lithium-ion transport and electron conduction, leading to increased polarization and rapid capacity decay of lithium cobalt oxide.

[0004] To improve the cycling performance of lithium cobalt oxide under high voltage, one of the current industry modification strategies is heavy Al doping. However, doping can lead to significant lattice distortion and stress-strain in lithium cobalt oxide. References *Chemistry of Materials*, 2018, 30(21):7545-7574 and *Journal of The Electrochemical Society*, 2012, 159(3):A253-A258 report that Mg and Al doping increases the lattice constant of the c-axis of lithium cobalt oxide, while also increasing its stress-strain. The study in *Chemistry of Materials*, 2018, 30(21):7545-7574 focuses on LiCoO2 and LiCoO2. 0.95 Al 0.05 O2, LiCo 0.9 Al 0.1 O2, LiCo 0.8 Al 0.2O2, with corresponding doping amounts of 0, 14000, 28000, and 56000 mg / kg; the literature Journal of The Electrochemical Society, 1999, 146(3):862-868 reported that heavily Al-doped lithium cobalt oxide exhibits severe strain and high dislocation density after cycling compared to undoped lithium cobalt oxide. Since dopants are generally electrochemically inert, excessively high doping amounts weaken the electronic and ionic conductivity of lithium cobalt oxide (Physical Review B, 2006, 74(9):094105), thereby worsening the rate performance of lithium cobalt oxide. In addition, at a given charging cutoff voltage, increasing the Al doping amount will result in a loss of some discharge specific capacity, causing Al-doped lithium cobalt oxide to require a higher charging cutoff voltage to release the same discharge specific capacity as undoped lithium cobalt oxide. A higher charging cutoff voltage means that lithium cobalt oxide will undergo more intense side reactions with the electrolyte, making it easier to form a passivation layer and CEI, which has a very adverse effect on the cycling performance of lithium cobalt oxide.

[0005] In summary, the heavy Al doping technology used in currently commercially available lithium cobalt oxide not only leads to problems such as increased stress and strain, intensified side reactions, and poorer cycle stability, but also sacrifices a portion of the discharge specific capacity of lithium cobalt oxide. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a low-strain lithium cobalt oxide, its preparation method, and its applications. By adding alkali metal salts and / or alkaline earth metal salts with melting points below 900°C and boiling points above 1200°C that do not react with lithium cobalt oxide as sintering aids during the preparation process, the LiCoO2 generated from the reaction of lithium carbonate and cobalt tetroxide undergoes fusion growth in the liquid phase formed by the sintering aids. Utilizing the advantages of liquid-phase reaction, the reaction kinetics are accelerated, reducing defects such as dislocations, grain boundaries, twin boundaries, and stacking faults. This reduces the strain of lithium cobalt oxide, enabling it to achieve a discharge specific capacity at a lower charging cutoff voltage compared to highly doped lithium cobalt oxide at a higher charging cutoff voltage, and also improving cycle performance.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing low-strain lithium cobalt oxide, comprising:

[0008] Cobalt tetroxide, lithium carbonate, and sintering aids are mixed together, and no dopant or no more than a certain mass of dopant is added to obtain a blended powder.

[0009] The blended powder is sintered by first heating it to 680℃-780℃ and holding it at that temperature for 3-8 hours, then heating it to 900℃-1100℃ and holding it at that temperature for 8-24 hours, and finally cooling it to 300℃ at a cooling rate not exceeding 5℃ / min to obtain the sintered material. During the sintering process, LiCoO2 generated from the reaction of lithium carbonate and cobalt tetroxide undergoes fusion growth in the liquid phase formed by the sintering aid. The sintering aid is an alkali metal salt and / or alkaline earth metal salt with a melting point below 900℃ and a boiling point above 1200℃ that does not react with lithium cobalt oxide, and has a solubility in water greater than 200 g / L at 25℃. The total molar number of alkali metal elements in the alkali metal salt and / or alkaline earth metal elements in the alkaline earth metal salt is greater than or equal to 3 and less than or equal to 15 per 100 molar parts of lithium cobalt oxide matrix.

[0010] The sintered material is crushed, pulverized, washed, dried, and sieved to obtain a lithium cobalt oxide matrix.

[0011] The lithium cobalt oxide matrix is ​​coated, and then the resulting material containing the coating layer is ground and sieved to obtain the low-strain lithium cobalt oxide.

[0012] Preferably, the coating process includes: mixing the lithium cobalt oxide matrix with a lithium source and an M1 source to obtain a mixed powder, wherein M1 is one or more of Si, Ti, Zr, Nb, Mo, and Ta; and / or mixing the lithium cobalt oxide matrix with a lithium source, an M2 source, and a phosphorus source to obtain a mixed powder, wherein M2 is one or more of Ti, Ge, Zr, Sn, and Hf;

[0013] The mixed powder is heated to 600℃-1000℃ and held at that temperature for 2h-12h, and then cooled to 300℃ at a cooling rate not exceeding 5℃ / min to obtain the material containing the coating layer.

[0014] More preferably, the coating layer of the material containing the coating layer is specifically a lithium oxide coating layer and / or a lithium phosphate coating layer;

[0015] The chemical formula of the lithium oxide coating layer is: Li a M1 b O3, where the average valence state of M1 is +m, satisfying a+mb=6; the Li a M1 b O3 includes: Li2SiO3, Li2TiO3, LiTi 1.25 One or more of O3, Li2ZrO3, LiNbO3, Li2MoO3, and LiTaO3;

[0016] The chemical formula of the lithium phosphate coating is: Li c M2d (PO4)3, where the average valence state of M2 is +n, satisfying c+nd=9; the Li c M2 d (PO4)3 includes: LiTi2(PO4)3, LiGe2(PO4)3, LiZr2(PO4)3, and Li3Zr. 1.5 One or more of (PO4)3, LiSn2(PO4)3, and LiHf2(PO4)3;

[0017] The total mass fraction of lithium oxide coating and / or lithium phosphate coating is less than or equal to 1 per 100 parts by mass of lithium cobalt oxide matrix.

[0018] More preferably, the lithium source includes one or more of the following: lithium-containing oxides, inorganic salts, organic salts, alkoxides, and phosphates;

[0019] The M1 source includes one or more of the following: oxides, inorganic salts, organic salts, alkoxides, and phosphates of M1;

[0020] The M2 source includes one or more of the following: oxides, inorganic salts, organic salts, alkoxides, and phosphates of M2;

[0021] The phosphorus source includes: inorganic phosphorus compounds and / or organic phosphorus compounds.

[0022] More preferably, the lithium source includes one or more of the following: Li2O, Li2CO3, LiOH, LiNO3, lithium acetate, lithium oxalate, lithium isopropoxide, Li3PO4, Li2HPO4, and LiH2PO4;

[0023] The M1 source includes one or more of the following: SiO2, H4SiO4, tetraethyl silicate, TiO2, TiOSO4, titanium isopropoxide, titanium n-butoxide, ZrO2, zirconium ethoxide, zirconium isopropoxide, zirconium n-butoxide, Nb2O5, niobium oxalate, niobium ethoxide, niobium n-butoxide, Nb3(PO4)5, MoO2, molybdenum isopropoxide, Ta2O5, tantalum ethoxide, and tantalum isopropoxide;

[0024] The M2 source includes one or more of the following: TiO2, TiOSO4, titanium isopropoxide, titanium n-butoxide, GeO2, germanium ethanol, germanium isopropoxide, ZrO2, zirconium ethanol, zirconium isopropoxide, zirconium n-butoxide, SnO2, tin ethanol, tin isopropoxide, tin tert-butoxide, HfO2, hafnium ethanol, and hafnium isopropoxide.

[0025] The phosphorus source includes one or more of the following: H3PO4, NH4H2PO4, (NH4)2HPO4, (NH4)3PO4, Li3PO4, Li2HPO4, LiH2PO4, tributyl phosphate, and dodecyl phosphate monoester.

[0026] Preferably, the doping reagent is a nano-oxide of a doping element, wherein the doping element includes one or more of Mg, Al, Ti, Mn, Ni, Y, Zr, Nb, Mo, La, Ce, and W; the Dv50 of the doping reagent is less than or equal to 100 nm; and the addition of a doping reagent not exceeding a certain mass specifically means that the total mass of the doping element is less than or equal to 0.3 parts per 100 parts per mass of lithium cobalt oxide matrix.

[0027] More preferably, the sintering aid includes one or more of LiCl, NaCl, KCl, Li2SO4, Na2SO4, Na2CO3, CaCl2, and SrCl2.

[0028] Preferably, in the blended powder, the amount of lithium carbonate is 1%-5% excess of lithium in the lithium carbonate relative to the molar amount of lithium in the lithium cobalt oxide matrix, preferably 3%.

[0029] Secondly, embodiments of the present invention provide a low-strain lithium cobalt oxide prepared by the preparation method described in the first aspect above, characterized in that the strain of the low-strain lithium cobalt oxide is 3.0 × 10⁻⁶. -4 the following;

[0030] In systems using lithium metal as both the counter and reference electrodes, low-strain lithium cobalt oxide prepared with no or no more than a certain mass of dopant can achieve a charging cutoff voltage of less than or equal to 4.54-4.57V (vsLi). + When the charge / discharge current density is 100 mA / g, the initial discharge specific capacity of the low-strain lithium cobalt oxide is less than or equal to 208-213 mAh / g, and the capacity retention rate is higher than 95% after 50 cycles.

[0031] Thirdly, embodiments of the present invention provide an application of the low-strain lithium cobalt oxide prepared by the preparation method described in the first aspect above, wherein the low-strain lithium cobalt oxide is used in lithium secondary batteries, cells, or battery packs.

[0032] The method for preparing low-strain lithium cobalt oxide provided in this invention involves adding alkali metal salts and / or alkaline earth metal salts with melting points below 900°C and boiling points above 1200°C, which do not react with lithium cobalt oxide, as sintering aids. This allows LiCoO2, generated from the reaction of lithium carbonate and cobalt tetroxide, to fuse and grow in the liquid phase formed by the sintering aids during sintering. Utilizing the advantages of liquid-phase reaction, the reaction kinetics are accelerated, reducing defects such as dislocations, grain boundaries, twin boundaries, and stacking faults, thereby lowering the strain of lithium cobalt oxide. Furthermore, by adding or adding doping agents in quantities not exceeding a certain mass, undoped or low-doped lithium cobalt oxide is achieved, further reducing strain. This also allows the discharge specific capacity to be achieved at a lower charging cutoff voltage compared to that of highly doped lithium cobalt oxide at a higher charging cutoff voltage, which is beneficial for improving cycle performance. Furthermore, this method also improves the surface coating material of lithium cobalt oxide to match the lithium cobalt oxide matrix, achieving a synergistic effect between the coating material and the lithium cobalt oxide matrix, significantly improving the electrochemical performance of low-strain lithium cobalt oxide. To address the problem that traditional Al2O3-coated aluminum elements easily diffuse into the lithium cobalt oxide matrix during sintering, increasing the stress and strain of lithium cobalt oxide and affecting its cycle performance, this invention effectively avoids this problem by using lithium-containing oxides of elements such as Si, Ti, Zr, Nb, Mo, and Ta, and lithium-containing phosphates of elements such as Ti, Ge, Zr, Sn, and Hf, which have properties significantly different from Co, as coating materials. These materials are less likely to diffuse into the lithium cobalt oxide lattice during sintering and, as lithium-ion conductors, can effectively improve the lithium-ion conductivity of the lithium cobalt oxide cathode material. The surface coating layer obtained by this method not only reduces side reactions between lithium cobalt oxide and the electrolyte under high voltage and slows down the formation of the Co3O4 passivation layer, but also prevents excessive CEI formation, significantly improving the cycle life and stability of the battery. Therefore, the low-strain lithium cobalt oxide material prepared by this invention can be used with a lower charging cutoff voltage, exhibits fewer surface side reactions, and has better cycle performance. Attached Figure Description

[0033] Figure 1 A flowchart illustrating the preparation method of low-strain lithium cobalt oxide provided by the present invention;

[0034] Figure 2 A schematic diagram illustrating the mechanism by which the sintering aid provided by this invention reduces defects in lithium cobalt oxide;

[0035] Figure 3 X-ray diffraction (XRD) Le Bail refinement images of Examples 1-11 and Comparative Examples 1-20 provided for this invention;

[0036] Figure 4 In-situ XRD grayscale images of Embodiment 1, Comparative Examples 1-2, and Comparative Example 20 provided by the present invention;

[0037] Figure 5 The graph shows the change of discharge specific capacity of coin half-cells with cycle number under similar initial discharge specific capacity in Embodiment 1, Comparative Examples 1-2, and Comparative Example 20 provided by the present invention.

[0038] Figure 6 The graphs showing the change of discharge specific capacity of coin half-cells with cycle number under similar initial discharge specific capacity in Examples 1-2 and Comparative Examples 1-2 provided by the present invention;

[0039] Figure 7 The graph shows the change in the discharge specific capacity of a coin cell with the number of cycles under different charging cutoff voltages in Embodiment 1 of the present invention.

[0040] Figure 8 The graphs showing the change of discharge specific capacity of coin half-cells with cycle number under similar initial discharge specific capacity provided by the present invention in Examples 3-4 and Comparative Examples 3-4;

[0041] Figure 9 The graph shows the change of discharge specific capacity of coin half-cells with cycle number under similar initial discharge specific capacity in Examples 1, 3, 4, and 20 of the present invention.

[0042] Figure 10 The graphs showing the change of discharge specific capacity of coin half-cells with cycle number under similar initial discharge specific capacity provided by the present invention (Example 1 and Comparative Examples 5-7);

[0043] Figure 11 The graphs showing the change of discharge specific capacity of coin half-cells with cycle number under similar initial discharge specific capacity provided by the present invention in Embodiment 3 and Comparative Examples 8-10;

[0044] Figure 12 The graphs showing the change of discharge specific capacity of coin half-cells with cycle number under similar initial discharge specific capacity provided by the present invention in Embodiment 5 and Comparative Examples 11-13;

[0045] Figure 13 The graphs showing the change of discharge specific capacity of coin half-cells with cycle number under similar initial discharge specific capacity in Examples 6-7 and Comparative Examples 14-15 provided for this invention;

[0046] Figure 14 The graphs showing the change of discharge specific capacity of coin half-cells with cycle number under similar initial discharge specific capacity in Examples 8-9 and Comparative Examples 16-17 provided for the present invention;

[0047] Figure 15 The graphs showing the change of discharge specific capacity of coin half-cells with cycle number under similar initial discharge specific capacity in Examples 10-11 and Comparative Examples 18-19 provided for this invention;

[0048] Figure 16 Comparison chart of the rate performance of Embodiment 1, Comparative Examples 1-2, and Comparative Example 20 provided by the present invention;

[0049] Figure 17 Comparison chart of cycle performance of pouch cells in Example 1 and Comparative Example 20 provided by the present invention;

[0050] Figure 18 XRD Le Bail refinement images of Example 1 and Comparative Example 20 after cycling, provided for the present invention;

[0051] Figure 19 Cross-sectional scanning electron microscope (SEM) images of Example 1 and Comparative Example 20 after cycling, provided for the present invention. Detailed Implementation

[0052] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for a better understanding of the present invention and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0053] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0054] To facilitate a better understanding of the present invention, some technical terms will be explained below.

[0055] The technical term "blended powder" refers to a mixture of cobalt tetroxide, lithium carbonate, sintering aids, and / or doping agents.

[0056] The technical term "lithium cobalt oxide matrix" refers to uncoated and unmodified lithium cobalt oxide.

[0057] In this invention, the technical term "low doping" refers to a total doping element content greater than 0 and less than or equal to 3000 mg / kg; the technical term "high doping" refers to a total doping element content greater than 3000 mg / kg. A total doping element content of 3000 mg / kg means that, relative to 100 parts by mass of lithium cobalt oxide matrix, the total mass parts of doping elements are 0.3.

[0058] The technical term "Dv50" refers to the particle size at which the cumulative volume distribution of a sample reaches 50%. Physically, it means that the volume of particles larger than Dv50 constitutes 50% of the total sample volume, and the volume of particles smaller than Dv50 also constitutes 50% of the total sample volume.

[0059] The technical term "Le Bail method" refers to a method for refining X-ray diffraction (XRD) spectra, which is particularly suitable for strain measurement. Two other methods for refining XRD spectra are the Pawley method and the Rietveld method, which are not used in this invention.

[0060] The technical term is “Williamson-Hall equation”, which is shown in formula (1):

[0061]

[0062] β is the peak width of the diffraction peak in the XRD spectrum, θ is the diffraction angle, K is a constant, λ is the X-ray wavelength, D is the lithium cobalt oxide particle size, and ε is the strain. A scatter plot is created with βcosθ as the vertical axis and sinθ as the horizontal axis. A linear fit is then performed on these scatter plots; the slope of the straight line is 1 / 4 of the strain ε.

[0063] The technical term "elastic modulus" is the ratio of stress to strain. Elastic modulus is one of the most stable properties of a material; its magnitude depends primarily on the material's inherent properties. Aside from gradually decreasing with increasing temperature, other strengthening methods such as heat treatment, hot and cold working, and alloying have little effect on the elastic modulus. Therefore, at a constant temperature, the elastic modulus of lithium cobalt oxide is a constant. It is evident that stress and strain have a strict correspondence. In this invention, for the sake of logical flow, sometimes only stress is emphasized while strain is not, and sometimes only strain is emphasized while stress is not.

[0064] The technical term "commercially available 4.48V lithium cobalt oxide" refers to commercially available lithium cobalt oxide that can stably cycle in a 4.48V full cell. Commercially available lithium cobalt oxide is classified into models such as 4.35V, 4.4V, 4.45V, 4.48V, and 4.5V based on its charging cut-off voltage in a full cell. The doping amount and energy density of lithium cobalt oxide increase with the increase of the charging cut-off voltage, and the corresponding battery standby time also increases.

[0065] The technical terms "first charge specific capacity" and "first discharge specific capacity" refer to the charge specific capacity and discharge specific capacity of the first cycle, respectively.

[0066] The technical term "initial discharge specific capacity" refers to the discharge specific capacity of the third cycle, that is, the discharge specific capacity when cycling at a current density of 100 mA / g at the beginning.

[0067] The technical term "activation" refers to the initial two cycles at a current density of 10 mA / g.

[0068] Next, based on the understanding of the above technical terms, the technical solution of the present invention will be further described in detail with reference to the accompanying drawings and embodiments.

[0069] Because the inventors discovered that the failure of lithium cobalt oxide during operation is accompanied by particle cracking, and particle cracking is directly related to stress accumulation and release within the particles, they believed that reducing the initial strain of lithium cobalt oxide and minimizing stress accumulation during cycling would improve its cycling performance. Based on this, this invention provides a method for preparing low-strain lithium cobalt oxide, the main steps of which are as follows: Figure 1 As shown, it includes:

[0070] Step 110: Mix cobalt tetroxide, lithium carbonate, and sintering aid together, and add no or no more than a certain mass of doping reagent to obtain a blended powder;

[0071] The sintering aid is an alkali metal salt and / or alkaline earth metal salt that does not react with lithium cobalt oxide, has a melting point below 900℃ and a boiling point above 1200℃, and has a solubility in water greater than 200 g / L at 25℃; the total molar fraction of alkali metal in the alkali metal salt and / or alkaline earth metal in the alkaline earth metal salt is greater than or equal to 3 and less than or equal to 15. Specifically, the sintering aid preferably includes one or more of the following: LiCl, NaCl, KCl, Li₂SO₄, Na₂SO₄, Na₂CO₃, CaCl₂, and SrCl₂.

[0072] The molar amount of lithium in lithium carbonate is 101-105, preferably 103, relative to 100 molar parts of lithium cobalt oxide in the lithium cobalt oxide matrix to be prepared. During the sintering process, a small amount of lithium will volatilize at high temperature. Therefore, the amount of lithium carbonate needs to be 1%-5% in excess, preferably 3% in excess, so as to obtain lithium cobalt oxide with fewer defects.

[0073] The low-strain lithium cobalt oxide prepared by this invention can be doped or undoped.

[0074] Because the ionic radius, valence state, and electronegativity of the dopant element are all similar to those of Co... 3+Differences in dopant content can cause lattice distortion in lithium cobalt oxide, thus increasing defects and strain. Furthermore, dopant elements are not easily uniformly distributed in the bulk phase of lithium cobalt oxide, leading to localized high strain. Therefore, in the case of doping, this invention controls the amount of dopant added, ensuring that the total mass parts of the dopant element are less than or equal to 0.3 per 100 parts by mass of the lithium cobalt oxide matrix. The mass parts of the dopant element can be any value within the above range; for example, the total mass parts of the dopant element relative to 100 parts by mass of the lithium cobalt oxide matrix can be 0.3, 0.28, 0.25, 0.21, 0.18, 0.15, 0.12, 0.10, 0.08, 0.05, 0.02, or 0 parts by mass. By reducing the content of the dopant element, lattice distortion of lithium cobalt oxide due to its introduction can be prevented. This invention preferably uses undoped lithium cobalt oxide, meaning that distortion will not occur due to impurity elements. This invention significantly reduces the strain of lithium cobalt oxide by reducing the doping level.

[0075] The doping reagent can be a nano-oxide of a doping element, including one or more of Mg, Al, Ti, Mn, Ni, Y, Zr, Nb, Mo, La, Ce, and W; the Dv50 of the doping reagent is less than or equal to 100 nm.

[0076] Step 120: Sinter the blended powder. First, heat the blended powder to 680℃-780℃ and hold it for 3h-8h. Then, heat it to 900℃-1100℃ and hold it for 8h-24h. Finally, cool it to 300℃ at a cooling rate not exceeding 5℃ / min to obtain the sintered material.

[0077] The process of heating the blended powder to 680-780℃ and holding it at that temperature for 3-8 hours is to allow the lithium carbonate to melt and flow into the gaps between the cobalt tetroxide particles, thereby ensuring full contact with the cobalt tetroxide and facilitating the subsequent reaction to produce lithium cobalt oxide.

[0078] During sintering, LiCoO2, generated from the reaction of lithium carbonate and cobalt tetroxide, undergoes fusion growth in the liquid phase formed by the sintering aid. This is because the sintering aid used in this invention is an alkali metal salt or alkaline earth metal salt with a melting point below 900℃ and a boiling point above 1200℃, while Li2CO3 has a melting point of 723℃ (it can melt below 723℃ with cobalt tetroxide catalysis) and a boiling point of 1310℃. Therefore, Li2CO3 exists in a liquid state during sintering. In the sintering process, the first stage is the reaction of liquid Li2CO3 with solid Co3O4 to generate solid LiCoO2, and the second stage is the displacement of LiCoO2 grain boundaries, i.e., the fusion and growth of small LiCoO2 particles into large LiCoO2 particles. Figure 2As shown, without the addition of sintering aids, the fusion and growth of LiCoO2 particles in the second stage is a purely solid-phase reaction because the liquid Li2CO3 is completely consumed in the first stage. However, in this invention, sintering aids are added, so the fusion and growth of LiCoO2 particles in the second stage takes place in the liquid phase formed by the sintering aids. Since the liquid-phase reaction kinetics are superior to the solid-phase reaction kinetics, i.e., the liquid-phase mass transfer is faster than the solid-phase mass transfer, it is beneficial for eliminating defects (dislocations, grain boundaries, twin boundaries, stacking faults, etc.) and reducing initial strain.

[0079] Since the sintering aids used in this invention have a solubility in water greater than 200 g / L (25°C), they can be easily removed from the surface of the sintered lithium cobalt oxide matrix through a subsequent water washing step. Furthermore, the cations and anions in LiCl, NaCl, KCl, Li₂SO₄, Na₂SO₄, Na₂CO₃, CaCl₂, and SrCl₂ have strong bond energies and exist in a molten state at high temperatures without decomposition. Therefore, they do not react with lithium cobalt oxide, nor with cobalt tetroxide, lithium carbonate, or dopant reagents, making them excellent molten salts.

[0080] Step 130: The sintered material is crushed, pulverized, washed, dried and sieved to obtain a lithium cobalt oxide matrix;

[0081] Specifically, the washing process involves water washing, and the sieving is preferably done through a 300-mesh sieve.

[0082] Step 140: The lithium cobalt oxide matrix is ​​coated, and then the resulting material containing the coating layer is ground and sieved to obtain low-strain lithium cobalt oxide.

[0083] Surface coating can reduce side reactions between lithium cobalt oxide and the electrolyte under high voltage, thereby slowing down the formation of a Co3O4 passivation layer on the lithium cobalt oxide surface and preventing the excessive formation of CEI. However, the inventors discovered in their research that the Al2O3 coating commonly used in the industry is not compatible with the low-strain lithium cobalt oxide proposed in this invention. This is because coating modification involves a sintering process, during which Al diffuses into the lithium cobalt oxide bulk phase to form LiCo. y Al 1-y O2 solid solution increases the stress and strain of lithium cobalt oxide. To obtain low-strain lithium cobalt oxide, this invention not only improves the preparation of the lithium cobalt oxide matrix but also improves the surface coating material to match the lithium cobalt oxide matrix, thereby synergistically obtaining a low-strain lithium cobalt oxide cathode material.

[0084] The improved coating process of this invention includes: mixing a lithium cobalt oxide matrix with a lithium source and an M1 source to obtain a mixed powder, wherein M1 is one or more of Si, Ti, Zr, Nb, Mo, and Ta; and / or mixing a lithium cobalt oxide matrix with a lithium source, an M2 source, and a phosphorus source to obtain a mixed powder, wherein M2 is one or more of Ti, Ge, Zr, Sn, and Hf; heating the mixed powder to 600℃-1000℃ and holding it at that temperature for 2h-12h, and then cooling it to 300℃ at a cooling rate not exceeding 5℃ / min to obtain a material containing a coating layer.

[0085] The lithium source includes one or more of lithium-containing oxides, inorganic salts, organic salts, alkoxides, and phosphates; preferably, it includes one or more of Li2O, Li2CO3, LiOH, LiNO3, lithium acetate, lithium oxalate, lithium isopropoxide, Li3PO4, Li2HPO4, and LiH2PO4.

[0086] The M1 source includes one or more of the following: oxides, inorganic salts, organic salts, alkoxides, and phosphates of M1; preferably, it includes one or more of the following: SiO2, H4SiO4, tetraethyl silicate, TiO2, TiOSO4, titanium isopropoxide, titanium n-butoxide, ZrO2, zirconium ethoxide, zirconium isopropoxide, zirconium n-butoxide, Nb2O5, niobium oxalate, niobium ethoxide, niobium n-butoxide, Nb3(PO4)5, MoO2, molybdenum isopropoxide, Ta2O5, tantalum ethoxide, and tantalum isopropoxide.

[0087] The M2 source includes one or more of the following: oxides, inorganic salts, organic salts, alkoxides, and phosphates of M2; preferably including one or more of the following: TiO2, TiOSO4, titanium isopropoxide, titanium n-butoxide, GeO2, germanium ethoxide, germanium isopropoxide, ZrO2, zirconium ethoxide, zirconium isopropoxide, zirconium n-butoxide, SnO2, tin ethoxide, tin isopropoxide, tin tert-butoxide, HfO2, hafnium ethoxide, and hafnium isopropoxide.

[0088] The phosphorus source includes inorganic phosphorus compounds and / or organic phosphorus compounds; preferably, it includes one or more of the following: H3PO4, NH4H2PO4, (NH4)2HPO4, (NH4)3PO4, Li3PO4, Li2HPO4, LiH2PO4, tributyl phosphate, and monobutyl dodecyl phosphate.

[0089] The inventors chose the aforementioned M1 or M2 source and phosphorus source because they discovered that, on the one hand, Si, Ti, Zr, Nb, Mo, Ta, and Co have significantly different properties, making them difficult to diffuse into the lithium cobalt oxide lattice and instead tending to accumulate on the surface of lithium cobalt oxide grains. Therefore, using Si, Ti, Ge, Zr, Nb, Mo, Sn, Hf, and Ta as components of the coating layer would hardly increase the strain of lithium cobalt oxide. On the other hand, lithium oxides containing Si, Ti, Zr, Nb, Mo, and Ta (such as Li2SiO3, Li2TiO3, LiTi) are also suitable for this purpose. 1.25 Lithium oxides (Si, Ti, Zr, Nb, Mo, Ta) are lithium-ion conductors. Therefore, using lithium-containing oxides of Si, Ti, Zr, Nb, Mo, and Ta as coating layers can prevent metal elements in the coating reagent from diffusing into the lithium cobalt oxide lattice and increasing the stress-strain of lithium cobalt oxide. Furthermore, they exhibit better lithium-ion conductivity than Al2O3 coating layers. In addition, lithium-containing phosphates such as LiTi2(PO4)3, LiGe2(PO4)3, LiZr2(PO4)3, and Li3Zr... 1.5 Li₂(PO₄)₃, LiSn₂(PO₄)₃, and LiHf₂(PO₄)₃ are also lithium-ion conductors. Meanwhile, Ti, Ge, Zr, Sn, and Hf are relatively difficult to diffuse into the lithium cobalt oxide lattice. Therefore, these phosphates can also be used as coating layers. This invention, by using the above coating materials to modify lithium cobalt oxide, still yields low-strain lithium cobalt oxide. Furthermore, it not only reduces side reactions between lithium cobalt oxide and the electrolyte but also provides better surface ion transport performance compared to alumina coating. Therefore, it can obtain lithium cobalt oxide with excellent electrochemical performance that meets application requirements.

[0090] More specifically, the coating layer of the material containing the coating layer obtained by the present invention is specifically a lithium oxide coating layer and / or a lithium phosphate coating layer;

[0091] The chemical formula of the lithium oxide coating is: Li a M1 b O3, where the average valence state of M1 is +m, satisfying a + mb = 6; Li a M1 b O3 includes: Li2SiO3, Li2TiO3, LiTi 1.25 One or more of O3, Li2ZrO3, LiNbO3, Li2MoO3, and LiTaO3;

[0092] The chemical formula of the lithium phosphate coating is: Li c M2 d (PO4)3, where the average valence state of M2 is +n, satisfying c+nd=9; Li c M2 d(PO4)3 includes: LiTi2(PO4)3, LiGe2(PO4)3, LiZr2(PO4)3, and Li3Zr. 1.5 One or more of (PO4)3, LiSn2(PO4)3, and LiHf2(PO4)3;

[0093] The total mass fraction of the lithium oxide coating and / or lithium phosphate coating is less than or equal to 1 per 100 parts by mass of the lithium cobalt oxide matrix. Specifically, the mass fraction of the lithium oxide coating or lithium phosphate coating can be any value within the above range. For example, the total mass fraction of the lithium oxide coating and / or lithium phosphate coating can be 1 part by mass, 0.98 parts by mass, 0.85 parts by mass, 0.72 parts by mass, 0.6 parts by mass, 0.58 parts by mass, 0.46 parts by mass, 0.35 parts by mass, 0.23 parts by mass, 0.12 parts by mass, or 0.01 parts by mass relative to 100 parts by mass of the lithium cobalt oxide matrix.

[0094] The low-strain lithium cobalt oxide preparation method proposed above can yield lithium cobalt oxide with a strain of 3.0 × 10⁻⁶. -4 The following are examples of low-strain lithium cobalt oxide. Lower strain indicates less lattice distortion and fewer defects in the lithium cobalt oxide. In the actual tests of this invention, when the strain is below 1.0 × 10⁻⁶... -4 At that time, the capacity retention rate was higher than 97% after 50 cycles.

[0095] Here, low strain and low doping are further explained to better understand the intent of the invention and the principle by which the invention improves the performance of lithium cobalt oxide through low doping and low strain.

[0096] First, since defects are closely related to lattice deformation, the quantity of defects can be measured by the magnitude of material strain. Strain, defined in mechanics as the deformation intensity of a tiny material element under stress, is a dimensionless quantity. During charging and discharging, the lithium cobalt oxide lattice undergoes regular expansion and contraction. Defects are prone to stress accumulation due to volume changes, leading to microcrack initiation and propagation, ultimately causing particle cracking. Therefore, reducing defects in lithium cobalt oxide is crucial for improving its cycle performance. Completely defect-free lithium cobalt oxide is practically nonexistent and cannot be synthesized; therefore, the only option is to minimize defects. The inventors discovered that doping levels above 3000 mg / kg significantly increase the stress and strain of lithium cobalt oxide. Furthermore, doping elements exceeding this level are difficult to achieve a completely uniform distribution in the lithium cobalt oxide bulk phase, resulting in excessive localized stress and strain. Defects in the lithium cobalt oxide crystal are more susceptible to stress accumulation due to volume changes during cycling, leading to microcrack initiation and propagation, ultimately causing particle cracking. This invention reduces defects and strain by using low doping, and by using sintering aids to change the fusion and growth of lithium cobalt oxide particles from solid-phase to liquid-phase reaction, thereby accelerating reaction kinetics and reducing defects (dislocations, grain boundaries, twin boundaries, stacking faults, etc.), thus reducing the strain of lithium cobalt oxide.

[0097] The strain of the material obtained by this invention is measured by the following method: First, the peak width of the diffraction peaks of the powder X-ray diffraction spectrum of the low-strain lithium cobalt oxide is refined by the Le Bail method. Then, a scatter plot is made with βcosθ as the vertical axis and sinθ as the horizontal axis. The Williamson-Hall equation is used to linearly fit these scatter points, and 1 / 4 of the slope of the straight line equation is the strain ε.

[0098] Secondly, it is generally believed in industry and academia that when the charging voltage of lithium cobalt oxide exceeds 4.55V (vsLi + When lithium cobalt oxide (Li) is charged, an irreversible transformation from the O3 phase to the H1-3 phase occurs, leading to a significant decrease in the performance of lithium cobalt oxide. Therefore, to improve the cycling performance of lithium cobalt oxide at high voltages, the industry often uses Al doping to enhance its structural stability; and the higher the charging cut-off voltage, the greater the Al doping amount. However, the inventors discovered through research that, as... Figure 3 Electrochemical in-situ X-ray diffraction (ECRD) showed that at a current density of 10 mA / g, undoped lithium cobalt oxide, lithium cobalt oxide doped with 4000 mg / kg Al, lithium cobalt oxide doped with 8000 mg / kg Al, and commercially available 4.48V lithium cobalt oxide all underwent a transformation from the O3 phase to the H1-3 phase when the initial charge specific capacity was around 225 mAh / g. This initial charge specific capacity corresponds to the initial charge specific capacity of undoped lithium cobalt oxide at 4.55V (vs Li). +Lithium cobalt oxide doped with 4000 mg / kg Al was charged to 4.59V (vs Li). + Lithium cobalt oxide doped with 8000 mg / kg Al was charged to 4.63V (vs Li). + / Li), commercially available 4.48V lithium cobalt oxide can be charged to 4.62V (vs Li). + / Li). It is evident that, compared to undoped lithium cobalt oxide, Al-doped lithium cobalt oxide requires charging to at least 4.55V (vs Li). + The transformation from the O3 phase to the H1-3 phase only occurs when Al is doped with Li, which creates the illusion that Al doping can delay the phase transition. In fact, the inventors found through research that the specific charge capacity of Al-doped lithium cobalt oxide during the O3-H1-3 phase transition does not change, remaining at around 225 mAh / g. In other words, from the perspective of the amount of lithium removed, Al doping cannot delay the O3-H1-3 phase transition.

[0099] The inventors believe that the O3-to-H1-3 phase transition is triggered by the amount of lithium delithiation (charge specific capacity), not by the charging voltage; that is, the phase transition is determined by the amount of lithium delithiation, and is independent of the charging voltage. The amount of lithium delithiation determines the energy density of lithium cobalt oxide. According to the inventors' research, improving the electrochemical performance of lithium cobalt oxide should not involve increasing the dopant content, but rather considering the inherent structural damage during use. The microscopic mechanism of the O3-to-H1-3 phase transition is lattice slip, thus this phase transition significantly increases stress and strain accumulation during cycling. Furthermore, at the amount of lithium delithiation that triggers the O3-to-H1-3 phase transition, the c-axis lattice constant of lithium cobalt oxide also decreases rapidly, causing a significant volume change. Therefore, preventing the O3-to-H1-3 phase transition of lithium cobalt oxide and reducing volume changes are key to improving its performance.

[0100] Based on the above mechanism, the inventors believe that the reversible specific capacity, rather than the charging cut-off voltage, determines the cycle performance of lithium cobalt oxide. Therefore, by re-examining the Al doping technology currently used in the industry, they found that commercially available lithium cobalt oxide (such as the commercially available 4.48V lithium cobalt oxide shown in Comparative Example 20 of this invention) at 4.60V (vs Li) + At the charging cutoff voltage of lithium cobalt oxide (Li), with a charge / discharge current density of 100 mA / g, the initial discharge specific capacity is only about 200 mAh / g, far lower than 225 mAh / g. This discharge specific capacity is insufficient to cause lithium cobalt oxide to transform from the O3 phase to the H1-3 phase. Therefore, based on the analysis of the structural damage mechanism of lithium cobalt oxide, although it is generally accepted in industry and academia that Al doping can suppress phase transition, the discharge specific capacity of currently commercially available lithium cobalt oxide is insufficient to trigger the transformation from the O3 phase to the H1-3 phase. Therefore, it is not necessary to suppress the phase transition by heavily doping with Al.

[0101] In view of this, unlike existing commercially available lithium cobalt oxide, this invention reverses the industry's approach to improving lithium cobalt oxide by reducing the Al doping level, even to zero. This is because the ionic radius, valence state, and electronegativity of impurity atoms in lithium cobalt oxide are similar to those of Co. 3+ Significant differences in doping levels can cause lattice distortion in lithium cobalt oxide. Therefore, the introduction of doping elements increases defects, i.e., increases the strain of lithium cobalt oxide. Reducing the doping amount can firstly reduce defects caused by impurity atoms, resulting in smaller lattice distortion and initial stress strain, thereby reducing crack initiation and growth; secondly, it can avoid reducing the ionic conductivity of lithium cobalt oxide by doping elements, thus ensuring good rate performance; and finally, it can enable lithium cobalt oxide to have higher capacity at lower voltages, reducing surface side reactions.

[0102] After making the above improvements, the present invention obtains low-strain lithium cobalt oxide and sets the charging cutoff voltage to less than or equal to 4.54-4.57V (vs Li + / Li). When the charging cutoff voltage is 4.54-4.57V (vs Li). + When the current density is 100 mA / g, the initial discharge specific capacity is controlled within 208-213 mAh / g (depending on whether no dopant is added or a suitable amount is added). This initial discharge specific capacity is slightly lower than the critical point for lithium cobalt oxide to transform from the O3 phase to the H1-3 phase. The inventors found that if the initial discharge specific capacity of lithium cobalt oxide is higher than the critical point, the transformation from the O3 phase to the H1-3 phase easily occurs during charging. The microscopic mechanism of this phase transformation is lattice slip, which introduces very large strain into lithium cobalt oxide, resulting in a large number of intragranular cracks and accelerating material failure. Therefore, the charging cutoff voltage of low-strain lithium cobalt oxide is set to less than or equal to 4.54-4.57V (vs Li). + / Li) can effectively prevent the formation of H1-3 phase during charge-discharge cycles, thereby effectively reducing stress and strain accumulation during the cycle.

[0103] If the discharge specific capacity remains constant, the type and amount of doping elements are directly related to the charging cut-off voltage of lithium cobalt oxide. Mg and Al doping both increase the activation barrier for lithium-ion diffusion in lithium cobalt oxide, hindering diffusion. Therefore, for the same discharge specific capacity, lower doping element content results in a lower charging cut-off voltage, leading to better cycle performance. This also makes the initial discharge specific capacity of undoped and low-doped lithium cobalt oxide at 100 mA / g current density very close to that at 10 mA / g current density, indicating better rate performance. Furthermore, at the same charging cut-off voltage, higher doping levels result in lower discharge specific capacity for lithium cobalt oxide, meaning doping sacrifices the reversible specific capacity. Therefore, at the same voltage, low-doped and undoped lithium cobalt oxide exhibit higher capacity utilization than high-doped lithium cobalt oxide. In other words, the discharge specific capacity of low-doped and undoped lithium cobalt oxide at lower charging cut-off voltages is comparable to that of high-doped lithium cobalt oxide at higher charging cut-off voltages. The lower charging cut-off voltage means that lithium cobalt oxide has fewer surface side reactions and its reaction with the electrolyte is greatly reduced, thus exhibiting excellent cycle performance.

[0104] The charging cutoff voltage of low-strain lithium cobalt oxide is related to the doping element and doping amount. A suitable charging cutoff voltage is set to avoid the transformation of low-strain lithium cobalt oxide from the O3 phase to the H1-3 phase. To ensure an initial discharge specific capacity below 208-213 mAh / g, the charging cutoff voltage of the low-strain lithium cobalt oxide of this invention is controlled to be less than or equal to 4.54-4.57 V (vsLi+ / Li) in application, corresponding to an initial discharge specific capacity less than or equal to 208-213 mAh / g.

[0105] The low-strain lithium cobalt oxide of this invention has an initial discharge specific capacity of 208-213 mAh / g, corresponding to a charging cutoff voltage of 4.54-4.57 V (vs Li). + / Li), significantly lower than the 4.60V of commercially available 4.48V lithium cobalt oxide (vs Li). + / Li). This is because at a given charging cutoff voltage (e.g., 4.54V vs Li), + Under Li / Li conditions, heavily doped Al loses some discharge specific capacity, which leads to a higher charging cutoff voltage (e.g., 4.60V vs. Li) required for heavily Al-doped lithium cobalt oxide. + Only with / Li)) can it release the same discharge specific capacity as undoped lithium cobalt oxide. Therefore, the discharge specific capacity of undoped and poorly doped lithium cobalt oxide at lower charge cutoff voltages is comparable to that of highly doped lithium cobalt oxide at higher charge cutoff voltages. Furthermore, a lower voltage is required to achieve the same discharge specific capacity, resulting in fewer side reactions between the lithium cobalt oxide and the electrolyte, and thus better structural stability.

[0106] In a specific example of this invention, with lithium metal as both the counter and reference electrodes, a charging cutoff voltage of 4.54-4.57V, and a charge / discharge current density of 100mA / g, the initial discharge specific capacity of low-strain lithium cobalt oxide is 208-213mAh / g. Experiments show that when the initial discharge specific capacity is 208-213mAh / g, the capacity retention rate is higher than 95% after 50 cycles; when the initial discharge specific capacity is lower than 208-213mAh / g, the capacity retention rate is higher than 98% after 50 cycles.

[0107] Therefore, the preparation method of low-strain lithium cobalt oxide of the present invention can reduce the strain of lithium cobalt oxide by introducing low doping and sintering aids, thereby giving it better electrochemical performance. The prepared low-strain lithium cobalt oxide has fewer defects and better crystallinity. During long cycling, it is not easy to induce a large number of cracks at the defect sites due to stress concentration. At the same time, it has good conductivity and cycling stability, and the side reactions with the electrolyte are greatly reduced. It can exert most of its capacity at a relatively low voltage.

[0108] Specific embodiments of the present invention are described in detail below. It should be understood that these embodiments are for illustrative purposes only and should not be construed as limiting the invention.

[0109] Example 1

[0110] 500g Co3O4, 237.05g Li2CO3, and 37.15g KCl were weighed and mixed in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. The blended powder was placed in an atmosphere-controlled box furnace and sintered at 700℃ for 6h, then at 960℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, a lithium cobalt oxide matrix was obtained. No doping or modification was performed on the lithium cobalt oxide matrix in this example. 8 moles of KCl were used as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0111] 0.0051 g lithium acetate, 0.0124 g nano TiO2, and 0.0267 g NH4H2PO4 were ultrasonically dispersed in 30 mL deionized water, and then 10 g lithium cobalt oxide matrix was added. The mixture was then dried in an oil bath at 100 °C. The dried material was sintered at 800 °C for 6 h in an atmosphere box furnace, and then ground and passed through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. Each 100 parts by mass of the lithium cobalt oxide matrix was coated with 0.3 parts by mass of LiTi2(PO4)3.

[0112] Example 2

[0113] Weigh out 500g Co3O4, 237.05g Li2CO3, 1.1519g nano Al2O3, and 37.15g KCl. Mix them in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous powder. Place the powder in an atmosphere-controlled furnace and sinter at 700℃ for 6h, then at 970℃ for 12h. After crushing, pulverizing, washing, drying, and sieving, obtain the lithium cobalt oxide matrix. In this example, the Al doping amount is 1000mg / kg, and 8 moles of KCl are used as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0114] 0.0051 g lithium acetate, 0.0124 g nano TiO2, and 0.0267 g NH4H2PO4 were ultrasonically dispersed in 30 mL deionized water, and then 10 g lithium cobalt oxide matrix was added. The mixture was then dried in an oil bath at 100 °C. The dried material was sintered at 800 °C for 6 h in an atmosphere box furnace, and then ground and passed through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. Specifically, 0.3 parts by mass of LiTi2(PO4)3 were coated on the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0115] Example 3

[0116] Weigh out 500g Co3O4, 237.05g Li2CO3, 1.0111g nano-MgO, 1.1519g nano-Al2O3, and 51.37g Li2SO4. Mix them in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. Place the blended powder in an atmosphere box furnace and sinter at 700℃ for 6h, then at 980℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, obtain the lithium cobalt oxide matrix. The Mg doping concentration is 1000mg / kg, and the Al doping concentration is 1000mg / kg. 7.5 moles of Li2SO4 are used as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0117] 0.0084 g of lithium isopropoxide, 0.0971 g of zirconium n-butoxide, and 0.1011 g of tributyl phosphate were dissolved in 30 mL of anhydrous ethanol. Then, 10 g of lithium cobalt oxide matrix was added, and the mixture was stirred to dryness in a water bath at 80 °C. The dried material was then sintered at 700 °C for 8 h in an atmosphere box furnace, followed by grinding and sieving through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. 0.6 parts by mass of LiZr2(PO4)3 were coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0118] Example 4

[0119] Weigh out 500g Co3O4, 237.05g Li2CO3, 1.0111g nano MgO, 2.3037g nano Al2O3, and 51.37g Li2SO4. Mix them in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. Place the blended powder in an atmosphere box furnace and sinter at 700℃ for 6h, then at 990℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, obtain the lithium cobalt oxide matrix. The Mg doping concentration is 1000mg / kg, and the Al doping concentration is 2000mg / kg. 7.5 moles of Li2SO4 are used as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0120] 0.0084 g of lithium isopropoxide, 0.0971 g of zirconium n-butoxide, and 0.1011 g of tributyl phosphate were dissolved in 30 mL of anhydrous ethanol. Then, 10 g of lithium cobalt oxide matrix was added, and the mixture was stirred to dryness in a water bath at 80 °C. The dried material was then sintered at 700 °C for 8 h in an atmosphere box furnace, followed by grinding and sieving through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. 0.6 parts by mass of LiZr2(PO4)3 were coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0121] Example 5

[0122] Weigh out 500g Co3O4, 237.05g Li2CO3, 0.7759g nano NiO, 0.9648g nano MnO2, and 26.41g LiCl. Mix them in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. Place the blended powder in an atmosphere-controlled furnace and sinter at 680℃ for 8h, then at 900℃ for 24h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, obtain the lithium cobalt oxide matrix. The Ni doping concentration is 1000mg / kg, and the Mn doping concentration is 1000mg / kg. Use 10 moles of LiCl as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0123] 0.0093 g LiNO3 and 0.0620 g n-butoxide niobium were dissolved in 30 mL of anhydrous ethanol, and then 10 g of lithium cobalt oxide matrix was added. The mixture was stirred to dryness in a water bath at 80 °C. The dried material was then sintered in an atmosphere box furnace at 600 °C for 12 h, followed by grinding and sieving through a 300-mesh sieve to obtain coated modified lithium cobalt oxide. 0.2 parts by mass of LiNbO3 were coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0124] Example 6

[0125] Weigh out 500g Co3O4, 237.05g Li2CO3, 0.3871g nano Y2O3, and 10.92g NaCl. Mix them in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous powder. Place the powder in an atmosphere-controlled furnace and sinter at 780℃ for 3h, then at 960℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, obtain the lithium cobalt oxide matrix. The Y doping concentration is 500mg / kg. Use 3 moles of NaCl as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0126] 0.0575 g of lithium acetate, 0.0870 g of nano-TiO2, and 10 g of lithium cobalt oxide matrix were mixed in a ball mill at 200 rpm for 1 hour, with a ball-to-material volume ratio of 1:1. The grinding balls were made of polyurethane. The mixed material was then sintered at 700℃ for 8 hours in an atmosphere-controlled box furnace, followed by grinding and sieving through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. One part by mass of LiTi was coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix. 1.25 O3.

[0127] Example 7

[0128] Weigh out 500g Co3O4, 237.05g Li2CO3, 0.4118g nano ZrO2, and 10.92g NaCl. Mix them in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous powder. Place the powder in an atmosphere-controlled furnace and sinter at 780℃ for 3h, then at 960℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, obtain the lithium cobalt oxide matrix. The Zr doping concentration is 500mg / kg. Use 3 moles of NaCl as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0129] 0.0575 g of lithium acetate, 0.0870 g of nano-TiO2, and 10 g of lithium cobalt oxide matrix were mixed in a ball mill at 200 rpm for 1 hour, with a ball-to-material volume ratio of 1:1. The grinding balls were made of polyurethane. The mixed material was then sintered at 700℃ for 8 hours in an atmosphere-controlled box furnace, followed by grinding and sieving through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. One part by mass of LiTi was coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix. 1.25 O3.

[0130] Example 8

[0131] Weigh out 500g Co3O4, 237.05g Li2CO3, 0.2617g nano Nb2O5, and 19.81g Na2CO3. Mix them in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. Place the blended powder in an atmosphere-controlled furnace and sinter at 700℃ for 6h, then at 960℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, obtain the lithium cobalt oxide matrix. The Nb doping concentration is 300mg / kg. Use 3 moles of Na2CO3 as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0132] 0.0690 g of lithium acetate and 0.0644 g of nano-ZrO2 were ultrasonically dispersed in 30 mL of deionized water, and then 10 g of lithium cobalt oxide matrix was added. The mixture was then dried in an oil bath at 100 °C. The dried material was sintered in an atmosphere box furnace at 1000 °C for 2 h, and then ground and passed through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. 0.8 parts by weight of Li2ZrO3 were coated on the surface of every 100 parts by weight of the lithium cobalt oxide matrix.

[0133] Example 9

[0134] Weigh out 500g Co3O4, 237.05g Li2CO3, 0.2145g nano La2O3, and 19.81g Na2CO3. Mix them in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. Place the blended powder in an atmosphere-controlled box furnace and sinter at 700℃ for 6h, then at 960℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, obtain the lithium cobalt oxide matrix. The La doping concentration is 300mg / kg. Use 3 moles of Na2CO3 as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0135] 0.0690 g of lithium acetate and 0.0644 g of nano-ZrO2 were ultrasonically dispersed in 30 mL of deionized water, and then 10 g of lithium cobalt oxide matrix was added. The mixture was then dried in an oil bath at 100 °C. The dried material was sintered in an atmosphere box furnace at 1000 °C for 2 h, and then ground and passed through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. 0.8 parts by mass of Li2ZrO3 were coated on the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0136] Example 10

[0137] 500g Co3O4, 237.05g Li2CO3, 0.5242g nano CeO2, and 88.88g SrCl2 were weighed and mixed in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. The blended powder was placed in an atmosphere box furnace and sintered at 780℃ for 8h, then at 1100℃ for 8h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, the lithium cobalt oxide matrix was obtained. The Ce doping amount was 700mg / kg. 9 moles of SrCl2 were used as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0138] 0.0100 g lithium acetate, 0.0456 g nano SnO2, and 0.0522 g NH4H2PO4 were ultrasonically dispersed in 30 mL deionized water, and then 10 g lithium cobalt oxide matrix was added. The mixture was stirred dry in an oil bath at 100 °C. The dried material was then sintered at 900 °C for 4 h in an atmosphere box furnace, followed by grinding and sieving through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. Each 100 parts by weight of the lithium cobalt oxide matrix was coated with 0.8 parts by weight of LiSn2(PO4)3.

[0139] Example 11

[0140] 500g Co3O4, 237.05g Li2CO3, 0.5382g nano WO3, and 88.88g SrCl2 were weighed and mixed in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. The blended powder was placed in an atmosphere box furnace and sintered at 780℃ for 8h, then at 1100℃ for 8h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, the lithium cobalt oxide matrix was obtained. The W doping amount was 700mg / kg. 9 moles of SrCl2 were used as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0141] 0.0100 g lithium acetate, 0.0456 g nano SnO2, and 0.0522 g NH4H2PO4 were ultrasonically dispersed in 30 mL deionized water, and then 10 g lithium cobalt oxide matrix was added. The mixture was stirred dry in an oil bath at 100 °C. The dried material was then sintered at 900 °C for 4 h in an atmosphere box furnace, followed by grinding and sieving through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. Each 100 parts by weight of the lithium cobalt oxide matrix was coated with 0.8 parts by weight of LiSn2(PO4)3.

[0142] Comparative Example 1

[0143] This comparative example is highly doped with Al.

[0144] 500g Co3O4, 237.05g Li2CO3, 4.6074g nano-Al2O3, and 37.15g KCl were weighed and mixed in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous powder. The powder was sintered in an atmosphere-controlled furnace at 700℃ for 6h, then at 1000℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, the lithium cobalt oxide matrix was obtained. The Al doping concentration was 4000mg / kg. 8 moles of KCl were used as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0145] 0.0051 g lithium acetate, 0.0124 g nano TiO2, and 0.0267 g NH4H2PO4 were ultrasonically dispersed in 30 mL deionized water, and then 10 g lithium cobalt oxide matrix was added. The mixture was then dried in an oil bath at 100 °C. The dried material was sintered at 800 °C for 6 h in an atmosphere box furnace, and then ground and passed through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. 0.3 parts by mass of LiTi2(PO4)3 were coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0146] Comparative Example 2

[0147] This comparative example is highly doped with Al.

[0148] 500g Co3O4, 237.05g Li2CO3, 9.2149g nano-Al2O3, and 37.15g KCl were weighed and mixed in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. The blended powder was placed in an atmosphere box furnace and sintered at 700℃ for 6h, then at 1050℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, the lithium cobalt oxide matrix was obtained. The Al doping amount was 8000mg / kg. 8 moles of KCl were used as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0149] 0.0051 g lithium acetate, 0.0124 g nano TiO2, and 0.0267 g NH4H2PO4 were ultrasonically dispersed in 30 mL deionized water, and then 10 g lithium cobalt oxide matrix was added. The mixture was then dried in an oil bath at 100 °C. The dried material was sintered at 800 °C for 6 h in an atmosphere box furnace, and then ground and passed through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. 0.3 parts by mass of LiTi2(PO4)3 were coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0150] Comparative Example 3

[0151] This comparative example is highly doped with Mg and Al.

[0152] Weigh out 500g Co3O4, 237.05g Li2CO3, 1.0111g nano-MgO, 3.4556g nano-Al2O3, and 51.37g Li2SO4. Mix them in an experimental mixer at 2000rpm for 2 minutes, then at 4000rpm for 2 minutes to obtain a homogeneous blended powder. Place the blended powder in an atmosphere-controlled furnace and sinter at 700℃ for 6 hours, then at 1000℃ for 12 hours. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, obtain the lithium cobalt oxide matrix. The Mg doping concentration is 1000mg / kg, and the Al doping concentration is 3000mg / kg. 7.5 moles of Li2SO4 are used as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0153] 0.0084 g of lithium isopropoxide, 0.0971 g of zirconium n-butoxide, and 0.1011 g of tributyl phosphate were dissolved in 30 mL of anhydrous ethanol. Then, 10 g of lithium cobalt oxide matrix was added, and the mixture was stirred to dryness in a water bath at 80 °C. The dried material was then sintered at 700 °C for 8 h in an atmosphere box furnace, followed by grinding and sieving through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. 0.6 parts by mass of LiZr2(PO4)3 were coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0154] Comparative Example 4

[0155] This comparative example is highly doped with Mg and Al.

[0156] Weigh out 500g Co3O4, 237.05g Li2CO3, 1.0111g nano MgO, 6.9112g nano Al2O3, and 51.37g Li2SO4. Mix them in an experimental mixer first at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. Place the blended powder in an atmosphere box furnace and sinter at 700℃ for 6h, then at 1040℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, obtain the lithium cobalt oxide matrix. The Mg doping concentration is 1000mg / kg, and the Al doping concentration is 6000mg / kg. 7.5 moles of Li2SO4 are used as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0157] 0.0084 g of lithium isopropoxide, 0.0971 g of zirconium n-butoxide, and 0.1011 g of tributyl phosphate were dissolved in 30 mL of anhydrous ethanol. Then, 10 g of lithium cobalt oxide matrix was added, and the mixture was stirred to dryness in a water bath at 80 °C. The dried material was then sintered at 700 °C for 8 h in an atmosphere box furnace, followed by grinding and sieving through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. 0.6 parts by mass of LiZr2(PO4)3 were coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0158] Comparative Example 5

[0159] This comparative example did not use sintering aids and did not modify the lithium cobalt oxide matrix.

[0160] Weigh 500g of Co3O4 and 237.05g of Li2CO3, and mix them in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. Place the blended powder in an atmosphere box furnace and sinter at 700℃ for 6h, then at 960℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, the lithium cobalt oxide matrix is ​​obtained.

[0161] Comparative Example 6

[0162] No sintering aids were used in this comparative example.

[0163] Weigh 500g of Co3O4 and 237.05g of Li2CO3, and mix them in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. Place the blended powder in an atmosphere box furnace and sinter at 700℃ for 6h, then at 960℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, the lithium cobalt oxide matrix is ​​obtained.

[0164] 0.0051 g lithium acetate, 0.0124 g nano TiO2, and 0.0267 g NH4H2PO4 were ultrasonically dispersed in 30 mL deionized water, and then 10 g lithium cobalt oxide matrix was added. The mixture was then dried in an oil bath at 100 °C. The dried material was sintered at 800 °C for 6 h in an atmosphere box furnace, and then ground and passed through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. 0.3 parts by mass of LiTi2(PO4)3 were coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0165] Comparative Example 7

[0166] This comparative example did not involve coating or modifying the lithium cobalt oxide matrix.

[0167] 500g of Co3O4, 237.05g of Li2CO3, and 37.15g of KCl were weighed and mixed in an experimental mixer at 2000 rpm for 2 min, then at 4000 rpm for 2 min, to obtain a homogeneous blended powder. The blended powder was placed in an atmosphere-controlled box furnace and sintered at 700℃ for 6 h, then at 960℃ for 12 h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, a lithium cobalt oxide matrix was obtained. The lithium cobalt oxide matrix was not doped or modified. 8 moles of KCl were used as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0168] Comparative Example 8

[0169] This comparative example involved high doping with Mg and Al, without the use of sintering aids, and without coating or modifying the lithium cobalt oxide matrix.

[0170] 500g Co3O4, 237.05g Li2CO3, 1.0111g nano-MgO, and 6.9112g nano-Al2O3 were weighed and mixed in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. The blended powder was placed in an atmosphere box furnace and sintered at 700℃ for 6h, then at 1040℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, lithium cobalt oxide matrix was obtained. The Mg doping concentration was 1000mg / kg, and the Al doping concentration was 6000mg / kg.

[0171] Comparative Example 9

[0172] This comparative example features high doping with Mg and Al, without the use of sintering aids.

[0173] 500g of Co3O4, 237.05g of Li2CO3, 1.0111g of nano-MgO, and 6.9112g of nano-Al2O3 were weighed and mixed in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. The blended powder was sintered in an atmosphere-controlled furnace at 700℃ for 6h, then at 1040℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, a lithium cobalt oxide matrix was obtained. The Mg doping concentration was 1000mg / kg, and the Al doping concentration was 6000mg / kg. No sintering aids were used.

[0174] 0.0084 g of lithium isopropoxide, 0.0971 g of zirconium n-butoxide, and 0.1011 g of tributyl phosphate were dissolved in 30 mL of anhydrous ethanol. Then, 10 g of lithium cobalt oxide matrix was added, and the mixture was stirred to dryness in a water bath at 80 °C. The dried material was then sintered at 700 °C for 8 h in an atmosphere box furnace, followed by grinding and sieving through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. 0.6 parts by mass of LiZr2(PO4)3 were coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0175] Comparative Example 10

[0176] This comparative example features high doping with Mg and Al, but the lithium cobalt oxide matrix is ​​not coated or modified.

[0177] Weigh out 500g Co3O4, 237.05g Li2CO3, 1.0111g nano MgO, 6.9112g nano Al2O3, and 51.37g Li2SO4. Mix them in an experimental mixer first at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. Place the blended powder in an atmosphere box furnace and sinter at 700℃ for 6h, then at 1040℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, obtain the lithium cobalt oxide matrix. The Mg doping concentration is 1000mg / kg, and the Al doping concentration is 6000mg / kg. 7.5 moles of Li2SO4 are used as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0178] Comparative Example 11

[0179] This comparative example features high doping with Ni and Mn.

[0180] Weigh out 500g Co3O4, 237.05g Li2CO3, 2.3276g nano-NiO, 2.8945g nano-MnO2, and 26.41g LiCl. Mix them in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. Place the blended powder in an atmosphere-controlled furnace and sinter at 680℃ for 8h, then at 960℃ for 24h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, obtain the lithium cobalt oxide matrix. The Ni doping concentration is 3000mg / kg, and the Mn doping concentration is 3000mg / kg. Use 10 moles of LiCl as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0181] 0.0093 g LiNO3 and 0.0620 g n-butoxide niobium were dissolved in 30 mL of anhydrous ethanol, and then 10 g of lithium cobalt oxide matrix was added. The mixture was stirred to dryness in a water bath at 80 °C. The dried material was then sintered in an atmosphere box furnace at 600 °C for 12 h, followed by grinding and sieving through a 300-mesh sieve to obtain coated modified lithium cobalt oxide. 0.2 parts by mass of LiNbO3 were coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0182] Comparative Example 12

[0183] No sintering aids were used in this comparative example.

[0184] 500g of Co3O4, 237.05g of Li2CO3, 0.7759g of nano-NiO, and 0.9648g of nano-MnO2 were weighed and mixed in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. The blended powder was placed in an atmosphere box furnace and sintered at 680℃ for 8h, then at 900℃ for 24h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, lithium cobalt oxide matrix was obtained. The Ni doping concentration was 1000mg / kg, and the Mn doping concentration was 1000mg / kg.

[0185] 0.0093 g LiNO3 and 0.0620 g n-butoxide niobium were dissolved in 30 mL of anhydrous ethanol, and then 10 g of lithium cobalt oxide matrix was added. The mixture was stirred to dryness in a water bath at 80 °C. The dried material was then sintered in an atmosphere box furnace at 600 °C for 12 h, followed by grinding and sieving through a 300-mesh sieve to obtain coated modified lithium cobalt oxide. 0.2 parts by mass of LiNbO3 were coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0186] Comparative Example 13

[0187] This comparative example did not involve coating or modifying the lithium cobalt oxide matrix.

[0188] Weigh out 500g Co3O4, 237.05g Li2CO3, 0.7759g nano NiO, 0.9648g nano MnO2, and 26.41g LiCl. Mix them in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. Place the blended powder in an atmosphere-controlled furnace and sinter at 680℃ for 8h, then at 900℃ for 24h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, obtain the lithium cobalt oxide matrix. The Ni doping concentration is 1000mg / kg, and the Mn doping concentration is 1000mg / kg. Use 10 moles of LiCl as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0189] Comparative Example 14

[0190] This comparative example is highly doped with Y.

[0191] Weigh out 500g Co3O4, 237.05g Li2CO3, 3.0969g nano Y2O3, and 10.92g NaCl. Mix them in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous powder. Place the powder in an atmosphere-controlled furnace and sinter at 780℃ for 3h, then at 1050℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, obtain the lithium cobalt oxide matrix. The Y doping concentration is 4000mg / kg. Use 3 moles of NaCl as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0192] 0.0575 g of lithium acetate, 0.0870 g of nano-TiO2, and 10 g of lithium cobalt oxide matrix were mixed in a ball mill at 200 rpm for 1 hour, with a ball-to-material volume ratio of 1:1. The grinding balls were made of polyurethane. The mixed material was then sintered at 700℃ for 8 hours in an atmosphere-controlled box furnace, followed by grinding and sieving through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. One part by mass of LiTi was coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix. 1.25 O3.

[0193] Comparative Example 15

[0194] This comparative example demonstrates high Zr doping.

[0195] Weigh out 500g Co3O4, 237.05g Li2CO3, 3.2942g nano ZrO2, and 10.92g NaCl. Mix them in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous powder. Place the powder in an atmosphere-controlled furnace and sinter at 780℃ for 3h, then at 1050℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, obtain the lithium cobalt oxide matrix. The Zr doping concentration is 4000mg / kg. Use 3 moles of NaCl as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0196] 0.0575 g of lithium acetate, 0.0870 g of nano-TiO2, and 10 g of lithium cobalt oxide matrix were mixed in a ball mill at 200 rpm for 1 hour, with a ball-to-material volume ratio of 1:1. The grinding balls were made of polyurethane. The mixed material was then sintered at 700℃ for 8 hours in an atmosphere-controlled box furnace, followed by grinding and sieving through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. One part by mass of LiTi was coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix. 1.25 O3.

[0197] Comparative Example 16

[0198] No sintering aids were used in this comparative example.

[0199] 500g of Co3O4, 237.05g of Li2CO3, and 0.2617g of nano-Nb2O5 were weighed and mixed in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. The blended powder was placed in an atmosphere box furnace and sintered at 700℃ for 6h, then at 960℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, lithium cobalt oxide matrix was obtained. The Nb doping concentration was 300mg / kg.

[0200] 0.0690 g of lithium acetate and 0.0644 g of nano-ZrO2 were ultrasonically dispersed in 30 mL of deionized water, and then 10 g of lithium cobalt oxide matrix was added. The mixture was then dried in an oil bath at 100 °C. The dried material was sintered in an atmosphere box furnace at 1000 °C for 2 h, and then ground and passed through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. 0.8 parts by mass of Li2ZrO3 were coated on the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0201] Comparative Example 17

[0202] No sintering aids were used in this comparative example.

[0203] 500g of Co3O4, 237.05g of Li2CO3, and 0.2145g of nano-La2O3 were weighed and mixed in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. The blended powder was placed in an atmosphere box furnace and sintered at 700℃ for 6h, then at 960℃ for 12h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, lithium cobalt oxide matrix was obtained. The La doping concentration was 300mg / kg.

[0204] 0.0690 g of lithium acetate and 0.0644 g of nano-ZrO2 were ultrasonically dispersed in 30 mL of deionized water, and then 10 g of lithium cobalt oxide matrix was added. The mixture was then dried in an oil bath at 100 °C. The dried material was sintered in an atmosphere box furnace at 1000 °C for 2 h, and then ground and passed through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. 0.8 parts by mass of Li2ZrO3 were coated on the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0205] Comparative Example 18

[0206] This comparative example uses Al2O3 coating.

[0207] 500g Co3O4, 237.05g Li2CO3, 0.5242g nano CeO2, and 88.88g SrCl2 were weighed and mixed in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. The blended powder was placed in an atmosphere box furnace and sintered at 780℃ for 8h, then at 1100℃ for 8h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, the lithium cobalt oxide matrix was obtained. The Ce doping amount was 700mg / kg. 9 moles of SrCl2 were used as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0208] 0.0200 g of nano-alumina was ultrasonically dispersed in 30 mL of anhydrous ethanol, then 10 g of lithium cobalt oxide matrix was added, and the mixture was dried in a water bath at 80 °C. The dried material was then sintered in an atmosphere box furnace at 500 °C for 4 h, followed by grinding and sieving through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. 0.2 parts by mass of Al2O3 were coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0209] Comparative Example 19

[0210] This comparative example uses Al2O3 coating.

[0211] 500g Co3O4, 237.05g Li2CO3, 0.5382g nano WO3, and 88.88g SrCl2 were weighed and mixed in an experimental mixer at 2000rpm for 2min, then at 4000rpm for 2min to obtain a homogeneous blended powder. The blended powder was placed in an atmosphere box furnace and sintered at 780℃ for 8h, then at 1100℃ for 8h. After crushing, pulverizing, washing, drying, and passing through a 300-mesh sieve, the lithium cobalt oxide matrix was obtained. The W doping amount was 700mg / kg. 9 moles of SrCl2 were used as a sintering aid per 100 moles of lithium cobalt oxide matrix.

[0212] 0.0200 g of nano-alumina was ultrasonically dispersed in 30 mL of anhydrous ethanol, then 10 g of lithium cobalt oxide matrix was added, and the mixture was dried in a water bath at 80 °C. The dried material was then sintered in an atmosphere box furnace at 500 °C for 4 h, followed by grinding and sieving through a 300-mesh sieve to obtain coated and modified lithium cobalt oxide. 0.2 parts by mass of Al2O3 were coated onto the surface of every 100 parts by mass of the lithium cobalt oxide matrix.

[0213] Comparative Example 20

[0214] This comparative example uses commercially available 4.48V lithium cobalt oxide.

[0215] The material used is commercially available 4.48V lithium cobalt oxide, with an Al doping content of 6500 mg / kg and a Mg doping content of 1000 mg / kg.

[0216] The above embodiments and comparative examples were tested:

[0217] 1. Powder XRD testing, Le Bail finishing, and strain analysis.

[0218] Powder XRD was performed using a Rigaku Smartlab 9KW X-ray diffractometer. The refined Le Bail patterns of Examples 1-11 and Comparative Examples 1-20 are shown below. Figure 3As shown in a1-a11 and b1-b20, the strain of the sample can be obtained by substituting the refined peak width and angle into the Williamson-Hall equation. Since the mass of the lithium oxide coating layer and / or the lithium phosphate coating layer is less than or equal to 1% of the mass of the lithium cobalt oxide matrix, and they are distributed on the surface of the lithium cobalt oxide matrix, their effect on the strain of the lithium cobalt oxide matrix is ​​very small.

[0219] The synthesis conditions and measured strains of Examples 1-11 and Comparative Examples 1-20 are summarized in Table 1.

[0220]

[0221]

[0222]

[0223] Table 1

[0224] As can be seen, the strains measured in Examples 1-11, Comparative Examples 7, 13, and 18-19 are all below 3 × 10⁻⁶ due to the absence of doping or low doping, coupled with the use of sintering aids. -4 In contrast, Comparative Examples 1-6, 8-12, 14-17, and 20, due to high doping or the absence of sintering aids, all showed strains higher than 3 × 10⁻⁶. -4 It is evident that increasing the doping amount significantly increases the strain of lithium cobalt oxide, while sintering aids can reduce the strain of lithium cobalt oxide to some extent.

[0225] 2. Electrochemical in-situ XRD testing.

[0226] Using Examples 1, Comparative Examples 1-2, and Comparative Example 20 as positive electrodes and lithium metal as the negative electrode, in-situ batteries were assembled. These batteries were placed on an X-ray diffractometer and charged at a current density of 10 mA / g. XRD patterns of the lithium cobalt oxide positive electrode were collected simultaneously with charging. One XRD pattern was collected every 20 minutes, with a range of 16°–65°. Grayscale images were plotted using XRD patterns from 18.3°–20.3°. Figure 4 As shown. Figure 4 The diffraction peaks on the (003) crystal plane belong to the O3 phase lithium cobalt oxide, while the diffraction peaks on the (006) crystal plane belong to the H1-3 phase lithium cobalt oxide. The O3 phase transforms into the H1-3 phase after lattice slip, as shown in… Figure 4 In the middle, the diffraction peak of the (003) crystal plane transforms into the diffraction peak of the (006) crystal plane. Therefore, it can be determined by... Figure 4The charging specific capacity corresponding to the appearance of the H1-3 phase was determined to identify the charging specific capacity and charging cutoff voltage at which low-strain lithium cobalt oxide can operate stably. In Examples 1, 1, and 2, the Al doping levels were 0, 4000 mg / kg, and 8000 mg / kg, respectively. In Comparative Example 20, the Al doping level was 6500 mg / kg and the Mg doping level was 1000 mg / kg. The appearance of the H1-3 phase in all of these examples corresponded to an initial charging specific capacity of approximately 225 mAh / g. Therefore, limiting the initial discharge specific capacity of low-strain lithium cobalt oxide to 208-213 mAh / g is reasonable.

[0227] 3. Electrochemical performance test of button half-cell.

[0228] The preparation steps of the coin cell half-cell are as follows: using N-methylpyrrolidone as a solvent, lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride are mixed in a mass ratio of 96:2:2 to form a homogeneous slurry. The slurry is then coated onto a 10 μm thick aluminum foil with an areal loading of 14 mg / cm³. 2 After drying, the material is cut into circular positive electrode sheets with a diameter of 12 mm. Using the prepared circular electrode sheets as the positive electrode, lithium metal as the negative electrode, and a PE separator coated with alumina on both sides, an R2032 coin cell is assembled with an electrolyte volume of 60 μL.

[0229] 1) Cyclic performance testing at 25°C: The lithium cobalt oxide assembled coin cells from Examples 1-11 and Comparative Examples 1-20 were tested using a charge / discharge tester, with the coin cells placed in a constant temperature chamber at 25°C. The charging cut-off voltage was determined by the initial discharge specific capacity, which was limited to within 208-213 mAh / g, and the discharge cut-off voltage was 3V (vsLi). + Lithium cobalt oxide (LiCO) without coating modification has a low initial discharge specific capacity. Therefore, the charging cutoff voltage of uncoated LiCO was set to be the same as that of coated LiCO with the same doping amount. The battery was charged at a constant current / constant voltage density of 10 mA / g, with a cutoff current density of 5 mA / g for constant voltage charging, and discharged at a constant current density of 10 mA / g for two cycles to activate the battery. Then, it was charged at a constant current / constant voltage density of 100 mA / g, with a cutoff current density of 5 mA / g for constant voltage charging, and discharged at a constant current density of 100 mA / g for 50 cycles. The initial discharge specific capacity, initial coulombic efficiency, initial discharge specific capacity (third discharge specific capacity), 52nd discharge specific capacity, and 52nd capacity retention rate were obtained.

[0230] 2) Rate charge / discharge performance testing at 25°C: The lithium cobalt oxide assembled coin cells from Examples 1, Comparative Examples 1-2, and Comparative Example 20 were tested using a charge / discharge tester. The coin cells were placed in a constant temperature chamber at 25°C. The charging cutoff voltage was 4.54V (vs Li). + / Li), 4.58V (vs Li) + / Li), 4.64V (vs Li) + / Li), 4.60V (vs Li + / Li), the discharge cutoff voltage is 3V (vs Li) + / Li). Constant current charge and discharge were performed at current densities of 20 mA / g (0.1C), 100 mA / g (0.5C), 200 mA / g (1C), 400 mA / g (2C), 800 mA / g (4C), and 1600 mA / g (8C), respectively.

[0231] Table 2 summarizes the charging cutoff voltage, initial discharge specific capacity, initial coulombic efficiency, initial discharge specific capacity (third discharge specific capacity), 52nd discharge specific capacity, and 52nd discharge capacity retention for Examples 1-11 and Comparative Examples 1-20. Specifically, the coin cell assembled with lithium cobalt oxide in Example 1 underwent cycle testing at charging cutoff voltages of 4.53V, 4.54V, and 4.55V to detect the initial discharge specific capacity corresponding to different charging cutoff voltages and their impact on cycle capacity retention.

[0232]

[0233]

[0234] Table 2

[0235] During testing, the charging cutoff voltage was adjusted according to the type and amount of doping elements to control the initial discharge specific capacity of Examples 1-11 at 208-213 mAh / g. After 50 cycles, the capacity retention of Examples 1-11 was all above 95%. Comparative Examples 5, 7, 8, 10, and 13, due to the lack of coating modification, experienced severe side reactions, resulting in significant capacity decay after the first cycle, leading to an initial discharge specific capacity (third discharge specific capacity) of less than 200 mAh / g. Furthermore, the discharge specific capacity also decreased significantly in the subsequent 50 cycles. This demonstrates that coating modification significantly improves the cycling performance of lithium cobalt oxide.

[0236] like Figure 5 , Figure 6As shown, the initial discharge specific capacity of Example 1 was 210.8 mAh / g, and that of Example 2 was 209.8 mAh / g. After 50 cycles, the capacity retention rate of Example 1 was 97.1%, and that of Example 2 was 95.6%, both higher than that of Comparative Examples 1-2 and Comparative Example 20. This indicates that, under the same initial discharge specific capacity, heavy Al doping leads to greater stress and strain, thereby deteriorating the cycling performance of lithium cobalt oxide.

[0237] In Examples 1, 1, and 2, the elemental doping concentrations increased sequentially by 4000 mg / kg. To achieve similar initial charge specific capacities, higher doping concentrations of lithium cobalt oxide require higher charge cut-off voltages. However, this leads to more severe side reactions, resulting in lower initial coulombic efficiency. Severe surface side reactions are also one of the reasons why the cycle performance of Comparative Examples 1 and 2 is inferior to that of Example 1.

[0238] like Figure 7 As shown, Example 1 was also cycled at charging cutoff voltages of 4.53V and 4.55V, respectively. At a charging cutoff voltage of 4.53V, the initial discharge specific capacity was 202.8 mAh / g, lower than 208-213 mAh / g. Due to the low amount of lithium delithiation, the strain during charging and discharging was small, and the capacity retention rate after 50 cycles was as high as 99.0%. At a charging cutoff voltage of 4.55V, the initial discharge specific capacity was 218.1 mAh / g, higher than 208-213 mAh / g. Because the high amount of lithium delithiation resulted in high strain, Example 1 only achieved an 89.0% capacity retention rate after 50 cycles at a charging cutoff voltage of 4.55V. Therefore, limiting the initial discharge specific capacity of lithium cobalt oxide to below 208-213 mAh / g is crucial for cycle performance and helps to improve cycle life.

[0239] like Figure 8 As shown, the initial discharge specific capacities of Examples 3 and 4 were 211.2 mAh / g and 210.9 mAh / g, respectively, while the initial discharge specific capacities of Comparative Examples 3 and 4 were 209.1 mAh / g and 204.7 mAh / g, respectively. After 50 cycles, the capacity retention rates of Examples 3 and 4, and Comparative Examples 3 and 4 were 97.9%, 95.3%, 90.0%, and 85.7%, respectively. This indicates that excessively high Mg and Al doping levels can also degrade the cycling performance of lithium cobalt oxide.

[0240] Since the strains in Examples 1 and 3 are 0.62 × 10⁻⁶ respectively... -4 0.86×10 -4 All are below 1×10 -4Thanks to lower strain and fewer defects, stress-strain changes are less likely to accumulate during long cycles, resulting in better cyclic performance. Figure 9 As shown, Example 1 has a capacity retention rate of 97.1% at a charging cutoff voltage of 4.54V, and Example 3 has a capacity retention rate of 97.9% at a charging cutoff voltage of 4.56V, both higher than 97%.

[0241] like Figure 10 As shown, no sintering aids were used in the synthesis of Comparative Example 5, and no coating modification was performed. Therefore, compared with Examples 1, 6, and 7, Comparative Example 5 exhibited the worst cycle performance. Comparative Example 7 used sintering aids but did not undergo coating modification, resulting in slightly better cycle performance than Comparative Example 5. Comparative Example 6 did not use sintering aids but underwent coating modification, thus its cycle performance was superior to Comparative Example 5. This demonstrates that coating modification is crucial for the cycle performance of lithium cobalt oxide; unmodified lithium cobalt oxide experiences a rapid decrease in discharge specific capacity during cycling. Sintering aids can further improve the cycle performance of lithium cobalt oxide. Therefore, sintering aids and coating modification are indispensable for lithium cobalt oxide.

[0242] like Figure 11 As shown, no sintering aid was used in the synthesis of Comparative Example 8, and no coating modification was performed. Therefore, compared with Examples 3, 9, and 10, Comparative Example 8 exhibits the worst cycling performance. Comparative Example 10 used a sintering aid but did not undergo coating modification, so its cycling performance is slightly better than Comparative Example 8. Comparative Example 9 did not use a sintering aid but underwent coating modification, so its cycling performance is also better than Comparative Example 8. Example 3, due to its low doping, use of a sintering aid, and coating modification, exhibits the best cycling performance.

[0243] like Figure 12 As shown, Example 5, doped with only 1000 mg / kg Ni and 1000 mg / kg Mn, and with the addition of sintering aids and coating modification, exhibited superior cycling performance compared to Comparative Examples 11-13. Comparative Example 11, with Ni and Mn doping amounts of 3000 mg / kg, still showed inferior cycling performance compared to Example 5 despite the use of sintering aids and coating modification. Comparative Example 12 used the same doping amount and coating modification method as Example 5, but due to the absence of sintering aids, its cycling performance was inferior to Example 5, with a capacity retention of 90.3% after 50 cycles. Comparative Example 13, lacking coating modification, exhibited inferior cycling performance compared to Examples 5 and Comparative Examples 11-12.

[0244] like Figure 13As shown, the cycling performance of Examples 6-7 is significantly better than that of Comparative Examples 14-15. The difference between Comparative Examples 14-15 and Examples 6-7 lies in the doping amount: Examples 6 and Comparative Examples 14 were doped with 500 mg / kg and 4000 mg / kg of Y, respectively, while Examples 7 and Comparative Examples 15 were doped with 500 mg / kg and 4000 mg / kg of Zr, respectively. It is evident that excessively high doping amounts lead to a rapid decay of the discharge specific capacity.

[0245] like Figure 14 As shown, the cycling performance of Examples 8-9 is superior to that of Comparative Examples 16-17. The difference between Examples 8-9 and Comparative Examples 16-17 is that Examples 8-9 used a sintering aid, while Comparative Examples 16-17 did not. Therefore, it can be seen that, under the premise of low doping and coating modification, the use of a sintering aid can further improve the cycling performance of lithium cobalt oxide.

[0246] like Figure 15 As shown, the cycle performance of Examples 10-11 is superior to that of Comparative Examples 18-19. The difference between Examples 10-11 and Comparative Examples 18-19 is that the surface coating of Examples 10-11 is LiSn2(PO4)3, while the surface coating of Comparative Examples 18-19 is Al2O3. This demonstrates that coating the surface of lithium cobalt oxide with lithium phosphate is superior to coating it with alumina.

[0247] The rate performance comparison between Example 1 and Comparative Examples 1-2 and 20 is shown in Table 3 and Figure 16 middle.

[0248]

[0249] Table 3

[0250] As can be seen, the higher the doping concentration, the worse the rate performance; Example 1 exhibits the best rate performance. Example 1 was cycled five times sequentially at current densities (where 1C = 200 mA / g) of 0.1C, 0.5C, 1C, 2C, 4C, and 8C. The discharge specific capacities at each current density were 208.1 mAh / g, 201.8 mAh / g, 192.9 mAh / g, 175.2 mAh / g, 140.6 mAh / g, and 89.9 mAh / g, respectively, with capacity retention rates of 100%, 97.0%, 92.7%, 84.2%, 67.6%, and 43.2%, respectively, significantly higher than Comparative Examples 1-2 and Comparative Example 20. This is because doping lithium cobalt oxide with Al not only increases strain but also increases the barrier to lithium-ion diffusion, thereby affecting the ionic conductivity of lithium cobalt oxide and consequently negatively impacting its rate performance.

[0251] 4. Soft-pack full battery test.

[0252] The steps for preparing a pouch cell include:

[0253] 1) Preparation of positive electrode: Using N-methylpyrrolidone as solvent, lithium cobalt oxide prepared in Example 1 and Comparative Example 20 was mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 96:2:2 to form a homogeneous slurry. This slurry was then coated onto a 10 μm thick aluminum foil to produce an areal capacity of 4.7 mAh / cm². 2 The positive electrode sheet has a compaction density of 4.15 g / cm³. 3 .

[0254] 2) Negative electrode preparation: Using deionized water as a solvent, silicon-carbon negative electrode material, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber were mixed in a mass ratio of 94.5:1.5:1.5:2.5 to form a homogeneous slurry. This slurry was then coated onto a 6μm thick copper foil to produce an areal capacity of 4.98 mAh / cm². 2 The negative electrode sheet has a compaction density of 1.55 g / cm³. 3 .

[0255] 3) Fabrication of pouch cells: In a cleanroom with a dew point below -50°C, positive and negative electrodes are stacked alternately to form cells using a conventional Z-shaped stacking method. The separator is a PE separator coated with alumina on both sides, and the electrolyte is a commercially available electrolyte with a filling coefficient of 2.5. Pouch cells are fabricated through stacking, welding, encapsulation, electrolyte filling, and formation.

[0256] The electrochemical performance of the prepared pouch cells was tested:

[0257] Throughout the testing process, the pouch cells were clamped in place. After being filled with electrolyte and allowed to settle, the pouch cells of Example 1 were first cycled twice at a current of 0.1C within a voltage range of 3.0-4.44V. The pouch cells of Comparative Example 20 were also first cycled twice at a current of 0.1C within a voltage range of 3.0-4.50V. After removing the air bags, the battery mass and volume were measured. Then, a long-cycle test was conducted at a current of 0.5C. The pouch cells of Example 1 were cycled within a voltage range of 3.0-4.44V, and the pouch cells of Comparative Example 20 were cycled within a voltage range of 3.0-4.50V. The mass energy density and volumetric energy density of the cells were calculated based on the energy of the second discharge at 0.5C, the cell mass, and the cell volume, respectively.

[0258] The 0.5C capacity, gravimetric energy density, volumetric energy density, and capacity retention after 500 cycles of the pouch cells of Example 1 and Comparative Example 20 are summarized in Table 4. A comparison of the cycling performance of the pouch cells of Example 1 and Comparative Example 20 at 0.5C is plotted in... Figure 17 middle.

[0259]

[0260] Table 4

[0261] As can be seen, Example 1 exhibits higher capacity performance compared to Comparative Example 20. At a 0.5C rate, the discharge capacities of Example 1 and Comparative Example 20 are 7.07 Ah and 6.81 Ah, respectively, corresponding to mass energy densities of 353.64 Wh / kg and 342.03 Wh / kg; and volumetric energy densities of 905.32 Wh / L and 880.16 Wh / L, respectively. Compared to commercially available 4.48V lithium cobalt oxide (Comparative Example 20), the lithium cobalt oxide prepared in this invention shows significant improvements in both volumetric and mass energy densities in pouch cells, with the volumetric energy density exceeding 900 Wh / L. This is of great significance for improving the battery life of consumer electronics. Furthermore, due to the reduction of internal stress and strain accumulation, the remaining capacity of the pouch cell after 500 cycles at a 0.5C rate increases from 80.76% of the currently available 4.48V lithium cobalt oxide to 88.67%. The performance of the pouch cell further demonstrates the practicality of the invention.

[0262] 5. Failure analysis.

[0263] The coin half-cells of Example 1 and Comparative Example 20, after 50 cycles, were disassembled, and the positive electrode was removed. XRD patterns were acquired using a Rigaku Smartlab 9KW X-ray diffractometer. The Le Bail refinement images of the positive electrode after 50 cycles of Example 1 and Comparative Example 20 are shown below. Figure 18 As shown, by substituting the refined peak width and angle into the Williamson-Hall equation, the strain of the sample can be obtained. In Example 1, the strain after 50 cycles was 7.4 × 10⁻⁶. -4 The strain of Comparative Example 20 after 50 cycles was 20.3 × 10⁻⁶. -4 As can be seen, Example 1, which has lower strain, also has lower strain after cycling, and the increase in strain is also smaller. Therefore, the particles are less likely to crack and have better cycling performance.

[0264] The coin half-cells of Example 1 and Comparative Example 20, after 50 cycles, were disassembled, and the positive electrode was removed. The cross-section of the positive electrode was polished using a NEC IB-19530CP argon-ion cross-section polisher, and then the morphology of the cross-section was observed using a Hitachi SU8100 scanning electron microscope (SEM). The cross-sectional morphology of the electrodes of Example 1 and Comparative Example 20 after 50 cycles is shown in the figure. Figure 19As shown, after 50 cycles, no cracks appeared inside the particles in Example 1, while obvious cracks appeared inside the particles in Comparative Example 20 after 50 cycles. This indicates that the stress accumulation in Comparative Example 20 was greater during cycling, causing the particles to crack. The material in Example 1 did not crack after cycling, which is attributed to two factors: firstly, the small initial strain, and secondly, the controlled initial discharge specific capacity, which prevented lattice slip from being triggered. Therefore, no cracks appeared inside the particles, resulting in better cycling performance.

[0265] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment 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 within the scope of protection of the present invention.

Claims

1. A method for preparing low-strain lithium cobalt oxide, characterized in that, The preparation method includes: Cobalt tetroxide, lithium carbonate, and sintering aids are mixed together, and no dopant or no more than a certain mass of dopant is added to obtain a blended powder. The blended powder is sintered by first heating it to 680℃-780℃ and holding it at that temperature for 3-8 hours, then heating it to 900℃-1100℃ and holding it at that temperature for 8-24 hours, and finally cooling it to 300℃ at a cooling rate not exceeding 5℃ / min to obtain the sintered material. During the sintering process, LiCoO2 generated from the reaction of lithium carbonate and cobalt tetroxide undergoes fusion growth in the liquid phase formed by the sintering aid. The sintering aid is an alkali metal salt and / or alkaline earth metal salt with a melting point below 900℃ and a boiling point above 1200℃ that does not react with lithium cobalt oxide, and has a solubility in water greater than 200 g / L at 25℃. The total molar number of alkali metal elements in the alkali metal salt and / or alkaline earth metal elements in the alkaline earth metal salt is greater than or equal to 3 and less than or equal to 15 per 100 molar parts of lithium cobalt oxide matrix. The sintered material is crushed, pulverized, washed, dried, and sieved to obtain a lithium cobalt oxide matrix. The lithium cobalt oxide matrix is ​​coated, and then the resulting material containing the coating layer is ground and sieved to obtain the low-strain lithium cobalt oxide.

2. The preparation method according to claim 1, characterized in that, The coating process includes: mixing the lithium cobalt oxide matrix with a lithium source and an M1 source to obtain a mixed powder, wherein M1 is one or more of Si, Ti, Zr, Nb, Mo, and Ta; and / or mixing the lithium cobalt oxide matrix with a lithium source, an M2 source, and a phosphorus source to obtain a mixed powder, wherein M2 is one or more of Ti, Ge, Zr, Sn, and Hf; The mixed powder is heated to 600℃-1000℃ and held at that temperature for 2h-12h, and then cooled to 300℃ at a cooling rate not exceeding 5℃ / min to obtain the material containing the coating layer.

3. The preparation method according to claim 2, characterized in that, The coating layer of the material containing the coating layer is specifically a lithium oxide coating layer and / or a lithium phosphate coating layer; The chemical formula of the lithium oxide coating layer is: Li a M1 b O3, where the average valence state of M1 is +m, satisfying a+mb=6; the Li a M1 b O3 includes: Li2SiO3, Li2TiO3, LiTi 1.25 One or more of O3, Li2ZrO3, LiNbO3, Li2MoO3, and LiTaO3; The chemical formula of the lithium phosphate coating is: Li c M2 d (PO4)3, where the average valence state of M2 is +n, satisfying c+nd=9; the Li c M2 d (PO4)3 includes: LiTi2(PO4)3, Li Ge2(PO4)3, LiZr2(PO4)3, Li3Zr 1.5 One or more of (PO4)3, LiSn2(PO4)3, and LiHf2(PO4)3; The total mass fraction of lithium oxide coating and / or lithium phosphate coating is less than or equal to 1 per 100 parts by mass of lithium cobalt oxide matrix.

4. The preparation method according to claim 2, characterized in that, The lithium source includes one or more of the following: lithium-containing oxides, inorganic salts, organic salts, alkoxides, and phosphates; The M1 source includes one or more of the following: oxides, inorganic salts, organic salts, alkoxides, and phosphates of M1; The M2 source includes one or more of the following: oxides, inorganic salts, organic salts, alkoxides, and phosphates of M2; The phosphorus source includes: inorganic phosphorus compounds and / or organic phosphorus compounds.

5. The preparation method according to claim 4, characterized in that, The lithium source includes one or more of the following: Li2O, Li2CO3, LiOH, LiNO3, lithium acetate, lithium oxalate, lithium isopropoxide, Li3PO4, Li2HPO4, and LiH2PO4; The M1 source includes one or more of the following: SiO2, H4SiO4, tetraethyl silicate, TiO2, TiOSO4, titanium isopropoxide, titanium n-butoxide, ZrO2, zirconium ethoxide, zirconium isopropoxide, zirconium n-butoxide, Nb2O5, niobium oxalate, niobium ethoxide, niobium n-butoxide, Nb3(PO4)5, MoO2, molybdenum isopropoxide, Ta2O5, tantalum ethoxide, and tantalum isopropoxide; The M2 source includes one or more of the following: TiO2, TiOSO4, titanium isopropoxide, titanium n-butoxide, GeO2, germanium ethanol, germanium isopropoxide, ZrO2, zirconium ethanol, zirconium isopropoxide, zirconium n-butoxide, SnO2, tin ethanol, tin isopropoxide, tin tert-butoxide, HfO2, hafnium ethanol, and hafnium isopropoxide. The phosphorus source includes one or more of the following: H3PO4, NH4H2PO4, (NH4)2HPO4, (NH4)3PO4, Li3PO4, Li2HPO4, Li H2PO4, tributyl phosphate, and monobutyl dodecyl phosphate.

6. The preparation method according to claim 1, characterized in that, The doping reagent is specifically a nano-oxide of a doping element, which includes one or more of Mg, Al, Ti, Mn, Ni, Y, Zr, Nb, Mo, La, Ce, and W; the Dv50 of the doping reagent is less than or equal to 100 nm; the doping reagent added in no more than a certain mass is specifically: the total mass of the doping element is less than or equal to 0.3 parts per 100 parts per mass of lithium cobalt oxide matrix.

7. The preparation method according to claim 1, characterized in that, The sintering aids include one or more of LiCl, NaCl, KCl, Li2SO4, Na2SO4, Na2CO3, CaCl2, and SrCl2.

8. The preparation method according to claim 1, characterized in that, In the blended powder, the amount of lithium carbonate is 1%-5% excess of lithium element in lithium carbonate relative to the molar amount of lithium element in lithium cobalt oxide matrix, preferably 3%.

9. A low-strain lithium cobalt oxide prepared by the preparation method according to any one of claims 1-8, characterized in that, The strain of the low-strain lithium cobalt oxide is 3.0 × 10⁻⁶. -4 the following; In systems using lithium metal as both the counter and reference electrodes, low-strain lithium cobalt oxide prepared with no or no more than a certain mass of dopant can achieve a charging cutoff voltage of less than or equal to 4.54-4.57V (vs Li). + When the charge / discharge current density is 100 mA / g, the initial discharge specific capacity of the low-strain lithium cobalt oxide is less than or equal to 208-213 mAh / g, and the capacity retention rate is higher than 95% after 50 cycles.

10. An application of the low-strain lithium cobalt oxide prepared by any one of the preparation methods according to claims 1-8, characterized in that, The low-strain lithium cobalt oxide is used in lithium secondary batteries, cells, or battery packs.

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