Positive electrode material, secondary battery, and electronic device

Abstract

A positive electrode material, a secondary battery, and an electronic device. The positive electrode material comprises a lithium cobalt composite oxide. The lithium cobalt composite oxide has a P63mc structure and a Cmca structure. The lithium-cobalt composite oxide comprises lithium, cobalt, and nickel. Based on metal elements other than the lithium in the lithium-cobalt composite oxide, the molar content of the nickel is m%, where 0.2 ≤ m ≤ 10. The lithium-cobalt composite oxide has an average length of L0 μm and an average width of W μm, where 4 ≤ L0 ≤ 30, and 1 ≤ L0 / W ≤ 1.5。 By performing element doping on the positive electrode material in combination with morphology optimization, the diffusion rate of lithium ions and structural stability can be improved, thereby improving both the rate performance and the thermal safety performance of the secondary battery.

Description

Positive electrode materials, secondary batteries and electronic devices Technical Field

[0001] This application belongs to the field of battery materials technology, specifically relating to a cathode material, a secondary battery, and an electronic device. Background Technology

[0002] As a high-efficiency energy storage device, the core performance of secondary batteries is closely related to the electrochemical characteristics of the cathode material. Currently, mainstream cathode materials include layered oxides (such as LiCoO2 and NCM ternary materials), polyanionic compounds (such as LiFePO4), and high-nickel, low-cobalt systems, which achieve energy storage and release through the reversible insertion and extraction of lithium ions during charging and discharging. However, existing materials are prone to polarization under high-rate charge and discharge conditions, leading to capacity decay. Furthermore, under extreme high-temperature conditions, the exothermic side reactions within secondary batteries can easily trigger chain-like thermal runaway.

[0003] Existing technologies, while addressing the aforementioned issues, struggle to simultaneously improve both high-rate performance and thermal safety. For instance, while nano-sized cathode particles can shorten the lithium-ion diffusion path, they exacerbate interfacial side reactions and reduce thermal stability; and while inert coatings can suppress electrolyte decomposition, they may hinder lithium-ion transport kinetics. Therefore, there is an urgent need to improve rechargeable batteries to overcome their technical bottleneck of poor electrochemical performance under high-power output and high-temperature conditions. Summary of the Invention

[0004] In view of this, this application provides a cathode material, a secondary battery, and an electronic device. By doping the cathode material with elements and optimizing its morphology, the diffusion rate of lithium ions and the stability of the structure can be improved, thereby improving both the rate performance and thermal safety performance of the secondary battery.

[0005] Firstly, this application provides a cathode material, including a lithium-cobalt composite oxide; the lithium-cobalt composite oxide has a P63mc structure and a Cmca structure; the lithium-cobalt composite oxide includes lithium, cobalt, and nickel, and based on the metal elements other than lithium in the lithium-cobalt composite oxide, the molar content of nickel is m%, 0.2≤m≤10; the average length of the lithium-cobalt composite oxide is L0μm, the average width is Wμm, 4≤L0≤30, and 1≤L0 / W≤1.5. This application dops the lithium-cobalt composite oxide with nickel, enabling nickel ions to replace some of the cobalt ions and potentially migrate to the lithium layer, mixing with lithium ions, thereby fine-tuning the crystal structure and improving the structural stability of the material. However, Ni... 3+ The migration of Ni can easily lead to local lattice distortion. This application reduces local stress concentration and suppresses Ni by precisely controlling the molar content of nickel and optimizing the aspect ratio of the lithium-cobalt composite oxide. 3+The migration of nickel improves the structural stability of the secondary battery, thereby enhancing its high-temperature safety performance. In addition, optimizing the aspect ratio can increase the packing density. Combined with the improvement of lithium-ion transport capability within the lattice by nickel, an efficient continuous transport path is formed, which synergistically improves the rate performance of the secondary battery.

[0006] In some embodiments, the lithium-cobalt composite oxide satisfies at least one of the following conditions:

[0007] (1) 1 ≤ m ≤ 4;

[0008] (2) 5 ≤ L0 ≤ 20;

[0009] (3) 1≤L0 / W≤1.3.

[0010] The above-mentioned solution can further improve the rate performance and high-temperature safety performance of secondary batteries.

[0011] In some embodiments, the lithium-cobalt composite oxide includes ytterbium and calcium; based on the metal elements other than lithium in the lithium-cobalt composite oxide, the molar content of ytterbium is a%, the molar content of calcium is b%, 0.01≤a+b≤1.8, 4≤a / b≤35. This application incorporates ytterbium and calcium into the lithium-cobalt composite oxide for coordination, with ytterbium ions (Yb)... 3+ ) and calcium ions (Ca 2+ Yb can act as a "support" in the lithium layer, reducing interlayer collapse and structural distortion, thereby improving the structural stability of the material under extreme high-temperature conditions. Furthermore, doping with Yb... 3+ and Ca 2+ This can alter the migration path of lithium ions within the crystal lattice, contributing to improved rate performance and charge / discharge rates in materials. Furthermore, Yb 3+ and Ca 2+ The "occupancy" in the lithium layer can also suppress Ni 3+ The migration of these elements, combined with nickel, can further improve the rate performance and high-temperature safety performance of secondary batteries.

[0012] In some implementations, 0.2 ≤ a + b ≤ 0.8, and / or 4.3 ≤ a / b ≤ 8.7. By adjusting the molar content of ytterbium and calcium to conform to the above relationship, the rate performance and high-temperature safety performance of the secondary battery can be further improved.

[0013] In some embodiments, the lithium-cobalt composite oxide includes molybdenum; based on the metal elements other than lithium in the lithium-cobalt composite oxide, the molar content of molybdenum is c%, 0.03 ≤ c ≤ 0.6. This application dops the lithium-cobalt composite oxide with molybdenum ions (Mo). 6+Doping can partially replace cobalt ions, leading to fine-tuning of the crystal lattice structure, reducing stress and defects in the lattice, and thus improving the overall stability of the material. Furthermore, molybdenum ions (Mo...) can be utilized... 6+ The high valence state provides additional charge compensation in the crystal lattice. This charge compensation helps maintain the charge balance of lithium cobalt composite oxides during charging and discharging, reduces phase transitions caused by charge imbalance, improves structural stability, and enhances its electronic conductivity, thereby further improving the rate performance and high-temperature safety performance of secondary batteries.

[0014] In some embodiments, the lithium cobalt composite oxide comprises a first particle and a second particle. The length of the first particle is L1 μm, 0.1 ≤ L1 ≤ 5, and the length of the second particle is L2 μm, 8 ≤ L2 ≤ 40. Based on the number of particles in the lithium cobalt composite oxide, the proportion of the first particle is N1%, and the proportion of the second particle is N2%; 2 ≤ N2 / N1 ≤ 49. When the length and proportion of the first and second particles in the lithium cobalt composite oxide are controlled to satisfy the above relationship, the large particles provide a continuous electron conduction path, and the small particles fill the gaps, which can improve the transport efficiency of the lithium-ion diffusion path and alleviate volume change stress, reducing the risk of electrode pulverization and structural collapse. The dense stacked structure, combined with the above aspect ratio characteristics, can reduce the contact between the lithium cobalt composite oxide and the electrolyte, thereby helping to reduce interfacial side reactions. Based on the above process, the rate performance and high-temperature safety performance of the secondary battery can be further improved.

[0015] In some embodiments, the lithium-cobalt composite oxide satisfies at least one of the following conditions:

[0016] (1) 1≤N2 / N1≤9;

[0017] (2) 10 ≤ N1 ≤ 50;

[0018] (3) 50≤N2≤90.

[0019] When the ratio of the first and second particles in the lithium cobalt composite oxide is adjusted to meet the above relationship, the rate performance and high-temperature safety performance of the secondary battery can be further improved.

[0020] In some embodiments, the lithium cobalt composite oxide further includes a third particle with a length of L3 μm, where 5 < L3 < 8; the third particle accounts for N3% of the total number of lithium cobalt composite oxide particles, where 0.5 ≤ N3 ≤ 4; and / or, the compacted density of the lithium cobalt composite oxide at a pressure of 180 MPa is dg / cm³. 3 3.8≤d≤4.5. Adjusting the particle size distribution and compaction density of lithium cobalt composite oxide to meet the above range can further improve the rate performance and high-temperature safety performance of secondary batteries.

[0021] Secondly, this application provides a secondary battery, including a positive electrode, a negative electrode and an electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector; the positive electrode material layer includes the aforementioned positive electrode material.

[0022] Thirdly, this application provides an electronic device including the aforementioned secondary battery. Attached Figure Description

[0023] Figure 1 is a SEM image of a lithium cobalt composite oxide provided in Embodiment 1-1 of this application;

[0024] Figure 2 is an EDS surface scan analysis diagram of a lithium cobalt composite oxide provided in Examples 2-9 of this application. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0026] The inventors discovered that under high-rate charge-discharge conditions, secondary batteries are prone to severe polarization due to sluggish lithium-ion diffusion kinetics, leading to capacity decay and increased internal resistance. Simultaneously, the bulk structure of lithium-cobalt composite oxides is susceptible to irreversible phase transitions or lattice oxygen precipitation under deep delithiation conditions, exacerbating interfacial side reactions and reducing cycle stability. Furthermore, under extreme operating conditions or thermal abuse, the exothermic reaction between the cathode material and the electrolyte can easily trigger chain thermal runaway, resulting in safety risks.

[0027] To address the aforementioned issues, this application employs a multi-dimensional approach, considering material crystal structure design, bulk doping, and morphological characteristics, to construct a cathode material possessing rapid ion transport channels, high structural stability, and low interfacial reactivity. Specifically, the cathode material includes a lithium-cobalt composite oxide; the lithium-cobalt composite oxide possesses a P63mc structure and a Cmca structure; the lithium-cobalt composite oxide includes lithium, cobalt, and nickel elements, with the molar content of nickel being m%, 0.2≤m≤10, based on the metal elements other than lithium in the lithium-cobalt composite oxide; the average length of the lithium-cobalt composite oxide is L0μm, the average width is Wμm, 4≤L0≤30, and 1≤L0 / W≤1.5. This application dops the lithium-cobalt composite oxide with nickel, enabling nickel ions to replace some of the cobalt ion positions and potentially migrate to the lithium layer, mixing with lithium ions and thus fine-tuning the crystal structure. Specifically, nickel ions replacing cobalt ions can form a more stable layered structure, reducing stress and defects in the crystal lattice and improving the overall stability of the material. Furthermore, when mixed with lithium ions, they occupy Li sites, creating a pillar effect, expanding the interlayer spacing of lithium ion diffusion channels, and improving the interlayer stability of the CoO6 octahedral structure. Nickel doping also enhances the bonding energy of the transition metal-oxygen bond, reduces the release of lattice oxygen at high temperatures, and improves the thermal stability of the lithium-cobalt composite oxide.

[0028] However, Ni 3+ The migration of Ni can easily lead to local lattice distortion, resulting in structural instability. Based on this, this application reduces local stress concentration and suppresses Ni by precisely controlling the molar content of nickel and optimizing the aspect ratio of the lithium-cobalt composite oxide. 3+ The migration of nickel enhances the stability of the lithium cobalt composite oxide crystal structure and also helps reduce its specific surface area, suppressing interfacial side reactions and thus improving the high-temperature safety performance of secondary batteries. Furthermore, controlling the aspect ratio and average length of the lithium cobalt composite oxide within the aforementioned ranges can increase the packing density, forming a dense electrode structure. This improves the loading of the positive electrode active material and the continuity of the electrode conductive network. Combined with the improvement of lithium-ion transport within the crystal lattice by nickel, an efficient continuous transport path can be formed, synergistically enhancing the rate performance of the secondary battery.

[0029] In some embodiments, based on the metallic elements other than lithium in the lithium-cobalt composite oxide, the molar content of nickel is m%, 0.2 ≤ m ≤ 10; preferably 1 ≤ m ≤ 4. Exemplarily, m is a value within the range of 0.2, 0.7, 1.0, 1.6, 2.0, 3.0, 4.2, 5.8, 6.1, 7.9, 8.2, 9.1, 10, or any two of these ranges. Adjusting the molar content of nickel to meet the above range can further improve the rate performance and high-temperature safety performance of the secondary battery.

[0030] In some embodiments, 4 ≤ L0 ≤ 30, preferably 5 ≤ L0 ≤ 20. Exemplarily, the value of L0 is a value within the range of 4, 8, 10, 15, 16, 21, 22, 27, 30, or any two of these. Adjusting the average length of the lithium cobalt composite oxide to meet the above range can further improve the rate performance and high-temperature safety performance of the secondary battery.

[0031] In some embodiments, 1 ≤ L0 / W ≤ 1.5, preferably 1 ≤ L0 / W ≤ 1.3. Exemplarily, the value of L0 / W is a value within the range of 1, 1.1, 1.2, 1.3, 1.4, 1.5, or any two of these ranges. Adjusting the ratio of the average length to the average width of the lithium cobalt composite oxide to satisfy the above range can further improve the rate performance and high-temperature safety performance of the secondary battery.

[0032] In some embodiments, the lithium-cobalt composite oxide includes ytterbium and calcium; based on the metal elements other than lithium in the lithium-cobalt composite oxide, the molar content of ytterbium is a%, the molar content of calcium is b%, 0.01≤a+b≤1.8, 4.3≤a / b≤35. This application incorporates ytterbium and calcium into the lithium-cobalt composite oxide for coordination, wherein the ytterbium ion (Yb 3+ )radius Calcium ions (Ca 2+ )radius And Li ions (Li + radius is Yb 3+ and Ca 2+ Doping into the Li layer, due to Yb 3+ and Ca 2+ Greater than Li + radius, in Li + During the embedding / de-embedding process, Yb 3+ and Ca 2+ It acts as a "support" in the lithium layer, reducing interlayer collapse and structural distortion, thereby improving the structural stability of the material under extreme high-temperature conditions. Furthermore, doping with Yb... 3+ and Ca 2+ Altering the migration path of lithium ions in the crystal lattice can potentially broaden or optimize the migration channels, thereby increasing the lithium ion diffusion coefficient. This contributes to improving the rate performance and charge / discharge rate of the material. Furthermore, Yb 3+ and Ca 2+ The "occupancy" in the lithium layer can also suppress Ni 3+ The migration of these elements, combined with nickel, can further improve the rate performance and high-temperature safety performance of secondary batteries.

[0033] In some embodiments, 0.01 ≤ a + b ≤ 1.8, preferably 0.2 ≤ a + b ≤ 0.8, for example, the value of a + b is within the range of 0.01, 0.06, 0.1, 0.2, 0.4, 0.5, 0.8, 0.9, 1.2, 1.3, 1.5, 1.7, 1.8, or any two of these ranges. By adjusting the molar content of ytterbium and calcium to conform to the above relationship, the rate performance and high-temperature safety performance of the secondary battery can be further improved.

[0034] In some embodiments, 4 ≤ a / b ≤ 35, preferably 4.3 ≤ a / b ≤ 8.7. Exemplarily, the value of a / b is a value within the range of 4, 5.4, 11.0, 14.1, 16.5, 18.7, 22.9, 26.4, 29.4, 34.2, 35, or any two of these ranges. By adjusting the molar content of ytterbium and calcium to conform to the above relationship, the rate performance and high-temperature safety performance of the secondary battery can be further improved.

[0035] In some embodiments, 0.008 ≤ a ≤ 1.75. For example, a can be a value within the range of 0.008, 0.01, 0.08, 0.31, 0.55, 0.69, 0.83, 1.03, 1.34, 1.39, 1.72, 1.75, or any two of these values. In some embodiments, 0.002 ≤ b ≤ 0.18. For example, b can be a value within the range of 0.002, 0.01, 0.02, 0.03, 0.05, 0.08, 0.09, 0.12, 0.13, 0.15, 0.17, 0.18, or any two of these values. By adjusting the molar content of ytterbium and calcium to conform to the above relationship, the rate performance and high-temperature safety performance of the secondary battery can be further improved.

[0036] In some embodiments, the lithium-cobalt composite oxide includes molybdenum; based on the metal elements other than lithium in the lithium-cobalt composite oxide, the molar content of molybdenum is c%, 0.03 ≤ c ≤ 0.6. Exemplarily, c can be a value within the range of 0.03, 0.07, 0.13, 0.20, 0.27, 0.30, 0.35, 0.47, 0.50, 0.55, 0.6, or any two of these. This application dops the lithium-cobalt composite oxide with molybdenum ions (Mo). 6+ Doping can partially replace cobalt ions, leading to fine-tuning of the crystal lattice structure, reducing stress and defects in the lattice, and thus improving the overall stability of the material. Furthermore, molybdenum ions (Mo...) can be utilized... 6+The high valence state provides additional charge compensation in the crystal lattice. This charge compensation helps maintain the charge balance of lithium cobalt composite oxides during charging and discharging, reduces phase transitions caused by charge imbalance, improves structural stability, and enhances its electronic conductivity, thereby further improving the rate performance and high-temperature safety performance of secondary batteries.

[0037] In some embodiments, the lithium cobalt composite oxide comprises a first particle and a second particle. The length of the first particle is L1 μm, 0.1 ≤ L1 ≤ 5, and the length of the second particle is L2 μm, 8 ≤ L2 ≤ 40. Based on the number of particles in the lithium cobalt composite oxide, the proportion of the first particle is N1%, and the proportion of the second particle is N2%; 1 ≤ N2 / N1 ≤ 9. When the length and proportion of the first and second particles in the lithium cobalt composite oxide are controlled to satisfy the above relationship, the large particles provide a continuous electron conduction path, and the small particles fill the gaps, which can improve the transport efficiency of the lithium-ion diffusion path and alleviate volume change stress, reducing the risk of electrode pulverization and structural collapse. The dense stacked structure, combined with the above aspect ratio characteristics, can reduce the contact between the lithium cobalt composite oxide and the electrolyte, thereby helping to reduce interfacial side reactions. Based on the above process, the rate performance and high-temperature safety performance of the secondary battery can be further improved.

[0038] In some embodiments, 1 ≤ N2 / N1 ≤ 9, preferably 1.5 ≤ N2 / N1 ≤ 6. Exemplarily, the value of N2 / N1 is a value within the range of 2, 3, 4, 5, 6, or any two of these. When the ratio of the first and second particles in the lithium cobalt composite oxide is adjusted to satisfy the above relationship, the rate performance and high-temperature safety performance of the secondary battery can be further improved.

[0039] In some embodiments, 10 ≤ N1 ≤ 50; for example, the value of N1 is a value within the range of 12, 15, 20, 24, 29, 36, 40, 45, 50, or any two of these. When the proportion of the first particles in the lithium cobalt composite oxide is adjusted to satisfy the above relationship, the rate performance and high-temperature safety performance of the secondary battery can be further improved.

[0040] In some embodiments, 50 ≤ N2 ≤ 90. Exemplarily, the value of N2 is a value within the range of 55, 63, 69, 75, 78, 81, 86, 90, or any two of these. When the proportion of the second particles in the lithium cobalt composite oxide is adjusted to satisfy the above relationship, the rate performance and high-temperature safety performance of the secondary battery can be further improved.

[0041] In some embodiments, the lithium cobalt composite oxide further includes a third particle with a length of L3 μm, where 5 < L3 < 8; the third particle accounts for N3% of the total number of lithium cobalt composite oxide particles, where 0.5 ≤ N3 ≤ 4. For example, the value of N3 is within the range of 0.5, 0.8, 0.9, 1.4, 1.7, 2.2, 2.5, 3.1, 3.5, 3.7, 4, or any two of these values.

[0042] In some embodiments, the compaction density of the lithium cobalt composite oxide under a pressure of 180 MPa is dg / cm³. 3 The density of lithium cobalt composite oxide is 3.8 ≤ d ≤ 4.5. For example, d can be a value within the range of 3.8, 3.8, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, or any two of these values. Adjusting the compaction density of lithium cobalt composite oxide to meet the above range can further improve the rate performance and high-temperature safety performance of secondary batteries.

[0043] The lithium-cobalt composite oxide of this application can be prepared by a method including the following steps:

[0044] 1. Preparation of sodium-containing cobalt oxides

[0045] Cobalt sulfate (CoSO4) and nickel sulfate (NiSO4) were weighed according to the molar ratio, then deionized water was added and stirred rapidly to dissolve them. Ammonium carbonate was then slowly added to adjust the pH to 12-13 until the reaction was complete, forming a homogeneous carbonate precipitate. The precipitate was sintered at 600-800℃ for 10-24 hours. After crushing and sieving, Ni-doped Co3O4 metal oxide material was obtained.

[0046] Sodium carbonate (Na2CO3) and the above-mentioned Ni-doped Co3O4 metal oxide are weighed and mixed at a ratio of (0.7-0.8):1. Then, ytterbium nitrate hexahydrate (Yb(NO3)3·6H2O), calcium oxide (CaO) and molybdenum trioxide (Mo2O3) can be added as needed. After mixing evenly, the mixture is kept at 700-900℃, for example, 800℃ for 24-48 hours. After post-treatment, the corresponding sodium-cobalt oxide material is obtained.

[0047] 2. Preparation of lithium cobalt oxide

[0048] The above-mentioned sodium cobalt oxide material, lithium nitrate, and lithium sulfate were mixed uniformly at a molar ratio of 1:(1-2.5):(0-4), for example, a molar ratio of 1:2:1. The mixture was then placed in an alumina crucible and reacted in a solid-state environment at 240°C to 320°C, for example, 250°C, for 4 to 18 hours. After cooling, a mixture of lithium cobalt oxides was obtained. The resulting lithium cobalt oxides had a P63mc, Cmca structure.

[0049] This application also provides a secondary battery, including a positive electrode, a negative electrode, and an electrolyte.

[0050] Secondary batteries

[0051] The secondary battery described in this application is not particularly limited and can be classified into various categories based on the type of electron transport material. For example, when the electron transport material is lithium (Li, including ions), the secondary battery is a lithium-ion battery.

[0052] According to one embodiment of this application, a secondary battery may include a battery cell and an electrolyte. The battery cell may include packaging material and an electrode assembly disposed within the packaging material, and the electrolyte may fill the internal space formed by the packaging material. The packaging material may protect the electrode assembly from external impacts and prevent electrolyte leakage to the outside. Depending on the shape of the packaging material, the battery cell may be prismatic, cylindrical, or pouch-type.

[0053] The motor assembly includes a positive electrode, a negative electrode, and a separator, as well as other components known in the art for secondary batteries, which are not limited in this application. The separator may be located between the positive and negative electrodes.

[0054] This application does not impose any particular limitation on the preparation method of the secondary battery. For example, it may include the following steps: stacking the positive electrode, separator and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain an electrode assembly; placing the electrode assembly into packaging material; injecting electrolyte into the packaging material and sealing it to obtain a secondary battery.

[0055] positive electrode

[0056] In this application, there are no particular limitations on the positive electrode, as long as the purpose of this application can be achieved. The positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector; the aforementioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be located on one surface of the positive electrode current collector along its own thickness direction, or it can be located on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive electrode current collector, or it can be a part of the surface of the positive electrode current collector. This application has no particular limitations, as long as the purpose of this application can be achieved.

[0057] This application does not impose any particular restrictions on the type, size, or shape of the positive electrode current collector, as long as it does not cause chemical changes in the battery cell and is conductive. For example, the positive electrode current collector can be made of materials such as stainless steel, aluminum, nickel, titanium, calcined carbon, or a substance that has been surface-treated with carbon, nickel, titanium, or silver on aluminum or stainless steel. In this application, the positive electrode current collector may also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, and sulfur.

[0058] The positive current collector can have an appropriate thickness as needed. Although there are no particular limitations, the positive current collector can have a thickness in the range of 1 μm to 500 μm, or a thickness in the range of 1 μm to 300 μm, or a thickness in the range of 1 μm to 100 μm, or a thickness in the range of 1 μm to 50 μm, or a thickness in the range of 1 μm to 20 μm.

[0059] Unless otherwise specified, the terms thickness (or height), width, and length used in this invention refer to average values ​​and can be measured by a measuring instrument capable of measuring thickness (or height), width, and length separately and in accordance with methods in the art.

[0060] The positive electrode current collector can have fine irregularities formed on its surface, thereby further enhancing its adhesion to the positive electrode material layer. For example, the positive electrode current collector can be selected from one or more of the following: membrane, sheet, foil, mesh, porous body, foam, and nonwoven fabric.

[0061] In this application, the positive electrode material layer includes any of the aforementioned positive electrode materials. In some embodiments, the positive electrode material layer may further include a positive electrode binder. This application does not particularly limit the type of positive electrode binder, as long as it can achieve the purpose of this application. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified styrene-butadiene rubber (SBR), or polyurethane. In some embodiments, polyolefin binders include at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0062] In some embodiments, the positive electrode material layer may further include a conductive agent. This application does not impose any particular limitation on the type of conductive agent in the positive electrode material layer, as long as it achieves the purpose of this application. In some exemplary embodiments, the conductive agent includes carbon-based materials, such as graphite (natural or artificial graphite), carbon black (acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, etc.), or carbon fibers; metal-based materials, such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; conductive metal oxides, such as zinc oxide, titanium oxide, etc.; conductive whiskers, such as potassium titanate, etc.; or mixtures formed by any combination of these substances.

[0063] In this application, the positive electrode material layer can be formed by coating a positive electrode slurry onto at least one side of the positive electrode current collector and drying it, and calendering can be performed after drying if necessary. The positive electrode slurry includes the aforementioned positive electrode material and a positive electrode binder, and may further include a conductive agent if necessary. In addition, the positive electrode slurry may also contain a solvent. This application does not have any particular limitation on the type of solvent, as long as it can achieve the purpose of this application. For example, the solvent may be an organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, methyl propionate, alcohol, or ethyl propionate, or an aqueous solvent such as water, or a mixed solvent composed of two or more of the above solvents.

[0064] This application does not impose any particular restrictions on the mass ratio of the positive electrode material, conductive agent, and positive electrode binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. These mass ratios can be those that are known to be applicable.

[0065] negative electrode

[0066] This application does not impose any particular limitation on the negative electrode, as long as the purpose of this application can be achieved. For example, the negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. In this application, the negative electrode material layer can be disposed on one surface or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a part of the negative electrode current collector; this application does not impose any particular limitation, as long as the purpose of this application can be achieved.

[0067] This application does not impose any particular restrictions on the type, size, or shape of the negative electrode current collector, as long as it does not cause a chemical change in the battery cell and is conductive. For example, the negative electrode current collector can be made of materials such as stainless steel, copper, nickel, titanium, calcined carbon, or a substance that has been surface-treated with carbon, nickel, titanium, or silver on the surface of copper or stainless steel.

[0068] The negative electrode current collector can have an appropriate thickness as needed. Although there are no particular limitations, the negative electrode current collector can have a thickness in the range of 1 μm to 500 μm, or in the range of 1 μm to 300 μm, or in the range of 1 μm to 100 μm, or in the range of 1 μm to 50 μm, or in the range of 1 μm to 20 μm, or in the range of 5 μm to 10 μm.

[0069] The negative electrode current collector can have fine irregularities formed on its surface, thereby further enhancing its adhesion to the negative electrode material layer. For example, the negative electrode current collector can be selected from one or more of the following: membrane, sheet, foil, mesh, porous body, foam, and nonwoven fabric.

[0070] The negative electrode material layer of this application includes a negative electrode material. This application does not impose any particular limitation on the negative electrode material, as long as it enables reversible insertion and extraction of electron transport substances such as lithium. For example, the negative electrode material can include, but is not limited to, carbon materials such as graphite (artificial graphite, natural graphite, or graphitized carbon fiber) or amorphous carbon; metals that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys, or their alloys with lithium; SiO... β (0<β≤2), SnO, SnO2, vanadium oxide, lithium vanadium oxide, and other lithium-doped or de-doped metal oxides or their alloys with lithium; or Si-C composites or Sn-C composites containing the aforementioned metals and carbon materials; or spinel-structured lithium titanate lithiation TiO2-Li4Ti5O 12 Furthermore, any one or a mixture of two or more of them can be used. Additionally, the negative electrode material can also be a thin film of metallic lithium. Specifically, the carbon material can be low-crystallinity carbon and high-crystallinity carbon, etc. Representative low-crystallinity carbons are soft carbon and hard carbon. Examples of high-crystallinity carbons include amorphous, plate-like, sheet-like, spherical, or fibrous natural or artificial graphite, primary graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, carbon microspheres (mesophase carbon microspheres), mesophase pitch, and high-temperature calcined carbons such as petroleum and coal-based coke (coke derived from petroleum or coal tar pitch).

[0071] The negative electrode material layer in this application may further include a negative electrode binder and a conductive agent. This application does not impose any particular limitation on the types of negative electrode binders and conductive agents, as long as they can achieve the purpose of this application. For example, the negative electrode binder may include, but is not limited to, at least one selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol, styrene-butadiene rubber (SBR), polyethylene oxide, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, cellulose acetate, diacetyl cellulose, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyarylate, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber, acrylic (esterified) styrene-butadiene rubber, epoxy resin, or nylon.

[0072] This application does not impose any particular limitation on the type of conductive agent in the negative electrode material layer, as long as it can achieve the purpose of this application. In some exemplary embodiments, the conductive agent includes carbon-based materials, such as graphite (natural or artificial graphite), carbon black (acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, etc.), or carbon fibers; metal-based materials, such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; conductive metal oxides, such as zinc oxide, titanium oxide, etc.; conductive whiskers, such as potassium titanate, etc.; or mixtures formed by any combination of these substances.

[0073] This application does not impose any particular restrictions on the mass ratio of negative electrode active material, negative electrode conductive agent, and negative electrode binder in the negative electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0074] In this application, the negative electrode material layer can be formed by coating a negative electrode slurry onto at least one side of the negative electrode current collector and drying it, and calendering can be performed after drying if necessary. The negative electrode slurry includes the aforementioned negative electrode material and a negative electrode binder, and may further include a conductive agent if necessary. In addition, the negative electrode slurry may also contain a solvent. This application does not have any particular limitation on the type of solvent, as long as it can achieve the purpose of this application. For example, the solvent may be an organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, methyl propionate, alcohol, or ethyl propionate, or an aqueous solvent such as water, or a mixed solvent composed of two or more of the above solvents.

[0075] This application does not impose any particular restrictions on the mass ratio of negative electrode material, conductive agent and negative electrode binder in the negative electrode material layer, as long as the purpose of this application can be achieved, and these mass ratios can be the well-known mass ratios.

[0076] diaphragm

[0077] The diaphragm in this application refers to a membrane that prevents short circuits between the positive and negative electrodes while allowing electron transport substances to pass through. This application does not impose any particular limitations on the diaphragm, as long as it can achieve the purpose of this application. For example, the material of the diaphragm may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, and aramid; the type of diaphragm may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, and spun membrane.

[0078] According to some embodiments of this application, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used.

[0079] Optionally, a surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder. This application does not have any particular limitation on the inorganic particles, which may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. This application does not have any particular limitation on the binder, which may be at least one of the above-mentioned positive electrode binders or negative electrode binders. The polymer layer contains a polymer. This application does not have any particular limitation on the polymer, which may include at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride and poly(vinylidene fluoride-hexafluoropropylene). In this application, there is no particular limitation on the thickness of the diaphragm, as long as it can achieve the purpose of this application. For example, the thickness of the diaphragm can be from 5 μm to 500 μm.

[0080] electrolyte

[0081] In this application, the electrolyte refers to the medium that facilitates the movement of electron transport substances to enable the electrochemical reactions at the positive and negative electrodes. The electrolyte can be a commonly used organic liquid electrolyte, inorganic liquid electrolyte, gel-type polymer electrolyte, molten inorganic electrolyte, etc., but is not limited to these. Solid electrolytes such as gel-type polymer electrolytes can also be used instead of the electrolyte. Batteries using solid electrolytes are generally called solid-state batteries or all-solid-state batteries. Liquid electrolytes (electrolytes) typically contain non-aqueous solvents and lithium salts.

[0082] According to some embodiments of this application, lithium salts may include, but are not limited to, at least one of: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide {LiN(CF3SO2)2, LiTFSI)}, lithium bis(fluorosulfonyl)imide {Li(N(SO2F)2), LiFSI}, lithium bis(oxalateborate)borate {LiB(C2O4)2, LiBOB}, lithium difluorooxalateborate {LiBF2(C2O4), LiDFOB}, LiNO3, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, Li2SiF6, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or lithium difluoroborate. This application does not limit the content of lithium salts in the electrolyte, as long as the purpose of this application is achieved.

[0083] This application does not impose any particular limitation on non-aqueous solvents, as long as they can serve as a medium for the movement of ions participating in the electrochemical reactions of the battery cell. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl ethyl carbonate (EMC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, or vinyl ethylene carbonate. The aforementioned fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of 1,3-dioxapentane (DOL), ethylene glycol dimethyl ether (1,2-dimethoxyethane, DME), dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvents mentioned above may include, but are not limited to, ketone solvents such as 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, and cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; alcohol solvents such as ethanol and isopropanol; nitrile solvents such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and may include double bonds, aromatic rings, or ether bonds) (e.g., acetonitrile); amide solvents such as dimethylformamide; dioxolane solvents such as 1,2-dioxolane and 1,3-dioxolane; or sulfone solvents such as dimethyl sulfoxide, sulfolane, and methyl sulfolane; or phosphate solvents such as trimethyl phosphate, triethyl phosphate, and trioctyl phosphate. In the above text, the hydrocarbon group may be selected from one or more of alkyl, alkenyl, or alkynyl groups.

[0084] Electronic devices

[0085] This application provides an electronic device including the aforementioned secondary battery. The electronic device in this application is not particularly limited and can be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0086] Measurement methods

[0087] The physical properties mentioned in this application can be measured using the following methods, and the physical properties in the following embodiments and comparative examples are measured using the following methods.

[0088] Crystal structure testing:

[0089] The crystal structure of lithium cobalt composite oxide was determined using an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE) with Cu Kα as the target material; the voltage and current were 40 kV / 35 mA, the scanning angle range was 10° to 70°, and the scanning rate was 5° / min. The crystal phase structure of the lithium cobalt composite oxide was determined based on the obtained XRD pattern.

[0090] Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) tests

[0091] The microstructure of lithium cobalt composite oxides was observed using a scanning electron microscope (SEM, JEOL, JSM-6390LV). For cross-sectional SEM, a FEI Scios 2HiVac focused ion beam scanning electron microscope (FIB-SEM) was used. The elemental distribution of the lithium cobalt composite oxides was obtained by using an X-Max energy dispersive spectrometer (EDS) from Oxford Instruments, UK, for line or area scanning of the surface or cross-section.

[0092] Figure 1 shows scanning electron microscope (SEM) images of the lithium cobalt composite oxide in Example 1-1 at different magnifications. As can be seen from the figure, the length and width of the lithium cobalt composite oxide in Example 1-1 are relatively uniformly distributed.

[0093] Figure 2 shows a cross-sectional SEM image and EDS surface scan analysis image of a lithium cobalt composite oxide provided in Examples 2-9. As can be seen from the figures, the cross-section of the lithium cobalt composite oxide in Examples 2-9 exhibits a uniform distribution of nickel, yttrium, calcium, and molybdenum elements.

[0094] (Based on the molar content test of metallic elements other than lithium)

[0095] The lithium cobalt composite oxide was completely digested with aqua regia to obtain the test solution. The test solution was then analyzed using an Optima 7000DV inductively coupled plasma atomic emission spectrometer (ICP-AES) from Pepperl, Inc. (USA) to obtain the molar content of the analyte.

[0096] Average length and average width test

[0097] The surface of lithium cobalt composite oxides was imaged using a scanning electron microscope. Ten lithium cobalt composite oxides were randomly selected, and the longest distance between any two points on the edge of each of the ten lithium cobalt composite oxides was taken as the length of each lithium cobalt composite oxide. The arithmetic mean of the lengths of the ten lithium cobalt composite oxides was calculated as the average length of the lithium cobalt composite oxide. The longest distance between the line segment perpendicular to the length of the lithium cobalt composite oxide and its edge was taken as the width of each lithium cobalt composite oxide. The arithmetic mean of the widths of the ten lithium cobalt composite oxides was calculated as the average width of the lithium cobalt composite oxide.

[0098] Hot box test

[0099] At 25℃±1℃, the lithium-ion battery was charged at a constant current of 4.0C to 4.35V, then charged at a constant voltage of 4.35V until the current dropped to 0.05C. The battery was then discharged at a constant current of 1.0C to 3.0V. The lithium-ion battery was then placed in a hot chamber and heated from 25℃ to 150℃ at a rate of 5℃ / min. Once 150℃ was reached, the temperature was maintained and timing began. After maintaining the temperature for 1 hour, the state of the lithium-ion battery was observed. A lithium-ion battery that did not emit smoke, catch fire, or explode was considered to have passed the test. Each example tested 10 lithium-ion batteries. "1 / 10" indicates that one out of 10 lithium-ion batteries passed the test.

[0100] Ratio Performance Test

[0101] The lithium-ion battery used in the example / comparative test was placed at a test temperature of 25°C and allowed to stand for 5 minutes. Then, it was charged at a constant current of 0.2C to 4.55V, followed by constant voltage charging at 4.55V to 0.05C. After standing for 5 minutes, it was discharged at a constant current of 0.2C to 2.8V, and the 0.2C discharge capacity was recorded. This process was repeated for another 5 minutes, followed by constant current discharge at 1.5C, and the 1.5C discharge capacity was recorded. Rate capacity retention = (0.2C discharge capacity / 1.5C discharge capacity) × 100%.

[0102] The following uses a lithium-ion battery as an example to illustrate the solution of this application with reference to the specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available products, and the devices or equipment used are all purchased from conventional market sales channels.

[0103] Example 1-1

[0104] Methods for preparing cathode materials:

[0105] 1. Preparation of sodium-containing cobalt oxides

[0106] Cobalt sulfate (CoSO4) and nickel sulfate (NiSO4) were weighed according to a molar ratio of 96:4. Then, deionized water was added and stirred rapidly to dissolve them. Ammonium carbonate was then slowly added to adjust the pH to 12.8 until the reaction was complete, forming a homogeneous carbonate precipitate. The precipitate was sintered at 750℃ for 16 hours. After crushing and sieving, Ni-doped Co3O4 metal oxide material was obtained.

[0107] Sodium carbonate (Na2CO3) and the above-mentioned Ni-doped Co3O4 metal oxide were weighed and mixed evenly at a molar ratio of 0.75:1, and kept at 800℃ for 24 hours. After post-processing, the corresponding sodium-cobalt oxide material was obtained.

[0108] 2. Preparation of lithium cobalt oxide

[0109] The above-mentioned sodium cobalt oxide material, lithium nitrate, and lithium sulfate were mixed uniformly at a molar ratio of 1:2:1, placed in an alumina crucible, and reacted in a solid-state environment at 250°C for 8 hours. After cooling, a mixture of lithium cobalt oxides was obtained. The resulting lithium cobalt oxides had a P63mc, Cmca structure.

[0110] Preparation of the positive electrode:

[0111] The above-mentioned lithium cobalt composite oxide (97 wt%), conductive carbon black (1.5 wt%), and polyvinylidene fluoride (1.5 wt%) were dissolved in N-methylpyrrolidone to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated onto one surface of an aluminum foil, and after drying, the coating process was repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. The coated aluminum foil was dried, pressure-treated, and then cut into specified sizes to fabricate the positive electrode.

[0112] Preparation of the diaphragm: A 12μm thick polyethylene (PE) microporous membrane was selected as the diaphragm.

[0113] Preparation of the negative electrode:

[0114] Artificial graphite (95 wt%), conductive carbon black (0.5 wt%), polyacrylic acid (3.5%), and carboxymethyl cellulose (1%) were mixed, then deionized water was added and stirred until homogeneous to prepare a negative electrode slurry. This negative electrode slurry was uniformly coated onto one surface of a copper foil. After drying, the above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. The coated copper foil was dried, pressure-treated, and then cut into specified sizes to fabricate the negative electrode.

[0115] Electrolyte preparation:

[0116] In an argon-atmosphere glove box with a water content of less than 10 ppm, dimethyl carbonate, diethyl carbonate, and ethylene carbonate (mass ratio 1:1:1) were mixed to obtain a base solvent. Lithium hexafluorophosphate and adiponitrile were then added to the base solvent and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate was 12.5%, and the mass content of adiponitrile was 1%.

[0117] Battery making:

[0118] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up to form an electrode assembly. The electrode assembly is placed in an outer aluminum-plastic film, baked, and then injected with the electrolyte. After vacuum sealing, settling, formation, shaping, and capacity testing, a lithium-ion battery is obtained.

[0119] Examples 1-2 to 1-10, Comparative Examples 1-1 to 1-6

[0120] The only difference from Example 1-1 is that the molar content of nickel (m%) and the average length L0 μm and average width W μm of the lithium-cobalt composite oxide were adjusted according to Table 1. Specific adjustment parameters and performance test results are shown in Table 1. In Comparative Example 1-1, the lithium-cobalt composite oxide was prepared by controlling the molar ratio of sodium carbonate (Na2CO3) to Ni-doped Co3O4 to be 0.9:1, resulting in a matrix with a P63mc structure and no Cmca structure. The average length L0 μm and average width W μm of the lithium-cobalt composite oxide were increased by raising the sintering temperature during the preparation of the Ni-doped Co3O4 metal oxide. The average length and average width of the lithium-cobalt composite oxide were further controlled by combining this with a sieving process.

[0121] Table 1

[0122] As shown in Table 1, this application improves the high-temperature safety and rate performance of secondary batteries by adding nickel to the matrix of lithium cobalt composite oxide, controlling the molar content of nickel (m%) to satisfy 0.2 ≤ m ≤ 10, and ensuring that the average length (L0 μm) and average width (W μm) of the lithium cobalt composite oxide satisfy 4 ≤ L0 ≤ 30 and 1 ≤ L0 / W ≤ 1.5, respectively. Specifically, further improvements in rate performance and high-temperature safety performance are achieved when 1 ≤ m ≤ 4, 5 ≤ L0 ≤ 20, and / or 1 ≤ L0 / W ≤ 1.3 are satisfied.

[0123] Examples 2-1 to 2-9

[0124] The only difference from Example 1-1 is that a mixture of ytterbium nitrate hexahydrate (Yb(NO3)3·6H2O) and calcium oxide (CaO), and / or molybdenum trioxide (Mo2O3), corresponding molar amounts of these components, are added to a mixture of sodium carbonate (Na2CO3) and Ni-doped Co3O4 before the subsequent preparation of sodium-cobalt oxide materials. Specifically, the molar proportions of each raw material component are controlled, and the metal elements in the lithium-cobalt composite oxide (excluding lithium) are adjusted according to Table 2: ytterbium molar content a%, calcium molar content b%, and molybdenum molar content c%. The specific adjustment parameters and performance test results are shown in Table 2.

[0125] Table 2

[0126] Table 2 shows that by adding ytterbium and calcium to the lithium-cobalt composite oxide matrix and adjusting the molar content of ytterbium (a%) and calcium (b%) to satisfy the following conditions: 0.01 ≤ a + b ≤ 1.8, 4 ≤ a / b ≤ 35, the high-temperature safety and rate performance of the secondary battery can be further improved. In particular, satisfying the relationships 0.2 ≤ a + b ≤ 0.8 and / or 4.3 ≤ a / b ≤ 8.7 further improves the high-temperature safety and rate performance. Furthermore, adding molybdenum to the lithium-cobalt composite oxide, with a molar content (c%) satisfying 0.03 ≤ c ≤ 0.6, further improves the high-temperature safety and rate performance of the secondary battery.

[0127] Examples 3-1 to 3-5

[0128] The only difference from Examples 2-9 is that the proportions of the first particle (N1%), the second particle (N2%), and the third particle (N3%) in the lithium cobalt composite oxide are adjusted according to Table 3. Specific adjustment parameters and performance test results are shown in Table 3.

[0129] Table 3

[0130] As shown in Table 3, by adjusting the proportions of the first particles (N1%) and the second particles (N2%) in the lithium cobalt composite oxide, this application can further improve the high-temperature safety and rate performance of the secondary battery by satisfying the conditions 1≤N2 / N1≤9; 10≤N1≤50; and 50≤N2≤90. Specifically, when the proportion of the second particles (N3%) is further adjusted to satisfy 0.5≤N3≤4, the high-temperature safety and rate performance of the secondary battery can be further improved.

[0131] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the principles of this application should be included within the protection scope of this application.

Claims

1. A positive electrode material, characterized in that, The invention includes a lithium-cobalt composite oxide; the lithium-cobalt composite oxide has a P63mc structure and a Cmca structure; the lithium-cobalt composite oxide includes lithium, cobalt and nickel, and based on the metal elements other than lithium in the lithium-cobalt composite oxide, the molar content of nickel is m%, 0.2≤m≤10. The average length of the lithium cobalt composite oxide is L0μm, the average width is Wμm, 4≤L0≤30, and 1≤L0 / W≤1.

5.

2. The cathode material according to claim 1, characterized in that, The lithium-cobalt composite oxide satisfies at least one of the following conditions: (1)1≤m≤4； (2)5≤L0≤20； (3) 1≤L0 / W≤1.

3.

3. The cathode material according to claim 1 or 2, characterized in that, The lithium-cobalt composite oxide includes ytterbium and calcium. Based on the metal elements other than lithium in the lithium-cobalt composite oxide, the molar content of ytterbium is a%, the molar content of calcium is b%, and 0.01≤a+b≤1.8, 4≤a / b≤35.

4. The cathode material according to claim 3, characterized in that, 0.2≤a+b≤0.8, and / or, 4.3≤a / b≤8.

7.

5. The cathode material according to claim 1 or 2, characterized in that, The lithium-cobalt composite oxide includes molybdenum; based on the metal elements other than lithium in the lithium-cobalt composite oxide, the molar content of molybdenum is c%, 0.03≤c≤0.

6.

6. The cathode material according to claim 1 or 2, characterized in that, The lithium cobalt composite oxide comprises a first particle and a second particle, wherein the length of the first particle is L1μm, 0.1≤L1≤5, and the length of the second particle is L2μm, 8≤L2≤40. Based on the number of particles of the lithium cobalt composite oxide, the first particle accounts for N1% and the second particle accounts for N2%; 2≤N2 / N1≤49.

7. The cathode material according to claim 6, characterized in that, The lithium-cobalt composite oxide satisfies at least one of the following conditions: (1) 1≤N2 / N1≤9; (2)10≤N1≤50； (3)50≤N2≤90。 8. The cathode material according to claim 1 or 2, characterized in that, The lithium-cobalt composite oxide further includes a third particle with a length of L3μm, where 5 < L3 < 8; based on the number of particles in the lithium-cobalt composite oxide, the proportion of the third particle is N3%, where 0.5 ≤ N3 ≤ 4; and / or, The compaction density of the lithium-cobalt composite oxide under a pressure of 180 MPa is dg / cm³. 3 , 3.8≤d≤4.

5.

9. A secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector; the positive electrode material layer includes the positive electrode material according to any one of claims 1 to 8.

10. An electronic device, characterized in that, Includes the secondary battery as described in claim 9.

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