Battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery. The battery comprises an electrode assembly and electrolyte, wherein the electrode assembly comprises a positive plate; the positive plate comprises a positive current collector and a positive active layer located on the surface of at least one side of the positive current collector in the thickness direction, lithium manganate particles A exist in any 120 [mu] m * 120 [mu] m plane area of the positive active layer, and lithium manganate particles with the longest diameter larger than 5 [mu] m do not exist in the circumferential direction of the lithium manganate particles A and make direct contact with the lithium manganate particles A; based on the total number of the lithium manganate particles in the plane area, the number proportion of the lithium manganate particles A is P, and P is larger than or equal to 30% and smaller than or equal to 80%; the electrolyte comprises fluoroethylene carbonate, and the mass content of the fluoroethylene carbonate is F wt% on the basis of the total mass of the electrolyte; f and P meet the following relational expression: 0.05 < = F * P < = 0.28. The battery has the advantages of long cycle life, excellent rate capability and high-current discharge capability.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a battery. Background Technology

[0002] In recent years, lithium-ion batteries have been increasingly widely used in electric vehicles, smartphones, laptops, and smart homes. The market has placed higher demands on the energy density, safety performance, and range of lithium-ion batteries, especially developing lithium-ion batteries that combine high energy density and long cycle life, which has become a major direction for current industry development. Regarding cathode materials, lithium manganese oxide has consistently been an important candidate material for power and energy storage batteries due to its abundant raw materials, low cost, and high safety. However, in practical applications, especially during high-temperature cycling, lithium manganese oxide faces a long-standing bottleneck: the dissolution of manganese ions. This problem is mainly caused by two factors: firstly, trace amounts of water and acids (such as HF) in the electrolyte corrode the material surface, causing manganese to dissolve in the form of Mn²⁺; secondly, the Jahn-Teller distortion and oxygen evolution that may occur in the material itself at high potentials also exacerbate structural instability and manganese dissolution. The dissolved manganese ions migrate to the negative electrode in the electrolyte and undergo reduction deposition on the surface of negative electrodes such as graphite. Deposited manganese strongly catalyzes the decomposition and regeneration of the solid electrolyte interphase (SEI) membrane, continuously consuming electrolyte and active lithium, leading to a sharp increase in battery internal resistance and rapid capacity decay, which severely restricts the cycle life and high-temperature performance of lithium manganese oxide batteries.

[0003] Therefore, how to solve the above-mentioned problems of lithium manganese oxide materials and obtain high-performance batteries has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] Research has shown that a cathode system combining lithium manganese oxide and high-nickel ternary materials significantly improves energy density while also offering a clear cost advantage. However, high-nickel ternary materials and lithium manganese oxide suffer from a trade-off between high rate performance, high current discharge capability, and cycle life during charge and discharge.

[0005] To address the issue that battery rate performance, high-current discharge capability, and cycle life cannot be simultaneously achieved when using materials and lithium manganese oxide during charge and discharge, this invention provides a battery that, through synergistic optimization of the cathode material and electrolyte system, can significantly reduce the battery's internal resistance, improve its long cycle life, and simultaneously possess excellent rate performance and high-current discharge capability.

[0006] To solve the above-mentioned technical problems, this application is implemented as follows: According to one aspect of this application, an embodiment of this application provides a battery, the battery including an electrode assembly and an electrolyte, the electrode assembly including a positive electrode, a separator, and a negative electrode sequentially stacked; the positive electrode includes a positive current collector and a positive active layer located on at least one surface of the positive current collector along its thickness direction, the positive active layer including a first positive active material and a second positive active material, the first positive active material including LiNi x Co y M 1-x-y O2, 0.8≤x<1, 0<y<0.2, M is selected from at least one of Mn and Al; the second positive electrode active material includes lithium manganese oxide, and the positive electrode active layer contains lithium manganese oxide particles A in any 120μm×120μm planar region. There are no lithium manganese oxide particles with a longest diameter greater than 5μm in direct contact with the lithium manganese oxide particles A in the circumferential direction. Based on the total number of lithium manganese oxide particles in the planar region, the proportion of the number of lithium manganese oxide particles A is P, 30%≤P≤80%; The electrolyte includes fluoroethylene carbonate, and the mass content of the fluoroethylene carbonate is F, in wt%, based on the total mass of the electrolyte; the relationship between F and P is as follows: 0.05≤F×P≤0.28.

[0007] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects: (1) This invention introduces a ternary cathode material into the lithium manganese oxide system. The mixed system contains lithium manganese oxide particles A. The proportion of lithium manganese oxide particles A is controlled at 30% to 80%, which ensures that most of the lithium manganese oxide particles are effectively physically isolated by the high-nickel ternary material, slows down the contact between lithium manganese oxide and electrolyte, and thus significantly reduces the phenomenon of manganese ion dissolution, while effectively maintaining the structural stability of the cathode material. (2) The present invention introduces fluoroethylene carbonate into the electrolyte and controls 0.05≤F×P≤0.28, which can effectively resist the catalytic damage of the SEI film by the trace manganese ions that still inevitably dissolve and migrate to the negative electrode. Ultimately, it ensures that the positive electrode system battery using high nickel ternary material and lithium manganese oxide has a long cycle life while also having excellent rate performance and high current discharge capability.

[0008] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0009] Figure 1 The image shown is a scanning electron microscope (SEM) image of the surface of the positive electrode sheet in Embodiment 1 of the present invention.

[0010] Figure 2The image shown is a scanning electron microscope (SEM) image of the surface of the positive electrode sheet in Embodiment 1 of the present invention.

[0011] Figure 3 The image shown is an EDS energy spectrum of the positive electrode surface in Embodiment 1 of the present invention. Detailed Implementation

[0012] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0013] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0014] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0015] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0016] This application provides a battery comprising an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a separator, and a negative electrode stacked sequentially. The positive electrode includes a positive current collector and a positive active layer located on at least one surface of the positive current collector along its thickness direction. The positive active layer includes a first positive active material and a second positive active material, wherein the first positive active material includes LiNi. x Co y M 1-x-y O2, 0.8≤x<1, 0<y<0.2, M is selected from at least one of Mn and Al; the second positive electrode active material includes lithium manganese oxide, and the positive electrode active layer contains lithium manganese oxide particles A in any 120μm×120μm planar region. There are no lithium manganese oxide particles with a longest diameter greater than 5μm in direct contact with the lithium manganese oxide particles A in the circumferential direction. Based on the total number of lithium manganese oxide particles in the planar region, the proportion of the number of lithium manganese oxide particles A is P, 30%≤P≤80%; The electrolyte comprises fluoroethylene carbonate, and the mass content of the fluoroethylene carbonate is F, in wt%, based on the total mass of the electrolyte; F and P satisfy the following relationship: 0.05 ≤ F × P ≤ 0.28. It should be noted that in the F × P calculation, their respective physical units are considered; for example, if F = 25% and P = 60%, F × P = 0.25 × 0.6 = 0.15.

[0017] It should be explained that "longest diameter" refers to the length of the longest line segment among all possible straight line segments that can be drawn within the two-dimensional projection outline of any lithium manganese oxide particle when the positive electrode active layer is observed in a surface scanning electron microscope (SEM) image within any 120μm×120μm planar area.

[0018] In one example, the second positive electrode active material is lithium manganese oxide. In this invention, lithium manganese oxide particles have a broad meaning, encompassing various physicochemical variations and derivatives of LiMn₂O₄. For example, when lithium manganese oxide has a coating layer on its surface, the core-shell structure of the lithium manganese oxide particles is also included within the meaning of the term "lithium manganese oxide."

[0019] In the lithium manganese oxide system, the aforementioned ternary cathode material is introduced. The lithium manganese oxide particles exist in a relatively dispersed form, surrounded by the first cathode active material particles and not in contact with other lithium manganese oxide particles with larger particle sizes (longest diameter greater than 5 μm). These isolated lithium manganese oxide particles are referred to as lithium manganese oxide particles A, and those not in an isolated state are referred to as lithium manganese oxide particles B. Lithium manganese oxide particles A exist in any 120 μm × 120 μm planar region of the cathode active layer. Based on the total number of lithium manganese oxide particles in this planar region, the proportion of lithium manganese oxide particles A is P, where 30% ≤ P ≤ 80%, for example, it can be 30%, 40%, 50%, 60%, 70%, 80%, or within any two of the above values.

[0020] In this invention, the percentage P of the lithium manganese oxide particles A can be obtained by the following test method: randomly cut 10 pcs (5mm) from the positive electrode sheet to be tested. A 5 mm sample block was observed using a field emission scanning electron microscope (FE-SEM) and its associated energy dispersive X-ray spectrometer (EDS) in backscattered electron (BSE) mode. At least five non-overlapping observation regions of 120 μm × 120 μm were randomly selected from each sample block. BSE images were acquired for each region, and EDS area scanning was performed simultaneously to obtain the elemental distribution maps of Mn, Ni, and Co. All lithium manganese oxide particles were identified based on differences in elemental distribution: regions enriched in Mn but with negligible Ni and Co signals. The longest diameter of each particle was measured. The identified lithium manganese oxide particles were classified according to the following rules: Lithium manganese oxide particle A (island state): This particle does not contact any other lithium manganese oxide particle with a longest diameter greater than 5 μm. Lithium manganese oxide particle B (non-island state): Particles that do not meet the above category A criteria. The number N of category A particles in each observation region was counted. A The number N of type B particles B Calculate the proportion of type A particles, Pi=N, within a single region. A / (N A +N B ) 100%. The final result, P, is the arithmetic mean of Pi for all valid observation areas.

[0021] In this invention, within any 120μm × 120μm planar region of the positive electrode active layer, there are no lithium manganese oxide particles A with a longest diameter greater than 5μm in direct contact with it in the circumferential direction. Furthermore, lithium manganese oxide particles A account for 30% to 80% of the total number of lithium manganese oxide particles in the planar region. At this point, the lithium manganese oxide particles can be effectively dispersed in the first positive electrode material, and the surface of lithium manganese oxide particles A is coated with particles of the first positive electrode material. This configuration of the mixed positive electrode material reduces the contact between lithium manganese oxide and the electrolyte, minimizing the dissolution of manganese ions at high temperatures. If the proportion of lithium manganese oxide particles A is too low (e.g., <30%), most of the lithium manganese oxide particles will be in direct contact, forming continuous lithium manganese oxide agglomerates, which become rapid channels for electrolyte penetration, leading to increased manganese dissolution. This, in turn, triggers lattice defects and phase transitions in lithium manganese oxide, resulting in particle pulverization and electrode structure collapse, thus affecting the cycle life of the battery. Furthermore, after migrating to the negative electrode, manganese ions deposit on the surface of the negative electrode active material and participate in the formation of the SEI film, which also leads to structural instability. If the proportion of lithium manganese oxide particles A is too high (e.g., >80%), although the problem of manganese leaching can be effectively solved, there are a large number of small high-nickel ternary materials around the lithium manganese oxide particles. These small particles tend to form a denser, less porous filling matrix during electrode preparation. This not only limits the effective wetting of the active material surface by the electrolyte, but also hinders the rapid exchange of lithium ions between the solid and liquid interfaces. As a result, the polarization of the electrode increases and the effective capacity decreases during high-rate charge and discharge, ultimately damaging the rate performance and high-current discharge capability of the battery.

[0022] Furthermore, although controlling the proportion of lithium manganese oxide particles A to 30%~80% can minimize the dissolution of manganese ions, a small amount of manganese ions will still dissolve and migrate to the negative electrode. Therefore, this application introduces fluoroethylene carbonate into the electrolyte and limits the proportion of lithium manganese oxide particles A to P, with the mass content F of fluoroethylene carbonate satisfying the relationship: 0.05≤F×P≤0.28 (e.g., 0.05, 0.1, 0.12, 0.14, 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, 0.28, or within any two of the above values). The fluoroethylene carbonate is preferentially reduced on the surface of the negative electrode active material (graphite / silicon carbon), forming a dense, tough, and LiF-rich SEI film, which can effectively resist the catalytic decomposition of the SEI film by manganese particles on the negative electrode surface. If the F×P value is too low (e.g., <0.05), the high-nickel ternary particles will not effectively coat the lithium manganese oxide particles, or the negative electrode chemical protective film will be weak. This will lead to a large amount of dissolved manganese ions depositing on the negative electrode surface and violently catalyzing the decomposition of the fragile SEI film, resulting in rapid and irreversible consumption of active lithium, a sharp increase in battery internal resistance, and impaired cycle life. If the F×P value is too high (e.g., >0.28), a large number of lithium manganese oxide particles will be coated by high-nickel ternary particles. The dense protective layer will increase the diffusion resistance of lithium ions inside the positive electrode active particles. In addition, an excessively thick SEI film will form on the surface of the negative electrode active material, further affecting the battery's rate performance and reducing the initial coulombic efficiency.

[0023] In one specific embodiment, the mass content F of fluoroethylene carbonate in the electrolyte is 3% to 40%, for example, it can be 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or within any two of the above values.

[0024] In this application, the content of fluoroethylene carbonate in the electrolyte is obtained by gas chromatography or gas chromatography-mass spectrometry.

[0025] In one specific embodiment, the number of lithium manganese oxide particles A in any 120μm×120μm planar region of the positive electrode active layer is 15 to 60, for example, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, or within the integer range of any two of the above values.

[0026] In one specific embodiment, the electrolyte further includes lithium hexafluorophosphate. Based on the total mass of the electrolyte, the mass content of lithium hexafluorophosphate is C (wt%), and the manganese content of the positive electrode active layer in any 120μm × 120μm planar region is M (wt%). C and M satisfy the following relationship: 0.2 ≤ C / M ≤ 1.3. For example, it can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, or any two of the above values.

[0027] In one specific embodiment, the mass content of lithium hexafluorophosphate in the electrolyte is 5% to 15%, for example, it can be 5%, 8%, 10%, 12%, 14%, 15%, or within any two of the above values. In this invention, the mass content of lithium hexafluorophosphate can be obtained by the following test method: ① Under an inert atmosphere, accurately weigh an appropriate amount of electrolyte sample and quantitatively dilute it using an organic solvent (such as acetonitrile) and / or deionized water. ② Use an ion chromatograph equipped with an anion exchange column and a suppressed conductivity detector. Use a carbonate solution or potassium hydroxide solution of appropriate concentration as the eluent. ③ Prepare a series of standard solutions of known concentrations using high-purity lithium hexafluorophosphate standards and analyze them under the same conditions. Analyze the target ion (PF6). - A standard curve was plotted based on the peak area of ​​PF6 and its concentration. ④ The prepared sample solution was injected into an ion chromatograph for analysis to obtain PF6. - The chromatographic peak area was calculated based on the standard curve. The concentration of PF6 in the sample solution was then calculated. - The concentration was determined, and then the mass percentage of lithium hexafluorophosphate in the electrolyte was calculated by converting the concentration using the dilution factor and sample mass. The result was the average of at least two parallel tests.

[0028] In a preferred embodiment, M satisfies 10%≤M≤50%, for example, 10%, 20%, 30%, 40%, 50%, or within the range of any two of the above values.

[0029] In this application, the method for testing the manganese content in any 120μm × 120μm planar region of the positive electrode active layer can be as follows: Sample preparation: The positive electrode sheet to be tested is cut and fixed on the SEM test sample stage, and at least five different 120μm × 120μm square regions are randomly selected. The morphology of each region is observed using SEM in backscatter mode, and EDS elemental surface scanning is performed simultaneously to acquire the characteristic X-ray signal of manganese (Mn). The scan data of each region is processed by EDS analysis software to directly obtain the mass percentage content of Mn in that region. The arithmetic mean of the Mn content in all selected regions is calculated as the surface distribution content of manganese in the positive electrode active layer at the stated scale.

[0030] Correspondingly, in lithium-ion battery systems, the presence of trace amounts of moisture triggers the decomposition reaction of lithium hexafluorophosphate (LiPF6) in the electrolyte, following the chemical equilibrium described below: LiPF6+ H2O LiF + POF3 + 2HF The generated hydrofluoric acid (HF) will continuously etch the surface of lithium manganese oxide (LiMn2O4), destroying its crystal structure and exacerbating the reaction of manganese ions (Mn²⁺). + The dissolution of LiPF6 in the electrolyte leads to battery capacity decay and deterioration of cycle performance. The inventors of this application discovered that the higher the concentration of LiPF6 in the electrolyte, the greater the potential total amount of HF generated under the same trace moisture conditions, and the greater the risk of acid corrosion to the positive electrode active material. Simultaneously, if the manganese content in the positive electrode is too high, it means that the lithium manganese oxide phase is more likely to be directly exposed to the electrolyte, increasing the number of "target sites" for HF attack and making manganese dissolution more likely. However, when the mass content of lithium hexafluorophosphate (C) and the manganese content (M) satisfy 0.2 ≤ C / M ≤ 1.3, the battery can provide sufficient free Li+ through adequate LiPF6. + This ensures good ionic conductivity and rate performance while keeping the manganese dissolution rate at a low level, thus achieving excellent long cycle life. If the ratio is too high (e.g., >1.3), meaning the concentration of LiPF6 is too high relative to the manganese content, it will lead to a large accumulation of HF in the electrolyte, exacerbating the erosion of the lithium manganese oxide surface, and consequently causing Mn²⁺ leaching. + Rapid and large-volume dissolution, the dissolved Mn² + Lithium migrates to the negative electrode surface, disrupting the stability of the solid electrolyte interphase (SEI) film, accelerating the consumption of active lithium and increasing impedance, severely impairing cycle life. If the ratio is too low (e.g., <0.2), the LiPF6 concentration is insufficient, and migratable Li+ molecules in the electrolyte will increase. +Limited quantity leads to a decrease in overall battery ionic conductivity and a significant increase in internal resistance, thereby deteriorating the battery's rate performance. In summary, by adjusting C and M within the aforementioned ranges, a balance between rate performance and cycle life can be achieved.

[0031] In one specific embodiment, the Dv50 of the first positive electrode active material is 1 μm to 6 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, or within any two of the above values; the Dv90 is 3 μm to 10 μm, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or within any two of the above values; the Dv10 is 0.8 μm to 4 μm, for example, 0.8 μm, 1.2 μm, 1.6 μm, 2 μm, 2.4 μm, 2.8 μm, 3.2 μm, 3.6 μm, 4 μm, or within any two of the above values. This is achieved by controlling the particle size distribution of the first positive electrode active material within the aforementioned ranges.

[0032] In one specific embodiment, the lithium manganese oxide particle size Dv50 is 6μm~13μm, for example, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm or within any two of the above values; Dv90 is 15μm~25μm, for example, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm or within any two of the above values; Dv10 is 1μm~7μm, for example, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm or within any two of the above values.

[0033] In this invention, Dv50, Dv90, and Dv10 can be obtained through the following testing method: ① Take an appropriate amount of the powder sample to be tested, add it to suitable deionized water, and disperse it fully and stably by ultrasonication to form the suspension to be tested. ② Inject the prepared suspension into the sample cell of the laser particle size analyzer. Under an appropriate stirring rate, ensure that the sample passes uniformly through the laser beam. The instrument measures and calculates the volumetric particle size distribution of the particle group in the sample based on the diffraction signal of the particles to the laser. ③ The instrument's software automatically analyzes the data and generates a cumulative volume distribution curve. The particle size values ​​corresponding to the cumulative volume percentages of 10%, 50%, and 90% are directly read from this curve, which are Dv10, Dv50, and Dv90, respectively. The measurement is repeated at least three times, and the average value is taken as the final reported value.

[0034] It should be noted that when the lithium manganese oxide has a coating layer, the particle size of the lithium manganese oxide includes the thickness of the coating layer.

[0035] During long-term charge-discharge cycles, lithium manganese oxide and the first positive electrode active material undergo inconsistent volume expansion and contraction due to differences in their crystal structures and chemical properties, resulting in significant interlayer stress at the interface between the two materials. This repeated stress weakens the bonding force between active material particles, leading to a "powder shedding" phenomenon, where the active material detaches from the current collector or electrode sheet. Powder shedding not only reduces the effective reaction area but also increases the battery's internal resistance, accelerates capacity decay, and restricts the overall cycle life of the battery. Therefore, this invention controls the particle size of lithium manganese oxide and the first positive electrode active material within the aforementioned range, achieving effective coating of lithium manganese oxide particles with a high-nickel ternary positive electrode material. This helps reduce the direct contact area between lithium manganese oxide and the electrolyte, inhibits the dissolution of manganese ions, and effectively improves the battery's cycle life. Furthermore, the aforementioned control of the particle size of the two materials promotes more coordinated expansion behavior during cycling. When the volume changes of the two materials tend to match, the stress concentration phenomenon inside the electrode is alleviated, thus avoiding the powder shedding problem caused by uneven stress. This allows the electrode to maintain structural integrity and improves the battery's capacity retention rate.

[0036] In one specific embodiment, the first positive electrode active material further includes one or more of the following doping elements: Al, Zr, Mg, Y, Ti, B, Sr, W, Si, La, and Nb.

[0037] In one specific embodiment, the mass content Z of Zr element in the first positive electrode active material satisfies: 880ppm~4200ppm, for example, 880ppm, 1000ppm, 1580ppm, 2000ppm, 2390ppm, 3000ppm, 3180ppm, 4000ppm, 4200ppm or within any two of the above values.

[0038] Controlling the ratio (Z / E) of the Zr content (Z) to the ethylene carbonate content (E) in the first positive electrode active material within the aforementioned range is beneficial for the battery to achieve both high capacity and long cycle life. Specifically, controlling the Zr content within the specified range... 4+When doped into the high-nickel cathode material lattice, the strong Zr-O bonds stabilize the structure from within, effectively suppressing harmful phase transitions during charging and discharging. This stable bulk structure lays the foundation for the formation of the CEI film. Simultaneously, ethylene carbonate (EC) in the electrolyte preferentially oxidizes and decomposes on the cathode surface, forming a dense and stable CEI protective film that isolates the material from continuous electrolyte erosion, further stabilizing the structure of the high-nickel ternary material. If this ratio is too low (<80), the Zr content is too low compared to the ethylene carbonate content, resulting in a fragile intrinsic structure that can lead to structural collapse, electrolyte decomposition, and increased battery capacity decay. If the ratio is too high (>600), poor protective film quality or excessive zirconium doping may create a high-resistance interface, increasing the battery's internal resistance and deteriorating its rate performance.

[0039] In one example, the sum of the mass contents of Al, Mg and Zr elements in the first positive electrode active material is 1000ppm to 7000ppm, for example, 1000ppm, 2000ppm, 3000ppm, 4000ppm, 5000ppm, 6000ppm, 7000ppm or within any two of the above values.

[0040] The doping elements in the first cathode active material are uniformly introduced into the material system in the form of oxides. These doping elements not only effectively stabilize the highly active crystal structure of the material surface, suppress interfacial side reactions between the material and the electrolyte, and reduce harmful phase transitions and uneven growth of the surface film, but also regulate the volume change of the high-nickel ternary material (the first cathode active material) during repeated lithium-ion insertion and extraction, making its volume expansion-contraction behavior more coordinated with the strain characteristics of the lithium manganese oxide component in the system. This further reduces the accumulation of mechanical stress between electrode layers and inside particles, delays crack initiation and propagation, and thus further reduces the capacity decay rate during battery cycling, thereby extending the battery's cycle life.

[0041] In one specific embodiment, the sum of the mass contents of Al, Mg and Zr elements in the first positive electrode active material is 1000ppm to 7000ppm, for example, 1000ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm, 5000ppm, 5500ppm, 6000ppm, 6500ppm, 7000ppm or within any two of the above values.

[0042] In this application, the method for testing the content of doped elements includes: determination using inductively coupled plasma optical emission spectrometry (ICP-OES or ICP-AES), with the following steps: ① Accurately weigh a certain mass (denoted as m, accurate to 0.0001 g) of the first positive electrode active material powder sample. Completely digest the sample using aqua regia (the volume ratio of concentrated hydrochloric acid to concentrated nitric acid is approximately 3:1), and dilute the digested solution to a certain volume (denoted as V) to obtain the test solution. Simultaneously, prepare a blank solution. ② Using high-purity single-element or multi-element standard substances, prepare a series of mixed standard solutions of Al, Mg, and Zr covering the target content range (e.g., 0.1 mg / L ~ 10 mg / L). Optimize the parameters of the inductively coupled plasma optical emission spectrometer according to the instrument operating conditions. Sequentially measure the blank solution, the series of standard solutions, and the test solution, and record the spectral intensity (or emission intensity) of Al, Mg, and Zr elements at specific analytical wavelengths. ③ Based on the concentrations and spectral intensities of the standard solutions, plot standard curves for each element. After subtracting the blank value from the spectral intensity of the test solution, determine the concentrations of Al, Mg, and Zr in the test solution from the standard curves. Calculate the sum of the mass contents (in ppm) of Al, Mg, and Zr in the first positive electrode active material using the following formula: M （Al+Mg+Zr） Total content (ppm) = [1000 × (C)] Al +C Mg +C Zr [×V] / m. Perform at least two parallel tests on the same sample and take the arithmetic mean as the final result.

[0043] In one specific embodiment, the electrolyte further includes ethylene carbonate, the content of ethylene carbonate in the electrolyte is E wt%, and the mass content of Zr element in the first positive electrode active material is Z ppm. The relationship between E and Z is as follows: 80≤Z / E≤600, for example, Z / E is 80, 160, 240, 320, 400, 480, 560, 600 or within any two of the above values.

[0044] It should be noted that in the Z / E calculation, their respective physical units are not considered. For example, if Z = 3200 ppm and E = 10%, Z / E = 3200 / 10 = 320.

[0045] In one specific embodiment, the content of ethylene carbonate in the electrolyte is E such that 5% ≤ E ≤ 50%, and in another example, 20% ≤ E ≤ 40%, for example, 5%, 10%, 20%, 30%, 40%, 50%, 60%, or within any two of the above values.

[0046] In this invention, the content of ethylene carbonate in the electrolyte can be obtained by gas chromatography or gas chromatography coupled with mass spectrometry.

[0047] In one specific embodiment, the positive electrode active layer further includes a conductive agent.

[0048] In one specific embodiment, the conductive agent includes carbon nanotubes.

[0049] In one specific embodiment, the length of the carbon nanotube is 0.1μm to 10μm, for example, 0.1μm, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or within any two of the above values.

[0050] In one specific embodiment, the tube diameter is 1nm to 20nm, for example, 1nm, 4nm, 7nm, 10nm, 11nm, 14nm, 17nm, 20nm, or within any two of the above values.

[0051] By controlling the length and diameter of carbon nanotubes within the aforementioned range, a three-dimensional continuous conductive network can be formed between the positive electrode active material particles, thereby improving the overall conductivity of the electrode. In addition, its flexible fibrous structure can wrap around the surface of active material particles (especially large-sized lithium manganese oxide particles). During charging and discharging, when the particles expand in volume, the carbon nanotube network can provide buffer space through its own elastic deformation and mutual sliding, effectively absorbing and dissipating mechanical stress, thereby further improving the cycle life of the battery.

[0052] In this invention, the length and diameter of the carbon nanotubes can be obtained by the following testing method: Testing is performed using transmission electron microscopy (TEM), with the following steps: ① Take a small amount of carbon nanotube sample, place it in ethanol, disperse it ultrasonically, and then drop it onto a copper grid supported by an ultrathin carbon film. Dry it for later use. ② Observe the morphology of the sample using a transmission electron microscope. Randomly select at least 50 well-dispersed and clearly outlined carbon nanotubes from at least 3 TEM images with different fields of view. Measure the outer diameter of each carbon nanotube and record the measurement value. In the above images, for at least 30 carbon nanotubes that are sufficiently straight and fully displayed, measure their straightened length from one end to the other and record the measurement value. ③ Diameter: Calculate the arithmetic mean of all measured values ​​as the average diameter of the carbon nanotube sample; Length: Calculate the arithmetic mean of all measured values ​​as the average length of the carbon nanotube sample.

[0053] In one specific embodiment, the mass percentage of the conductive agent in the positive electrode active layer is 0.5% to 1.5%, for example, 0.5%, 0.8%, 1%, 1.1%, 1.2%, 1.5%, or within any two of the above values. Accordingly, limiting the mass percentage of the conductive agent to the above range can not only improve electron transport efficiency and reduce polarization and internal resistance, but also maximize the energy density of the electrode without significantly encroaching on the space of the active material.

[0054] In one specific embodiment, the surface of the lithium manganese oxide is further provided with a magnesium oxide coating layer. The thickness of the magnesium oxide coating layer is 2nm to 100nm, for example, 2nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, or within any two of the above values. The magnesium oxide (MgO) coating layer can enhance the adhesion strength between carbon nanotubes (CNTs) and lithium manganese oxide particles, thereby improving the overall reliability of the buffer network in the composite electrode. If the coating thickness is too high (e.g., >100nm), although it can further enhance the connection effect between lithium manganese oxide and carbon nanotubes, the excessively thick MgO layer will prolong the diffusion path of lithium ions from the electrolyte to the bulk phase of lithium manganese oxide, increase the ion migration barrier, and affect the rate performance of the battery. If the coating layer thickness is too low (e.g., <2nm), the thin coating may not be able to cover the surface of the lithium manganese oxide particles, weakening the connection effect between carbon nanotubes and lithium manganese oxide, thereby affecting the cycle stability of the battery.

[0055] In this application, the method for testing the thickness of the magnesium oxide (MgO) coating layer includes: testing using a high-resolution transmission electron microscope (HRTEM) and its equipped X-ray energy dispersive spectroscopy (EDS), with the following specific steps: ① The coated lithium manganese oxide powder sample is placed in an ethanol solvent, ultrasonically dispersed, and then dropped onto a copper grid supported by an ultrathin carbon film, and dried for later use. ② Using HRTEM, a cross-section of a single particle with clear edges and an intact coating layer is located and imaged at high resolution. ③ On the HRTEM image, the distance from the outermost edge of the particle to the starting point of the clear lattice structure of the internal lithium manganese oxide matrix is ​​measured along a direction perpendicular to the particle surface. Measurements are taken at at least three different locations on the single particle. ④ Simultaneous EDS line scan or area scan analysis can be performed to help confirm the interface between the coating layer and the matrix by observing the enrichment of Mg element signal at the particle edge and the abrupt change location of Mn element signal. ⑤ The arithmetic mean of all valid measurements is the average thickness of the magnesium oxide coating layer of the sample.

[0056] In one specific embodiment, the Mohs hardness of the first positive electrode active material is 6 to 8, for example, 6, 7, 8 or within any two of the above values.

[0057] In one specific embodiment, the lithium manganese oxide has a Mohs hardness of 4 to 6, for example, 4, 5, 6 or within any two of the above values.

[0058] By combining small particles of high-hardness ternary materials with large particles of low-hardness lithium manganese oxide, the small particles fill and adapt to the expansion gaps of the large particles during cycling, thereby uniformly dispersing interlayer stress, suppressing the shedding of electrode active materials caused by uneven expansion, and thus improving the cycle life and capacity retention of the battery.

[0059] In one specific embodiment, the separator includes a carrier layer and an adhesive layer located on one or both surfaces of the carrier layer. The adhesive layer includes first particles and second particles. The first particles are dispersed, while the second particles are agglomerated. The first particles are composed of acrylate polymers, and their average particle size is 0.5 μm to 1.2 μm, for example, 0.5 μm, 0.7 μm, 0.9 μm, 1 μm, 1.2 μm, or any two of the above values. The average particle size of the second particles is 2 μm to 20 μm, for example, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, or any two of the above values. Using the above separator structure can effectively disperse and absorb the local stress generated by the volume change of the positive electrode particles during charging and discharging, thereby helping to improve the cycle life and rate performance of the battery.

[0060] In this invention, the average particle size of the first and second particles can be obtained by the following testing method: Scanning electron microscopy (SEM) is used for testing, with the specific steps as follows: ① The sample is fixed on the SEM sample stage; the morphology of the adhesive layer is observed using a field emission scanning electron microscope (FE-SEM) in backscattered electron (BSE) mode. The first and second particles are distinguished by compositional contrast (grayscale value). ② First and second particles: At least 20 particles are randomly selected from at least 3 different fields of view, and the longest diameter of each particle is measured and the data is recorded. ③ The arithmetic mean of all measured values ​​for the first and second particles is calculated as their respective average particle size.

[0061] In one specific embodiment, the acrylate polymer includes one or more of the following: polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, acrylate monomer-acrylonitrile copolymer, styrene-acrylate monomer copolymer, acrylate monomer-acrylonitrile-ethylene copolymer, styrene-acrylate monomer-acrylonitrile copolymer, acrylate monomer-ethylene copolymer, ethylhexyl acrylate-methyl methacrylate copolymer, butyl acrylate-methyl methacrylate copolymer, methyl acrylate-N,N-dimethylacrylamide copolymer, ethyl acrylate-2-(diethylamino)ethyl acrylate copolymer, ethyl acrylate-N,N-diethylacrylamide copolymer, and ethyl acrylate-2-(diethylamino)ethyl acrylate.

[0062] In one specific embodiment, the second particle comprises one or more of the following: polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, fluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, acrylate monomer-acrylonitrile copolymer, styrene-acrylate monomer copolymer, acrylate monomer-acrylonitrile-ethylene copolymer, acrylate monomer-ethylene copolymer, styrene-acrylate monomer-acrylonitrile copolymer, ethylhexyl acrylate-methyl methacrylate copolymer, butyl acrylate-methyl methacrylate copolymer, methyl acrylate-N,N-dimethylacrylamide copolymer, ethyl acrylate-2-(diethylamino)ethyl acrylate copolymer, ethyl acrylate-N,N-diethylacrylamide copolymer, and ethyl acrylate-2-(diethylamino)ethyl acrylate.

[0063] In one specific embodiment, the puncture strength of the separator is 270 gf to 340 gf, preferably 300 gf to 320 gf, for example, 270 gf, 280 gf, 290 gf, 300 gf, 310 gf, 315 gf, 320 gf, 330 gf, 340 gf, or within any two of the above values. Controlling the puncture strength of the separator within the above range can resist the stress generated by positive electrode particles, especially the silicon-carbon material of the negative electrode, during cycle expansion, thereby helping to improve the cycle life and rate performance of the battery.

[0064] In one specific embodiment, the carrier layer includes a substrate layer and a heat-resistant coating located on one or both surfaces of the substrate layer, the heat-resistant coating including heat-resistant particles.

[0065] In one specific embodiment, the heat-resistant particles are composed of at least one of the following: alumina, boehmite, magnesium oxide, magnesium hydroxide, barium sulfate, barium titanate, zinc oxide, calcium oxide, silicon dioxide, silicon carbide, boron nitride, polyacrylonitrile, nitrile rubber, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, melamine thiocyanate, 2,4,6-tris(2-pyridyl)triazine, and 2,4,6-triphenyl-1.

[0066] In one specific embodiment, the positive electrode active layer further includes a binder, a conductive agent, and other optional additives. As examples, the binder may include at least one selected from styrene-butadiene rubber (SBR), waterborne acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB); the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers. These materials are all commercially available.

[0067] In one specific embodiment, the negative electrode includes a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector.

[0068] In one specific embodiment, the negative electrode active layer comprises a silicon-based material.

[0069] In one specific embodiment, the silicon-based material includes one or more of elemental silicon particles, silicon-oxygen particles, silicon-carbon particles, silicon-nitrogen particles, and silicon alloy particles.

[0070] In one specific embodiment, the average particle size of the silicon-carbon particles is 6 μm to 10 μm.

[0071] In one specific embodiment, the weight percentage of silicon in the negative electrode active layer is 4% to 50%.

[0072] In one specific embodiment, the negative electrode active layer further includes a carbon-based material, a negative electrode conductive agent, and a negative electrode binder. The negative electrode conductive agent and the negative electrode binder can be conventional materials in the art.

[0073] In one specific embodiment, the carbon-based material includes one or more of artificial graphite and natural graphite.

[0074] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0075] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0076] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention.

[0077] Example 1 (1) Preparation of positive electrode sheet Preparation of the first positive electrode active material: Ni cobalt manganese hydroxide precursor Ni 0.83 Co 0.12 Mn 0.05 OH2 and lithium hydroxide were mixed at a lithium molar ratio of (1.05) to 1.08. The mixture was then sintered at 780°C for 15 hours in an oxygen atmosphere to generate a well-crystallized high-nickel ternary basic material. The sintered product was crushed and pulverized, and the particle size was controlled by airflow classification. Aluminum nitrate and zirconium oxychloride were dissolved in a solvent to prepare a mixed salt solution of the target concentration. The graded basic material and the coating salt solution were uniformly mixed in a mixer. After drying, the mixture was subjected to a second heat treatment at 550°C in an oxygen atmosphere for 8 hours. The resulting material was a high-nickel ternary material co-coated with Al and Zr oxides, with an Al content of 600 ppm, a Zr content of 3200 ppm, and a Mohs hardness of 7. The first positive electrode active material particles were obtained, with a median particle size of 3.5 μm for Dv50, 6 μm for Dv90, and 2.4 μm for Dv10. The morphology of the first positive electrode active material was confirmed to be a single crystal by scanning electron microscopy (SEM).

[0078] Preparation of lithium manganese oxide material: Electrolytic manganese dioxide (EMD) and lithium salt (such as lithium carbonate) were mixed in a stoichiometric ratio and sintered at 850℃ for 15 hours in air to generate a spinel-structured lithium manganese oxide base material. The sintering process and particle size classification were controlled. The base material was dispersed in a magnesium nitrate solution, and the pH value was controlled to ensure uniform precipitation of magnesium ions on the particle surface. After drying, a second heat treatment was performed at 600℃ for 6 hours to form a stable magnesium oxide coating layer with a thickness of 50 nm. The resulting magnesium oxide-coated lithium manganese oxide material had a median Dv50 particle size of 9.5 μm, a Dv90 of 20 μm, a Dv10 of 4 μm, and a Mohs hardness of 5. Scanning electron microscopy (SEM) confirmed that the lithium manganese oxide material was polycrystalline.

[0079] The first positive electrode active material and lithium manganese oxide were used as the positive electrode active material, with lithium manganese oxide accounting for 60% of the total mass of the positive electrode active material. The positive electrode active material, carbon nanotubes (5.6 μm in length and 15 nm in diameter), and polyvinylidene fluoride were mixed in N-methylpyrrolidone at a mass ratio of 96:2:2 to prepare a slurry, which was then coated onto a 10 μm thick aluminum foil. After drying, rolling, and slitting, the positive electrode sheet was obtained. The coated electrode sheet was transferred to a vacuum drying oven and baked at 120°C for 12 hours. The electrode sheet was then rolled and sliced ​​to obtain the positive electrode sheet. Testing showed that the proportion of lithium manganese oxide particles A (P) in any 120 μm × 120 μm planar region was 60%; and the mass content M of manganese in the positive electrode active layer was 20% in any 120 μm × 120 μm planar region.

[0080] SEM scanning of the active layer of the positive electrode, such as... Figure 1 and Figure 2 As shown.

[0081] Energy-dispersive X-ray spectroscopy was performed on the active layer of the positive electrode, such as... Figure 3 As shown.

[0082] (2) Preparation of negative electrode sheet Carbon-based material (artificial graphite), silicon-based material (silicon-carbon material), negative electrode conductive agent (conductive carbon black: carbon nanotubes = 1:1), negative electrode binder (styrene-butadiene rubber: polyacrylic acid = 1:1), and sodium carboxymethyl cellulose (CMC) were mixed in an aqueous solvent at a weight ratio of 77.3:19.3:0.4:2.8:0.2. After being stirred evenly using a vacuum mixer, the slurry was uniformly coated onto the surface of a 6 μm thick high-strength carbon-coated copper foil. The single-sided areal density of the coated negative electrode active coating was 8.1 mg / cm³. 2 The coated electrode sheets were transferred to a vacuum drying oven and baked at 85°C for 12 hours. The sheets were then rolled using a two-roll press (compacted density 1.7 g / cm³). 3The negative electrode sheet is obtained by slicing the negative electrode.

[0083] (3) Preparation of diaphragm Heat-resistant granules (alumina) were dispersed in deionized water, and polyacrylic acid was added. After stirring evenly, a mixed slurry with a solid content of 25% was obtained. The mixed slurry was continuously coated onto one side of the substrate layer (polyethylene) using a gravure roller, and then dried and shaped in a multi-section oven at 60°C to obtain the heat-resistant layer. Polymethyl acrylate (first granules) and polyvinylidene fluoride (second granules) were mixed and dispersed in water at a weight ratio of 60:40. After stirring evenly, a mixed slurry with a solid content of 10% was obtained. The mixed slurry was continuously coated onto the side of the heat-resistant layer away from the first substrate layer using a gravure roller. The mixed slurry of the first and second granules was continuously coated onto the other surface of the substrate layer using a gravure roller, and dried and shaped in a multi-section oven at 60°C to obtain the desired diaphragm. The average particle size of the first granules was 0.8 μm, and the average particle size of the secondary particles of the second granules was 11 μm.

[0084] (4) Preparation of electrolyte In an argon-filled glove box (H2O < 0.05 ppm, O2 < 0.05 ppm), ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC) were mixed uniformly at a mass ratio of 1:4.5:4.5 to obtain an electrolyte solvent. Then, 15 wt% LiPF6 and 1 wt% LiTFSI based on the total mass of the electrolyte were added to the electrolyte solvent and dissolved. After dissolving, 25 wt% fluoroethylene carbonate based on the total mass of the electrolyte was added and stirred evenly. After passing the moisture and free acid tests, the electrolyte was obtained.

[0085] (5) Battery manufacturing The positive electrode sheet prepared in step (1), the separator prepared in step (3), and the negative electrode sheet prepared in step (2) are wound together to form a bare cell. Then the bare cell is placed in an aluminum-plastic film, and the electrolyte prepared in step (4) is injected into the dried bare cell. After vacuum sealing, room temperature standing, high temperature formation and other processes, a lithium-ion battery is obtained.

[0086] Example 2 group This comparative example is based on Example 1, except that the content of fluoroethylene carbonate (F, in wt%) and the percentage (P) of lithium manganese oxide particles (A) are changed. The change in the percentage (P) of lithium manganese oxide particles (A) can be achieved by adjusting the solid content and viscosity of the positive electrode slurry. See Table 1 for details.

[0087] Comparative Example 1 Comparative Example 1-1 The comparative example is based on Example 1, except that the product of F×P in this comparative example is less than 0.05, as detailed in Table 1.

[0088] Comparative Examples 1-2 The comparative example is the same as in Example 1, except that the product of F×P in the comparative example is higher than 0.28, as shown in Table 1.

[0089] Table 1 Example 3 Group This embodiment is based on Example 1, except that the content C of lithium hexafluorophosphate in the electrolyte and the content M of manganese in any 120μm×120μm planar region of the positive electrode active layer are changed, as detailed in Table 2.

[0090] Table 2 Example 4 group This embodiment is based on Example 1, except that the mass content Z (ppm) of Zr element in the first positive electrode active material is changed, and the content of ethylene carbonate in the electrolyte is E, in wt%. See Table 3 for details.

[0091] Table 3 Example 5 group This embodiment is based on Embodiment 1, and the specific differences are shown in Table 4.

[0092] Table 4 Test case The batteries prepared in the examples and comparative examples were subjected to the following performance tests: (1) Internal resistance test The initial voltage V1 of the batteries prepared in each embodiment and comparative example was measured using a DC internal resistance meter at 25°C. After being left to stand for 5 days, the standing voltage V2 was measured. The internal resistance K value was measured using the following formula: K = (V2 - V1) / (5 × 24).

[0093] (2) Cyclic performance The batteries prepared in each embodiment and comparative example were charged to full capacity of 4.3V at 2C constant current and constant voltage under 25°C conditions, cut off at 0.05C current, and discharged to 2.5V at 4C. This constituted one charge-discharge cycle. The battery capacity retention rate was confirmed after 800 cycles.

[0094] (3) Ratio performance A lithium-ion secondary battery was charged to full capacity (4.3V) at 0.5C constant current and constant voltage at 25℃, then the current was cut off at 0.05C, and then discharged to 2.5V at 0.2C. The capacity discharged was recorded as the initial discharge capacity. Subsequently, the lithium-ion secondary battery was charged to full capacity at 25℃ using the same charging method, and after resting for 2 hours, it was discharged to 2.5V at 3C and 5C respectively. The discharged capacities were recorded as C1 and C2. The capacity retention rate at different discharge rates = final discharge capacity / initial discharge capacity. 100%.

[0095] (4) Pulse discharge test The lithium-ion secondary battery was charged to full capacity (4.3V) at 0.5C constant current and constant voltage at 25℃, with a cutoff current of 0.05C. After resting for 30 minutes, it was discharged at 50C current for 5 seconds (voltage was collected every 0.1 seconds). The voltage V at the end of the discharge was recorded (the higher the test value, the better the high current discharge capability).

[0096] The test results of each embodiment and comparative example are shown in Table 5.

[0097] Table 5 As shown in Table 5, the battery of the present invention introduces a ternary cathode material into a lithium manganese oxide system. The mixed system contains lithium manganese oxide particles A, and fluoroethylene carbonate is introduced into the electrolyte. The product (F×P) of the proportion of lithium manganese oxide particles A (P) and the content of fluoroethylene carbonate in the electrolyte (F) is controlled within the specified range. Ultimately, the battery exhibits a long cycle life while also possessing excellent rate performance and high-current discharge capability.

[0098] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0099] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery, characterized by, The battery comprises an electrode assembly and an electrolyte, the electrode assembly comprises a positive electrode sheet, a separator and a negative electrode sheet which are sequentially stacked; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer located on at least one side surface of the positive electrode current collector in the thickness direction, the positive electrode active layer comprises a first positive electrode active material and a second positive electrode active material, the first positive electrode active material comprises LiNi x Co y M 1-x-y O2, 0.8≤x<1, 0 The second positive electrode active material comprises lithium manganate, the positive electrode active layer has lithium manganate particles A in any 120 μm×120 μm planar area, the circumferential direction of the lithium manganate particles A is free of direct contact with lithium manganate particles with a longest diameter greater than 5 μm, the number proportion of the lithium manganate particles A accounts for P based on the total number of lithium manganate particles in the planar area, 30%≤P≤80%. The electrolyte comprises fluoroethylene carbonate, the mass content of the fluoroethylene carbonate is F, unit: wt%, based on the total mass of the electrolyte; F and P satisfy the following relationship: 0.05≤F×P≤0.

28.

2. The battery of claim 1, wherein, The number of lithium manganate particles A in the positive electrode active layer in any 120μm×120μm planar region is 15-60.

3. The battery according to any one of claims 1 to 2, characterized in that, The electrolyte further comprises lithium hexafluorophosphate, the mass content of the lithium hexafluorophosphate is C, unit: wt%, based on the total mass of the electrolyte, the content of manganese element in the positive electrode active layer in any 120μm×120μm planar region is M, unit: wt%, C and M satisfy the following relationship: 0.2≤C / M≤1.

3. Preferably, M satisfies 10%≤M≤50%.

4. The battery according to any one of claims 1 to 2, characterized in that, The Dv50 of the first positive electrode active material is 1μm-6μm, the Dv90 is 3μm-10μm, and the Dv10 is 0.8μm-4μm; and / or, The Dv50 of the lithium manganate particle size is 6μm-13μm, the Dv90 is 15μm-25μm, and the Dv10 is 1μm-7μm.

5. The battery according to any one of claims 1 to 2, wherein The first positive electrode active material further comprises one or more of the doping elements Al, Zr, Mg, Y, Ti, B, Sr, W, Si, La, and Nb; preferably, the mass content of Zr element in the first positive electrode active material Z satisfies: 880ppm-4200ppm.

6. The battery of claim 5, wherein, The electrolyte further comprises ethylene carbonate, the content of ethylene carbonate in the electrolyte is E, unit: wt%, the mass content of Zr element in the first positive electrode active material is Z, unit: ppm, E and Z satisfy the following relationship: 80≤Z / E≤600; and / or, The content of ethylene carbonate in the electrolyte E satisfies: 5%≤E≤50%.

7. The battery of any one of claims 1-2, wherein, The positive electrode active layer further comprises a conductive agent; the conductive agent comprises carbon nanotubes, the length of the carbon nanotubes is 0.1μm-10μm, and the diameter is 1nm-20nm.

8. The battery of any one of claims 1-2, wherein, The surface of the lithium manganate is further provided with a magnesium oxide coating layer, the thickness of the magnesium oxide coating layer is 2nm-100nm.

9. The battery of any one of claim 8, wherein, The Mohs hardness of the first positive electrode active material is 6-8; and / or, The Mohs hardness of the lithium manganate is 4-6.

10. The battery of claim 1, wherein, The separator comprises a carrier layer and a glue layer on one side or both sides of the carrier layer, the glue layer comprises first particles and second particles, the first particles are dispersedly distributed, the second particles are agglomerated particles, the composition of the first particles comprises an acrylate polymer, the average particle size of the first particles is 0.5μm-1.2μm, and the average particle size of secondary particles of the second particles is 2μm-20μm; and / or, The acrylate-based polymer includes one or more of polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, acrylate-based monomer-acrylonitrile copolymer, copolymer of styrene-acrylate-based monomer, acrylate-based monomer-acrylonitrile-ethylene copolymer, copolymer of styrene-acrylate-based monomer-acrylonitrile, copolymer of acrylate-based monomer-ethylene, copolymer of ethylhexyl acrylate-methyl methacrylate, copolymer of butyl acrylate-methyl methacrylate, copolymer of methyl acrylate-N,N-dimethyl acrylamide acrylate, copolymer of ethyl acrylate-2-(diethylamino)ethyl acrylate-acrylic acid, copolymer of ethyl acrylate-N,N-diethyl acrylamide acrylate, and / or ethyl acrylate-2-(diethylamino)ethyl acrylate-acrylic acid; and / or The component of the second particle includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyfluoroethylene, polyhexafluoropropylene, fluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, acrylate-based monomer-acrylonitrile copolymer, copolymer of styrene-acrylate-based monomer, acrylate-based monomer-acrylonitrile-ethylene copolymer, copolymer of acrylate-based monomer-ethylene, copolymer of styrene-acrylate-based monomer-acrylonitrile, copolymer of ethylhexyl acrylate-methyl methacrylate, copolymer of butyl acrylate-methyl methacrylate, copolymer of methyl acrylate-N,N-dimethyl acrylamide acrylate, copolymer of ethyl acrylate-2-(diethylamino)ethyl acrylate-acrylic acid, copolymer of ethyl acrylate-N,N-diethyl acrylamide acrylate, and / or ethyl acrylate-2-(diethylamino)ethyl acrylate-acrylic acid; and / or The puncture strength of the diaphragm is 270 gf to 340 gf, preferably 300 gf to 320 gf.

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