Secondary battery

Abstract

The invention discloses a secondary battery, which belongs to the technical field of batteries, and is characterized in that the lithium-nickel mixing rate and the unit cell volume of a ternary material in a positive pole piece after charge-discharge cycle are cooperatively regulated, and the particle size ratio coefficient of the positive pole material is synchronously regulated; according to the present invention, the overall pole piece stability and the lithium ion de-intercalation reversibility of the positive pole piece can be effectively considered, the cycle stability of the secondary battery is improved, the efficiency of the lithium ion transmission process of the ternary material in the pole piece is improved, the good dynamic performance is ensured, and the DCR after the cycle is low.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a secondary battery. Background Technology

[0002] Ternary cathode materials in lithium-ion rechargeable batteries possess high energy density. However, the presence of nickel ions in these materials occupies lithium sites, affecting lithium ion extraction and subsequent reversibility of insertion, ultimately impacting cycle performance. Therefore, improving cycle stability remains a key area for improvement. Simultaneously, some methods for improving the cycle stability of ternary cathode materials can reduce the material's lithium-ion transport efficiency, deteriorate discharge capacity, decrease kinetic performance, and significantly increase the discharge coefficient (DCR) after cycling, failing to balance overall product performance. Summary of the Invention

[0003] The purpose of this application is to overcome the shortcomings of the existing technology and provide a secondary battery. By synergistically controlling the lithium-nickel mixing ratio and cell volume of the ternary material in the positive electrode after charge-discharge cycles, and simultaneously adjusting the particle size ratio coefficient of the positive electrode material, the overall electrode stability and lithium-ion intercalation / deintercalation reversibility of the positive electrode can be effectively improved, thereby enhancing the cycle stability of the secondary battery. At the same time, the efficiency of the ternary material in the electrode during the lithium-ion transport process is improved, ensuring good kinetic performance and low DCR after cycling.

[0004] To achieve the above objectives, in a first aspect of this application, this application provides a secondary battery, including a positive electrode sheet, the positive electrode sheet including a positive active material layer, the positive active material layer including a positive electrode material, and the positive electrode material including lithium nickel cobalt manganese oxide; The positive electrode plate satisfies: a×b / c=0.18~6.63; Wherein, 'a' represents the lithium-nickel mixing ratio of the cathode material after 200 charge-discharge cycles, and 'b' represents the cell volume of the cathode material after 200 charge-discharge cycles, in Å. 3 The c = C1 × C2, where C1 is the particle size value corresponding to the highest peak of the particle size frequency distribution curve of the cathode material, and C2 is the proportion of the area of ​​the curve part with a particle size value less than or equal to the particle size value corresponding to the highest peak in the total area of ​​the particle size frequency distribution curve of the cathode material. The unit of c is μm.

[0005] The beneficial effects of this application are as follows: This application provides a secondary battery that, by synergistically regulating the lithium-nickel mixing ratio and cell volume of the ternary material in the positive electrode after charge-discharge cycles, and simultaneously adjusting the particle size ratio coefficient of the positive electrode material, can effectively improve the overall electrode stability and lithium-ion insertion / extraction reversibility of the positive electrode, thereby enhancing the cycle stability of the secondary battery. At the same time, it improves the efficiency of the ternary material in the electrode during the lithium-ion transport process, ensuring good kinetic performance and low DCR after cycling. Attached Figure Description

[0006] Figure 1 This is the particle size frequency distribution curve of the cathode material described in Example 40 of this application. Detailed Implementation

[0007] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0008] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0009] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0010] The present application is further illustrated below with specific embodiments: A secondary battery includes a positive electrode sheet, the positive electrode sheet including a positive electrode active material layer, the positive electrode active material layer including a positive electrode material, and the positive electrode material including lithium nickel cobalt manganese oxide; The positive electrode plate satisfies: a×b / c=0.18~6.63; Wherein, 'a' represents the lithium-nickel mixing ratio of the cathode material after 200 charge-discharge cycles, and 'b' represents the cell volume of the cathode material after 200 charge-discharge cycles, in Å. 3The c = C1 × C2, where C1 is the particle size value corresponding to the highest peak of the particle size frequency distribution curve of the cathode material, and C2 is the proportion of the area of ​​the curve part with a particle size value less than or equal to the particle size value corresponding to the highest peak in the total area of ​​the particle size frequency distribution curve of the cathode material. The unit of c is μm.

[0011] While lithium nickel cobalt manganese oxide (LCO) offers higher energy density compared to other cathode materials, the nickel ions in the ternary material have radii close to those of lithium ions during cycling. This can lead to nickel ions occupying lithium sites after compounding, affecting lithium ion extraction and subsequent reversible insertion / extraction, ultimately impacting cycle performance. Therefore, in this application's technical solution, after introducing LCO as the active material, the lithium-nickel mixing ratio and cell volume of the cathode material are controlled after charge-discharge cycles. Lowering the lithium-nickel mixing ratio and reducing the cell volume effectively improves the material's structural stability, preventing nickel ions from occupying lithium sites and increasing cell volume, which would reduce the reversible insertion / extraction capability of lithium ions and improve cycle stability. However, both are not necessarily better the lower they are. As mentioned above, after cycling, the a-axis of lithium nickel cobalt manganese oxide decreases, the c-axis increases, and the cell volume increases. Controlling its upper limit can improve the structural stability of the material. However, if the increased cell volume is too small, it means that the interlayer spacing of the lithium nickel cobalt manganese oxide material is too small, which is not conducive to lithium ion extraction. Similarly, although a decrease in the lithium-nickel mixing ratio 'a' of lithium nickel cobalt manganese oxide after cycling can optimize the diffusion path and diffusion rate of lithium ions in the material and improve the overall structural stability of lithium ions during insertion and extraction, an excessively low lithium-nickel mixing ratio also means that the material is too ordered, which may sacrifice some lithium ion diffusion channels and adversely affect the rate performance of the product. Therefore, the lithium-nickel mixing ratio 'a' and the cell volume 'b' of lithium nickel cobalt manganese oxide should not be too small.

[0012] Simultaneously, to effectively improve the reversibility of lithium-ion insertion / extraction and achieve ideal material cycle stability, it is also necessary to simultaneously adjust the particle size distribution relationship of the material itself to match the lithium-nickel mixing ratio and cell volume after cycling. In the technical solution of this application, the particle size distribution relationship coefficient c of the material is the product of the particle size value C1 corresponding to the highest peak of the particle size distribution curve of the cathode material and the proportion of the curve area corresponding to the particle size less than or equal to that value C2. The former reflects the size corresponding to the most numerous particle size in the lithium nickel cobalt manganese oxide particles, while the latter reflects the proportion of particles smaller than that particle size value. By controlling the relationship between the two, more lithium nickel cobalt manganese oxide particles can be placed within a suitable particle size range, improving the structural stability of the particles, reducing the risk of structural collapse of the particles during charging cycles, and improving cycle performance. However, if only C1 or C2 is controlled, although the former can control the most numerous particle size within a certain range, it cannot control the distribution of different particle sizes, affecting the stability of the material; the latter cannot control the size range corresponding to most particle sizes, cannot match the cell volume and lithium-nickel mixing ratio of the material, which is also not conducive to the cycle stability of the material. Increasing the particle size distribution coefficient c, for example, by increasing C1, can effectively improve the stability of the material during lithium insertion / extraction. However, if the particle size distribution coefficient c increases too much, it will lead to reduced electrolyte wettability and fewer lithium-ion insertion / extraction sites, resulting in poorer lithium-ion transport performance, affecting kinetic performance, and hindering the reduction of DCR after battery cycling. In this case, adjusting C2 can introduce more small-sized particles to improve the overall kinetic performance of the material. Similarly, if C1 is too small, the overall stability of the material is low. In this case, adjusting C2 to reduce the proportion of small-sized particles can improve the overall stability of the material.

[0013] Therefore, in the technical solution of this application, although reducing the cell volume of the particles and the lithium-nickel mixing ratio after cycling can improve the structural stability of the particles and enhance the cycling performance, it also carries the risk of reducing the interlayer spacing of the particles, sacrificing the lithium-ion diffusion channels, and reducing the kinetic performance. However, by further matching and controlling the particle size distribution coefficient c, and through the synergistic control of C1 and C2, the lithium-ion transport path can be effectively improved while taking into account the structural stability.

[0014] In some implementations, the range of a×b / c = 0.18, 0.20, 0.25, 0.28, 0.3, 0.35, 0.38, 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 6.6, 6.63 or any two of these values.

[0015] More preferably, a×b / c = 0.38~3.4.

[0016] As mentioned above, by synchronously controlling the lithium-nickel mixing ratio, cell volume, and particle size distribution coefficient of the cathode material after cycling, the stability of the material during reversible insertion / extraction cycling can be effectively optimized, enabling the secondary battery to have ideal cycle performance. At the same time, it can also ensure that the material has high kinetic performance and the cycle DCR of the secondary battery is low. When the regulation relationship of the above three factors is further optimized within the above range, the overall performance of the secondary battery is even better.

[0017] In some implementations, a = 0.013 to 0.065.

[0018] In some implementations, a = is a range of one or both of the following: 0.013, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, and 0.065.

[0019] More preferably, a = 0.015~0.045.

[0020] The lithium-nickel mixing ratio refers to the proportion of nickel ions occupying the crystal positions that belong to lithium ions in lithium nickel cobalt manganese oxide particles. The higher the lithium-nickel mixing ratio, the more it affects the insertion and extraction of lithium ions. However, if the lithium-nickel mixing ratio is too low, it will cause some lithium ion diffusion channels to be sacrificed, thereby affecting the rate performance of the secondary battery.

[0021] By optimizing the lithium-nickel mixing ratio 'a' of the cathode material after cycling within the aforementioned range, not only can the impact of nickel ions occupying lithium sites on the reversible insertion / extraction of lithium ions be reduced, but also the excessive sacrifice of lithium ion diffusion channels can be avoided based on the reduction of the lithium ion diffusion barrier, thereby improving the lithium ion diffusion rate and achieving better cycle stability and kinetic performance.

[0022] In some implementations, b = 100~103.

[0023] In some implementations, b is a range of one or any two of the following: 100, 100.2, 100.5, 100.8, 101, 101.2, 101.5, 101.8, 102, 102.5, and 103.

[0024] More preferably, b = 101~102.

[0025] When the cell volume of the positive electrode material in the secondary battery is preferably within the above-mentioned range after cycling, the stability of the material structure can be effectively improved, and the cell interlayer spacing is larger, making it easier for lithium ions to be extracted, which is more conducive to achieving reversible and rapid conduction and improving kinetic performance.

[0026] It should be noted that the lithium-nickel mixing ratio 'a' and cell volume 'b' of the positive electrode material in the secondary battery after 200 cycles can be confirmed by, but is not limited to, the following method: The secondary battery is discharged at a rate of 0.33C to the lower limit of 2.5V, left to stand for 30 minutes, then charged at 1C to the upper limit of 4.25V, then charged at a constant voltage to the cutoff current of 0.05C, and then discharged at 1C to the lower limit of 2.5V. This constitutes one cycle, and 200 charge-discharge cycles are performed. The positive electrode sheet in the cycled secondary battery is disassembled, soaked in dimethyl carbonate solution for 4 hours, dried, and the positive electrode active material layer powder is scraped off. The obtained powder is then used as a test sample and placed in a BRUKER D8 XRD instrument. The test is performed at a scan rate of 1° / min with a step of 0.02°, and the angle range is set from 10° to 90°. After the test, the obtained characteristic peak spectrum is refined using TOPAS software to confirm the Li / Ni mixing ratio 'a' and cell volume 'b' in the sample.

[0027] In some implementations, c = 0.6~8.

[0028] More preferably, C1 = 2~15μm and C2 = 0.2~0.6.

[0029] In some implementations, c is a range of one or any two of the following: 0.6, 0.8, 1, 1.2, 1.4, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8.

[0030] In some implementations, C1 is a range of one or any two of the following: 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 12μm, 13μm, and 15μm.

[0031] In some implementations, C2 is a range of one or both of the following: 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, and 0.6.

[0032] More preferably, c = 1~4.5.

[0033] More preferably, c is a range of one or any two of the following: 1, 1.1, 1.2, 1.4, 1.5, 2, 2.5, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5.

[0034] By optimizing the particle size distribution coefficient c of the cathode material, the cell parameters of lithium nickel cobalt manganese oxide and the lithium-nickel mixing ratio of lithium nickel cobalt manganese oxide particles can be effectively matched, ensuring the reversible insertion / extraction efficiency of lithium ions. At the same time, it can also ensure the high wettability of the particle material and the high content of lithium insertion / extraction sites, ensuring the high rate of lithium ion insertion / extraction, the better diffusion path of lithium ions, and the better kinetic performance of the cathode material. The secondary battery can achieve both high cycle stability and low DCR.

[0035] It should be noted that the particle size distribution coefficient c of the positive electrode material described in this application can be confirmed by, but is not limited to, the following methods: The secondary battery is discharged to the lower limit of 2.5V at 0.33C, and then the positive electrode sheet is disassembled and soaked in dimethyl carbonate (DMC) for 2 hours and vacuum dried. Then, the positive electrode active material layer of the positive electrode material is scraped off, and the resulting powder is used as a test sample. Using a Malvern Master Size 3000 instrument, GB / T 19077-2016 is used as the test method standard. Ethanol is used as the dispersant, and the parameters are selected as the shading range of 10~20% and the particle refractive index of 1.81. Ultrasonic particle size detection is performed, and the frequency distribution model is selected for the output of the particle size data. After obtaining the frequency distribution curve of the sample, the corresponding particle size value C1 at the highest peak position of the curve is read. The proportion C2 of the area of ​​the part of the curve with a particle size smaller than the particle size value C1 is confirmed by curve area integration analysis. c is calculated by C1×C2.

[0036] In some embodiments, the lithium nickel cobalt manganese oxide has the chemical formula Li. x Ni o Co p Mn q O2, where x is greater than or equal to 0.9 and less than or equal to 1.1; o is greater than or equal to 0.5 and less than 1; p is greater than 0 and less than 1; q is greater than 0 and less than 1; o+p+q=1; More preferably, the lithium nickel cobalt manganese oxide further contains a metal element, which includes at least one of Zr, Y, Al, W, Nb, La, Mo, Ti, Mg, Ta, Ca, Cs, and Sb.

[0037] In some embodiments, the molar percentage of cobalt in the transition metal elements in the cathode material is 2-25 mol.

[0038] More preferably, the transition metal element includes nickel, cobalt, and manganese.

[0039] In some embodiments, the molar percentage of nickel in the transition metal elements in the cathode material is 50-95%.

[0040] In some embodiments, the molar percentage of manganese in the transition metal elements in the cathode material is 3 to 25 mol.

[0041] The introduction of cobalt into the cathode material can effectively improve the structural stability of the material, thereby reducing the lithium-nickel mixing rate after cycling, especially when it is preferably within the above range, which can make the secondary battery have better cycle stability.

[0042] In some embodiments, the molar percentage of nickel in the transition metal elements in the cathode material is 50-95 mol%, and c = 1-8.

[0043] When the proportion of nickel in the cathode material is high, the overall energy density of the material is higher. However, due to the increased proportion of nickel ions in the system, their ionic radius is close to that of lithium ions, and their electronic configuration (d... 8 In an octahedral field, lithium cobalt manganese oxide exhibits a significant Jahn-Teller effect, making it more unstable under certain conditions and prone to migration. Consequently, the initial lithium-nickel mixing ratio of lithium cobalt manganese oxide in the cathode material is also relatively high. At this point, further optimization of the lithium-nickel mixing ratio and cell volume of lithium cobalt manganese oxide in the secondary battery after cycling, along with simultaneous optimization of particle distribution, can effectively maintain the cycle stability of the battery under high nickel conditions and improve the overall performance of the battery.

[0044] It should be noted that the molar percentage of cobalt, nickel, and manganese in the transition metal elements of the positive electrode material can be confirmed by, but is not limited to, the following method: Discharge the secondary battery to the lower limit voltage of 2.5V at 0.33C, disassemble the positive electrode sheet, soak the positive electrode sheet in dimethyl carbonate at room temperature for 60 minutes, remove it, dry it, and scrape off the positive electrode active material layer powder from the surface of the current collector; accurately weigh 0.5±0.0005g of powder, add 5mL of hydrochloric acid, place it in a dry, clean, and impurity-free quartz crucible, add 5mL of hydrochloric acid, digest at 190℃ for 15 minutes, add 10mL of ultrapure water along the wall of the crucible, digest for another 15 minutes, and add 1mL of water dropwise. Digest with HNO3 for 2 minutes, remove and cool to room temperature, transfer the solution to a 50 mL centrifuge tube, dilute to the mark with ultrapure water, mix well, and obtain the test solution; perform ICP test on the test solution. Before the test, a standard solution must be prepared. The linear correlation coefficient of the standard concentration must be above 0.999 to be used as a normal standard. The 1000 mg / L standard solution was diluted with deionized water to different concentrations (generally 0, 1 mg / 100mL, 2 mg / 100mL, 3 mg / 100mL), and the element detection wavelength was selected. Experimental conditions were set: based on the sample characteristics and the element to be detected, appropriate ICP instrument operating conditions were set: gas flow rate 0.5 L / min, power 1150 W, and the element detection wavelength was selected, depending on the element being tested (e.g., Ni wavelength 231.60 nm; Co wavelength 228.6 nm; Mn wavelength 257.6 nm). The self-service analysis function of the ICP testing software can read the element content in the sample. The standard solution refers to a solution containing the element to be tested, which can be obtained commercially.

[0045] In some embodiments, the cathode material includes lithium nickel cobalt manganese oxide particles, which include monocrystalline particles and / or polycrystalline particles.

[0046] It should be noted that the single crystal particles mentioned in this application refer to a single particle with a complete crystal shape or an aggregate of less than 3 primary particles; the polycrystalline particles mentioned in this application refer to a particle containing at least 3 or more crystal grains.

[0047] In some embodiments, the lithium nickel cobalt manganese oxide particles are polycrystalline particles, and the secondary battery satisfies: a×b / c=0.18~2.10.

[0048] In some embodiments, the lithium nickel cobalt manganese oxide particles are polycrystalline particles, and the a×b / c can be a range of one or any two of the following: 0.18, 0.2, 0.25, 0.3, 0.5, 0.8, 1, 1.2, 1.25, 1.5, 1.8, 1.9, 2, 2.05, 2.1.

[0049] Polycrystalline particles are composed of multiple particles. When the lithium nickel cobalt manganese oxide particles are polycrystalline, the diffusion path of lithium ions inside the grains is very short, and the grain boundaries can provide transport channels under certain conditions, enabling lithium ions to be quickly inserted and extracted. At this time, when the lithium-nickel mixing ratio, cell volume and particle size distribution coefficient after particle cycling are further synergistically controlled to the above range, the kinetic performance of the material can be effectively optimized while taking into account structural stability, thereby improving its fast charging capability and resulting in better rate performance of the secondary battery.

[0050] In some embodiments, the lithium nickel cobalt manganese oxide particles are single-crystal particles, and the secondary battery satisfies: a×b / c=0.43~6.63.

[0051] In some embodiments, the lithium nickel cobalt manganese oxide particles are single-crystal particles, and the a×b / c can be a range of one or any two of the following: 0.43, 0.45, 0.5, 0.8, 1, 1.5, 1.55, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 6.6, 6.63.

[0052] When lithium nickel cobalt manganese oxide particles are single-crystal particles, they have high particle strength and good structural stability. During the repeated insertion and extraction of lithium ions, the volume change is uniform and they are not easily broken, thus maintaining the integrity of the particles. Furthermore, when the lithium-nickel mixing rate, cell volume, and particle size distribution coefficient after particle cycling are synergistically controlled to the above range, the stability of lithium ion insertion and extraction can be improved while taking into account the lithium ion diffusion and transport efficiency, thereby improving the cycle stability of the secondary battery.

[0053] More preferably, the lithium nickel cobalt manganese oxide particles include polycrystalline particles and monocrystalline particles.

[0054] When lithium nickel cobalt manganese oxide particles contain both single-crystal and polycrystalline particles, the advantages of both types of particles can be combined. This can improve the overall material's ability to rapidly insert and extract lithium ions, while also ensuring structural stability during lithium ion insertion and extraction. The secondary battery can thus balance kinetic and cycle performance.

[0055] In some embodiments, the particle size distribution curve of the polycrystalline particles corresponds to a peak particle size of 4-15 μm, and the particle size distribution curve of the single-crystal particles corresponds to a peak particle size of 1-4 μm.

[0056] In some embodiments, the cathode material further includes a doping element, which includes at least one of Zr, Y, Al, W, Nb, B, La, Mo, Ti, Mg, P, Ta, Ca, Si, F, Cs, and Sb.

[0057] By introducing doping elements into cathode materials containing lithium nickel cobalt manganese oxide, the stability of the metal MO bond in the material can be effectively improved, thereby enhancing the stability of the material's crystal structure, reducing the lithium-nickel mixing rate and crystal defects, and enabling the cathode material to have better reversible stability during lithium insertion / extraction cycling.

[0058] In some embodiments, the positive electrode material is further provided with a surface coating layer containing a metal element, the metal including at least one selected from Zr, Y, Al, W, Nb, La, Mo, Ti, Mg, Ta, Ca, Cs, and Sb.

[0059] By setting the oxides or salts of the aforementioned metals on the surface of the cathode material to form a passivation layer or a fast ion conductor layer, the corrosion effect of the electrolyte on the cathode material during the charging and discharging process of the secondary battery can be effectively reduced, further improving the structural stability of lithium nickel cobalt manganese oxide during the cycle process, thereby giving the secondary battery better cycle stability.

[0060] In some embodiments, the minimum particle size in the particle size frequency distribution curve of the cathode material is 0.2~1μm, and the maximum particle size is 8.6~20μm.

[0061] In some embodiments, the minimum particle size value in the particle size frequency distribution curve of the cathode material is a range of one or any two of 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.8μm, and 1μm, and the maximum particle size value is a range of one or any two of 8.6μm, 8.8μm, 9μm, 10μm, 11μm, 12μm, 12.5μm, 13μm, 14μm, 15μm, 16μm, 18μm, and 20μm.

[0062] It should be noted that the minimum and maximum particle size values ​​of the cathode material are defined as the minimum and maximum particle size values ​​corresponding to the intersection of the curve and the horizontal axis in the particle size frequency distribution curve, respectively.

[0063] When the minimum particle size of the cathode material is preferably within the above range, the lithium ion transport rate in the cathode material can be effectively improved, the dynamic performance of the secondary battery can be improved, and the DCR after cycling is lower. Furthermore, when the maximum particle size is preferably within the above range, the cycling stability of the material can be taken into account, resulting in better overall performance of the secondary battery.

[0064] In some embodiments, the lithium nickel cobalt manganese oxide particles comprise monocrystalline particles and / or polycrystalline particles; More preferably, the minimum particle size of the single crystal particles is 0.2~0.8μm, and the maximum particle size is 8~11.4μm; More preferably, the minimum particle size of the single crystal particles is within the range of one or any two of 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, and 0.8μm, and the maximum particle size is within the range of one or any two of 8μm, 8.5μm, 9μm, 9.2μm, 9.5μm, 9.8μm, 10μm, 10.2μm, 10.5μm, 10.8μm, 11μm, 11.2μm, and 11.4μm.

[0065] More preferably, the minimum particle size of the polycrystalline particles is 0.3~1μm, and the maximum particle size is 10~20μm.

[0066] More preferably, the minimum particle size of the polycrystalline particles is within the range of one or any two of 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.8μm, and 1μm, and the maximum particle size is within the range of one or any two of 10μm, 12μm, 12.5μm, 13μm, 15μm, 16μm, 16.5μm, 18μm, and 20μm.

[0067] It should be noted that the minimum and maximum particle size values ​​of the single-crystal particles and / or polycrystalline particles are defined as the minimum and maximum particle size values ​​corresponding to the intersection of the curve and the horizontal axis in the particle size frequency distribution curve, which are the minimum particle size value and the maximum particle size value, respectively.

[0068] It should be noted that the maximum and minimum particle size values ​​of the single-crystal and polycrystalline particles in the cathode material can be confirmed by, but not limited to, the following methods: The secondary battery is discharged at 0.33C to the lower limit voltage of 2.5V for venting treatment. The cathode electrode is then disassembled, soaked in dimethyl carbonate (DMC) solution at 25°C for 4 hours, dried, and the positive electrode active material layer powder is scraped off. This powder is fixed to a scanning electron microscope (SEM) sample holder using conductive adhesive, polished with CP argon ion, and coated with a conductive layer. Three locations are then randomly selected under the SEM at 3kx magnification for photographing. The number of particle agglomerates and particle diameter are used to determine the single-crystal and polycrystalline particles. The powder particles in the obtained areas are identified, and the particle size is measured using the diagonal tracing method with Mearsure Nano software. The particle size of 50 single-crystal particles is statistically analyzed to obtain their frequency distribution curves, thus determining their minimum and maximum particle sizes. Similarly, the particle size of 50 polycrystalline particles is statistically analyzed, and their frequency distribution curves are also statistically analyzed to obtain their minimum and maximum particle sizes.

[0069] In some embodiments, the positive electrode material further includes at least one of lithium iron phosphate and lithium manganese iron phosphate, and the secondary battery satisfies: a×b / c=0.25~5.1.

[0070] In the case of lithium nickel cobalt manganese oxide particles, the cathode material is further incorporating olivine-type lithium iron phosphate or lithium manganese iron phosphate, which can effectively improve the structural stability of the cathode material during lithium ion insertion and extraction, and the cycle stability of the secondary battery is better.

[0071] In some embodiments, the mass percentage of lithium iron phosphate in the cathode material is 5-30%.

[0072] In some embodiments, the mass percentage of lithium manganese iron phosphate in the cathode material is 5-30%.

[0073] More preferably, the lithium nickel cobalt manganese oxide can be a commercially available product, or it can be prepared by, but is not limited to, the following methods: Nickel, cobalt, and manganese sources are mixed in a solvent, a precipitant is added to precipitate the reaction, the mixture is allowed to stand, and after filtration, washing, and drying, a precursor is obtained. The obtained precursor is mixed with a lithium source and a dopant M and then calcined. The resulting material is crushed and the powder is sieved to obtain lithium nickel cobalt manganese oxide particles.

[0074] In some embodiments, the nickel source includes at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate; In some embodiments, the cobalt source used includes at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate; In some embodiments, the manganese source includes at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate; In some embodiments, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium dihydrogen phosphate, lithium citrate, and lithium acetate. In some embodiments, the precipitant includes at least one of sodium hydroxide, sodium carbonate, oxalic acid, and ammonia.

[0075] In some embodiments, the pH of the mixed solution during the precipitation reaction is 10 to 12.5.

[0076] In some embodiments, the ratio of the molar amount of lithium in the lithium source to the total molar amount of transition metal elements in the precursor is 1.01 to 1.06.

[0077] In some embodiments, the solvent includes water.

[0078] In some embodiments, the precipitation reaction takes 0.5 to 1.5 hours.

[0079] In some embodiments, the calcination may comprise three calcinations; the first calcination step involves preheating to 450-550°C and holding for 4-6 hours, followed by heating to 700-1000°C and holding for 10-18 hours; the second calcination temperature is 500-750°C, and the holding time is 4-8 hours; the third calcination temperature is 300-550°C, and the holding time is 3-8 hours. The heating rate during calcination is 2-10°C / min.

[0080] In some embodiments, those skilled in the art can control the secondary batteries a and b by adjusting the molar ratio of lithium and transition metal elements added to the raw materials, as well as the temperature and time during calcination. The calcination temperature is especially the temperature of the first stage of calcination, but is not limited to this. Those skilled in the art can also control them in other ways.

[0081] In some embodiments, the dopant M is an oxide or salt of a dopant element, including at least one of Zr, Y, Al, W, Nb, La, Mo, Ti, Mg, Ta, Ca, Cs, and Sb.

[0082] In some embodiments, the coating agent is a metal oxide and / or a metal salt, wherein the metal includes, but is not limited to, at least one of Al, W, and B.

[0083] In some embodiments, the atmosphere during calcination is an oxygen atmosphere, and the oxygen content of the oxygen atmosphere is 90-99%.

[0084] In some embodiments, the cooling rate during and after calcination is 5~15℃ / min.

[0085] In some embodiments, the particles obtained after the first calcination are further subjected to a water washing treatment, wherein the solid-liquid ratio during the water washing treatment is 1:(20~30), and the water washing treatment time is 1~5 min.

[0086] In some embodiments, the crushing is performed by an air jet mill, and the frequency of the air jet mill crushing is 15~65Hz.

[0087] As mentioned above, those skilled in the art can also use other means to regulate a and b, such as adjusting the oxygen concentration in the atmosphere during calcination, or controlling the particles by washing them with water. In addition, the cooling rate during and after calcination will also affect the parameter changes. Furthermore, during the preparation process, the pH of the solution during the precipitation reaction, the temperature and time of calcination, and the frequency of air jet milling will cause changes in the particle size parameters C1 and C2, and lead to the formation of single crystal particles and / or polycrystalline particles. Those skilled in the art can use these means to make comprehensive controls, without making any special limitations.

[0088] In some embodiments, the positive electrode active material layer in the positive electrode sheet includes a positive electrode material, a binder, and a conductive agent. The positive electrode material includes lithium nickel cobalt manganese oxide, and the mass percentage of the positive electrode material in the positive electrode active material layer is 70-99%.

[0089] More preferably, the mass percentage of the positive electrode material in the positive electrode active material layer is 92-99%.

[0090] By further increasing the content of positive electrode material, the energy density of the overall positive electrode active material layer can be effectively improved. Under the synergistic regulation of the secondary battery as defined above in this application, the cycle and kinetic performance of the secondary battery can be balanced.

[0091] In some embodiments, the binder is used to improve the adhesion between cathode material particles and the adhesion between the cathode material and the cathode current collector. Any binder can be used without particular limitation, as long as it has suitable adhesive properties and does not significantly cause adverse chemical changes in the battery. For example, the binder includes fluorinated polyolefin binders, including but not limited to polyvinylidene fluoride (PVDF), PVDF copolymers, or their modified derivatives (e.g., modified with carboxylic acids, acrylic acid, acrylonitrile, etc.).

[0092] Specifically, the adhesive is selected from polytetrafluoroethylene or polyvinylidene fluoride.

[0093] In some embodiments, the mass percentage of the binder in the positive electrode active material layer is 1% to 4.0%, such as 1%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.7%, 3.0%, 3.2%, 3.5%, 3.8%, 4.0%, or any range formed by any two of the above values.

[0094] In some embodiments, the conductive agent is used to provide conductivity. Any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. Exemplary examples of conductive agents in the positive electrode active material layer include, but are not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fibers, activated carbon, mesoporous carbon, and fullerenes, wherein carbon fibers are, for example, carbon nanofibers; and carbon black is, for example, SP (Super P), acetylene black, Ketjen black, etc.

[0095] In some embodiments, the mass percentage of the conductive agent in the positive electrode active material layer is 1.0% to 4.0%, such as 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.5%, 3%, 3.5%, 4%, or any range formed by any two of the above values.

[0096] In some embodiments, the positive electrode sheet can be prepared by, but is not limited to, the following methods: The positive electrode material, conductive agent, and binder are mixed in a solvent and then stirred to prepare a slurry. The slurry is coated onto a current collector in one or two layers, dried, rolled, and cut to obtain the positive electrode sheet.

[0097] In some embodiments, the solvent includes N-methylpyrrolidone (NMP).

[0098] In some embodiments, the porosity of the positive electrode active material layer is 10-30%.

[0099] More preferably, the porosity of the positive electrode active material layer is a value within the range of one or any two of 10%, 15%, 20%, 22%, 25%, 28%, and 30%.

[0100] The porosity of the positive electrode active material layer will result in different wetting spaces for the electrolyte during wetting. When the porosity of the positive electrode active material layer is preferably within the above range, the wetting space of the electrolyte can be effectively improved, which is beneficial to the liquid phase diffusion efficiency of lithium ions, controls the liquid phase diffusion path, ensures reduced battery diffusion impedance, and improves the battery dynamic performance.

[0101] It should be noted that the porosity of the positive electrode active material layer described in this application can be confirmed by, but is not limited to, the following methods: The secondary battery was discharged at 0.33C to the lower limit voltage of 2.5V. Then, the empty battery was disassembled, the positive electrode was removed, and soaked in DMC solution for 2 hours. After drying, the positive electrode was cut into circular pieces with a diameter D = 12mm. Simultaneously, the thickness of the electrode and the current collector was measured using a thickness gauge and recorded as h1 and h2, respectively. The result was obtained using V1 = πR. 2 Calculate the volume V1 of the positive electrode active material layer (h1-h2), then weigh the electrode and record the mass as m1. Next, immerse the electrode completely in a sealed container of hexadecane for 1 hour (the volume of hexadecane in the sealed container is not critical, but the amount must be sufficient to completely submerge the electrode). Remove the electrode and dry it with filter paper until a constant weight is achieved (generally after 1 hour). Weigh the electrode and record the weight as m2. Calculate the porosity of the positive electrode active material layer using the formula: porosity% = [(m2-m1) / ρ] / V1 × 100%, where ρ is the density of hexadecane, 0.7734 g / cm³. 3 .

[0102] In some embodiments, the compaction density of the positive electrode active material layer is 3~3.8 g / cm³. 3 The surface density is 200~700 g / m³ 2 .

[0103] It should be noted that the compaction density and areal density of the positive electrode active material layer described in this application can be confirmed by, but are not limited to, the following methods: The secondary battery was discharged at 0.33C to the lower limit voltage of 2.5V. Then, the empty battery was disassembled, the positive electrode was removed, and soaked in DMC solution for 2 hours. After drying, the pretreated positive electrode was punched into circular pieces of a fixed area using a punching machine. The area is denoted as S0, and the unit is m. 2 To ensure testing accuracy, select a flat location in the middle of the electrode sheet and take three or more discs as parallel samples. Weigh each of the three discs using an electronic balance, and record the mass of each disc as M1 (g). Measure the thickness of the active material layer (after removing the current collector) in each of the three discs using a micrometer, and record it as H (m). Take the average value. Finally, add an appropriate amount of deionized water to each of the three discs, gently wipe off the coating with lint-free paper to expose the current collector, and let them stand (dry) at room temperature for 10 minutes. After the current collector is dry, weigh each of the three current collectors and record it as M0. Take the average value and calculate the compaction density of the positive electrode active material layer using the following formulas: (M1-M0) / (H×S0), and areal density = (M1-M0) / S0.

[0104] In some embodiments, the secondary battery further includes a negative electrode.

[0105] In some embodiments, the negative electrode sheet includes a negative electrode active material layer, which includes a negative electrode material.

[0106] In some embodiments, the negative electrode material includes silicon.

[0107] More preferably, the silicon content in the negative electrode active material layer is 8-20% by mass.

[0108] It should be noted that the mass percentage of silicon in the negative electrode active material layer described in this application is confirmed by, but not limited to, the following methods: The secondary battery was discharged at 0.33C to the lower limit voltage of 2.5V. The empty battery was disassembled and the negative electrode was removed. It was soaked in DMC solution for 4 hours, dried, and the negative electrode active material powder on the surface of the electrode was scraped off with a ceramic knife. The silicon content in the negative electrode was tested using the alkaline dissolution-ICP method. The scraped negative electrode active material powder was weighed and placed in a nickel crucible pre-filled with potassium hydroxide. A small amount of potassium hydroxide was added to cover the sample surface, and two drops of ethanol were added. The mixture was heated on an electric furnace until the potassium hydroxide melted and dehydrated. Then it was transferred to a muffle furnace at 1100°C and kept at the melting temperature for 8 hours. The nickel crucible was removed and allowed to cool slightly. It was placed in a 300mL plastic beaker and extracted with hot water. After the reaction, the crucible was washed out. HCl was added to the extract for acidification, and hydrogen peroxide and hydrochloric acid were added to form a mixed acid to make the conversion of silicon compounds to silicon ions more complete. After cooling, the extract was washed out with water, transferred to a 100mL volumetric flask, diluted to volume, and shaken well. After standing, a portion of the solution was transferred to another 100 mL volumetric flask, diluted to volume, shaken well, and allowed to stand until clear to obtain the test solution. Simultaneously, a blank solution was prepared as a control. No powder was added to the blank solution. Following the operating procedure, a blank sample control was prepared to eliminate any potential influences from the operation. ICP testing was performed on the test solution. The elemental detection wavelength was selected, and the experimental conditions were set: based on the sample characteristics and the ICP testing of the test solution, the Si elemental detection wavelength of 288.158 nm was selected. The Si content of the element was determined by ICP testing.

[0109] More preferably, the negative electrode material further includes graphite material.

[0110] More preferably, the graphite includes at least one of artificial graphite and natural graphite.

[0111] When lithium nickel cobalt manganese oxide particles are selected as the active material for the positive electrode and silicon is used for the negative electrode, the overall energy density of the secondary battery can be effectively improved.

[0112] In some embodiments, the negative electrode material includes a silicon-based material.

[0113] More preferably, the silicon-based material includes at least one of elemental silicon, silicon suboxide, silicon carbide, and silicon-carbon composite materials.

[0114] In some embodiments, the negative electrode active material layer includes a negative electrode material, a conductive agent, and a binder.

[0115] The conductive agent in the negative electrode active material layer is used to provide conductivity. Any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. For example, the conductive agent includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fibers, activated carbon, mesoporous carbon, and fullerenes, wherein carbon fibers are, for example, carbon nanofibers; and carbon black is, for example, SP, acetylene black, Ketjen black, etc.

[0116] In some embodiments, the mass percentage of the conductive agent in the negative electrode active material layer is 0.4% to 2%, such as 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or any range formed by any two of the above values.

[0117] The binder in the negative electrode active material layer is used to improve the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Any binder can be used without particular limitation, as long as it has suitable adhesive properties and does not significantly cause adverse chemical changes in the battery. For example, the binder includes, but is not limited to, at least one of carboxymethyl cellulose (CMC), styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, and aqueous acrylic resin.

[0118] In some embodiments, the mass percentage of the binder in the negative electrode active material layer is 1.0% to 4.5%, such as 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.7%, 3.0%, 3.2%, 3.5%, 3.8%, 4.0%, 4.2%, 4.5%, or any range formed by any two of the above values.

[0119] In some embodiments, the negative electrode material has a mass percentage content of 70-99% in the negative electrode active material layer.

[0120] In some embodiments, the secondary battery satisfies: Dμm=1.5~10μm, where D=D1×D2, where D1 is the particle size value corresponding to the highest peak of the particle size frequency distribution curve of the negative electrode material, and D2 is the proportion of the area of ​​the curve portion with a particle size value less than or equal to the particle size value corresponding to the highest peak in the particle size frequency distribution curve of the negative electrode material in the total area of ​​the particle size frequency distribution curve.

[0121] In some implementations, Dμm can be a range of one or any two of 1.5μm, 2μm, 2.5μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, and 10μm.

[0122] In this application, similar to the positive electrode material, when the particle size distribution coefficient of the secondary battery is preferably within the above range, it can not only effectively optimize the stability of the negative electrode material particles, especially when silicon is contained, the probability of material expansion and breakage is lower, but also improve the dynamic performance of the negative electrode material, ensuring that the negative electrode sheet can take into account better dynamic performance and cycle stability when applied to the secondary battery.

[0123] It should be noted that the test method for D1 is similar to that for C1 mentioned above, and the test method for D2 is similar to that for C2 mentioned above. The only difference is that the positive electrode is replaced with the negative electrode. The pretreatment methods and detection methods can be the same, and will not be repeated here.

[0124] In some implementations, D1μm = 5~20μm.

[0125] In some implementations, D2 = 0.2 to 0.6.

[0126] More preferably, the secondary battery satisfies: D / c = 0.35~7.7.

[0127] More preferably, the D / c can be a range of one or any two of the following: 0.35, 0.5, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 7.7.

[0128] More preferably, the secondary battery satisfies: D / c = 1~4.5.

[0129] By controlling the particle size distribution relationship coefficients of the negative and positive electrode materials and optimizing them within the aforementioned range, the consistency of lithium-ion transport performance between the positive and negative electrodes can be synergistically adjusted. c and D represent the relationship between the highest particle size frequency distribution value in the positive and negative electrode materials and the proportion of particles smaller than that value. When D is greater than c and the difference is large, because most particles in the positive electrode material have small particle sizes, the lithium-ion transport path is short, allowing a large number of lithium ions to quickly reach the negative electrode. However, because most particles in the negative electrode material have large particle sizes, lithium ions may not be able to quickly embed from the surface into the negative electrode material layer, affecting kinetic performance and potentially leading to lithium ion surface enrichment and lithium dendrite formation. Conversely, when D is less than c and the difference is large, most particles in the positive electrode material are large, resulting in a long lithium-ion transport path. Although the negative electrode material has small particle sizes, allowing for rapid lithium ion entry, the time it takes for lithium ions to reach the negative electrode from the positive electrode is too long, also affecting kinetic performance. Therefore, targeted matching of the two coefficients simultaneously considers both the lithium-ion extraction and embedding rates, further improving the kinetic performance of the secondary battery.

[0130] In some embodiments, the secondary battery further includes an electrolyte.

[0131] In some embodiments, the electrolyte includes additives, solvents, and lithium salts.

[0132] In some embodiments, the solvent includes at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate ester solvents.

[0133] Exemplary examples include, but are not limited to, at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC); carboxylic acid ester solvents include, but are not limited to, at least one of ethyl acetate (EA), methyl formate, and 1,4-butyrolactone; ether solvents include, at least one of dimethyltetrahydrofuran, tetrahydrofuran, and 1,2-dimethoxyethane; sulfone solvents include, at least one of methyl sulfone and dimethyl sulfoxide; nitrile solvents include, at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole, and 1,3,6-hexanetrionitrile; and phosphate ester solvents include, at least one of trimethyl triphosphate and triethyl phosphate.

[0134] More preferably, the solvent of the electrolyte includes at least one of EC, DMC, EMC, DEC, and EA, and the mass percentage of the solvent in the electrolyte is 70-95%.

[0135] When the above-mentioned preferred solvents are selected for combination, they can be better adapted to the positive electrode of the secondary battery described in this application, improve the ionic conductivity of the electrolyte, and make the lithium ion insertion / extraction rate higher, the kinetic performance of the secondary battery better, and the cycle DCR lower.

[0136] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium difluorosulfonylimide, lithium difluoromethanesulfonylimide, lithium ditrifluoromethanesulfonylimide, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0137] More preferably, the lithium salt includes at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0138] More preferably, the additive includes at least one of vinylene carbonate, propylene sulfite (PS), vinyl sulfate (DTD), and methylene disulfonate (MMDS).

[0139] More preferably, the additive has a mass percentage content of 0.1-1% in the electrolyte.

[0140] When the above-mentioned additives are used in a preferred manner, the thermal stability of the electrolyte can be effectively improved, the decomposition behavior of the electrolyte during battery cycling can be suppressed, and the viscosity of the electrolyte can be prevented from changing significantly, thereby ensuring both the cycle stability and kinetic performance of the battery.

[0141] In some embodiments, the secondary battery has a wound cell structure.

[0142] The term "wound cell structure" generally refers to a cell structure prepared by winding continuous positive electrode plates, negative electrode plates, and separators, with the separator located between adjacent positive and negative electrode plates.

[0143] When the secondary battery adopts a wound cell structure, the positive and negative electrode plates in the cell have a higher contact density. In order to ensure the lithium-ion transmission efficiency, the secondary battery is regulated by the synergistic parameters described in this application, and the secondary battery can achieve better performance.

[0144] More preferably, the secondary battery is a cylindrical battery.

[0145] A cylindrical battery refers to a battery whose outer casing is cylindrical, with a cylindrical cavity inside. The outer casing can be made of aluminum, aluminum alloy, or composite metal materials.

[0146] When a cylindrical cell structure is used, the electrode stacking density is higher, which reduces the lithium-ion transport impedance and increases the tolerance for lithium-nickel mixing rate. However, the internal space of the cylindrical cell is insufficient, and the amount of electrolyte ionization is low, especially after cycling. Therefore, the cell volume of the positive electrode material after cycling cannot be too small, otherwise it will result in small interlayer spacing and poor lithium-ion transport rate. In addition, the low amount of electrolyte ionization will also affect lithium-ion transport.

[0147] In some embodiments, the secondary battery is a cylindrical battery, including a casing and a cell, wherein the diameter of the cell is less than or equal to 30 mm and the height is less than or equal to 60 mm, and the secondary battery satisfies: a×b / c=0.4~5.15.

[0148] When the size of the cylindrical battery is further set to the aforementioned small cylindrical size, the lithium-ion transport path and current transport path are shorter, the tolerance for cell volume and other factors is improved, and a slightly larger cell volume and lithium-nickel mixing ratio can be allowed. However, with a smaller cylinder, the amount of electrolyte injected is less. In order to ensure better lithium-ion transport efficiency, the relationship value of the secondary battery is preferably within the above range, which can further improve the cycle and kinetic performance of the secondary battery.

[0149] More preferably, the battery cell includes tabs that extend from the battery cell body, and the number of tabs is less than or equal to 3.

[0150] It should be noted that the tab refers to a single polarity tab, and the electrode is a positive electrode or a negative electrode, that is, the number of tabs of a single polarity is less than or equal to 3.

[0151] In the secondary battery, the tabs are used to transmit the current inside the cell. By controlling the number of tabs, the uniformity of lithium ion and current transmission can be balanced, thereby improving the dynamic performance of the secondary battery and reducing the DCR.

[0152] In some embodiments, the battery is a cylindrical battery, including a casing and a cell, wherein the diameter of the cell is greater than or equal to 40 mm and the height is greater than or equal to 80 mm, and the secondary battery satisfies: a×b / c=0.18~4.29.

[0153] When configured as a large-sized cylindrical battery, the internal space of the battery is larger, the electrolyte volume is greater, and the amount of free electrolyte is higher. However, the lithium-ion transport path and current transport path are longer, and the tolerance for cell volume and other factors is reduced. Further optimization of the numerical relationship range of the secondary battery within the above-mentioned preferred range can effectively balance the rate of lithium-ion transport and structural stability, and further improve the cycle and kinetic performance of the secondary battery.

[0154] In some embodiments, the secondary battery has a stacked cell structure.

[0155] The stacked cell structure refers to a cell structure made by stacking positive electrode plates, negative electrode plates, and separators. The positive and negative electrode plates are separated by a separator, and adjacent positive and / or negative electrode plates within the cell are discontinuous. The stacking process includes layering or Z-shaped folding. When the secondary battery adopts a stacked structure, due to the gaps between the electrodes, the secondary battery can be controlled using the synergistic parameters described in this application to ensure that the lithium-ion transport rate is at a high level and improve the dynamic performance of the secondary battery.

[0156] In some embodiments, the secondary battery has a stacked cell structure, and the secondary battery is a prism battery.

[0157] It should be noted that, depending on the cell structure, the secondary battery may be, but is not limited to, a cylindrical battery, a prism-shaped battery, or other battery shapes.

[0158] In some embodiments, the secondary battery includes a cell and a casing; More preferably, the secondary battery cell includes tabs, the number of tabs is greater than 1, and the secondary battery satisfies V1 / V2=0.15~0.5, where V1 is the area of ​​the tabs and V2 is the end face area of ​​the cell.

[0159] The secondary battery tabs are used to transmit the current inside the cell. By controlling the number of tabs, the uniformity of lithium ion and current transmission is balanced, improving the dynamic performance of the battery. Especially when the cylindrical size is relatively large, the uniformity of lithium ion and electron transmission is improved, and the DCR is reduced.

[0160] It should be noted that the end face of the battery cell refers to the end face of the battery cell with the tabs on it in the axial direction.

[0161] More preferably, the housing comprises an aluminum-plastic film or a metal shell; In some embodiments, the aluminum-plastic film includes an adhesive layer, a metal layer, and a protective layer. The metal layer is disposed between the adhesive layer and the protective layer. The protective layer serves as an outer insulating layer. The material of the protective layer can be one or more of the following: polycaprolactam (nylon 6), PET (polyethylene terephthalate), polybutylene succinate, etc.

[0162] In some embodiments, the metal layer may be one or more of metals or alloys such as aluminum, aluminum alloy, copper, and nickel; the adhesive layer, as the inner insulating layer, may be one or more of materials such as polypropylene film (PP) and cast polypropylene film (CPP).

[0163] More preferably, the metal shell can be, but is not limited to, at least one of aluminum or its alloy shell, steel shell, titanium or its alloy shell, specifically a shell made of materials such as aluminum-magnesium alloy, aluminum-manganese alloy, etc., and the steel shell can be stainless steel, carbon steel, nickel-plated steel, etc.

[0164] In this application, there are no special restrictions on the specific type of metal casing used for the secondary battery. For example, the metal casing can be an aluminum casing, an aluminum alloy casing, a titanium casing, or a titanium alloy casing. The metal casing can also be a steel casing, specifically a stainless steel casing, a nickel-plated steel casing, a carbon steel casing, etc., depending on the actual needs.

[0165] More preferably, the secondary battery includes a casing and a cell, the casing includes an aluminum-plastic film, and a = 0.013~0.045.

[0166] When aluminum-plastic film is selected as the casing material, the corresponding secondary battery is a pouch battery. After long-term cycling, the gas generated inside and the micro-expansion may lead to poor interfacial contact and faster life decay. Therefore, further regulation of the lithium-nickel mixing ratio of the cathode material after cycling can effectively improve the structural order of the cathode material, optimize the diffusion path and diffusion rate of lithium ions, improve the structural stability of lithium ions during insertion and extraction, reduce the probability of internal gas generation and micro-expansion, and extend the cycle life of the secondary battery.

[0167] The present invention is further illustrated below with specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention: Example 1 A secondary battery, the preparation method comprising the following steps: (1) Preparation of lithium nickel cobalt manganese oxide particles: Nickel sulfate solution, cobalt sulfate solution and manganese sulfate solution were mixed in stoichiometric ratio, and then sodium hydroxide precipitant was added. The pH was adjusted to within the range of 10.4 and the temperature was 55℃ for 1h. After filtration, washing and drying, the resulting precursor and lithium carbonate were mixed with each other according to the molar ratio X of lithium atoms to the total atoms of nickel, cobalt and manganese in the precursor of 1.02:1. After adding dopant M and mixing evenly, the mixture was calcined once in an oxygen atmosphere of 97.5%. During the first calcination, the temperature was first raised to 500℃ at 5℃ / min and held for 4h, and then raised to 850℃ and held for 12.5h. No water washing was performed. Then, the coating material was added and mixed and calcined a second time. During the second calcination, the temperature was lowered to 500℃ at 8℃ / s and held for 4h. Finally, the temperature was lowered to 300℃ at 8℃ / s and held for 4h. The mixture was dried at 60℃ for 24h, crushed by air jet milling at 50Hz, and sieved to obtain lithium nickel cobalt manganese oxide. (2) Preparation of the positive electrode sheet: Lithium nickel cobalt manganese oxide is used as the positive electrode material. Then, the positive electrode material, conductive agent acetylene black, and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 98:1:1. The mixture is prepared by vacuum stirring and then coated onto the current collector aluminum foil. After coating, drying, cold pressing, slitting, and rolling, the positive electrode sheet is obtained. The areal density of the positive active material layer of the positive electrode sheet is 350 g / m³. 2 The compacted density is 3.3 g / cm³. 3 ; (2) Preparation of negative electrode sheet: The negative electrode material artificial graphite, conductive agent SP, binder sodium carboxymethyl cellulose, and binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, and a slurry is prepared by vacuum stirring. The slurry is then coated onto the current collector copper foil. After coating, drying, cold pressing, slitting, and rolling, the negative electrode sheet is obtained. The areal density of the negative electrode active material layer of the negative electrode sheet is 150 g / m³. 2 The compacted density is 1.6 g / cm³. 3 ; (3) Preparation of electrolyte: EC, DMC and EMC were mixed in a volume ratio of 3:4:3 as solvent. Then, based on the total mass of the electrolyte, LiPF6:LiFSI (molar ratio) = 0.8:0.2 was added to prepare a lithium salt concentration of 1 mol / L. Additives PS with a mass content of 0.5% and DTD with a mass content of 0.5% were added to prepare the electrolyte. (4) The positive electrode, commercially available PP separator (including a base film and an alumina coating on both sides of the base film, wherein the thickness of the base film is 10 μm and the alumina coating on one side of the base film is 3 μm) and negative electrode are stacked in sequence to form a battery cell. The battery cell is placed in an aluminum quadrangular prism-shaped outer packaging shell, dried, injected with electrolyte, vacuum-sealed, and left to stand, and then formed. After setting the glass to rest at 25℃ for 24 hours, place it in the glass clamp with a clamping pressure of 0.5MPa, let it stand for 10 minutes, then charge it at a rate of 0.02C, with a cutoff voltage of 3.2V; let it stand for 10 minutes, then charge it at a rate of 0.05C, with a cutoff voltage of 3.4V; let it stand for 10 minutes, then charge it at a rate of 0.08C, with a cutoff voltage of 3.75V. After completing the formation process, the lithium-ion secondary battery is obtained.

[0168] Examples 2-40, Comparative Examples 1-6 A secondary battery differs from Example 1 only in the preparation process of the positive electrode sheet. The parameters for the preparation are shown in Table 1, and the parameters of the resulting product are shown in Table 2. Figure 1 As shown, the solid-liquid ratio of each lithium nickel cobalt manganese oxide particle during washing is 1g:25mL. The preparation process of the battery cell described in Examples 20 and 32-34 is as follows: the positive electrode sheet, commercially available PP separator (including a base film and an alumina coating disposed on both sides of the base film, the thickness of the base film is 10μm, and the alumina coating on one side of the base film is 3μm) and negative electrode sheet are wound and assembled into a battery cell in sequence. The battery cell is placed in an aluminum cylindrical shell (diameter 20mm, height 60mm), dried, and then injected with electrolyte. After vacuum sealing, standing, and formation (same as in Example 1), the lithium-ion secondary battery is obtained. The manufacturing process of the battery cell described in Examples 35-37 is as follows: the positive electrode sheet, a commercially available PP separator (including a base film and an alumina coating disposed on both sides of the base film, wherein the thickness of the base film is 10 μm and the alumina coating on one side of the base film is 3 μm) and the negative electrode sheet are wound and assembled into a battery cell in sequence. The battery cell is placed in an aluminum cylindrical shell (48 mm in diameter and 90 mm in height), dried, and then injected with electrolyte. After vacuum sealing, standing, and formation (same as in Example 1), the lithium-ion secondary battery is obtained. The preparation process of the battery cell described in Examples 38-39 is as follows: the positive electrode sheet, commercially available PP separator (including a base film and an alumina coating disposed on both sides of the base film, the thickness of the base film is 10μm, and the alumina coating on one side of the base film is 3μm) and negative electrode sheet are stacked and assembled into a battery cell in sequence. The battery cell is placed in an aluminum-plastic film, dried, and then injected with electrolyte. After vacuum sealing, standing, and formation (same as in Example 1), the soft-pack lithium-ion secondary battery is obtained. In each embodiment and comparative example, D1 and D2 are obtained by using artificial graphite of different sizes and specifications for blending and control.

[0169] The doping element concentration in Table 2 refers to the total concentration of all doping elements in the positive electrode active material layer, and the doping element is at least one of Zr, Y, Al, W, Nb, La, Mo, Ti, Mg, Ta, Ca, Cs, and Sb.

[0170] Table 1 Continued from Table 1 Continued from Table 1 Continued from Table 1 Continued from Table 1 Table 2 Continued from Table 2 Continued from Table 2 Continued from Table 2 Continued from Table 2 Continued from Table 2 Example of effect The lithium-ion batteries obtained in each embodiment and comparative example were tested as follows: (1) Cyclic performance test: The secondary batteries obtained in each embodiment and comparative example were placed at 45°C for 24 hours. A constant temperature environment was set, and the batteries were pre-charged to 4.25V with a constant current of 1C, then charged to the cutoff at 0.05C with a constant voltage, and then discharged to 2.5V with a constant current of 1C. This was one cycle, and the discharge capacity Q1 was recorded. After repeating the cycle 400 times, record the discharge capacity Q2 of the 400th cycle, and calculate the capacity retention rate of the secondary battery = 100% × Q2 / Q1; (2) DCR test: The secondary battery was charged at 25°C with a constant current and constant voltage of 0.33C to 4.25V, with a cutoff current of 0.05C. After resting for 10 minutes, it was discharged at a constant current of 0.33C to 2.5V. This cycle was repeated twice. After resting for 10 minutes, it was charged at a constant current and constant voltage of 0.33C to 4.25V. After discharging to 50% of the discharge capacity of the second cycle, it was rested for 2 hours. The initial voltage was recorded as V1. The battery was discharged at a 1C rate for 18 seconds with a sampling interval of 0.1 seconds. After the discharge ended, the voltage was recorded as V2, and the discharge current for 18 seconds was recorded as I1. The DCR discharge (I1, 18s) = |V2-V1| / I1×1000.

[0171] The test results are shown in Table 3.

[0172] Table 3 As can be seen from Table 3: The secondary battery described in this application can effectively optimize the stability of the cathode material during reversible insertion / extraction cycling by synchronously controlling the lithium-nickel mixing ratio, cell volume, and cathode material particle size distribution coefficient after cycling. This results in ideal cycling performance for the secondary battery, with each secondary battery achieving a capacity retention rate of over 85% after 400 cycles. At the same time, it also ensures high kinetic performance of the material. The cycle DCR of the secondary battery is low, with the DCR of both the soft non-pack and soft pack batteries being controllable below 8mΩ.

[0173] Meanwhile, as can be seen from the various embodiments, adjusting the cell volume of the particles and the lithium-nickel mixing ratio after cycling will simultaneously affect the cycle performance and kinetic performance of the secondary battery. Furthermore, by further matching and controlling the particle size distribution coefficient c, the secondary battery can be further optimized within the range of a×b / c=0.38~3.4, resulting in better overall performance.

[0174] Furthermore, the lithium-nickel mixing ratio refers to the proportion of nickel ions occupying crystal sites that are not lithium ions in lithium nickel cobalt manganese oxide particles. A higher lithium-nickel mixing ratio has a greater impact on lithium ion insertion and extraction. However, if the lithium-nickel mixing ratio is too low, it will lead to the sacrifice of some lithium ion diffusion channels, thereby affecting the rate performance of the secondary battery. When the lithium-nickel mixing ratio 'a' of the cathode material particles after cycling is preferably in the range of 1.5% to 4.5%, it can not only reduce the impact of nickel ions occupying lithium sites on the reversible insertion and extraction of lithium ions, but also avoid excessive sacrifice of lithium ion diffusion channels based on the reduction of the lithium ion diffusion barrier, thereby improving the lithium ion diffusion rate. On the other hand, when the cell volume 'b' of the cathode material after cycling is preferably in the range of 101 to 102 Å... 3This method can effectively improve the stability of the material structure, and the larger interlayer spacing makes lithium ion extraction easier, which is more conducive to achieving reversible and rapid conduction and improving kinetic performance. In addition, by optimizing the particle size distribution coefficient c of the cathode material (cμm=1~4.5μm), the cell parameters of lithium nickel cobalt manganese oxide and the lithium-nickel mixing ratio of lithium nickel cobalt manganese oxide particles can be effectively matched, ensuring the reversible insertion and extraction efficiency of lithium ions. At the same time, it can also ensure the high wettability of the particle material and the high content of lithium insertion and extraction sites, ensuring the high rate of lithium ion insertion and extraction. The lithium ion diffusion path is better, and the kinetic performance of the cathode material is better. The secondary battery can achieve both high cycle stability and low DCR.

[0175] After adjusting the particle size distribution coefficient c of the positive electrode material, the particle size distribution coefficient D of the negative electrode material is further matched so that the secondary battery satisfies D / c = 0.35~7.7. This can further improve the kinetic performance of the secondary battery. This is because when the D / c ratio is large, since most particles in the positive electrode material have small particle sizes, the lithium ion transport path is short, and a large number of lithium ions can quickly reach the negative electrode. However, since most particles in the negative electrode material have large particle sizes, lithium ions are not able to quickly embed from the surface into the negative electrode material layer, affecting the kinetic performance and also easily causing lithium ion enrichment on the surface and the risk of lithium dendrites. Conversely, when D / c is small, most particles in the positive electrode material are large in size, and the lithium ion transport path is long. Although the particle size of the negative electrode material is small, allowing lithium ions to enter quickly, the time for lithium ions to reach the negative electrode from the positive electrode is too long, which also affects the kinetic performance.

Claims

1. A secondary battery, characterized in that, It includes a positive electrode sheet, the positive electrode sheet includes a positive active material layer, the positive active material layer includes a positive electrode material, and the positive electrode material includes lithium nickel cobalt manganese oxide; The positive electrode plate satisfies: a×b / c=0.18~6.63; Wherein, 'a' represents the lithium-nickel mixing ratio of the cathode material after 200 charge-discharge cycles, and 'b' represents the cell volume of the cathode material after 200 charge-discharge cycles, in Å. 3 The c = C1 × C2, where C1 is the particle size value corresponding to the highest peak of the particle size frequency distribution curve of the cathode material, and C2 is the proportion of the area of ​​the curve part with a particle size value less than or equal to the particle size value corresponding to the highest peak in the total area of ​​the particle size frequency distribution curve of the cathode material. The unit of c is μm.

2. The secondary battery as described in claim 1, characterized in that, The value of a×b / c is 0.38~3.

4.

3. The secondary battery as described in claim 1, characterized in that, a = 0.013~0.065, and / or b = 100~103, and / or c = 0.6~8.

4. The secondary battery as described in claim 3, characterized in that, a = 0.015~0.045, and / or b = 101~102, and / or c = 1~4.

5.

5. The secondary battery as described in claim 1, characterized in that, The chemical formula of the lithium nickel cobalt manganese oxide is Li x Ni o Co p Mn q O2, where x is greater than or equal to 0.9 and less than or equal to 1.1; o is greater than or equal to 0.5 and less than 1; p is greater than 0 and less than 1; q is greater than 0 and less than 1; o+p+q=1.

6. The secondary battery as described in claim 5, characterized in that, The lithium nickel cobalt manganese oxide also contains metal elements, including at least one of Zr, Y, Al, W, Nb, La, Mo, Ti, Mg, Ta, Ca, Cs, and Sb.

7. The secondary battery as described in claim 5 or 6, characterized in that, The value of o is greater than or equal to 0.5 and less than 0.95, and the value of c is 1 to 8.

8. The secondary battery as described in claim 5 or 6, characterized in that, The x is greater than or equal to 0.85 and less than or equal to 0.

93.

9. The secondary battery as described in claim 1, characterized in that, The cathode material includes lithium nickel cobalt manganese oxide particles, which include single-crystal particles and / or polycrystalline particles.

10. The secondary battery as described in claim 9, characterized in that, The lithium nickel cobalt manganese oxide particles are polycrystalline particles, and the secondary battery satisfies: a×b / c=0.18~2.10, or the positive electrode material is a monocrystalline particle, and the secondary battery satisfies: a×b / c=0.43~6.

63.

11. The secondary battery as described in claim 9, characterized in that, The lithium nickel cobalt manganese oxide particles include monocrystalline particles and polycrystalline particles.

12. The secondary battery as described in claim 9, characterized in that, The particle size value corresponding to the highest peak of the particle size frequency distribution curve of the single crystal particles is 1~4μm, and / or the particle size value corresponding to the highest peak of the particle size frequency distribution curve of the polycrystalline particles is 4~15μm.

13. The secondary battery as described in claim 1, characterized in that, The cathode material is further provided with a surface coating layer containing a metal element, the metal element including at least one of Zr, Y, Al, W, Nb, La, Mo, Ti, Mg, Ta, Ca, Cs, and Sb.

14. The secondary battery as described in claim 9, characterized in that, The minimum particle size in the particle size frequency distribution curve of the cathode material is 0.2~1μm, and the maximum particle size is 8.6~20μm.

15. The secondary battery as described in claim 14, characterized in that, The lithium nickel cobalt manganese oxide particles include single-crystal particles and / or polycrystalline particles. The minimum particle size of the single-crystal particles is 0.2~0.8μm and the maximum particle size is 8~11.4μm, and / or the minimum particle size of the polycrystalline particles is 0.3~1μm and the maximum particle size is 10~20μm.

16. The secondary battery as described in claim 1, characterized in that, In the cathode material, the molar percentage of cobalt in the transition metal elements is 2-25 mol.

17. The secondary battery as described in claim 1, characterized in that, The positive electrode material also includes at least one of lithium iron phosphate and lithium manganese iron phosphate, and the secondary battery satisfies: a×b / c=0.25~5.

1.

18. The secondary battery as described in claim 1, characterized in that, The porosity of the positive electrode active material layer is 10-30%, and / or the compaction density of the positive electrode active material layer is 3-3.8 g / cm³. 3 ; and or, with a surface density of 200~700 g / m³ 2 .

19. The secondary battery as described in claim 1, characterized in that, The secondary battery also includes a negative electrode sheet, which includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode material.

20. The secondary battery as described in claim 19, characterized in that, The negative electrode material includes silicon, and the mass percentage of silicon in the negative electrode active material layer is 8-20%.

21. The secondary battery as described in claim 19, characterized in that, The secondary battery satisfies: Dμm=1.5~10μm, where D=D1×D2, where D1 is the particle size value corresponding to the highest peak of the particle size frequency distribution curve of the negative electrode material, and D2 is the proportion of the area of ​​the curve part corresponding to the particle size value less than or equal to the highest peak in the particle size frequency distribution curve of the negative electrode material in the total area of ​​the particle size frequency distribution curve.

22. The secondary battery as described in claim 21, characterized in that, The D1 = 5~20μm, and / or, D2 = 0.2~0.

6.

23. The secondary battery as described in claim 21, characterized in that, The secondary battery satisfies the following conditions: D / c = 0.35~7.

7.

24. The secondary battery as described in claim 1, characterized in that, The secondary battery also includes an electrolyte; the electrolyte includes additives, solvents and lithium salts.

25. The secondary battery as described in claim 24, characterized in that, The solvent includes at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate ester solvents.

26. The secondary battery as described in claim 25, characterized in that, The solvent of the electrolyte includes at least one of EC, DMC, EMC, DEC, and EA, and the mass percentage of the solvent in the electrolyte is 70-95%.

27. The secondary battery as described in claim 24, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium difluorosulfonylimide, lithium difluoromethanesulfonylimide, lithium ditrifluoromethanesulfonylimide, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

28. The secondary battery as described in claim 27, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate and lithium difluorosulfonylimide.

29. The secondary battery as described in claim 24, characterized in that, The additive includes at least one of vinylene carbonate, propylene sulfite, vinyl sulfate, and methylene disulfonate, and the total mass percentage of the additive in the electrolyte is 0.1-10%.

30. The secondary battery as described in claim 1, characterized in that, The secondary battery is a cylindrical battery.

31. The secondary battery as described in claim 30, characterized in that, A cylindrical battery includes a casing and a cell. The diameter of the cell is less than or equal to 30 mm and the height is less than or equal to 60 mm. The secondary battery satisfies the following condition: a×b / c=0.4~5.

15.

32. The secondary battery as described in claim 31, characterized in that, The battery cell includes tabs, which are led out from the battery cell body, and the number of tabs is less than or equal to 3.

33. The secondary battery as described in claim 30, characterized in that, The cylindrical battery includes a casing and a cell. The diameter of the cell is greater than or equal to 40 mm and the height is greater than or equal to 80 mm. The secondary battery satisfies the following condition: a×b / c=0.18~4.

29.

34. The secondary battery as described in claim 33, characterized in that, The secondary battery includes a casing and a cell. The cell includes tabs, and the number of tabs is greater than 1. The secondary battery satisfies V1 / V2 = 0.15~0.5, where V1 is the area of ​​the tabs and V2 is the end face area of ​​the cell.

35. The secondary battery as described in claim 1, characterized in that, The secondary battery includes a casing and a cell, the casing includes an aluminum-plastic film, and a = 0.013~0.045.

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