Secondary batteries and battery packs

Abstract

The present application discloses a secondary battery and a battery pack, in which the non-Faraday capacity of the negative electrode sheet and the crystal grain size of the negative electrode active material are controlled within predetermined ranges to provide the negative electrode sheet and the secondary battery with good multiplication performance, and the particle size distribution of the positive electrode active material and the particle size distribution of the negative electrode active material are controlled within predetermined ranges to provide the secondary battery with high multiplication performance and a relatively high energy density.

Description

[Technical Field]

[0001] This application claims priority from a Chinese patent application, application number 202310030037.8, filed with the China Patent Office on January 9, 2023, for the invention "Secondary Battery and Battery Pack," the entire contents of which are incorporated herein by reference.

[0002] The present application relates to the field of battery technology, and more particularly to secondary batteries and battery packs. [Background technology]

[0003] With the rapid development of electric vehicles and digital electronic products, there is a demand for power secondary batteries with higher power density, energy density, and fast charging and discharging capabilities for use in electric vehicles and related electronic products. For secondary batteries such as lithium-ion batteries, increasing the energy density of the lithium-ion battery is a direct and effective way to improve the driving range of the lithium-ion battery.

[0004] High energy density secondary batteries require higher material packing densities and fewer auxiliary materials to provide space for the active materials, while designing secondary batteries for high rate discharge requires relatively low material packing densities, more conductive material, and thicker current collectors to achieve high rate discharge performance, thereby avoiding deterioration of cycle performance due to excessive temperature rise and lithium precipitation.

[0005] Therefore, High cycle and multiplication performance It is necessary to provide a secondary battery having the above. Summary of the Invention

[0006] In a first aspect, the present application provides a secondary battery, the secondary battery including a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material, the negative electrode active material including a carbon material, and the crystal grain size of the negative electrode active material is XS nm. The non-Faraday capacity of the negative electrode sheet is Cdl nF, where 0.05≦Cdl≦10,

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[0007] In some embodiments, 0.01≦XS≦6.

[0008] In some embodiments, the pore volume of the negative electrode active material is α cm 3 / g, and 0.5≦Cdl+10×α≦8.

[0009] In some embodiments, the pore volume of the negative electrode active material is α cm 3 / g, and 0.001≦α≦0.5.

[0010] In some embodiments, the negative electrode active material has a powder resistivity of R Ω·cm at 20 KN, and 0.01≦10R / Cdl≦5.

[0011] In some embodiments, the negative electrode active material has a powder resistivity R Ω·cm at 20 KN, where 0.002≦R≦2.

[0012] In some embodiments, the secondary battery further includes a positive electrode sheet, the positive electrode sheet including a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material.

[0013] In some embodiments, the particle size distribution of the negative electrode active material is A, and the particle size distribution of the positive electrode active material is B, and A and B satisfy at least one of the following characteristics: (a) 0.5≦A≦2.5; (b) 1.0≦B≦5.0; or (c) 0.5≦B / A≦2.5.

[0014] In some embodiments, the negative electrode active material layer has a thickness of C μm, the positive electrode active material layer has a thickness of D μm, and C and D satisfy at least one of the following characteristics: (i) 99≦C≦160; (ii) 80≦D≦130; or (iii) 0.1≦1−(D / C)≦0.5.

[0015] In some embodiments, the surface of the negative electrode active material is coated with a first coating layer, and the thickness of the first coating layer is H1 nm, where 5≦H1≦200 and 10≦Cdl×H1≦250.

[0016] In some embodiments, the surface of the positive electrode active material is coated with a second coating layer, and the thickness of the second coating layer is H2 nm, where 5≦H2≦60.

[0017] In a second aspect, the present application further provides a battery pack, which includes the above secondary battery. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a fitting curve of a scanning speed-current scatter diagram of the negative electrode sheet prepared in Example 1 of the present application. [Figure 2] 1 shows test results for the secondary batteries manufactured in Examples 1 to 20 of the present application. [Figure 3] 1 shows test results for the secondary batteries manufactured in Examples 21 to 30 and Comparative Examples 1 to 4 of the present application. [Figure 4] 1 shows test data results, cycle performance test results, and power supply performance test results for the secondary batteries manufactured in Examples 1 to 20 of the present application. [Figure 5]1 shows test data results, cycle performance test results, and power supply performance test results for the secondary batteries manufactured in Examples 21 to 30 and Comparative Examples 1 to 4 of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present application provides a secondary battery and a battery pack. In order to clarify and clarify the purpose, technical idea, and effects of the present application, the present application will be described in more detail below by giving examples with reference to the drawings. It should be understood that the specific examples described in this specification are merely for the purpose of explaining the present application and are not intended to limit the present application.

[0020] The embodiments of the present application provide a secondary battery and a battery pack including the secondary battery, in which the non-Faraday capacity of the negative electrode sheet is controlled within a predetermined range, and at the same time, the crystal grain size of the negative electrode active material and the non-Faraday capacity of the negative electrode sheet are controlled within a predetermined range, thereby increasing the number of electrochemically active sites on the surface of the negative electrode sheet in the secondary battery, favoring contact between the negative electrode active material and the electrolyte, accelerating the conduction rate of ions and electrons, and reducing the charge transport resistance. At the same time, the actual contact area between the negative electrode sheet and the electrolyte is increased, shortening the distance for ion and electron transport, increasing the number of reactive active sites on the surface of the negative electrode sheet, improving the non-Faraday reaction strength, and allowing the secondary battery to have a smaller charge transfer resistance, thereby significantly improving the multiplier performance of the secondary battery.

[0021] An embodiment of the present application provides a secondary battery, which includes a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and a housing.

[0022] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material, and the negative electrode active material including a carbon material.

[0023] The negative electrode sheet may be a single-sided sheet or a double-sided sheet. When the negative electrode sheet is a single-sided sheet, the negative electrode active material layer is disposed on one surface of the negative electrode current collector. When the negative electrode sheet is a double-sided sheet, the negative electrode active material layer is disposed on both surfaces of the negative electrode current collector. The negative electrode sheet may have a single-sided negative electrode sheet region and a double-sided negative electrode sheet region at the same time.

[0024] In some embodiments, the negative electrode active material includes graphite. In some embodiments, the relationship between the grain size XS of the negative electrode active material and the non-Faraday capacity Cdl of the negative electrode sheet is

number

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[0025] In some embodiments, the relationship between XS and Cdl is:

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[0026] In some embodiments, the relationship between XS and Cdl is:

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[0027] In some embodiments, the non-faradaic capacity of the negative electrode sheet is Cdl nF, and the numerical range of Cdl is 0.05≦Cdl≦10. Specifically, Cdl may be any one of, or a range consisting of any two of, 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, and 10. The faradaic reaction in a secondary battery is a process in which the oxidation state of an active material changes and charge is transferred through a double charge layer through the electrode interface and into the active material. Non-Faradaic reactions are reactions in which charge is accumulated and released by the physical adsorption and desorption of ions on the electrode surface, without charge transfer across the electrode interface. The non-Faradaic capacitance (Cdl) indicates the number of electrochemically active sites on the negative electrode sheet. Within a certain range, increasing Cdl increases the number of electrochemically active sites, which is beneficial for the contact between the negative electrode active material and the electrolyte, accelerating the rate of ionic and electronic conduction, reducing charge transport resistance, and effectively improving the charge multiplier performance of secondary batteries.

[0028] In some embodiments, 0.1≦Cdl≦10, and when the non-Faraday capacity value of the negative electrode sheet satisfies the above range, the overall performance of the secondary battery is further improved.

[0029] In some embodiments, when the non-Faraday capacity of the negative electrode sheet satisfies the above range, 0.5≦Cdl≦9, the internal structure of the negative electrode sheet can be further optimized, and the number of electrochemically active sites on the surface of the negative electrode sheet can be more appropriately adjusted, thereby further improving the overall performance of the secondary battery.

[0030] In some embodiments, when the non-Faraday capacity value of the negative electrode sheet satisfies the above range, 1.5≦Cdl≦8.0, the overall performance of the secondary battery is well-balanced, and the overall performance of the secondary battery can be improved.

[0031] In some embodiments, the negative electrode active material has a crystal grain size of XS nm, where XS is in the range of 0.01≦XS≦6, and specifically, XS may be any of 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, and 6.0, or a range consisting of any two of these numbers. The XRD pattern of the negative electrode active material is refined to obtain the crystal grain size XS, and the XRD measurement conditions are stepwise scanning, a step size of ≦0.02°, a dwell time of ≧2 s, and a scanning range of 10° to 90°.

[0032] The electron conduction characteristics affect the rechargeability of secondary batteries, and the grain size XS can affect the rechargeability of secondary batteries at high voltages, high temperature cycles, and high currents. Research has shown that increasing the charge transfer activation energy and ion diffusion activation energy of the negative electrode active material can partially suppress the reaction between the negative electrode sheet and the electrolyte interface, thereby affecting the properties of the negative electrode active material. Controlling the grain size XS of the negative electrode active material can affect the actual contact area between the negative electrode sheet and the electrolyte, shortening the distance for ion-electron transport, increasing the number of reactive sites on the surface of the negative electrode sheet, improving the strength of non-Faradaic reactions, and reducing the charge transfer resistance, thereby significantly improving the rechargeability of secondary batteries. The grain size can be controlled by various means, such as the particle size of the negative electrode active material, graphitization temperature, graphitization time, and doping modification. Therefore, the relationship between the grain size XS of the non-negative electrode active material in the negative electrode sheet and the non-Faradaic capacity Cdl of the negative electrode sheet can be calculated.

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[0033] In some embodiments, the negative electrode active material has a grain size of XS nm, where XS is in the range of 0.1≦XS≦5.5. When the grain size of the negative electrode active material satisfies this range, the negative electrode active material exhibits excellent high-voltage and high-temperature cycling and high-current capacity, and the actual contact area between the electrolyte and the negative electrode active material granules is in a more suitable range, thereby further improving the overall performance of the secondary battery.

[0034] In some embodiments, the negative electrode active material has a crystal grain size of XS nm, where XS is in the numerical range of 0.2≦XS≦5. When the crystal grain size of the negative electrode active material satisfies the above range, the overall performance of the secondary battery can be further improved.

[0035] In some embodiments, the negative electrode active material has a crystal grain size of XS nm, where XS is in the numerical range of 0.4≦XS≦4.5.

[0036] In some embodiments, the negative electrode active material has a grain size of XS nm, where XS is in the range of 0.4≦XS≦4.2.

[0037] In some embodiments, the negative electrode active material has a grain size of XS nm, where XS is in the range of 0.52≦XS≦3.9.

[0038] In some examples, the pore volume of the negative electrode active material is α cm 3The relationship between the pore volume α cm3 / g and the non-Faraday capacity Cdl nF of the negative electrode sheet is 0.5≦Cdl+10×α≦8, and specifically, the numerical range of Cdl+10×α may be any one of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, and 8.0, or a range consisting of any two of these numbers. 3 / g refers to the total pore volume per unit mass of the porous solid. When Cdl+10×α is within the above range, the negative electrode active material has many pore structures, which improves the contact area between the negative electrode sheet and the electrolyte, further shortens the lithium ion transport path, realizes rapid impregnation of the electrolyte, allows lithium ions to be rapidly absorbed and released on the surface of the negative electrode material, accelerates the reaction kinetics, reduces the polarization on the negative electrode surface, makes the current distribution more uniform, and allows more negative electrode active material to simultaneously absorb Li + This effectively prevents lithium deposition on the negative electrode surface.

[0039] In some embodiments, the pore volume of the negative electrode active material is α cm 3 The relationship between / g and the non-Faraday capacity Cdl nF of the negative electrode sheet is 0.8≦Cdl+10×α≦6.8. When Cdl+10×α satisfies the above range, the negative electrode sheet can provide sufficient electrochemical reaction active sites in the electrochemical process, accelerating the non-Faraday reaction process of the negative electrode and favoring the transfer of electrons and ions between the solid and liquid phases, improving the electrochemical reaction kinetics and further improving the multiplication performance of the material.

[0040] In some embodiments, the pore volume of the negative electrode active material is α cm 3 The relationship between the non-Faraday capacity Cdl nF of the negative electrode sheet and the α / g is 1.1≦Cdl+10×α≦6.2.

[0041] In some embodiments, the pore volume of the negative electrode active material is α cm 3The relationship between / g and the non-Faradaic capacity Cdl nF of the negative electrode sheet is 1.3≦Cdl+10×α≦5.9. When Cdl+10×α satisfies this range, the pore structure of the negative electrode active material can be further optimized, the non-Faradaic reaction of the negative electrode sheet can be strengthened, and the overall performance of the secondary battery can be further improved.

[0042] In some embodiments, the pore volume of the negative electrode active material is α cm 3 / g, and the numerical range of α is 0.001≦α≦0.5, and specifically, α may be any one of 0.001, 0.005, 0.01, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, and 0.5, or a range consisting of any two of these numbers. When the pore volume of the negative electrode active material satisfies the above range, the pore structure of the negative electrode active material granules is increased, which not only increases the contact area between the electrode and the electrolyte, but also shortens the lithium ion transport path, realizes rapid impregnation of the electrolyte, provides a smooth charge transport path at the solid-liquid interface, reduces the diffusion barrier, and allows lithium ions to be rapidly absorbed and released from the surface of the negative electrode material, accelerating the reaction kinetics.

[0043] In some embodiments, the pore volume of the negative electrode active material is α cm 3 / g, and the numerical range of α is 0.005≦α≦0.45.

[0044] In some embodiments, the pore volume of the negative electrode active material is α cm 3 / g, and the numerical range of α is 0.008≦α≦0.42.

[0045] In some embodiments, the pore volume of the negative electrode active material is α cm 3 / g, and the numerical range of α is 0.01≦α≦0.38. When the pore volume of the negative electrode active material satisfies the above range, the pore structure of the negative electrode active material can be further optimized, and the overall performance of the secondary battery can be further improved.

[0046] In some embodiments, the pore volume of the negative electrode active material is α cm 3 / g, and the numerical range of α is 0.05≦α≦0.38.

[0047] In some embodiments, the pore volume of the negative electrode active material is α cm 3 / g, and the numerical range of α is 0.08≦α≦0.38.

[0048] In some embodiments, the pore volume of the negative electrode active material is α cm 3 / g, and the numerical range of α is 0.1≦α≦0.38.

[0049] In some embodiments, the pore volume of the negative electrode active material is α cm 3 / g, and the numerical range of α is 0.12≦α≦0.38. When the pore volume α of the negative electrode active material satisfies the above range, the number of active sites on the surface of the negative electrode sheet increases, which is favorable for lithium ions to exchange charges on the surface of the negative electrode active material, improving the battery's power-saving performance and favoring the diffusion of lithium ions into the negative electrode active material, improving the solid-state conductivity of lithium ions, reducing the resistance of the secondary battery, and extending the service life of the secondary battery.

[0050] In some embodiments, the powder resistivity of the negative electrode active material at 20 KN is R Ω·cm, and in some embodiments, the relationship between R and Cdl is 0.01≦10R / Cdl≦5. Specifically, the numerical range of 10R / Cdl may be any one of 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0, or a range consisting of any two of these numbers. When the negative electrode sheet satisfies the above relationship, the electronic conductivity of the negative electrode active material is relatively high, the interfacial resistance between the electrolyte and the negative electrode active material is low, and the polarization of the secondary battery is small, thereby improving the cycle performance and power supply performance of the secondary battery.

[0051] In some embodiments, the powder resistivity of the negative electrode active material at 20 KN is R Ω·cm, and in some embodiments, the relationship between R and Cdl is 0.12≦10R / Cdl≦4.3.

[0052] In some embodiments, the powder resistivity of the negative electrode active material at 20 KN is R Ω·cm, and in some embodiments, the relationship between R and Cdl is 0.18≦10R / Cdl≦3.9.

[0053] In some embodiments, the powder resistivity R of the negative electrode active material at 20 KN is R Ω·cm, and is 0.002≦R≦2. Specifically, R may be in the range of 0.002, 0.005, 0.01, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.5, or 2.0, or a range consisting of any two of these numbers. When the powder resistivity of the negative electrode active material at 20 KN satisfies the above range, the negative electrode sheet may have better electrical conductivity, which may affect the performance of the negative electrode sheet to some extent and further improve the overall performance of the secondary battery.

[0054] In some embodiments, the powder resistivity of the negative electrode active material at 20 KN is R Ω·cm, and 0.008≦R≦1.8.

[0055] In some embodiments, the powder resistivity of the negative electrode active material at 20 KN is R Ω·cm, where 0.011≦R≦1.4.

[0056] In some embodiments, the powder resistivity of the negative electrode active material at 20 KN is R Ω·cm, and 0.021≦R≦1.4.

[0057] The powder resistivity R of the negative electrode active material can be measured by the four-point probe method of GB / T 39978-2021.

[0058] In some embodiments, the particle size distribution of the negative electrode active material is A, and in some embodiments, 0.5≦A≦2.5. Specifically, A may be in the range of 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0, 2.3, or 2.5, or a range consisting of any two of these numbers.

[0059] In some embodiments, the particle size distribution of the negative electrode active material is A, and in some embodiments, 0.7≦A≦2.

[0060] In some embodiments, the particle size distribution of the negative electrode active material is A, and in some embodiments, 0.7≦A≦1.9. The particle size distribution value is (D99−D10) / D50, where D99 represents the particle size corresponding to a cumulative particle size volume distribution percentage of the active material granules of 99%, D10 represents the particle size corresponding to a cumulative particle size volume distribution percentage of the active material granules of 10%, and D50 represents the particle size corresponding to a cumulative particle size volume distribution percentage of the active material granules of 50%. The particle size distribution characterizes the dispersion of various particle size components. A smaller particle size distribution indicates a more concentrated particle size distribution, which improves the dispersion of powder materials during the stirring process, reduces settling of the slurry, and results in relatively good uniformity and stability of the resulting slurry. This effectively controls the uniformity of the electrode sheet coating weight, thereby enhancing the electrode sheet stability and controlling the non-Faraday reaction process, improving the transport efficiency of lithium ions between the positive and negative electrode sheets and improving the battery's power rating. A larger particle size distribution indicates a broader particle size distribution, which leads to smaller particles of negative active material being more likely to be absorbed between larger particles of negative active material, resulting in too dense a particle gap between the negative active material particles, which affects the absorption and desorption of lithium ions and reduces the cycle and dynamic performance of the negative electrode sheet. It also makes slurry preparation more difficult.

[0061] When the particle size distribution A of the negative electrode active material in the negative electrode sheet satisfies the above range, the stability of the negative electrode sheet is enhanced, and the power-reducing performance of the secondary battery is improved.

[0062] The particle size distribution A of the negative electrode active material can be calculated by measuring the D99, D10, and D50 of the negative electrode active material using a laser granulometer. Specifically, the negative electrode active material can be obtained from the negative electrode sheet as follows: The secondary battery is discharged to a lower limit voltage at a constant current of 0.04 C and disassembled to obtain a negative electrode sheet. The negative electrode sheet is then immersed and washed in a DMC (dimethyl carbonate) solution, rinsed several times with deionized water, the upper layer solution is removed, the lower layer solution is left to dry, and the test sample is obtained by heat-treating the negative electrode sheet in an argon atmosphere at 800°C for 2 hours.

[0063] The thickness of the negative electrode active material layer is C μm, and in some embodiments, C is in the range of 99≦C≦160. Specifically, C may be any one of 99, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, and 160, or any two of these values. When the thickness of the negative electrode active material layer falls within this range, the tortuosity and length of the lithium ion and electron transfer pathways are small, which enhances the diffusion ability of lithium ions and electrons in the negative electrode sheet, thereby further improving the battery's power rating. Furthermore, the thickness of the negative electrode active material layer may also affect the adhesive strength between the negative electrode active material layer and the negative electrode current collector, thereby affecting the performance of the negative electrode sheet.

[0064] In some embodiments, the thickness of the negative electrode active material layer is C μm, where C is in the range of 116≦C≦155.

[0065] In some embodiments, the thickness of the negative electrode active material layer is C μm, and the numerical range of C is 116≦C≦149. When the thickness C of the negative electrode active material layer satisfies the above range, the diffusion ability of lithium ions in the negative electrode active material layer is enhanced, and the secondary battery has relatively high rated power and energy density.

[0066] In some embodiments, the negative electrode active material layer is disposed on one surface of the negative electrode current collector.

[0067] In some embodiments, the negative electrode active material layers are disposed on two surfaces of the negative electrode current collector.

[0068] When the negative electrode sheet has both an active material layer region on one side and an active material layer region on both sides, the thickness of the negative electrode sheet is the thickness of the negative electrode active material layer region on both sides. The thickness of the negative electrode active material layer can be measured with a vernier caliper.

[0069] In some embodiments, a first coating layer is disposed on a surface of the negative electrode active material, and the first coating layer has a thickness H1 nm. In some embodiments, the relationship between H1 and Cdl is 10≦Cdl×H1≦250. Specifically, the numerical range of Cdl×H1 may be any one of 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, and 250, or a range consisting of any two of these numbers.

[0070] In some embodiments, a first coating layer is disposed on the surface of the negative electrode active material, and the first coating layer has a thickness H1 nm, and in some embodiments, the relationship between H1 and Cdl is 20≦Cdl×H1≦230.

[0071] In some embodiments, a first coating layer is disposed on the surface of the negative electrode active material, and the first coating layer has a thickness H1 nm, and in some embodiments, the relationship between H1 and Cdl is 31≦Cdl×H1≦210.

[0072] In some embodiments, the thickness of the first coating layer is H1 nm, and 5≦H1≦200. Specifically, the numerical range of H1 may be any one of 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, and 200, or a range consisting of any two of these numbers.

[0073] In some embodiments, the first coating layer has a thickness H1 nm, where 11≦H1≦180.

[0074] In some embodiments, the thickness of the first coating layer is H1 nm, where 21≦H1≦165.

[0075] In some embodiments, the first coating layer is a carbon coating layer, which is formed by a heat treatment process such as sintering any one of organic resin, asphalt, citric acid, glucose, and hard carbon.

[0076] The manufacturing of secondary batteries involves a heat treatment process during which the negative electrode active material is subjected to varying degrees of centrifugal pressure, and the action of external forces from various directions can cause internal defects in the negative electrode active material, such as a relatively loose interior and prone to collapse. By uniformly coating the negative electrode active material granules with a first coating layer, the resulting negative electrode active material has relatively strong structural stability, and the outer coating structure formed by the first coating layer eliminates internal defects, improves the diffusion of lithium ions therein, and reduces material expansion, thereby improving the secondary battery's electrochemical performance, such as its charge / discharge rate and cycle life. Furthermore, the carbon coating layer can provide more active sites, thereby reducing the transport resistance of lithium ions between the surface and transport channels of the negative electrode active material, favoring the absorption and release of lithium ions, lowering the resistance of the negative electrode active material and improving its liquid absorption capacity, thereby improving charge / discharge performance.

[0077] In some embodiments, referring to FIG. 1, a test method for the non-Faraday capacitance value Cdl of a negative electrode sheet includes the following steps:

[0078] In step S1, the non-Faraday potential range confirmation step, the negative electrode sheet is assembled into a half cell (abbreviated as button cell) and subjected to a cyclic voltammogram (CV) test, where the voltage range is 0.005 V to 3.0 V, the scan rate is 0.1 mV / s to 1 mV / s, and the non-Faraday potential range is the flat section of the curve, i.e., the range of 2 V to 3 V.

[0079] In step S2, the non-Faraday range cathodic scan step, a potential range of 2 V to 3 V determined in step S1 is selected to perform a linear scan voltammogram (LSV) test, scanning from high potential to low potential, and collecting a voltage-current curve. Here, the selected potential range is 2.6 V to 2.7 V, and the scan rate is 0.05 mV / s to 5 mV / s.

[0080] Furthermore, select the median U value in the potential range of 2.6 V to 2.7 V at a scan rate of 0.1 mV / s, and obtain the corresponding current value with U = 2.65. Select the current value corresponding to the median U value at each different scan rate within the scan rate range of 0.055 mV / s to 5 mV / s, and obtain a scatter diagram of scan rate vs. current density.

[0081] In step S3, the non-Faraday capacitance calculation step, a linear function is obtained by fitting based on the scan rate-current density scatter diagram collected in step S2, and the slope K of the linear function is the non-Faraday capacitance value Cdl of the negative electrode sheet in the cathode scan direction.

[0082] The button cell was assembled as follows: The resulting negative electrode sheet was dried, cut into small circular sheets, weighed, and then transferred to a vacuum oven where it was dried at 100°C for 8 hours. The cells were then transferred to a glove box filled with argon gas for assembly. The assembly method is standard in the art. The non-Faraday potential range was determined using a cyclic Voltammogram curve, and the current value was measured using a linear scan Voltammogram curve within the potential range. The non-Faraday capacitance value Cdl was calculated by fitting.

[0083] In some embodiments, the negative electrode current collector includes, but is not limited to, a metal foil, a metal cylinder, a metal tape roll, a metal sheet, a metal thin film, a metal sheet mesh, a metal stamping, a metal foam, etc. In some embodiments, the negative electrode current collector is a metal foil. In some embodiments, the negative electrode current collector is an aluminum foil or a copper foil. As used herein, the term "copper foil" includes copper alloy foil.

[0084] In some embodiments, the negative electrode current collector is a composite current collector, and the composite current collector comprises a conductive resin.

[0085] In some embodiments, the negative electrode current collector is a polypropylene film coated with copper by vapor deposition.

[0086] In some embodiments, the negative electrode active material layer includes a negative electrode active material, a conductive agent, an adhesive, and a dispersant.

[0087] In some embodiments, the negative electrode active material comprises one or more of natural graphite, artificial graphite, hard carbon, soft carbon, and mesocarbon microspheres.

[0088] In some embodiments, a method for producing an active negative electrode material includes the following steps.

[0089] The raw materials are pre-processed by grinding and premixing, resulting in a particle size of 8μm to 10μm. The ground material is then graphitized at high temperatures of 2800℃ to 3000℃ under a protective atmosphere, with the temperature maintained at 3000℃ for 30 to 60 hours. The protective atmosphere is inert gas. The product is then polished and shaped for 4 to 12 hours to smooth the surface of the granules, resulting in a negative electrode active material with a particle size D50 of 10μm to 20μm and a crystal grain size XS nm of 0.01nm to 6nm.

[0090] In some embodiments, the conductive agent comprises one or more of carbon black, graphite, carbon fiber, carbon nanotubes, or graphene.

[0091] The adhesive improves adhesion between the negative electrode active materials. There are no particular restrictions on the type of adhesive, and it is sufficient if it is a material that is stable against the electrolyte solution and the solvent used in producing the electrode.

[0092] In some embodiments, the adhesive comprises sodium carboxymethyl cellulose and styrene butadiene rubber.

[0093] In some embodiments, the adhesive comprises sodium carboxymethyl cellulose, oxidized starch, and styrene butadiene rubber.

[0094] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0095] The positive electrode sheet is a single-sided sheet or a double-sided sheet. When the positive electrode sheet is a single-sided sheet, the positive electrode active material layer is disposed on one surface of the positive electrode current collector. When the positive electrode sheet is a double-sided sheet, the positive electrode active material layer is disposed on both surfaces of the positive electrode current collector. The positive electrode sheet may simultaneously have a positive electrode active material layer region on one side and a positive electrode active material layer region on both sides.

[0096] When a positive electrode sheet has a positive electrode active material layer region on one side and a positive electrode active material layer region on both sides at the same time, the thickness of the positive electrode sheet is the thickness of the positive electrode active material layer regions on both sides.

[0097] In some embodiments, the particle size distribution of the positive electrode active material is B, and 1.0≦B≦5.0. Specifically, B may be in the range of 1.0, 1.2, 1.5, 1.8, 2.0, 2.3, 2.5, 2.8, 3.0, 3.2, 3.5, 3.8, 4.0, 4.2, 4.5, 4.8, or 5.0, or a range consisting of any two of these numbers.

[0098] In some embodiments, the particle size distribution of the positive electrode active material is B, where 1.3≦B≦4.5.

[0099] In some embodiments, the particle size distribution of the positive electrode active material is B, where 1.9≦B≦3.9.

[0100] In some embodiments, the particle size distribution of the positive electrode active material is B, where 2.1≦B≦3.9.

[0101] The particle size distribution value is (D99-D10) / D50, where D99 is the particle size corresponding to 99% of the cumulative particle size volume distribution of the active material granules, D10 is the particle size corresponding to 10% of the cumulative particle size volume distribution of the active material granules, and D50 is the particle size corresponding to 50% of the cumulative particle size volume distribution of the active material granules. The particle size distribution is used to characterize the degree of dispersion of various particle size components. A smaller particle size distribution indicates a more concentrated particle size distribution, which improves the dispersion effect of the powder material during the stirring process, reduces slurry settling, and results in relatively good uniformity and stability of the resulting slurry. This effectively controls the uniformity of the coating weight of the positive electrode sheet, thereby enhancing the stability of the positive electrode sheet and controlling non-Faraday reaction processes, thereby improving the transport efficiency of lithium ions between the positive and negative electrode sheets and improving the battery's power rating. An excessively large particle size distribution indicates that the particle size distribution is too broad, and small granules of the positive electrode active material are easily absorbed between large granules of the positive electrode active material, resulting in excessively dense spaces between the granules of the positive electrode active material, which affects the absorption and release of lithium ions and reduces the cycle performance and kinetic performance of the positive electrode sheet, and also makes it difficult to prepare a slurry.

[0102] When the particle size distribution A of the positive electrode active material in the positive electrode sheet satisfies the above range, the stability of the positive electrode sheet is enhanced, and the power-reducing performance of the secondary battery is improved.

[0103] The relationship between the particle size distribution A of the negative electrode active material and the particle size distribution B of the positive electrode active material is 0.1≦A / B≦2.5, and specifically, the numerical range of the ratio A / B may be any one of 0.1, 0.2, 0.3, 0.5, 0.7, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0, 2.3, and 2.5, or a range consisting of any two of these numbers. When the particle size distribution A of the negative electrode active material and the particle size distribution B of the positive electrode active material satisfy the above range, the negative electrode sheet and the positive electrode sheet have high tap density, and both the positive electrode sheet and the negative electrode sheet have high electron and lithium ion transport performance. The electron and lithium ion transport efficiencies in the positive electrode sheet and the negative electrode sheet are better matched, and the secondary battery has high multiplier performance and relatively high charge / discharge performance, while also having a relatively high energy density.

[0104] In some embodiments, the relationship between particle size distribution A of the negative electrode active material and particle size distribution B of the positive electrode active material is 0.3≦A / B≦2.2.

[0105] In some embodiments, the relationship between particle size distribution A of the negative electrode active material and particle size distribution B of the positive electrode active material is 0.5≦A / B≦1.9.

[0106] The particle size distribution B of the positive electrode active material in the positive electrode sheet can be calculated directly by measuring the particle size of the positive electrode active material using a laser granulometer. Alternatively, a secondary battery can be discharged at a constant current of 0.04 C to a lower voltage limit, disassembled to obtain a positive electrode sheet, immersed in a DMC (dimethyl carbonate) solution, washed, baked in a muffle furnace at 400°C for 5 hours to remove the powder, washed with deionized water 2-3 times, and left to stand after each wash to remove the supernatant liquid. The lower layer solution can be left to dry to obtain a test sample.

[0107] In some embodiments, the thickness of the positive electrode active material layer is D μm, where D is in the range of 80≦D≦130, and specifically, D may be in the range of 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, or 130, or a range consisting of any two of these numbers. When positive electrode active material layers are disposed on both sides of the positive electrode current collector, D μm is the total thickness of the two positive electrode active material layers.

[0108] When the thickness of the positive electrode active material layer satisfies the above range, the tortuosity and length of the lithium ion and electron transfer paths are within appropriate ranges, lithium ions and electrons have excellent diffusion ability in the positive electrode sheet, and the secondary battery has good multiplication performance and can ensure the specific capacity and energy density of the secondary battery within appropriate ranges.In addition, the binding strength between the positive electrode active material layer and the positive electrode current collector is within an appropriate range, allowing the positive electrode sheet performance to be fully exhibited.

[0109] In some embodiments, the thickness of the positive electrode active material layer is D μm, and D is in the numerical range of 91≦D≦125. When the thickness D of the positive electrode active material layer satisfies the above range, the diffusion ability of lithium ions in the positive electrode active material layer is enhanced, and the secondary battery has relatively high foldability and energy density.

[0110] In some embodiments, the thickness of the positive electrode active material layer is D μm, where D is in the range of 101≦D≦125.

[0111] In some embodiments, the relationship between the thickness C μm of the negative electrode active material layer and the thickness D μm of the positive electrode active material layer is 0.1≦1−(D / C)≦0.5, and specifically, the numerical range of 1−(D / C) may be any one of 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, and 0.5, or a range consisting of any two of these numbers. When the thickness C of the negative electrode active material layer and the thickness D of the positive electrode active material layer satisfy the above range, the electrolyte can be sufficiently diffused in the positive electrode sheet and the negative electrode sheet, reducing the ohmic resistance of the electrode sheet and preventing lithium deposition on the negative electrode sheet, improving the dynamic performance of the secondary battery and ensuring a high energy density.

[0112] In some embodiments, the relationship between the thickness C μm of the negative electrode active material layer and the thickness D μm of the positive electrode active material layer is 0.13≦1−(D / C)≦0.45.

[0113] In some embodiments, the relationship between the thickness C μm of the negative electrode active material layer and the thickness D μm of the positive electrode active material layer is 0.17≦1−(D / C)≦0.40.

[0114] A second coating layer is disposed on the surface of the positive electrode active material, and the second coating layer has a thickness H2 nm, and in some embodiments, 5≦H2≦60. Specifically, H2 may be in the range of 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60, or a range consisting of any two of these numbers.

[0115] In some embodiments, the second coating layer comprises a coating element, the coating element including at least one of F, Al, Mg, Ti, and Zr.

[0116] In some embodiments, the second coating layer is selected from organic polymers, inorganic metal fluorides, oxides, and lithiates.

[0117] By applying a coating modification to the positive electrode active material, it is possible to suppress the occurrence of side reactions between the positive electrode active material and the electrolyte, prevent chemical erosion of the electrolyte, reduce the elution of transition metals, improve the structural stability of the positive electrode active material layer, improve the conductivity of the positive electrode active material layer, and further improve the cycle stability and power rating performance of the secondary battery.

[0118] The positive electrode active material layer may be one or more layers. Each layer in the multi-layer positive electrode active material may contain the same or different positive electrode active material. The positive electrode active material is any material that can reversibly absorb and release metal ions, such as lithium ions.

[0119] In some embodiments, the active cathode material includes a ternary material, which may include lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide.

[0120] In some embodiments, the cathode active material comprises lithium nickel cobalt manganese oxide, wherein the molar ratio of elemental nickel to elemental cobalt to elemental manganese is 1, and the content of elemental nickel is 0.5 or more.

[0121] In some embodiments, the cathode active material comprises lithium nickel cobalt manganese oxide, wherein the molar ratio of elemental nickel to elemental cobalt to elemental manganese is 1, and the content of elemental nickel is 0.85 or less.

[0122] In some embodiments, the active cathode material includes doping and / or coating elements.

[0123] The positive electrode active material layer further includes a positive electrode conductive agent and a positive electrode adhesive.

[0124] The type of positive electrode conductive agent is not particularly limited, and any known conductive agent can be used. Positive electrode conductive agents include, but are not limited to, carbon materials such as natural graphite, artificial graphite, acetylene black, and acicular coke, carbon nanotubes, and graphene. The positive electrode conductive agents may be used alone or in any combination.

[0125] The type of solvent used to form the positive electrode slurry is not limited, as long as it can dissolve or disperse the positive electrode active material, positive electrode conductive agent, and positive electrode adhesive. Examples of solvents used to form the positive electrode slurry include aqueous and organic solvents. The type of positive electrode current collector is not particularly limited, as long as it is a known material suitable for use as a positive electrode current collector. Examples of positive electrode current collectors include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; carbon materials such as carbon cloth and carbon paper; and composite materials composed of a polymer and a metal layer. In some embodiments, the positive electrode current collector is a metal material. In some embodiments, the positive electrode current collector is aluminum.

[0126] The form of the positive electrode current collector is not particularly limited. In some embodiments, the positive electrode current collector is a metal foil. In some embodiments, the thickness of the metal foil is greater than 1 μm, greater than 3 μm, or greater than 5 μm. In some embodiments, the thickness of the metal foil is less than 1 mm, less than 50 μm, or less than 20 μm. In some embodiments, the thickness of the metal foil is within a range consisting of any two of the above numbers.

[0127] The electrolyte includes a lithium salt, an organic solvent, and an additive.

[0128] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium organoborate, lithium perchlorate, and sulfonimide-type lithium salt. The amount of the lithium salt is not particularly limited as long as it does not impair the effects of the present application.

[0129] In some embodiments, the organic solvent comprises a cyclic carbonate and a linear carbonate.

[0130] Specifically, the organic solvent is a mixed solvent made of one or more of ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), propylene carbonate (PC), and methyl ethyl carbonate (EMC).

[0131] In some embodiments, the additive comprises at least one of vinylene carbonate, 1,3-propanesulfonate, lithium difluorophosphate, fluoroethylene carbonate (FEC), lithium difluorooxalate borate, tripropynyl phosphate, triallyl phosphate, and triallyl isocyanurate.

[0132] To prevent short circuits, a separator is usually placed between the positive electrode and the negative electrode, and in this case, the electrolyte of the present invention is usually used by permeating the separator.

[0133] Furthermore, an embodiment of the present application further provides a battery pack, which includes a secondary battery. Typical applications of the battery pack include, but are not limited to, electric toys, electric tools, battery-powered vehicles, electric vehicles, energy storage devices, ships, spacecraft, etc.

[0134] Hereinafter, the method for manufacturing a secondary battery provided by the present invention will be described based on specific examples.

[0135] Example 1

[0136] The positive electrode sheet was produced as follows.

[0137] Ternary cathode active material LiNi 0.8 Co 0.1 Mn 0.1O2 (NCM811) was added to an aluminum chloride solution, and aqueous ammonia was added to stabilize the solution's pH. After hydrolysis for 8 hours, the solution was filtered, washed repeatedly with deionized water and alcohol, dried, and then heat-treated in a horizontal furnace at 600°C for 5 hours to obtain an aluminum trioxide-coated cathode active material with a thickness of 30 nm. The coated ternary cathode active material NCM811 was calcined at 85°C for 8 hours, thoroughly mixed with conductive carbon black Super P and adhesive polyvinylidene fluoride (PVDF) in a 96:2:2 weight ratio, and then N-methylpyrrolidone (NMP) was added and the mixture was dispersed at high speed for 4 hours, scraped, and bottom-rotated. NMP was added again to adjust the slurry viscosity and defoamed. The final viscosity of the slurry was in the range of 2500-5000 mPa.s. The produced positive electrode slurry is uniformly coated on both sides of an aluminum foil positive electrode current collector, then baked and dried at 120°C, and then rolled and cut to obtain a positive electrode sheet, with the thickness D μm of the positive electrode active material layer being 90 μm.

[0138] The negative electrode sheet was produced as follows.

[0139] The manufacturing process for the negative electrode active material includes the following steps: Petroleum coke is crushed with abrasive rolls and pre-mixed, resulting in a particle size of 9 μm after crushing. The crushed product is then subjected to high-temperature graphitization at 2900°C in a protective atmosphere, and then held at 3000°C for 48 hours in an argon protective atmosphere. The product is then polished and shaped in a continuous shaping system for 8 hours to smooth and flatten the surface of the product granules, resulting in artificial graphite as the negative electrode active material with a particle size D50 of 13 μm and a grain size XS of 0.5 nm.

[0140] The negative electrode active material, artificial graphite, and the first coating layer, asphalt, were placed in a thermal reactor, stirred and mixed for 6 hours, and then heat-treated at 1200°C for 2 hours under inert gas protection to obtain a negative electrode active material with a first coating layer, the thickness of which was 77 nm. The negative electrode active material, conductive carbon black Super P, adhesive sodium carboxymethylcellulose, starch oxide, and styrene butadiene rubber were mixed in a weight ratio of 96.5:1.2:1.1:0.2:1.0 to prepare a negative electrode slurry. First, graphite, carbon black, and 80% sodium carboxymethylcellulose were mixed at low speed to achieve a uniform mixture. Then, the remaining 20% ​​sodium carboxymethylcellulose, 50% oxidized starch, and deionized water were added and stirred at high speed for 2 hours. Next, 50% oxidized starch and styrene-butadiene rubber were added and stirred at low speed. The viscosity of the slurry was then adjusted to 2500 mPa·s to 4000 mPa·s and the mixture was passed through a 200-mesh sieve to produce a negative electrode slurry. The resulting negative electrode slurry was then uniformly coated onto one or both sides of a copper foil negative electrode current collector. The negative electrode current collector was then baked and dried in five stages at 90°C to 110°C, rolled, and cut to obtain a negative electrode sheet with a negative electrode active material layer thickness (C μm) of 110 μm.

[0141] The electrolyte solution was prepared as follows.

[0142] Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (EDC) are mixed in a volume ratio of 1:1:1, and then 1 mol / L of LiPF6 is added and mixed uniformly to prepare an electrolyte.

[0143] The secondary battery is manufactured as follows.

[0144] The negative and positive electrode sheets prepared using the above steps are dried and then wound together with a separator using a winding machine to produce an electric core, and the positive electrode aluminum tab and the negative electrode copper-nickel plated tab are welded to the electric core. The welded electric core is then packaged in a pre-punched aluminum plastic film, and the separator is made of PP film. After filling and chemically forming the battery, a secondary battery is produced.

[0145] The non-Faraday capacitance Cdl test is as follows.

[0146] Step 1: The secondary battery prepared in Example 1 is disassembled in a glove box, and the sheet in the negative electrode overhang region is obtained. The sheet is immersed in a dimethyl carbonate (DMC) solution and cut. Then, a button half-cell is assembled using the cut negative electrode sheet and a metallic lithium sheet. Alternatively, a button half-cell is assembled using the cut negative electrode sheet that is not assembled into a battery and a metallic lithium piece.

[0147] Step 2: Perform a CV test on the button half-cell in the voltage range of 0.005 V to 3.0 V, with a scan rate of 0.1 mV / s, ensuring that the non-Faraday potential range is 2.5 V to 2.6 V.

[0148] Step 3: Next, perform LSV test from 2.6V to 2.5V, with the scan rates of 0.1mV / s, 0.2mV / s, 0.5mV / s, 1mV / s, and 2mV / s, respectively. Select the middle value of the potential range, 2.55V, to obtain the corresponding current values ​​of 1.96E-05A, 1.83E-05A, 1.71E-05A, 1.58E-05A, and 1.36E-05A.

[0149] Step 4: Based on the scan rate and current values ​​obtained in Step 3, a scatter plot of scan rate versus current density shown in Figure 1 was created and fitted to obtain a linear function. The slope of the linear function was -2.86E-06, i.e., the non-Faraday capacitance value Cdl of the negative electrode sheet in the cathode scan direction was 2.86 nF.

[0150] The non-Faraday capacitance (Cdl) can be evaluated by measuring the non-Faraday curves of linear scan voltammograms (LSVs) at different scan rates, i.e., the linear change in current with the scan rate. This plays an important role in characterizing the number of active sites. Increasing Cdl within a certain range increases the number of electrochemically active sites, which favors contact between the negative electrode active material and the electrolyte, accelerates ionic and electronic conduction, reduces charge transport resistance, and effectively improves the charge multiplier of secondary batteries.

[0151] Here, the negative electrode sheet overhang region refers to the portion of the negative electrode sheet that protrudes from the positive electrode sheet in the length and width directions.

[0152] Examples 2 to 16

[0153] A secondary battery is manufactured using the method described in Example 1, and the particle size of the crushed petroleum coke, the temperature of the graphitization treatment, the temperature rise temperature, the heat retention time, and the grinding and shaping time are controlled to make the characteristics of the negative electrode sheet and the negative electrode active material as shown in Figures 2 to 5.

[0154] Examples 17 to 30

[0155] A secondary battery was manufactured using the method described in Example 1, and the parameters of the positive electrode sheet and the negative electrode sheet were set to the values ​​shown in Figures 2 to 5 by controlling the particle size after crushing the petroleum coke, the temperature of the graphitization treatment, the temperature rise temperature, the heat retention time, and the grinding and shaping time.

[0156] Comparative Examples 1 to 4

[0157] A secondary battery was manufactured using the method described in Example 1, with the differences shown in FIGS.

[0158] The performance test process of the manufactured secondary battery is as follows.

[0159] The crystal grain size XS nm of the negative electrode active material is tested.

[0160] X-ray diffraction measurements using CuKα radiation were performed on the negative electrode active materials produced in the examples and comparative examples. The (002) peaks at diffraction angles 2θ in the range of 25° to 27°, which belong to the negative electrode active materials, were analyzed, and the crystal grain sizes of the negative electrode active materials were calculated using the Schrödinger equation. The test results are shown in Figures 2 and 3.

[0161] Pore ​​volume of negative electrode active material α cm 3 / g is tested.

[0162] The shapes of the negative electrode active materials prepared in the Examples and Comparative Examples were observed using a scanning electron microscope (SEM). The pore volumes of the negative active materials prepared in the Examples and Comparative Examples were measured using a porosity measuring analyzer (Bell Japan Inc., Belsorp-II mini) by a BET 6-point method based on nitrogen gas adsorption flow spectroscopy. The test results are shown in Figures 2 and 3.

[0163] Test the powder resistivity R Ω·cm of the negative electrode active material.

[0164] The negative active material powders prepared in the examples and comparative examples were dried and weighed. The powder was then measured using a powder resistivity tester (models Suzhou Jingge ST2722 or Sansi UTM7305). The dried powder sample was placed in the mold / sample chamber of the resistivity tester, with a depth of 20 mm and a cross-sectional area of ​​1 cm. 2 Then, the applied pressure was gradually increased, and the data was manually collected and the corresponding powder resistivity test results under different pressure points were recorded. The test results are shown in Figures 2 and 3.

[0165] The cycle performance test of the secondary battery was carried out as follows.

[0166] The secondary battery was charged and discharged at 25°C. Specifically, it was charged at a constant current of 1C, allowed to stand for 30 minutes, and then discharged at a constant current of 1C. The first discharge capacity was recorded, and the battery was cycled through 1000 1C / 1C charge-discharge cycles. The discharge capacity of the secondary battery at the 1000th cycle was recorded, and the discharge capacity of the battery at the 1000th cycle was divided by the discharge capacity of the first cycle to obtain the capacity retention rate of the secondary battery after 1000 charge-discharge cycles. The test results are shown in Figures 4 and 5.

[0167] The multiplication performance test for secondary batteries is as follows.

[0168] The secondary battery was subjected to high-power charging at 25° C. Specifically, it was discharged at a constant current of 1 C, allowed to stand for 10 minutes, and then charged at a constant current of 4 C. The first discharge capacity was recorded, and this charge capacity was divided by the first discharge capacity of the lithium-ion battery charged and discharged at 1 C / 1 C at 25° C. to obtain the 4 C power performance of the secondary battery. The test results are shown in Figures 4 and 5.

[0169] To facilitate understanding of the present application, the present application provides data relating to Examples 1 to 30 and Comparative Examples 1 to 4, as shown in Figures 2 to 5. Those skilled in the art should understand that these examples are merely intended to aid in understanding the present application and are not intended to limit the present application.

[0170] The non-Faraday capacity Cdl of the negative electrode sheet of a secondary battery affects the number of electrochemically active sites and the contact between the negative electrode active material and the electrolyte, and the non-Faraday capacity Cdl of the negative electrode sheet also affects the ion and electron conduction rate and charge transfer resistance, thereby effectively affecting the rechargeability of the secondary battery. The crystal grain size XS of the negative electrode active material is a factor that affects cycle performance at high voltages and temperatures and capacity at high currents. The crystal grain size XS of the negative electrode active material mainly affects the actual contact area between the electrode and the electrolyte, affecting the ion and electron transport distance and the number of electrochemically active sites, which in turn affects the non-Faraday reaction strength and charge transfer resistance of the negative electrode sheet and affects the rechargeability of the secondary battery.

[0171] Therefore, as shown in FIGS. 2 to 5, when the secondary batteries provided by Examples 1 to 16 are compared with the secondary battery provided by Comparative Example 1, the non-Faraday capacitance value of the negative electrode sheet is 0.05 nF to 10 nF, and the non-Faraday capacitance value is within the range of 0.05 nF to 10 nF.

number

[0172] Referring to Comparative Example 1, the non-Faraday capacity value Cdl of the secondary battery provided by Comparative Example 1 is significantly different from that of the crystal grain size XS.

number

number

[0173] Comparing Example 11 and Example 16, the non-Faraday capacitance value of the negative electrode sheet was 0.05 nF to 10 nF,

number

[0174] With reference to Examples 5 and 10, the secondary battery manufactured in Example 5 had a Cdl+10×α value of 9.5, which exceeded the upper limit of 0.5≦Cdl+10×α≦8 specified in the present application, and the cycle performance at 25°C of the secondary battery manufactured in Example 5 was 87% and the 4C multiplier performance was 85%. The secondary battery manufactured in Example 10 had a Cdl+10×α value of 5.9, which was within the range of 0.5≦Cdl+10×α≦8 specified in the present application, and the cycle performance at 25°C of the secondary battery manufactured in Example 10 was 90% and the 4C multiplier performance was 89%.

[0175] Therefore, referring to FIGS. 4 and 5, the secondary batteries manufactured in Examples 21 to 23 and Example 21 had B / A=2.5, which reached the upper limit. This indicates that the particle size distribution of the positive electrode active material and the particle size distribution of the negative electrode active material in the secondary batteries are significantly different. The particle size distribution is wide, and small granules of the positive electrode active material are easily absorbed between large granules of the positive electrode active material. As a result, the active material granules become too dense, which affects the absorption and release of lithium ions and the cycle performance and kinetic performance of the secondary batteries. The cycle performance and 4C multiplier performance at 25°C of the secondary batteries manufactured in Examples 22 and 23 were superior to those of Example 21.

[0176] Furthermore, when the thickness C of the negative electrode active material layer and the thickness D of the positive electrode active material layer are within the range of 0.1≦1−(D / C)≦0.5, the electrolyte can diffuse sufficiently in the positive and negative electrode sheets, thereby reducing the ohmic resistance of the electrode sheets, preventing lithium deposition on the negative electrode sheet, and improving kinetic performance while maintaining high energy density.

[0177] 4 and 5, the negative electrode active material layer thickness C of the secondary battery prepared in Example 24 was 160 μm, which is the upper limit of the range C defined in the present application, and the positive electrode active material layer thickness D was 80 μm, which is the lower limit of the range D defined in the present application, so 1-(D / C)=0.5. The relatively thick negative electrode active material layer thickness C increases the tortuosity and length of the lithium ion and electron transport pathways, reducing the diffusion ability of lithium ions and electrons in the positive electrode sheet and reducing the foldability of the negative electrode sheet. When the active material is bound to at least one surface of the current collector by a binder, a too thick active material layer reduces the binding strength between the active material layer and the current collector, affecting the performance of the electrode sheet. As a result, the secondary battery prepared in Example 24 had a cycle performance of 84% at 25°C and a 4C foldability of 84%.

[0178] With reference to Example 15 and Example 1, in Example 15, a second coating layer was not applied to the surface of the positive electrode active material, i.e., H2 was 0, and the secondary battery fabricated in Example 15 had a B / A ratio of 1.5. Therefore, the cycle performance at 25°C of the secondary battery fabricated in Example 15 was 82% and the 4C multiplier performance was 85%. Comparing Example 1 and Example 30, in Example 30, a first coating layer was not applied to the surface of the negative electrode active material, i.e., H1 was 0. Therefore, the cycle performance at 25°C of the secondary battery fabricated in Example 30 was 80% and the 4C multiplier performance was 80%. Therefore, providing a coating layer on the negative electrode active material can improve the cycle performance and multiplier performance of the secondary battery to some extent.

[0179] Although the present application has described in detail the secondary battery and battery pack according to the embodiments of the present application, and the present application has used specific examples to explain the principles and embodiments of the present application, the explanation of the above embodiments is intended to facilitate understanding of the technical solutions of the present application and their core ideas. Those skilled in the art should understand that some of the technical features described in the above embodiments may be modified or replaced with equivalents, and that such modifications and replacements do not deviate from the essence of the corresponding technical solutions and the scope of the technical solutions of each embodiment of the present application.

Claims

1. a negative electrode sheet, a positive electrode sheet, and an electrolyte solution, the negative electrode sheet including a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material, the negative electrode active material including a carbon material, The negative electrode active material has a crystal grain size of XS nm, The non-Faraday capacity of the negative electrode sheet is Cdl mF, where 0.05≦Cdl≦10; [0011] That is, Secondary battery.

2. 0.01≦XS≦6; The secondary battery according to claim 1 .

3. The pore volume of the negative electrode active material is α cm / g, and 0.001≦α≦0.

5. The secondary battery according to claim 1 .

4. The negative electrode active material has a powder resistivity of R Ω·cm at 20 KN, and 0.01≦10R / Cdl≦5. The secondary battery according to claim 1 .

5. The negative electrode active material has a powder resistivity of R Ω·cm at 20 KN, where 0.002≦R≦2. The secondary battery according to claim 1 .

6. the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material, The particle size distribution of the negative electrode active material is A, and 0.5≦A≦2.5 is satisfied; The particle size distribution value is (D99-D10) / D50, where D99 indicates the particle size corresponding to the cumulative particle size volume distribution percentage of the active material granules being 99%, D10 indicates the particle size corresponding to the cumulative particle size volume distribution percentage of the active material granules being 10%, and D50 indicates the particle size corresponding to the cumulative particle size volume distribution percentage of the active material granules being 50%. The secondary battery according to claim 1 .

7. The particle size distribution of the positive electrode active material is B, and 1.0≦B≦5.0 is satisfied; The particle size distribution value is (D99-D10) / D50, where D99 indicates the particle size corresponding to the cumulative particle size volume distribution percentage of the active material granules being 99%, D10 indicates the particle size corresponding to the cumulative particle size volume distribution percentage of the active material granules being 10%, and D50 indicates the particle size corresponding to the cumulative particle size volume distribution percentage of the active material granules being 50%. The secondary battery according to claim 6.

8. 0.5≦B / A≦2.5; The secondary battery according to claim 7 .

9. The thickness of the negative electrode active material layer is C μm, and 99 μm≦C≦160 μm. The secondary battery according to claim 6.

10. The thickness of the positive electrode active material layer is D μm, and 80 μm≦D≦130 μm. The secondary battery according to claim 9.

11. 0.1≦1−(D / C)≦0.5; The secondary battery according to claim 10.

12. The surface of the negative electrode active material is coated with a first coating layer, and the thickness of the first coating layer is H1 nm, where 5≦H1≦200 and 10≦Cdl×H1≦250. The secondary battery according to claim 1 .

13. The surface of the positive electrode active material is coated with a second coating layer, and the thickness of the second coating layer is H2 nm, where 5≦H2≦60 nm. The secondary battery according to claim 6.

14. The secondary battery according to any one of claims 1 to 13, Battery pack.

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