A method for adjusting the cobalt-lithium molar ratio of a lithium cobalt oxide positive electrode material, and lithium cobalt oxide and high-pressure lithium cobalt oxide positive electrode materials

Abstract

This application belongs to the field of lithium-ion battery technology and discloses a method for adjusting the cobalt-lithium molar ratio of a lithium cobalt oxide cathode material, as well as lithium cobalt oxide and high-voltage lithium cobalt oxide cathode materials. The method for adjusting the cobalt-lithium molar ratio of the lithium cobalt oxide cathode material involves determining the cobalt-lithium molar ratio of the coating agent based on the Li / Co molar ratio of the lithium cobalt oxide matrix obtained in the first calcination using the following mathematical model, followed by a second calcination to obtain the lithium cobalt oxide cathode material: Co / Li = k × (R - R0) + c; where Co / Li is the molar ratio of cobalt to lithium in the coating agent, R is the Li / Co molar ratio of the lithium cobalt oxide matrix obtained in the first calcination, R0 is the reference stoichiometric point, k is the adjustment coefficient, and c is the reference value; the value of k ranges from 10 to 40, and the value of c ranges from 0.9 to 1.1. This application provides a method for adjusting the cobalt-lithium molar ratio of a lithium cobalt oxide cathode material, employing a specific mathematical model to perform a second calcination coating of the lithium cobalt oxide matrix after the first calcination with a coating agent of a specific cobalt-lithium molar ratio, thereby achieving dynamic and precise control of the interfacial stoichiometry and optimizing the overall performance of the cathode material.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, specifically to a method for adjusting the cobalt-lithium molar ratio of a lithium cobalt oxide cathode material, and lithium cobalt oxide and high-voltage lithium cobalt oxide cathode materials. Background Technology

[0002] Lithium cobalt oxide (LiCoO2), as a cathode material for lithium-ion batteries, has advantages such as high energy density, stable discharge platform, and good cycle performance, and has always been the mainstream choice for cathode materials of lithium-ion batteries in consumer electronics products (such as smartphones and laptops) and high-rate power scenarios (such as drones and racing drones). With the increasing demands for battery life in 3C products, and the growing need for instantaneous burst power and sustained high-rate discharge performance in power devices such as drones and racing drones, the operating voltage of lithium cobalt oxide is constantly increasing (such as 4.40 V and above), which poses a dual challenge to the material's rate performance and structural stability.

[0003] Under high voltage, severe side reactions occur on the surface of lithium cobalt oxide, including oxidative decomposition of the electrolyte, dissolution of cobalt ions, and irreversible phase transitions, leading to a sharp deterioration in battery cycle performance. Furthermore, under high-rate discharge conditions, the internal lithium-ion diffusion resistance increases, and interfacial reaction kinetics become sluggish, easily causing problems such as intensified polarization and accelerated capacity decay, making it difficult to meet the instantaneous high-current output requirements of devices such as drones and racing drones. To address these issues, existing technologies typically employ bulk doping and surface coating modification of lithium cobalt oxide. A common process is the "two-stage sintering method": a first sintering (first sintering) yields a lithium cobalt oxide matrix with certain electrochemical activity, followed by a second sintering (second sintering) to introduce a coating layer on the matrix surface to suppress side reactions and optimize interfacial lithium conductivity.

[0004] However, existing coating schemes are often "static," employing fixed coating formulations and dosages. In actual production, regardless of whether pure-phase lithium cobalt oxide or doped / modified lithium cobalt oxide is used, and regardless of whether the primary particle morphology is single crystal, near-single crystal, or polycrystalline aggregate, the Li / Co stoichiometry of the lithium cobalt oxide matrix fluctuates during preparation due to differences in sintering temperature and lithium volatilization. This fluctuation is a common problem in lithium cobalt oxide material preparation, severely affecting the adaptability of subsequent coating processes and product consistency. If a uniform coating process is used, when the Li / Co ratio of the lithium cobalt oxide matrix is ​​high, if the coating layer cannot provide enough cobalt to "anchor" excess lithium on the surface, it will lead to excessive residual alkali on the material surface, exacerbating electrolyte decomposition and deteriorating rate performance. When the Li / Co ratio of the lithium cobalt oxide matrix is ​​low, if the coating layer cannot replenish enough lithium, it will lead to increased surface defects and excessive interfacial impedance, further limiting lithium-ion transport efficiency at high rates. This static coating cannot be adapted to the lithium abundance or scarcity state on the substrate surface, ultimately making it difficult to achieve high energy density, high rate performance, cycle performance, and thermal stability. It also affects the high voltage cycle stability of the material and product consistency.

[0005] Therefore, developing a lithium cobalt oxide modification technology that can dynamically adjust the content of coating components and optimize the coating amount based on the Li / Co ratio of lithium cobalt oxide to balance specific capacity, high rate capability, cycling performance, and thermal safety is of great practical significance and application value. Summary of the Invention

[0006] One of the objectives of this application is to provide a method for adjusting the cobalt-lithium molar ratio of a lithium cobalt oxide cathode material, which dynamically adjusts the cobalt-lithium ratio of the coating layer of the lithium cobalt oxide cathode material through a mathematical model.

[0007] Another objective of this application is to provide a lithium cobalt oxide cathode material, which is prepared using the adjustment method of this application and can take into account comprehensive performance such as specific capacity, high rate capability, cycle life, and thermal safety.

[0008] To achieve the above objectives, this application provides a method for adjusting the cobalt-lithium molar ratio in a lithium cobalt oxide cathode material. Based on the Li / Co molar ratio of the lithium cobalt oxide matrix obtained in the first calcination, the following mathematical model is used to determine the cobalt-lithium molar ratio of the coating agent for a second calcination to obtain the lithium cobalt oxide cathode material: Co / Li = k × (R - R0) + c; Where Co / Li is the molar ratio of cobalt to lithium in the coating agent, R is the Li / Co molar ratio of the lithium cobalt oxide matrix obtained by calcination, R0 is the reference stoichiometric point, k is the adjustment coefficient, and c is the reference value; the value of k ranges from 10 to 40, and the value of c ranges from 0.9 to 1.1. and, When R is between 0.95 and 0.98, the value of k ranges from 30 to 40. When R is between 0.98 and 1.05, the value of k ranges from 15 to 30. When R is between 1.05 and 1.10, the value of k ranges from 10 to 20. When the calculated Co / Li value is less than 0.1, the Co / Li value is between 0.1 and 0.3.

[0009] Preferably, the value of R0 is 1.02.

[0010] The mathematical model used in this application can effectively adjust the cobalt-lithium molar ratio of the lithium cobalt oxide cathode material dynamically, thereby effectively ensuring the various performance characteristics of the lithium cobalt oxide material.

[0011] Meanwhile, this application found that the values ​​of the adjustment coefficient k and the reference value c directly determine the final electrochemical performance of the material: When the k value is too small, the Co / Li ratio of the coating agent is not sensitive to changes in the R value and cannot effectively compensate for the interfacial differences caused by different R values, resulting in interfacial mismatch in some matrix states and a decrease in cycle performance and rate performance. When the k value is too large, the Co / Li ratio of the coating agent is overly sensitive to changes in the R value, and the coating thickness fluctuates drastically. In some matrix states, the coating is too thick or too thin, affecting rate performance or protective effect. Only when the values ​​of k and c are within an appropriate range can materials with different R values ​​achieve a balance of high specific capacity, high cycle stability and excellent rate performance.

[0012] The aforementioned dynamic control method is not only applicable to lithium cobalt oxide with specific compositions, but also generally applicable to various types of lithium cobalt oxide cathode materials, including but not limited to pure phase lithium cobalt oxide, single-element doped lithium cobalt oxide, multi-element doped lithium cobalt oxide, monocrystalline lithium cobalt oxide, polycrystalline lithium cobalt oxide, quasi-monocrystalline lithium cobalt oxide, and lithium cobalt oxide with different particle size distributions. Regardless of the specific composition, crystal form, or morphology of the matrix, as long as there is a fluctuation in the Li / Co ratio of the lithium cobalt oxide matrix, the dynamic control method of this application can effectively improve the interface matching and enhance the overall electrochemical performance.

[0013] The technical solution of this application is essentially to mathematically and accurately model the interface structure under different matrix conditions, so that the material can obtain the optimal comprehensive electrochemical performance under different R values.

[0014] Preferably, the method for adjusting the cobalt-lithium molar ratio of the lithium cobalt oxide cathode material specifically includes the following steps: Step 1: Preparation of lithium cobalt oxide matrix by calcination; Step 2: Determine the Li / Co molar ratio of the lithium cobalt oxide matrix; Step 3: Determine the cobalt-lithium molar ratio of the coating agent according to the mathematical model, and mix the coating agent and the lithium cobalt oxide matrix for secondary calcination to obtain the lithium cobalt oxide cathode material.

[0015] It should be noted that the first firing temperature and time are determined based on the composition of the lithium cobalt oxide matrix material, and those skilled in the art can select them according to existing technology and common knowledge in the field; the second firing temperature and time are determined based on the composition of the lithium cobalt oxide matrix material and the coating agent, and those skilled in the art can select them according to existing technology and common knowledge in the field.

[0016] More preferably, the total mass of the coating agent is calculated using the following mathematical model: W = W0 × [1 + β × (R - R0)]; Where W is the total mass of the coating agent, W0 is the standard coating amount, R is the Li / Co molar ratio of the lithium cobalt oxide matrix obtained by calcination, R0 is the reference stoichiometric point, and β is the adjustment coefficient, with a value ranging from 0 to 10.

[0017] Furthermore, the lithium cobalt oxide matrix includes pure-phase lithium cobalt oxide and doped modified lithium cobalt oxide.

[0018] Preferably, the chemical formula of the lithium cobalt oxide matrix is ​​Li 1+a Co 1-b M b O2, where -0.05≤a≤0.1, 0≤b≤0.05, and M is selected from at least one of Al, Mg, Ti, Zr, Mn, Y, La, Ni, Nb, Gd, and Ga.

[0019] Furthermore, the coating agent includes cobalt compounds and lithium salts.

[0020] The cobalt compound includes, but is not limited to, one or more of cobalt oxide, cobalt hydroxyoxide, cobalt hydroxide, cobalt carbonate, and cobalt oxalate; the lithium salt includes, but is not limited to, one or more of lithium hydroxide, lithium carbonate, and lithium nitrate.

[0021] Furthermore, the coating agent also includes at least one selected from oxides and oxyacid salts of Al, Mg, Ti, Zr, B, Y, La, P, and F.

[0022] This application also provides a lithium cobalt oxide cathode material, which is prepared using the above-mentioned method for adjusting the cobalt-lithium molar ratio of lithium cobalt oxide cathode materials.

[0023] Meanwhile, this application provides a high-voltage lithium cobalt oxide cathode material, which is prepared by the above-mentioned method for adjusting the cobalt-lithium molar ratio of lithium cobalt oxide cathode materials; The chemical formula of the lithium cobalt oxide matrix is ​​Li x Co 1-y My O2, wherein 0.95 ≤ x ≤ 1.07, 0 ≤ y ≤ 0.05, and M is selected from at least one of Al, Mg, Ti, Zr, Mn, Y, La, Ni, Nb, Gd, Ga, Fe, Sn, B, Bi, and Sr; The coating agent further includes at least one of the following: Li-AO system, Li-BF system, and sodium copper iron manganate; wherein A is at least one of Mg, Zn, Si, Ge, Ti, Al, Zr, Te, Mo, W, Sb, Nb, Ta, and La, and B is at least one of Mn, Ni, Al, Co, Mg, Ca, Y, La, Ti, and Fe.

[0024] In the preparation process of the high-voltage lithium cobalt oxide cathode material using the aforementioned method for adjusting the cobalt-lithium molar ratio, the lithium cobalt oxide matrix and the coating agent respectively form a lithium cobalt oxide core and a coating layer; the coating layer contains a cobalt-containing compound, and the high-voltage lithium cobalt oxide cathode material satisfies the following conditions in cross-sectional SEM-EDS line scan: Within a depth range of 10 nm to 50 nm from the surface of the coating layer towards the core, the absolute value of the atomic concentration gradient of cobalt, |ΔCo / Δd|, is negatively correlated with the value of x ((1) the higher x (lithium-rich): the higher the Co / Li coating, the more uniform the distribution of cobalt on the surface and the smoother the transition → smaller gradient; (2) the lower x (lithium-deficient): the lower the Co / Li coating, the more cobalt is concentrated on the surface → larger gradient; therefore, |ΔCo / Δd| decreases as x increases, showing a significant negative correlation).

[0025] As a preferred embodiment of this application, the average thickness of the coating layer is 5nm-100nm, and the thickness of the coating layer is positively correlated with the x value.

[0026] As a preferred embodiment of this application, the material is formed by the agglomeration of primary particles into secondary particles; The primary particles are nearly spherical in shape, with a particle size of 0.5-3 μm, and a dense, smooth surface without obvious pores or cracks; the secondary particles are nearly spherical or near-spherical in shape, with a particle size distribution of 1-15 μm. 50 The particle size is 5-7 μm, the particle surface is dense and smooth, and there is no obvious hard agglomeration.

[0027] Among them, (1) large single-crystal particles with a size of 8–10 μm; (2) medium-sized spherical particles with a size of 4–6 μm; and (3) nano-sized small particles with a size of 1–2 μm. The small particles are uniformly distributed on the surface and in the gaps of the large and medium particles, so that the material has both high solid density and high rate discharge performance.

[0028] Beneficial effects Compared with the prior art, this application provides a method for adjusting the cobalt-lithium molar ratio of lithium cobalt oxide cathode materials. By using a specific mathematical model, a specific cobalt-lithium molar ratio coating agent is applied to the lithium cobalt oxide matrix after one calcination for a second calcination, thereby achieving dynamic and precise control of the interfacial stoichiometry and optimizing the overall performance of the cathode material. Detailed Implementation

[0029] The present application will be further described below with reference to embodiments, but this does not constitute any limitation on the present application. Any limited modifications made within the scope of the claims of the present application shall still be within the scope of the claims of the present application.

[0030] To illustrate the technical content of this application in detail, the following description is provided in conjunction with the embodiments.

[0031] Preparation of lithium monocarbonate matrix: Lithium carbonate and cobalt tetroxide were mixed in a molar ratio of Li:Co = 1.03:1 and sintered at 950-1020℃ for 6-24 hours. After pulverization, lithium monocarbonate matrix was obtained.

[0032] Different batches of lithium monocobalt oxide matrix were obtained based on different sintering temperatures and sintering times. The actual Li / Co molar ratio R of each batch of lithium monocobalt oxide matrix was then determined by ICP-OES.

[0033] Example 1 A method for adjusting the cobalt-lithium molar ratio in a lithium cobalt oxide cathode material includes the following steps: Step 1: Take a lithium cobalt oxide matrix with R=1.01; Step 2: According to the formula Co / Li = k×(R-1.02)+c, take k=20, c=1.0, and calculate Co / Li = 0.8; prepare a coating agent of 6.0% of the mass of lithium cobalt oxide matrix according to the ratio of Co / Li = 0.8; mix the coating agent with the lithium cobalt oxide matrix evenly. Step 3: Sinter the mixture obtained in Step 2 at 950℃ for 6 hours to obtain lithium cobalt oxide cathode material.

[0034] Characterization results: SEM-EDS line scan showed that |ΔCo / Δd| = 2.3at% / nm in the range of 10-50nm from the surface inward.

[0035] Example 2 Step 1: Take a lithium cobalt oxide matrix with R=0.96;

[0036] Step 2: According to the formula Co / Li = k×(R-1.02)+c, take k=30, c=1.0, and calculate Co / Li =-0.8; Since the calculated value is negative, it indicates that when R is too low, the lithium salt ratio needs to be greatly increased. The actual Co / Li is taken to be close to 0. In this embodiment, Co3O4 and Li2CO3 are prepared according to the ratio of Co / Li = 0.2. 6.0% of the mass of the lithium cobalt oxide matrix is ​​weighed as a coating agent and the coating agent is mixed evenly with the lithium cobalt oxide matrix. Step 3: Sinter the mixture obtained in Step 2 at 950℃ for 6 hours to obtain lithium cobalt oxide cathode material.

[0037] Microscopic characterization results: SEM-EDS line scan showed |ΔCo / Δd| = 5.8 at% / nm.

[0038] Example 3 Step 1: Take a lithium cobalt oxide matrix with R=1.05; Step 2: According to the formula Co / Li = k×(R-1.02)+c, take k=20, c=1.0, and calculate Co / Li =1.6; prepare a coating agent of 6.0% of the mass of lithium cobalt oxide matrix according to the ratio of Co / Li =1.6, and mix the coating agent with the lithium cobalt oxide matrix evenly; Step 3: Sinter the mixture obtained in Step 2 at 950℃ for 6 hours to obtain lithium cobalt oxide cathode material.

[0039] Microscopic characterization results: SEM-EDS line scan showed |ΔCo / Δd| = 1.1 at% / nm.

[0040] Example 4 Step 1: Take a lithium cobalt oxide matrix with R=0.95; Step 2: According to the formula Co / Li = k×(R-1.02)+c, take k=40, c=1.0, and calculate Co / Li =-1.8; Since the calculated value is negative, it indicates that when R is too low, the lithium salt ratio needs to be greatly increased. The actual Co / Li is taken to be close to 0. In this embodiment, Co3O4 and Li2CO3 are prepared according to the ratio of Co / Li = 0.2. At the same time, according to the total amount adjustment formula W = W0×[1+β×(R -1.02)], take β=5, W0=6.0%, and calculate W = 3.9%. Weigh out 3.9% of the coating agent of the lithium cobalt oxide matrix and mix the coating agent with the lithium cobalt oxide matrix evenly. Step 3: Sinter the mixture obtained in Step 2 at 950℃ for 6 hours to obtain lithium cobalt oxide cathode material.

[0041] Microscopic characterization results: SEM-EDS line scan showed |ΔCo / Δd| = 6.5 at% / nm.

[0042] Example 5 A method for adjusting the cobalt-lithium molar ratio in a lithium cobalt oxide cathode material includes the following steps: Step 1: Take a lithium cobalt oxide matrix with R=1.01; Step 2: According to the formula Co / Li = k×(R-1.02)+c, take k=20, c=1.1, and calculate Co / Li = 0.9; prepare Co3O4 and Li2CO3 in a ratio of Co / Li = 0.9, weigh out 3.0% of the mass of the lithium cobalt oxide matrix as coating agent A, and then weigh out 3.0% of the mass of the lithium cobalt oxide matrix as coating agent B. Mix coating agent A, coating agent B and lithium cobalt oxide matrix evenly. Step 3: Sinter the mixture obtained in Step 2 at 950℃ for 6 hours to obtain lithium cobalt oxide cathode material.

[0043] Microscopic characterization results: SEM-EDS line scan showed |ΔCo / Δd| = 2.5 at% / nm.

[0044] Example 6 Step 1: Lithium carbonate, cobalt tetroxide and aluminum oxide were mixed in a molar ratio of Li:Co:Al = 1.015:1:0.01 and sintered at 1000℃ for 18 hours. After pulverization, a lithium cobalt oxide matrix was obtained, and R = 0.99 was determined by ICP-OES. Step 2: According to the formula Co / Li = k×(R-1.02)+c, take k=22, c=1.0, and calculate Co / Li = 0.34; prepare Co3O4 and Li2CO3 according to the ratio of Co / Li=0.34, and add 0.3% ZrO2 of the total mass of the coating agent. Weigh out 5.5% of the coating agent of the lithium cobalt oxide matrix and mix them evenly. Step 3: Sinter the mixture obtained in Step 2 at 950℃ for 6 hours to obtain lithium cobalt oxide cathode material.

[0045] Microscopic characterization results: STEM-EDS line scan showed |ΔCo / Δd| = 3.9 at% / nm.

[0046] Example 7 Step 1: Lithium carbonate, cobalt tetroxide and magnesium oxide were mixed in a molar ratio of Li:Co:Mg = 1.065:1:0.01 and sintered at 1000℃ for 18 hours. After pulverization, a lithium cobalt oxide matrix was obtained, and R = 1.05 was determined by ICP-OES. Step 2: According to the formula Co / Li = k×(R-1.02)+c, take k=20, c=1, and calculate Co / Li = 1.6; prepare a coating agent of 6.0% of the mass of lithium cobalt oxide matrix according to the ratio of Co / Li = 1.6; mix the coating agent with the lithium cobalt oxide matrix evenly. Step 3: Sinter the mixture obtained in Step 2 at 950℃ for 6 hours to obtain lithium cobalt oxide cathode material.

[0047] Microscopic characterization results: STEM-EDS line scan showed |ΔCo / Δd| = 1.33 at% / nm.

[0048] Example 8 Step 1: Lithium carbonate, cobalt tetroxide, aluminum oxide and titanium oxide were mixed in a molar ratio of Li:Co:Al:Ti = 1.048:1:0.02:0.01 and sintered at 1000℃ for 18 hours. After pulverization, a lithium cobalt oxide matrix was obtained, and R = 1.02 was determined by ICP-OES. Step 2: According to the formula Co / Li = k×(R-1.02)+c, take k=20, c=1.0, and calculate Co / Li = 1.0; prepare Co3O4 and Li2CO3 as coating agent A according to the ratio of Co / Li=1.0, and add Li-Mg-O system (Li2O to MgO molar ratio 2:1) as coating agent B. The mass of coating agent B is 0.8% of the total mass of coating agent A and coating agent B. The total mass of coating agent A and coating agent B accounts for 6.0% of the mass of lithium cobalt oxide matrix. Mix them evenly. Step 3: Sinter the mixture obtained in Step 2 at 950℃ for 6 hours to obtain high-voltage lithium cobalt oxide cathode material.

[0049] Microscopic characterization results: SEM-EDS line scan showed |ΔCo / Δd| = 2.0 at% / nm.

[0050] Comparative Example 1 A method for adjusting the cobalt-lithium molar ratio in a lithium cobalt oxide cathode material includes the following steps: Step 1: Take a lithium cobalt oxide matrix with R=1.01; Step 2: According to the formula Co / Li = k×(R-1.02)+c, take k=10 and c=1.0, and calculate Co / Li = 0.9; prepare a coating agent of 6.0% of the mass of the lithium cobalt oxide matrix according to the ratio of Co / Li = 0.9, and mix the coating agent with the lithium cobalt oxide matrix evenly; Step 3: Sinter the mixture obtained in Step 2 at 950℃ for 6 hours to obtain lithium cobalt oxide cathode material.

[0051] Comparative Example 2 A method for adjusting the cobalt-lithium molar ratio in a lithium cobalt oxide cathode material includes the following steps: Step 1: Take a lithium cobalt oxide matrix with R=1.01; Step 2: According to the formula Co / Li = k×(R-1.02)+c, take k=40, c=1.0, and calculate Co / Li = 0.6; prepare a coating agent of 6.0% of the mass of lithium cobalt oxide matrix according to the ratio of Co / Li = 0.6, and mix the coating agent with the lithium cobalt oxide matrix evenly; Step 3: Sinter the mixture obtained in Step 2 at 950℃ for 6 hours to obtain lithium cobalt oxide cathode material.

[0052] Comparative Example 3 A method for preparing a lithium cobalt oxide cathode material includes the following steps: Step 1: Take a lithium cobalt oxide matrix with R=1.01; Step 2: Prepare a coating agent of 6.0% of the mass of the lithium cobalt oxide matrix by mixing Co3O4 and Li2CO3 in a Co / Li ratio of 1. Mix the coating agent with the lithium cobalt oxide matrix evenly. Step 3: Sinter the mixture obtained in Step 2 at 950℃ for 6 hours to obtain lithium cobalt oxide cathode material.

[0053] Comparative Example 4 A method for adjusting the cobalt-lithium molar ratio in a lithium cobalt oxide cathode material includes the following steps: Step 1: Take a lithium cobalt oxide matrix with R=1.05; Step 2: According to the formula Co / Li = k×(R-1.02)+c, take k=5, c=1.0, and calculate Co / Li =1.3; prepare a coating agent of 6.0% of the mass of lithium cobalt oxide matrix according to the ratio of Co / Li =1.3, and mix the coating agent with the lithium cobalt oxide matrix evenly; Step 3: Sinter the mixture obtained in Step 2 at 950℃ for 6 hours to obtain lithium cobalt oxide cathode material.

[0054] Comparative Example 5 A method for adjusting the cobalt-lithium molar ratio in a lithium cobalt oxide cathode material includes the following steps: Step 1: Take a lithium cobalt oxide matrix with R=1.05; Step 2: According to the formula Co / Li = k×(R-1.02)+c, take k=30, c=1.0, and calculate Co / Li = 1.9; prepare a coating agent of 6.0% of the mass of lithium cobalt oxide matrix according to the ratio of Co / Li = 1.9, and mix the coating agent with the lithium cobalt oxide matrix evenly; Step 3: Sinter the mixture obtained in Step 2 at 950℃ for 6 hours to obtain lithium cobalt oxide cathode material.

[0055] Comparative Example 6 Step 1: Lithium carbonate, cobalt tetroxide and magnesium oxide were mixed in a molar ratio of Li:Co:Mg = 1.065:1:0.01 and sintered at 1000℃ for 18 hours. After pulverization, a lithium cobalt oxide matrix was obtained, and R = 1.05 was determined by ICP-OES. Step 2: According to the formula Co / Li = k×(R-1.02)+c, take k=5, c=1.0, and calculate Co / Li =1.3; prepare a coating agent of 6.0% of the mass of lithium cobalt oxide matrix according to the ratio of Co / Li =1.3, and mix the coating agent with the lithium cobalt oxide matrix evenly; Step 3: Sinter the mixture obtained in Step 2 at 950℃ for 6 hours to obtain lithium cobalt oxide cathode material.

[0056] Comparative Example 7 Step 1: Lithium carbonate, cobalt tetroxide and magnesium oxide were mixed in a molar ratio of Li:Co:Mg = 1.065:1:0.01 and sintered at 1000℃ for 18 hours. After pulverization, a lithium cobalt oxide matrix was obtained, and R = 1.05 was determined by ICP-OES. Step 2: According to the formula Co / Li = k×(R-1.02)+c, take k=30, c=1.0, and calculate Co / Li = 1.9; prepare a coating agent of 6.0% of the mass of lithium cobalt oxide matrix according to the ratio of Co / Li = 1.9, and mix the coating agent with the lithium cobalt oxide matrix evenly; Step 3: Sinter the mixture obtained in Step 2 at 950℃ for 6 hours to obtain lithium cobalt oxide cathode material.

[0057] The materials obtained in Examples 1-5 and Comparative Examples 1-3 were assembled into coin cells, and their electrochemical performance was tested in the voltage range of 3.0-4.55V. The results are shown in Table 1.

[0058] Table 1. Comparison of electrochemical performance between different embodiments and comparative examples Example 1 198 95.2 91.45 Example 2 197 94.1 90.25 Example 3 195 95.0 91.79 Example 4 196 97.24 92.19 Example 5 197 97.28 92.33 Example 6 196 95.6 90.96 Example 7 194 95.3 91.58 Example 8 200 96.1 91.11 Comparative Example 1 200 89.0 90.49 Comparative Example 2 192 87.5 88.75 Comparative Example 3 202 89.6 87.92 Comparative Example 4 196 90.1 88.14 Comparative Example 5 191 89.8 87.48 Comparative Example 6 194 82.5 85.41 Comparative Example 7 186 84.3 84.56

[0059] According to the results in Table 1: According to the results of Examples 1-8 of this application, this application has obtained a lithium cobalt oxide cathode material with excellent comprehensive electrochemical performance through a specific mathematical model and the selection of values ​​of k and c in the formula: specific capacity of 195-200mAh / g, cycle retention rate ≥94.1%, and 2C rate retention rate ≥90.25%.

[0060] In Example 4, under the extreme lithium deficiency condition of R=0.95, by simultaneously adjusting the total coating amount (β=5), a cycle retention rate of 97.24% and a rate performance of 92.19% were obtained, indicating that adjusting the total amount can further optimize the interface structure.

[0061] Based on the comparison of the results of Example 1 and Comparative Examples 1 and 2, and the comparison of the results of Example 3 and Comparative Examples 4 and 5, it can be seen that the value of k is very important in the technical solution of this application. Under a suitable value range, the cycle retention rate can be significantly improved, and the rate retention rate can also be significantly improved.

[0062] Based on the comparison of the results of Example 7 and Comparative Examples 6 and 7, and combined with the comparison of the results of Example 3 and Comparative Examples 4 and 5, the method for adjusting the cobalt-lithium molar ratio of lithium cobalt oxide cathode material of this application has a more significant impact on lithium cobalt oxide cathode materials containing doped elements. Dynamic adjustment can further improve the overall performance of the cathode material. The reason for this may be that: (1) If the cobalt-lithium ratio is not properly adjusted, the doping elements will have difficulty occupying the original lattice sites, forming a disordered phase or a second phase. External ions may further disturb the distorted layered structure, accelerating phase transition and capacity decay. (2) In the preparation method of this application, the sintering coating formed by appropriate cobalt-lithium ratio compensation can effectively improve the occupancy of the lattice sites of the doping element; or the doped element can be uniformly distributed in the lattice of the matrix and the coating layer, which further improves the performance of the doping element.

[0063] The embodiments presented herein are merely selected implementations based on combinations of all possible embodiments. The appended claims should not be limited to the embodiments described herein. Some numerical ranges used in the claims include sub-ranges within them, and variations within these ranges should also be covered by the appended claims.

Claims

1. A method for adjusting the cobalt-lithium molar ratio in a lithium cobalt oxide cathode material, characterized in that, Based on the Li / Co molar ratio of the lithium cobalt oxide matrix obtained from the first calcination, the following mathematical model is used to determine the cobalt-lithium molar ratio of the coating agent for the second calcination to obtain the lithium cobalt oxide cathode material: Co / Li = k × (R - R0) + c; Where Co / Li is the molar ratio of cobalt to lithium in the coating agent, R is the Li / Co molar ratio of the lithium cobalt oxide matrix obtained by calcination, R0 is the reference stoichiometric point, k is the adjustment coefficient, and c is the reference value; the value of k ranges from 10 to 40, the value of c ranges from 1.0 to 1.1, and R0 is 1.

02. and, When R is between 0.95 and 0.98, the value of k ranges from 30 to 40. When R is between 0.98 and 1.04, the value of k ranges from 15 to 30. When R is between 1.05 and 1.10, the value of k ranges from 10 to 20. When the calculated Co / Li value is less than 0.1, the Co / Li value should be between 0.1 and 0.

3. The total mass of the coating agent was calculated using the following mathematical model: W = W0 × [1 + β × (R - R0)]; Where W is the total mass of the coating agent, W0 is the standard coating amount (6wt%), R is the Li / Co molar ratio of the lithium cobalt oxide matrix obtained by calcination (R0 is the reference stoichiometric point), and β is the adjustment coefficient (0-10).

2. The method for adjusting the cobalt-lithium molar ratio of the lithium cobalt oxide cathode material according to claim 1, characterized in that, Specifically, the steps include the following: Step 1: Preparation of lithium cobalt oxide matrix by calcination; Step 2: Determine the Li / Co molar ratio of the lithium cobalt oxide matrix; Step 3: Determine the cobalt-lithium molar ratio of the coating agent according to the mathematical model, and mix the coating agent and the lithium cobalt oxide matrix for secondary calcination to obtain the lithium cobalt oxide cathode material.

3. The method for adjusting the cobalt-lithium molar ratio of the lithium cobalt oxide cathode material according to claim 1 or 2, characterized in that, The lithium cobalt oxide matrix includes pure-phase lithium cobalt oxide and doped / modified lithium cobalt oxide.

4. The method for adjusting the cobalt-lithium molar ratio of the lithium cobalt oxide cathode material according to claim 3, characterized in that, The chemical formula of the lithium cobalt oxide matrix is ​​Li 1+a Co 1-b M b O2, where -0.05≤a≤0.1, 0≤b≤0.05, and M is selected from at least one of Al, Mg, Ti, Zr, Mn, Y, La, Ni, Nb, Gd, and Ga.

5. The method for adjusting the cobalt-lithium molar ratio of the lithium cobalt oxide cathode material according to claim 1 or 2, characterized in that, The coating agent includes cobalt compounds and lithium salts.

6. The method for adjusting the cobalt-lithium molar ratio of the lithium cobalt oxide cathode material according to claim 5, characterized in that, The coating agent also includes at least one selected from oxides and oxyacids of Al, Mg, Ti, Zr, B, Y, La, P, and F.

7. A lithium cobalt oxide cathode material, characterized in that, It was prepared using the method for adjusting the cobalt-lithium molar ratio of the lithium cobalt oxide cathode material as described in any one of claims 1-6.

8. A high-voltage lithium cobalt oxide cathode material, characterized in that, The lithium cobalt oxide cathode material was prepared using the method for adjusting the cobalt-lithium molar ratio as described in any one of claims 1-3. The chemical formula of the lithium cobalt oxide matrix is ​​Li x Co 1-y M y O2, wherein 0.95 ≤ x ≤ 1.07, 0 ≤ y ≤ 0.05, and M is selected from at least one of Al, Mg, Ti, Zr, Mn, Y, La, Ni, Nb, Gd, Ga, Fe, Sn, B, Bi, and Sr; The coating agent further includes at least one of the following: Li-AO system, Li-BF system, and sodium copper iron manganate; wherein A is at least one of Mg, Zn, Si, Ge, Ti, Al, Zr, Te, Mo, W, Sb, Nb, Ta, and La, and B is at least one of Mn, Ni, Al, Co, Mg, Ca, Y, La, Ti, and Fe.