Positive electrode material, secondary battery, and electronic device

Abstract

A positive electrode material, a secondary battery, and an electronic device, relating to the technical field of battery materials. The positive electrode material comprises a lithium transition metal oxide. A region of the lithium transition metal oxide having a depth of x nm from the surface contains an aluminum element and a boron element, wherein 0≤x≤100, the atomic ratio of the aluminum element to the boron element is y, y=ax+b, 0.01≤a≤0.1, and 0.1≤b≤2.0. The present application can improve the structural stability of the positive electrode material under high temperature and high pressure, and can also reduce impedance growth during cycling.

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] Secondary batteries (such as nickel-metal hydride batteries, nickel-cadmium batteries, lead-acid batteries, lithium-ion batteries, and polymer lithium-ion batteries) achieve the interconversion of chemical energy and electrical energy through reversible electrochemical reactions. During discharge, the active materials undergo redox reactions to release electrical energy; during charging, external electrical energy drives the reaction in reverse, restoring the active materials to their original state. Typical secondary batteries have a cycle life of hundreds to thousands (lead-acid batteries) or thousands to tens of thousands (lithium-ion batteries).

[0003] However, secondary batteries still face the following technical challenges in practical applications: 1. High-temperature storage and gas generation: Under high-temperature (>45℃) environments, electrolyte decomposition (e.g., LiPF6 hydrolysis to generate HF) and positive electrode lattice oxygen release (e.g., LiNi) occur. x Co y Mn z Side reactions such as O2 deoxygenation and damage to the negative electrode SEI film are exacerbated, leading to the generation of large amounts of gases such as CO2, H2, and CH4. Gas production causes battery expansion and increased internal pressure, resulting in capacity decay and the risk of thermal runaway. 2. Gas production during float charging (constant voltage charging): Under long-term float charging conditions, continuous overcharging leads to the dissolution of transition metals in the positive electrode (such as Mn). 2+ / Co 3+ Dissolution), electrolyte oxidation (e.g., EC (ethylene carbonate) → CO3) 2- +CO↑) accelerates gas production and triggers the "lithium plating" phenomenon; the gas production rate is positively correlated with voltage, threatening the safety of energy storage systems. 3. Cyclic impedance growth: During cycling, the thickening of the CEI layer on the positive electrode surface, the reconstruction of the SEI film on the negative electrode, and the growth of lithium dendrites lead to an increase in interfacial ion transport resistance; after 500 cycles, the DC impedance (DCR) of conventional lithium-ion batteries increases by 30% to 50%, and the power density decreases significantly. Summary of the Invention

[0004] In view of this, this application provides a cathode material, a secondary battery, and an electronic device. By introducing aluminum and boron elements into lithium transition metal oxide and controlling their atomic ratio, the structural stability of the cathode material under high temperature and high pressure can be improved, while reducing impedance growth during cycling, thereby solving the above-mentioned problems.

[0005] In a first aspect, this application provides a cathode material comprising a lithium transition metal oxide. The lithium transition metal oxide contains aluminum and boron elements within a region at a depth of x nm from the surface, where 0 ≤ x ≤ 100, and the atomic ratio of aluminum to boron is y, where y = ax + b, 0.01 ≤ a ≤ 0.1, and 0.1 ≤ b ≤ 2.0. This application regulates the relative atomic ratio of aluminum and boron to linearly change with the depth of the lithium transition metal oxide, forming a relatively uniform protective layer on the surface of the lithium transition metal oxide. This adjusts the surface chemical properties, such as improving interfacial stability and reducing the activity of side reactions, effectively protecting the material structure, mitigating electrolyte erosion of the cathode material and side reactions, and improving the gas generation problem of secondary batteries under high temperature or float charging conditions. In addition, a reasonable design of the proportional distribution can provide additional mechanical strength to the cathode material, reduce microcracks caused by expansion and contraction, thereby extending battery life, reducing the growth of electrode surface resistance, and the appropriate atomic ratio of aluminum and boron can also improve ion transport efficiency, improve the high current performance of the battery, and improve the impedance growth during the secondary battery cycle.

[0006] In some implementations, 0.01 ≤ a ≤ 0.04, 0.7 ≤ b ≤ 1.0. Adjusting the values ​​of a and b to meet the above ranges can further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries.

[0007] In some embodiments, the mass content of aluminum is m1% based on the mass of the lithium transition metal oxide, where 0.1 ≤ m1 ≤ 5.0; preferably, 0.1 ≤ m1 ≤ 0.5. Adjusting the mass content of aluminum to meet the above range can further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries.

[0008] In some embodiments, the boron content is m2% based on the mass of the lithium transition metal oxide, with 0.1 ≤ m2 ≤ 1.0; preferably, 0.1 ≤ m2 ≤ 0.3. Adjusting the boron content to meet the above range can further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries.

[0009] In some embodiments, the lithium transition metal oxide contains element T, which includes at least one of nickel, cobalt, or manganese; the molar amount of element T is n0, and the cathode material satisfies at least one of the following conditions:

[0010] (a) The molar amount of nickel is n1, and 0.5 ≤ n1 / n0 ≤ 1;

[0011] (b) The molar amount of cobalt is n2, 0≤n2 / n0≤0.5;

[0012] (c) The molar amount of manganese is n3, and 0 ≤ n3 / n0 ≤ 0.5.

[0013] This application controls the lithium transition metal oxide to contain the aforementioned element T. By adjusting the molar relationship of specific elements in element T, the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries can be further improved.

[0014] In some embodiments, the lithium transition metal oxide contains sodium; the molar amount of sodium is n4, where 0 < n4 / n0 ≤ 0.02; preferably, 0.01 ≤ n4 / n0 ≤ 0.02. Adjusting the molar amount of sodium in the lithium transition metal oxide in conjunction with the amount of nitrogen (T) can further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries.

[0015] In some embodiments, the lithium transition metal oxide contains element R, which includes at least one of titanium, niobium, germanium, molybdenum, gallium, and tungsten; the molar amount of element R is n5, where 0 < n5 / n0 ≤ 0.2; preferably, 0.01 ≤ n5 / n0 ≤ 0.2. Adjusting the molar amount of element R in the lithium transition metal oxide in conjunction with element T can further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries.

[0016] In some embodiments, the lithium transition metal oxide contains fluorine, and the molar amount of fluorine is n. 61 0.01≤100×n 61 / n0≤0.5; and / or, the lithium transition metal oxide contains nitrogen; the molar amount of nitrogen is n. 62 0.01≤100×n 62 / n0≤1. Based on the above scheme, this application adjusts the molar amount of fluorine or nitrogen in lithium transition metal oxide in combination with T element, which can further improve the problems of high-temperature gas generation, float charging gas generation and impedance growth in secondary batteries.

[0017] In a second aspect, 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 positive electrode material described in the first aspect.

[0018] Thirdly, this application provides an electronic device including the secondary battery described in the second aspect above. Attached Figure Description

[0019] Figure 1 is an illustration of the linear fitting curves of x and y of a lithium transition metal oxide provided in a specific embodiment of this application.

[0020] Figure 2 shows the specific capacity curve of a lithium transition metal oxide preparation according to a specific embodiment of this application;

[0021] Figure 3 shows the voltage-capacity differential dQ / dV curve of a coin cell made of lithium transition metal oxide according to a specific embodiment of this application. Detailed Implementation

[0022] 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.

[0023] In a first aspect, this application provides a cathode material comprising a lithium transition metal oxide; the lithium transition metal oxide contains aluminum and boron elements within a region at a depth of x nm from the surface, where 0 ≤ x ≤ 100, and the atomic ratio of aluminum to boron is y, where y = ax + b, 0.01 ≤ a ≤ 0.1, and 0.1 ≤ b ≤ 2.0. That is, 0.01x + 0.1 ≤ y ≤ 0.1x + 2.0. For example, a is a value within the range of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any two of these values, and b is a value within the range of 0.1, 0.2, 0.4, 0.6, 0.9, 1.1, 1.4, 1.6, 1.7, 1.9, 2, or any two of these values. This application introduces aluminum and boron elements into lithium transition metal oxides. By controlling the change in the atomic ratio of aluminum and boron with depth to conform to the aforementioned rules, aluminum forms a Li-Al-O layer with oxygen to stabilize oxygen ions on the surface, while boron forms a Li-BO glass-ceramic thin film to reduce the contact area between the positive electrode and the electrolyte. The protective layer formed by the two elements can effectively mitigate electrolyte erosion and side reactions. At the same time, aluminum and boron can also adjust the surface chemical properties of lithium transition metal oxides, improve interface stability, and reduce the activity of side reactions. Under high temperature or float charging conditions, it can protect the positive electrode material structure and reduce gas production. Furthermore, an appropriate Al / B atomic ratio can reduce the growth of electrode surface impedance, improve ion transport efficiency, and reduce impedance during secondary battery cycling.

[0024] In some preferred embodiments, 0.01 ≤ a ≤ 0.04, 0.7 ≤ b ≤ 1.0. When the atomic ratio of aluminum and boron is further controlled to conform to the above-mentioned pattern with increasing depth, the atomic ratio of aluminum and boron in lithium transition metal oxides generally shows a relatively uniform increasing trend with increasing depth; that is, aluminum increases and boron decreases with increasing depth. Although the detailed mechanism is not yet clear, this feature is believed to promote better coordination between aluminum and boron, further improving the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries.

[0025] In this application, lithium transition metal oxide is a crystalline compound composed of lithium (Li) and one or more transition metals (such as Co, Ni, Mn, etc.) through oxygen bridging bonds, and its general formula can be represented as Li x TM z O y (TM = Transition Metal). Based on differences in crystal structure and composition, they are mainly divided into the following types: 1. Layered oxides: cobalt-based such as LiCoO2 (operating voltage 3.8-4.2V, energy density 270mAh / g), nickel-based such as LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811, capacity >200mAh / g), high nickel and cobalt-free: such as LiNi 0.9 Mn 0.1 O2; 2. Spinel structure: such as LiMn2O4; 3. Polyanionic type: such as LiFePO4. The structural stability and electrochemical performance of the above materials are optimized by controlling the transition metal ratio (such as Ni:Co:Mn = 6:2:2 or 8:1:1 in NCM) and doping (Al, Mg, etc.).

[0026] It should be noted that, in this field, the “surface” of an object is a physical layer with a physical structure. In this context, the surface of a solid refers to the physical layer consisting of one or more atomic layers of the outermost layer of the solid, which is the interface layer where the solid comes into contact with a vacuum or another substance.

[0027] The detection of elements in lithium transition metal oxides in this application can be performed using methods known in the art, such as X-ray photoelectron spectroscopy (XPS). XPS is a technique for analyzing the chemical properties of a material's surface. Specifically, it utilizes the absorption and scattering characteristics of X-rays as they pass through the surface of an object to detect its internal structure. XPS can measure the elemental composition, empirical formulas, chemical states, and electronic states of materials. It involves exciting a solid surface with a beam of X-rays and simultaneously measuring the kinetic energy of electrons emitted from a region greater than 0 nm and less than or equal to 100 nm from the surface of the material being analyzed; this yields the XPS spectrum. Photoelectron spectroscopy records electrons with energies exceeding a certain threshold. The spectral peaks appearing in the photoelectron spectrum represent the emission of electrons with specific energies from atoms. The energy and intensity of these peaks can be used for qualitative and quantitative analysis of the elements contained in the solid surface.

[0028] In some embodiments, based on the mass of the lithium transition metal oxide, the mass content of aluminum is m1%, where 0.1 ≤ m1 ≤ 5.0; preferably, 0.1 ≤ m1 ≤ 0.5. Exemplarily, m1 is a value within the range of 0.1, 0.3, 0.7, 1.5, 1.9, 2.5, 3.4, 3.5, 4.2, 4.9, 5, or any two of these. By controlling the mass content of aluminum to meet the above range, the Li-Al-O layer formed by Al and oxygen can stabilize oxygen ions on the surface. Furthermore, the high strength of the Al-O chemical bond can effectively reduce oxygen release under high voltage, lowering the possibility of performance degradation and byproduct formation, and reducing gas generation in the secondary battery under high temperature and float charging conditions. Additionally, an appropriate aluminum content can improve the mechanical strength of the cathode material, reduce physical degradation during cycling, and help improve the impedance growth during secondary battery cycling.

[0029] In some embodiments, based on the mass of lithium transition metal oxide, the mass content of boron is m2%, where 0.1 ≤ m2 ≤ 1.0; preferably, 0.1 ≤ m2 ≤ 0.3. Exemplarily, the value of m2 is within the range of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or any combination thereof. Controlling the boron mass content to meet the above range allows for the formation of a Li-BO glass-ceramic thin film, which helps reduce the specific surface area of ​​the cathode material and decreases the contact area between the cathode and the electrolyte, reducing the occurrence of side reactions. Simultaneously, utilizing the stable chemical properties of the Li-BO structure helps maintain the stability of oxygen ions, reducing oxidation reactions and improving the electrochemical stability of the material, thereby reducing gas production under high temperature and high voltage conditions during float charging. Furthermore, controlling the boron content to meet the above range also helps adjust the electrochemical properties of the electrode surface, enhancing the controllability of the reaction. It also helps to fully utilize the lightweight properties of boron, reducing stress accumulation in the cathode material due to volume changes during cycling, thereby reducing impedance growth during secondary battery cycling.

[0030] In some embodiments, the lithium transition metal oxide contains a T element, which includes at least one of nickel, cobalt, or manganese. The use of a T element in conjunction with the aluminum and boron elements described in this application can stabilize the structure of the cathode material, reduce the occurrence of side reactions, and also help improve ion migration rate and reaction rate, thereby promoting the reduction of gas generation in the secondary battery and reducing impedance growth.

[0031] In some embodiments, the molar amount of element T is n0, and the molar amount of element nickel is n1, where 0.5 ≤ n1 / n0 ≤ 1; for example, the value of n1 / n0 is within the range of 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or any two of these values. By controlling the molar ratio of element nickel within the above range, in combination with the elements aluminum and boron of this application, it is beneficial to improve battery capacity and energy density, optimize the electrochemical performance of the cathode material, and improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries.

[0032] In some embodiments, the molar amount of cobalt is n2, where 0 ≤ n2 / n0 ≤ 0.5; for example, the value of n2 / n0 is a value within the range of 0, 0.1, 0.2, 0.3, 0.4, 0.5, or any two of these. By controlling the molar ratio of cobalt within the above range, in combination with the aluminum and boron elements of this application, it is beneficial to improve battery capacity and energy density, optimize the electrochemical performance of the cathode material, and improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries.

[0033] In some embodiments, the molar amount of manganese is n3, where 0 ≤ n3 / n0 ≤ 0.5; for example, the value of n3 / n0 is a value within the range of 0, 0.1, 0.2, 0.3, 0.4, 0.5, or any two of these. By controlling the molar ratio of manganese within the above range, in combination with the aluminum and boron elements of this application, it is beneficial to improve battery capacity and energy density, optimize the electrochemical performance of the cathode material, and improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries.

[0034] In some embodiments, the lithium transition metal oxide contains sodium; the molar amount of sodium is n4, where 0 < n4 / n0 ≤ 0.02; preferably, 0.01 ≤ n4 / n0 ≤ 0.02. Controlling the presence of sodium in the lithium transition metal oxide and adjusting its molar amount to satisfy the above relationship, in combination with the aforementioned aluminum and boron elements, can stabilize the crystal structure of the lithium transition metal oxide, reduce structural changes or decomposition of the material under high temperature or float charge conditions, thereby improving gas generation problems, and also improving the interfacial compatibility between the cathode material and the electrolyte, reducing interfacial resistance, and thus lowering the cycle impedance of the secondary battery.

[0035] In some embodiments, the lithium transition metal oxide contains element R, which includes at least one of titanium, niobium, germanium, molybdenum, gallium, and tungsten. The molar amount of element R is n5, where 0 < n5 / n0 ≤ 0.2; preferably, 0.01 ≤ n5 / n0 ≤ 0.2. For example, the value of n5 / n0 is within the range of 0, 0.01, 0.03, 0.05, 0.08, 0.09, 0.12, 0.15, 0.17, 0.19, 0.2, or any two of these ranges. Adjusting the molar amount of element R in the lithium transition metal oxide in conjunction with element T can further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries.

[0036] In some embodiments, the lithium transition metal oxide contains fluorine; the molar amount of fluorine is n. 61 0.01≤100×n 61 / n0≤0.5; for example, n 61 The value of / n0 is within the range of 0.01, 0.04, 0.08, 0.17, 0.19, 0.26, 0.30, 0.35, 0.41, 0.48, 0.5, or any two of these values. Adjusting the molar amounts of fluorine and titanium in lithium transition metal oxides according to the above relationship can further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries.

[0037] In some embodiments, the lithium transition metal oxide contains nitrogen; the molar amount of nitrogen is n. 62 0.01≤100×n 62 / n0≤1. For example, n 62 The value of / n0 is within the range of 0.01, 0.11, 0.13, 0.32, 0.35, 0.48, 0.60, 0.77, 0.86, 0.97, 1, or any two of these values. Controlling the presence of nitrogen in lithium transition metal oxides and adjusting its molar ratio with T to conform to the above relationship can further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries.

[0038] In this application, the lithium transition metal oxide can be prepared by a method including the following steps:

[0039] S100: Preparation of sodium-based precursor

[0040] 1. Raw material ratio

[0041] Transition metal hydroxide (Ni) 0.5 Mn 0.5(OH)2) Sodium source (such as one or more of NaAc, Na2CO3, NaOH, NaNO3, NaHCO3) are mixed at a molar ratio of Na:TM (transition metals, including Ni and Mn) ≥ 1.0, for example Na:TM = (1.05~1.2):1.

[0042] 2. Pre-sintering pore formation

[0043] Porous NaNi is formed by heating to 450–550°C at a rate of 8°C / min in air and holding for 3 hours. 0.5 Mn 0.5 O2 precursor.

[0044] 3. High-temperature crystallization

[0045] Porous NaNi under airflow 0.5 Mn 0.5 The O2 precursor was heated to 800–1000℃ at a rate of 5℃ / min and held for 10–20 h to obtain layered NaNi. 0.5 Mn 0.5 O2 matrix, i.e. sodium-based precursor.

[0046] S200: Lithium-sodium ion exchange, selected from at least one of the following methods:

[0047] 1. Hydrothermal displacement method

[0048] The sodium-based precursor was mixed with a concentrated lithium salt solution (such as 6M LiOH) at a solid-liquid ratio of 1:20, and then subjected to hydrothermal treatment at 180–220 °C for 12–48 h to achieve the topological chemical substitution of Na+ by Li+.

[0049] 2. Solid-phase ion exchange

[0050] The sodium-based precursor was ground and mixed with an excess lithium salt (LiNO3:LiCl = 3:1) at a Li / Na molar ratio of 5:1, and the ion exchange reaction was carried out at temperatures above 200°C.

[0051] 3. Electrochemical displacement

[0052] A three-electrode system was constructed: a sodium-based precursor was used as the working electrode, and a Li foil was used as the counter electrode, with constant potential polarization (0.5V vs. Li). + / Li) in 1M LiPF6 / EC:DMC electrolyte, driving Na through potential difference + Dissolution / Li + Embedded.

[0053] 4. Solution impregnation method

[0054] The solution was cyclically impregnated with 0.1M LiAc solution (3 times × 2h / time), and after each impregnation, it was heat-treated at above 200℃ for 1h to promote ion migration. The final Li content was controlled by the number of impregnations.

[0055] S300: Post-processing

[0056] The material after lithium-sodium ion replacement was washed with deionized water until pH=7.0±0.5 to remove residual sodium salt, and then vacuum dried (120℃×6h) to obtain a lithium-based intermediate.

[0057] S400: Al-B composite gradient coating

[0058] 1. Preparation of coating precursor solution

[0059] Aluminum source: Aluminum nitrate (Al(NO3)3·9H2O) chelated with citric acid in a 1:2 molar ratio;

[0060] Boron source: Boric acid (H3BO3) and mannitol form a complex in a 1:1 molar ratio;

[0061] Solvent: Ethanol / water (4:1 volume ratio) mixture.

[0062] The aluminum and boron sources were dissolved in a solvent, with a total metal concentration of 0.1 M.

[0063] 2. Spray coating process

[0064] Equipment: Fluidized bed spray dryer (inlet air temperature 120℃, outlet air temperature 60℃).

[0065] Parameters: atomization pressure 0.3MPa, feed rate 5mL / min; three-stage gradient coating, each stage pre-cured at 80℃ for 30min.

[0066] 3. Heat treatment process

[0067] The spray-coated lithium-based intermediate is heated to above 150°C to form an AlBO3-Al2O3 composite layer.

[0068] Through the above preparation process, the double calcination process ensures the full utilization of doping and coating effects, allowing aluminum, boron and other elements to interact, which can improve the performance of the cathode material, especially in improving the problems of high-temperature gas generation, float charging gas generation and impedance growth in secondary batteries.

[0069] In this application, an electrode comprising a positive electrode material is assembled with lithium metal to form a coin cell. When the coin cell is charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V, the obtained voltage-capacity differential dQ / dV curve exhibits a first oxidation peak and a first reduction peak in the 4.2V to 4.5V range. The presence of the first oxidation peak and the first reduction peak in the 4.2V to 4.5V range of the coin cell's voltage-capacity differential dQ / dV curve indicates that, due to the presence of internal oxygen defects, the positive electrode material exhibits reversible charge-discharge capacity in the high voltage range of 4.2V to 4.5V, thereby enabling the positive electrode material to possess high energy density and good structural stability.

[0070] According to some embodiments of this application, the peak height of the first oxidation peak is greater than or equal to 300 mAh / g / V. In this case, the cathode material exhibits higher charging capacity in the high voltage range of 4.2V to 4.5V, thereby resulting in a higher energy density for the cathode material. According to some embodiments of this application, the peak height of the first oxidation peak ranges from 300 mAh / g / V to 2000 mAh / g / V.

[0071] According to some embodiments of this application, the absolute value of the peak height of the first reduction peak is greater than or equal to 300 mAh / g / V. In this case, the cathode material exhibits a higher discharge capacity in the high voltage range of 4.2V to 4.5V, thereby resulting in a higher energy density for the cathode material. According to some embodiments of this application, the absolute value of the peak height of the first reduction peak is between 300 mAh / g / V and 2000 mAh / g / V.

[0072] According to some embodiments of this application, the peak voltage of the first oxidation peak is Vo1, the peak voltage of the first reduction peak is Vr1, and |Vo1-Vr1|≤0.3V. In this case, the cathode material exhibits good reversibility of charge-discharge in the high voltage range of 4.2V to 4.5V and possesses good structural stability.

[0073] According to some embodiments of this application, the voltage-capacity differential dQ / dV curve exhibits a second oxidation peak and a second reduction peak in the 3.6V to 4.0V range. The peak voltage of the second oxidation peak is Vo2, and the peak voltage of the second reduction peak is Vr2, with |Vo2-Vr2| ≤ 0.2V. At this point, the cathode material in the 3.6V to 4.0V range primarily undergoes a hexagonal-to-monoclinic phase transition process, involving lithium-ion and electron transport. Due to the presence of oxygen vacancies, the overall lithium-ion and electron conductivity of the material is improved, significantly enhancing the material's kinetics. Consequently, the polarization of this process decreases, resulting in a smaller difference in the peak voltages of the second oxidation and second reduction peaks.

[0074] According to some embodiments of this application, when a button cell is charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V, the discharge curve in the obtained voltage-capacity curve has a plateau in the 4.2V to 4.5V range. The capacity of the discharge curve in the 4.2V to 4.5V range is Q1, and the capacity of the discharge curve in the 3.0V to 4.5V range is Q. t The condition is satisfied that: 0.14 ≤ Q1 / Q t ≤0.35. At this point, the cathode material exhibits higher capacity in the high voltage range of 4.2V to 4.5V, resulting in a higher energy density.

[0075] In a second aspect, 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 positive electrode material described in the first aspect.

[0076] In this application, there are no particular limitations on the positive electrode, as long as the purpose of this application can be achieved. 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 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 surface area of ​​the positive electrode current collector, or only a part of the surface area; this application has no particular limitations, as long as the purpose of this application can be achieved. This application also has no particular limitations on the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the positive electrode current collector can include aluminum foil, aluminum alloy foil, or composite current collectors (e.g., aluminum-carbon composite current collectors). In this application, the positive electrode active material can also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, and sulfur.

[0077] In this application, the positive electrode active material layer may further include a positive electrode binder and a conductive agent. This application does not impose any particular limitation on the type of positive electrode binder in the positive electrode active material layer, as long as it achieves 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, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0078] This application does not impose any particular limitation on the type of conductive agent in the positive electrode active material layer, as long as it can achieve the purpose of this application. In some embodiments, the conductive agent includes carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, or carbon fiber; metal-based materials, such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof. This application does not impose any particular limitation on the mass ratio of positive electrode active material, conductive agent, and positive electrode binder in the positive electrode active material layer. Those skilled in the art can choose according to actual needs, as long as it can achieve the purpose of this application. For example, the loading of positive electrode active material in the positive electrode sheet is 4.0 mg / cm³. 2 Up to 10.0 mg / cm 2 .

[0079] This application does not impose any particular limitation on the negative electrode sheet, as long as the purpose of this application can be achieved. For example, the negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector. In this application, the negative electrode material layer can be disposed on one surface or two surfaces in the thickness direction of the negative current collector. It should be noted that the "surface" here can be the entire area of ​​the negative current collector or a part of the negative current collector; this application does not impose any particular limitation, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the negative current collector, as long as the purpose of this application can be achieved. For example, it can include, but is not limited to, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collectors (e.g., carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.). In this application, there are no particular limitations on the thickness of the negative current collector, the negative electrode material layer, and the negative electrode sheet, as long as the purpose of this application can be achieved.

[0080] The negative electrode material layer of this application includes a negative electrode active material, which may include, but is not limited to, graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, and SiO2. x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate lithiation TiO2-Li4Ti5O 12 At least one of Li-Al alloy and metallic lithium.

[0081] The negative electrode material layer in this application may further include a negative electrode binder and a negative electrode conductive agent, or the negative electrode material layer may further include a negative electrode binder, a negative electrode conductive agent, and a thickener. This application does not particularly limit the types of negative electrode binders and negative electrode 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 of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylic acid (PAA), styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0082] The negative electrode conductive agent may include, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative. This application does not impose any particular limitation on the mass ratio of negative electrode material, conductive agent, and negative electrode binder in the negative electrode active material layer, as long as the purpose of this application can be achieved. For example, the loading of negative electrode active material in the negative electrode sheet is 1.0 mg / cm³. 2 Up to 1.5 mg / cm 2 .

[0083] This application does not impose any particular limitation on the type of thickener, as long as it can achieve the purpose of this application. For example, the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or carboxymethyl cellulose. This application does not impose any particular limitation on the mass ratio of negative electrode active material, negative electrode conductive agent, negative electrode binder, and thickener in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved.

[0084] According to some embodiments of this application, the electrolyte includes lithium salts and non-aqueous solvents. The 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.

[0085] This application does not impose any particular limitation on non-aqueous solvents, as long as they can achieve the purpose of this application. 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 fluorinated carbonate 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 aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxapentane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0086] The secondary battery of this application also includes a separator. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, and aramid. The type of separator may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, and spun membrane. For example, the separator 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. 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 a mixture of polymer and inorganic materials. 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 separator, as long as it can achieve the purpose of this application. For example, the thickness of the separator can be from 5 μm to 500 μm.

[0087] The secondary battery of this application also includes a packaging bag for containing the positive electrode, negative electrode, separator, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0088] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the secondary battery may include, but is not limited to, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.

[0089] 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 a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode, separator and negative electrode in sequence, and then fixing the four corners of the entire stacked structure to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery.

[0090] Thirdly, this application provides an electronic device including the secondary battery described in the second aspect above.

[0091] The electronic device described 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 input 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.

[0092] 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.

[0093] Test methods

[0094] Element content test

[0095] In this application, the elemental content of lithium transition metal oxides can be determined using an X-ray photoelectron spectrometer, referring to the "General Rules for X-ray Photoelectron Spectroscopy Analysis Methods GB / T19500-2004". The surface depth of the lithium transition metal oxides measured during XPS testing is between 0 and 100 nm.

[0096] High-temperature gas production test

[0097] The lithium-ion battery was placed in an environment of 25°C and left to stand for 30 minutes. Then, it was discharged at a constant current of 0.2C until the voltage reached 3.0V, and left to stand for 10 minutes. Subsequently, it was charged at a constant current of 0.5C until the full charge voltage reached 4.45V, and then charged at a constant voltage until the current reached 0.05C. After standing for 10 minutes, the thickness of the lithium-ion battery was measured and recorded using a micrometer, denoted as d0. After storing the lithium-ion battery at a high temperature (60°C) for 30 days, the thickness of the lithium-ion battery was measured and recorded using a micrometer, denoted as d1. The thickness expansion rate (%) during high-temperature storage is calculated as (d1 - d0) / d0 × 100%.

[0098] Float gas generation test

[0099] The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1C until the voltage reached 4.45V, followed by constant voltage charging until the current reached 0.05C. It was then discharged at a constant current of 1C until the voltage reached 2.8V. Afterward, it was charged at a constant current of 0.5C until the voltage reached 4.45V, followed by constant voltage charging until the current reached 0.05C. The thickness of the battery was measured and recorded using a micrometer, denoted as h0. The lithium-ion battery was then transferred to a 45°C constant temperature chamber and charged at a constant voltage of 4.45V for 30 days. After 30 days, the battery was transferred to a 25°C constant temperature chamber and left to stand for 60 minutes. It was then discharged at a constant current of 1C until the voltage reached 2.8V. It was then charged at a constant current of 0.5C until the voltage reached 4.45V, followed by constant voltage charging until the current reached 0.05C. The thickness of the lithium-ion battery was measured and recorded using a micrometer, denoted as h1. Float thickness expansion rate (%) = (h1-h0) / h0 × 100%.

[0100] Cyclic impedance test

[0101] Place the lithium-ion battery in a 25°C constant temperature chamber and let it stand for 30 minutes to allow it to reach a constant temperature. Charge it at a constant current of 1C until the voltage reaches 4.45V, then charge it at a constant voltage until the current reaches 0.05C, and then discharge it at a constant current of 1C for 1 second. Calculate the DC impedance corresponding to 100% SOC of the lithium-ion battery, and record it as the initial internal resistance R1 of the lithium-ion battery. Then perform the following charge-discharge steps: charge it at a constant current of 0.5C until the voltage reaches 4.45V, then charge it at a constant voltage until the current reaches 0.05C, and then discharge it at a constant current of 1C until the voltage reaches 2.8V. After 500 cycles of this charge-discharge steps, charge the cycled lithium-ion battery at a constant current of 1C until the voltage reaches 4.45V, then charge it at a constant voltage until the current reaches 0.05C, and then discharge it at a constant current of 1C for 1 second. Calculate the DC impedance corresponding to 100% SOC of the lithium-ion battery, and record it as the cycled internal resistance R2 of the lithium-ion battery. Cyclic impedance growth rate (%) = (R2-R1) / R1×100%.

[0102] Example 1-1

[0103] Preparation of lithium transition metal oxides:

[0104] S100: Preparation of sodium-based precursor

[0105] 1. Raw material ratio

[0106] Transition metal hydroxide (Ni) 0.5 Mn 0.5 (OH)2) Sodium source (NaNO3 and NaOH (molar ratio 0.01:0.99)) were mixed at a molar ratio of Na:TM (transition metals, including Ni and Mn) = 1.15:1. The mixing process was: ball milling for 4 hours (300 rpm, zirconia ball media, ball-to-material ratio 5:1), and then drying and passing through a 200-mesh sieve.

[0107] 2. Pre-sintering pore formation

[0108] Porous NaNi was formed by heating to 500℃ at 8℃ / min in air and holding for 3 hours. 0.5 Mn 0.5 O2 precursor.

[0109] 3. High-temperature crystallization

[0110] Porous NaNi under airflow 0.5 Mn 0.5 The O2 precursor was heated to 800–1000℃ at a rate of 5℃ / min and held for 10–20 h to obtain layered NaNi. 0.5 Mn 0.5 O2 matrix, i.e. sodium-based precursor.

[0111] S200: Lithium-sodium ion exchange (solid-phase ion exchange)

[0112] The sodium-based precursor was ground and mixed with an excess lithium salt (LiNO3:LiCl = 3:1) at a Li / Na molar ratio of 5:1, and the ion exchange reaction was carried out at temperatures above 200°C.

[0113] S300: Post-processing

[0114] The material after lithium-sodium ion replacement was washed with deionized water until pH=7.0±0.5 to remove residual sodium salt, and then vacuum dried (120℃×6h) to obtain a lithium-based intermediate.

[0115] S400: Al-B composite gradient coating

[0116] 1. Preparation of coating precursor solution

[0117] Aluminum source: 0.05 mol aluminum nitrate (Al(NO3)3·9H2O) and 0.1 mol citric acid;

[0118] Boron source: 0.05 mol boric acid (H3BO3) and 0.05 mol mannitol;

[0119] Solvent: Ethanol / water (4:1 volume ratio) mixture.

[0120] The aluminum and boron sources were dissolved in a solvent, with a total metal concentration of 0.1 M.

[0121] 2. Spray coating process

[0122] Equipment: Fluidized bed spray dryer (inlet air temperature 120℃, outlet air temperature 60℃).

[0123] Parameters: atomization pressure 0.3MPa, feed rate 5mL / min; three-stage gradient coating (Al:B = 5:1 → 3:1 → 1:1), pre-curing at 80℃ for 30min after each coating stage.

[0124] 3. Heat treatment process

[0125] In an air atmosphere, the spray-coated lithium-based intermediate was heated to above 150°C at a rate of 2°C / min and heat-treated for at least 2 hours. X-ray photoelectron spectroscopy (XPS) was performed on the lithium transition metal oxide from Example 1-1. The lithium transition metal oxide contained aluminum and boron elements within a region at a depth of x nm from the surface, where 0 ≤ x ≤ 100, and the atomic ratio of aluminum to boron was y. Linear fitting was performed on x and y, resulting in the curve y = 0.02x + 0.73, as shown in Figure 1. The linear fitting curve and the (x, y) data set are located within the region bounded by y1 = 0.02x + 0.60 and y2 = 0.024x + 0.80, meaning 0.02x + 0.60 ≤ y ≤ 0.024x + 0.80. Therefore, x and y conform to the relationship: y = ax + b, where 0.02 ≤ a ≤ 0.024 and 0.60 ≤ b ≤ 0.80.

[0126] Preparation of the positive electrode:

[0127] A positive electrode slurry was prepared by dissolving the aforementioned lithium transition metal oxide (97 wt%), conductive carbon black (1.5 wt%), and polyvinylidene fluoride (1.5 wt%) in N-methylpyrrolidone. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil used as a positive electrode current collector. The aluminum foil was dried at 120°C to obtain a positive electrode sheet with an 80 μm thick positive electrode material layer coated on one side. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode material layer. The coated aluminum foil was dried, pressurized, and then cut to the specified size to fabricate the positive electrode.

[0128] Preparation of the isolation membrane: A 12μm thick polyethylene (PE) microporous membrane was selected as the isolation membrane.

[0129] Preparation of the negative electrode:

[0130] A mixture of artificial graphite (96 wt%), styrene-butadiene rubber (2 wt%), polyacrylic acid (0.5%), carbon nanotubes (0.5%), and carboxymethyl cellulose (1%) was prepared by mixing deionized water as a solvent and stirring until homogeneous, resulting in a negative electrode slurry with a solid content of 45 wt%. This negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil current collector, and then dried to obtain a negative electrode sheet with a single-sided coating of the negative electrode mixture. 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 the negative electrode mixture. The coated copper foil was dried, pressurized, and then cut to the specified size to fabricate the negative electrode.

[0131] Electrolyte preparation:

[0132] In an argon-atmospheric glove box with a water content of less than 10 ppm, dimethyl carbonate and ethylene carbonate (dimethyl carbonate and ethylene carbonate in a mass ratio of 1:2) were mixed to obtain a base solvent. Then, lithium hexafluorophosphate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, and adiponitrile were added to the base solvent and mixed thoroughly to obtain the electrolyte. Based on the total mass of the electrolyte, the mass content of LiPF6 was 12.5%, the mass content of fluoroethylene carbonate was 3%, the mass content of 1,3-propanesulfonate lactone was 2%, the mass content of adiponitrile was 0.5%, and the remainder was the base solvent.

[0133] Battery making:

[0134] 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. After welding the tabs, the electrode assembly is placed in an outer aluminum-plastic film. After removing the moisture at 80°C, the electrolyte is injected. The lithium-ion battery is obtained through vacuum sealing, settling, formation, shaping, and capacity testing.

[0135] Examples 1-2 to 1-9 and Comparative Examples 1 to 3 differ from Example 1-1 in that the preparation method of lithium transition metal oxide is adjusted according to Table a below.

[0136] Table a

[0137] Table 1

[0138] As shown in Table 1, the relative atomic ratios of aluminum and boron in this application, when adjusted with the depth of lithium transition metal oxide, conform to the following relationship: y = ax + b, 0.01 ≤ a ≤ 0.1, 0.1 ≤ b ≤ 2.0. This balance of aluminum and boron can improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries. In particular, when 0.01 ≤ a ≤ 0.04 and 0.7 ≤ b ≤ 1.0 are satisfied, it is beneficial to further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries. Preferably, when 0.02 ≤ a ≤ 0.024 and 0.60 ≤ b ≤ 0.80 are satisfied, it can further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries.

[0139] In particular, when the mass content of aluminum in lithium transition metal oxide is adjusted to satisfy 0.1≤m1≤5.0, preferably 0.1≤m1≤0.5, the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries can be further improved. In particular, when the mass content of boron is adjusted to satisfy 0.1≤m2≤1.0, preferably 0.1≤m2≤0.3, the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries are improved more significantly.

[0140] The positive electrodes of Examples 1-1 and Comparative Example 1 were cut into circular electrode sheets with a diameter of 10 mm. Using lithium metal sheets and the circular electrode sheets as counter electrodes, they were assembled into coin cells in a glove box. The specific capacity curves obtained when the coin cells were charged and discharged at a current of 0.04 C within a voltage range of 2.8 V to 4.5 V are shown in Figure 2. It can be seen that the discharge curve of the coin cell of Example 1-1 has a plateau in the 4.2 V to 4.5 V range. The voltage-capacity differential dQ / dV curves obtained are shown in Figure 3. It can be seen that there are a first oxidation peak and a first reduction peak in the 4.2 V to 4.5 V range. The peak height of the first oxidation peak is 2000 mAh / g / V, the absolute value of the peak height of the first reduction peak is 2000 mAh / g / V, the peak voltage of the first oxidation peak is Vo1, and the peak voltage of the first reduction peak is Vr1, and |Vo1-Vr1|≤0.1V. This indicates that the cathode material of this application has reversible charge-discharge capacity in the high voltage range of 4.2V to 4.5V, and has high energy density and good structural stability.

[0141] Examples 2-1 to 2-14

[0142] Except for adjusting the parameters according to Table 2, the rest is the same as in Examples 1-7. The types and amounts of raw materials are adjusted according to Table b to achieve the types or mass contents of each dopant element as shown in Table 2.

[0143] Table b

[0144] Table 2

[0145] As shown in Table 2, by adjusting the molar amounts of specific elements in element T, this application can further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries. In particular, adjusting the molar amount of sodium in lithium transition metal oxide in combination with element T can further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries.

[0146] Specifically, adjusting the molar amount of element R in lithium transition metal oxides to meet the condition 0 < n5 / n0 ≤ 0.2, in combination with element T, can further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries. In particular, when 0.01 ≤ n5 / n0 ≤ 0.2 is satisfied, it can further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries.

[0147] Specifically, this application regulates the molar amounts of fluorine and titanium in lithium transition metal oxides to conform to the condition 0.01 ≤ 100 × n. 61 The relationship / n0≤0.5 can further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries. In particular, when 0.19≤100×n is satisfied... 61 With / n0≤0.35, the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries can be further improved.

[0148] Specifically, this application regulates the molar amounts of nitrogen and T in lithium transition metal oxides to conform to 0.01 ≤ 100 × n 62 The relationship / n0≤1 can further improve the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries. In particular, when 0.32≤100×n is satisfied... 62 With / n0≤0.77, the problems of high-temperature gas generation, float charging gas generation, and impedance growth in secondary batteries can be further improved.

[0149] 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 cathode material comprises lithium transition metal oxide; the lithium transition metal oxide contains aluminum and boron elements in a region at a depth of x nm from the surface, where 0 ≤ x ≤ 100, and the atomic ratio of aluminum to boron is y, where y = ax + b, 0.01 ≤ a ≤ 0.1, and 0.1 ≤ b ≤ 2.

0.

2. The cathode material according to claim 1, characterized in that, 0.01≤a≤0.04, 0.7≤b≤1.

0.

3. The cathode material according to claim 1 or 2, characterized in that, Based on the mass of the lithium transition metal oxide, the mass content of aluminum is m1%, 0.1≤m1≤5.0; preferably, 0.1≤m1≤0.

5.

4. The cathode material according to claim 1 or 2, characterized in that, Based on the mass of the lithium transition metal oxide, the mass content of the boron element is m2%, 0.1≤m2≤1.0; preferably, 0.1≤m2≤0.

3.

5. The cathode material according to claim 1 or 2, characterized in that, The lithium transition metal oxide contains element T, which includes at least one of nickel, cobalt, or manganese; the molar amount of element T is n0; and the cathode material satisfies at least one of the following conditions: (a) The molar amount of nickel is n1, and 0.5 ≤ n1 / n0 ≤ 1; (b) The molar amount of cobalt is n2, 0≤n2 / n0≤0.5; (c) The molar amount of manganese is n3, 0≤n3 / n0≤0.

5.

6. The cathode material according to claim 5, characterized in that, The lithium transition metal oxide contains sodium; the molar amount of sodium is n4, 0 < n4 / n0 ≤ 0.02; preferably, 0.01 ≤ n4 / n0 ≤ 0.

02.

7. The cathode material according to claim 5, characterized in that, The lithium transition metal oxide contains element R, which includes at least one of titanium, niobium, germanium, molybdenum, gallium, and tungsten. The molar amount of element R is n5, where 0 < n5 / n0 ≤ 0.2; preferably, 0.01 ≤ n5 / n0 ≤ 0.

2.

8. The positive electrode material according to claim 5, characterized in that, The lithium transition metal oxide contains fluorine; the molar amount of fluorine is n. 61 0.01≤100×n 61 / n0≤0.5; and / or, The lithium transition metal oxide contains nitrogen; the molar amount of nitrogen is n. 62 0.01≤100×n 62 / n0≤1.

9. A secondary battery, characterized in that, It includes 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 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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