A secondary battery and an electric device

Abstract

The application provides a secondary battery and a power utilization device, wherein the secondary battery comprises an electrode assembly and an electrolyte, the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, the positive electrode sheet comprises a positive electrode active material layer, the positive electrode active material layer comprises a positive electrode active material, the negative electrode sheet comprises a negative electrode active material layer, and the negative electrode active material layer comprises a negative electrode active material; the coating weight of the positive electrode active material layer is W z , the coating weight of the negative electrode active material layer is W f , W z and W f satisfy the following conditions: 1.6W f ≤W z ≤2.2W f , 3.25 mg / cm 2 ≤W f ≤5.84 mg / cm 2 ; the Dv99 of the positive electrode active material is 27 μm to 33 μm, and the Dv99 of the negative electrode active material is 23 μm to 28 μm; the electrolyte comprises an organic solvent, a lithium salt and a nitrile additive, the organic solvent comprises a chain carboxylic acid ester, the mass percentage of the chain carboxylic acid ester is 6% to 56% based on the mass of the electrolyte, and the mass percentage of the nitrile additive is 0.01% to 10%. The secondary battery has good cycle kinetics and high-temperature stability.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a secondary battery and an electrical device. Background Technology

[0002] Secondary batteries (such as lithium-ion batteries) possess characteristics such as high specific energy, high operating voltage, low self-discharge rate, small size, and light weight, and are widely used in various fields such as energy storage, portable electronic devices, and electric vehicles. With the continuous iterative development of consumer lithium-ion batteries in recent years, the market demand for their charging speed has been increasing, and the charging rate of lithium-ion batteries has been continuously improving. Consumer demand has gradually increased from 1C to over 5C. However, it is difficult to simultaneously achieve high charging rates (5C ≤ 15C) and high-temperature (≥60℃) stability in lithium-ion batteries. Therefore, how to improve the cycle dynamics performance of super-fast charging lithium-ion batteries while also ensuring their high-temperature stability has become a pressing technical problem for those skilled in the art. Summary of the Invention

[0003] The purpose of this application is to provide a secondary battery that improves the cycle dynamics performance of the secondary battery while taking into account its high-temperature stability, and to provide an electrical device using the secondary battery.

[0004] It should be noted that while this application uses lithium-ion batteries as an example of secondary batteries to explain the invention, the secondary battery in this application is not limited to lithium-ion batteries; it can also be used with sodium-ion batteries and other secondary batteries. The specific technical solution is as follows:

[0005] The first aspect of this application provides a secondary battery, wherein the secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The positive electrode includes a positive active material layer, and the positive active material layer includes a positive active material. The negative electrode includes a negative active material layer, and the negative active material layer includes a negative active material. The coating weight of the positive active material layer is W. z The coating weight of the negative electrode active material layer is W. f W z and W f The following conditions must be met: 1.6W f ≤W z ≤2.2W f 3.25 mg / cm 2 ≤W f ≤5.84mg / cm 2The Dv99 of the positive electrode active material is 27 μm to 33 μm, and the Dv99 of the negative electrode active material is 23 μm to 28 μm. The electrolyte includes an organic solvent, a lithium salt, and nitrile additives. The organic solvent includes a chain carboxylic acid ester, and the chain carboxylic acid ester has a mass percentage content of 6% to 56% based on the mass of the electrolyte. The nitrile additives have a mass percentage content of 0.01% to 10%. The use of lower coating weights for the positive and negative active material layers reduces their thickness and increases their porosity, thereby reducing ohmic and concentration polarization of the electrodes, shortening the lithium-ion transport distance within the electrodes, and thus improving the charging rate of the secondary battery. The selection of small-particle-size positive and negative active materials enhances their surface activity, shortens the lithium-ion transport distance within the particles, and reduces concentration polarization in the secondary battery. Simultaneously, the addition of chain carboxylic esters within the content range specified in this application to the electrolyte ensures its low viscosity, meeting the requirements for rapid lithium-ion transport during super-fast charging. The selection of the coating weight of the positive and negative electrode active material layers, the particle size of the positive and negative electrode active material, and the electrolyte composition enables the secondary battery to have high kinetics to meet the requirements of super-fast charging. However, the high kinetic design of the secondary battery brings the risk of high-temperature stability. Small-particle, highly active materials are prone to side reactions with chain carboxylic acid esters in the electrolyte, especially at high temperatures. The side reactions will cause violent gas generation inside the lithium-ion battery, resulting in the deterioration of the high-temperature storage performance and thermal performance of the secondary battery. To address this, nitrile additives within the content range of this application are added to the electrolyte to protect the positive and negative electrode plates while maintaining the high kinetics of the secondary battery, reduce the side reactions between the electrolyte and the positive and negative electrode plates, and improve the high-temperature stability of the secondary battery. Therefore, by combining the coating weight of the positive and negative active material layers, the Dv99 of the positive and negative active materials, and the composition and content of the electrolyte, this application achieves a good synergistic effect among the coating weight of the positive and negative active material layers, the Dv99 of the positive and negative active materials, and the electrolyte, which can improve the cycle dynamics performance of the secondary battery while taking into account the high-temperature stability of the secondary battery.

[0006] In one embodiment of this application, 6.49 mg / cm 2 ≤W z ≤11.69mg / cm 2 This application, by adjusting the coating weight of the positive electrode active material layer within the scope of this application, enables the secondary battery to possess good cycle dynamics performance while maintaining high-temperature stability.

[0007] In one embodiment of this application, 3.90 mg / cm 2 ≤W f ≤5.19mg / cm2 And / or, 7.80 mg / cm 2 ≤W z ≤10.38mg / cm 2 W z and / or W f Within the aforementioned range, the coating weight range of the positive electrode active material layer and / or the negative electrode active material layer is more favorable, which is beneficial for the secondary battery to further improve its cycle dynamics performance while taking into account high temperature stability.

[0008] In one embodiment of this application, the Dv99 of the positive electrode active material is 28 μm to 31 μm, and / or the Dv99 of the negative electrode active material is 24 μm to 26 μm. Controlling the Dv99 of the positive electrode active material and / or the Dv99 of the negative electrode active material within the above ranges provides a more favorable range, which is beneficial for further improving the cycle kinetics performance and high-temperature stability of the secondary battery.

[0009] In one embodiment of this application, the Dv50 of the positive electrode active material is 10 μm to 15 μm, and the Dv50 of the negative electrode active material is 7 μm to 12 μm. Controlling the Dv50 of the positive and negative electrode active materials within these ranges is beneficial for enabling the secondary battery to achieve high energy density while maintaining good cycle kinetics and high-temperature stability.

[0010] In one embodiment of this application, the negative electrode active material includes at least one of carbon-based, silicon-based, or tin-based materials. The carbon-based material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, or mesophase carbon microspheres. The silicon-based material includes at least one of elemental silicon, silicon-carbon materials, or silicon-oxygen materials. The tin-based material includes at least one of elemental tin, tin alloys, or tin oxides. The above-mentioned negative electrode active materials possess high surface activity, enabling the secondary battery to exhibit good cycle kinetic performance while maintaining high-temperature stability.

[0011] In one embodiment of this application, the peak intensity ratio I of the d-peak to the g-peak in Raman spectroscopy of the carbon-based material is... d / I g Satisfy: 0.1≤I d / I g ≤1.0. This will satisfy the above condition I. d / I g The application of valuable carbon-based materials in secondary batteries can help improve their cycle dynamics performance while maintaining good high-temperature stability.

[0012] In one embodiment of this application, the positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. The above-mentioned positive electrode active materials possess high surface activity, enabling the secondary battery to exhibit good cycle kinetic performance while maintaining high-temperature stability.

[0013] In one embodiment of this application, the positive electrode active material further includes a non-metallic element, which includes at least one selected from fluorine, phosphorus, boron, chlorine, silicon, or sulfur. The inclusion of such non-metallic elements in the positive electrode active material further improves its stability. These non-metallic elements can be added to the positive electrode active material through bulk doping or surface coating.

[0014] In one embodiment of this application, the chain carboxylic acid ester includes at least one of methyl formate, methyl acetate, ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, n-propyl propionate, isopropyl propionate, methyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl n-butyrate, n-propyl n-butyrate, propyl isobutyrate, n-pentyl n-butyrate, n-pentyl isobutyrate, n-butyl isobutyrate, or n-pentyl valerate. The above-mentioned chain carboxylic acid esters have high electrical conductivity and low viscosity, facilitating lithium-ion transport. Using these types of chain carboxylic acid esters enables the secondary battery to have good cycle kinetics performance and high-temperature stability.

[0015] In one embodiment of this application, the mass percentage of the chain carboxylic acid ester is 18% to 40% based on the mass of the electrolyte. By controlling the mass percentage of the chain carboxylic acid ester within the above range, lithium ions exhibit a faster transport rate in the electrolyte, thereby further improving the cycle dynamics performance of the secondary battery while maintaining good high-temperature stability.

[0016] In one embodiment of this application, the nitrile additive includes at least one selected from malononitrile, butadionitrile, glutaronitrile, adiponitrile, heptanonitrile, octadionitrile, sebaconitol, 3,3'-oxodipropionitrile, hex-2-enadionitrile, trans-butenedionitrile, 2-pentenedionitrile, methylglutaronitrile, 4-cyanohepanilide, (Z)-but-2-enadionitrile, 2,2,3,3-tetrafluorobutadionitrile, ethylene glycol bis(propionitrile) ether, 1,3,5-pentanetricarboxylon, 1,3,6-hexanetricarboxylon, 1,2,6-hexanetricarboxylon, 1,2,3-tris(2-cyanoethoxy)propane, 1,1,3,3-propanetetracarboxylon, 2,2'-(1,4-phenylene)dipropionitrile, 1,1,5,5-pentanetetracarboxylon, 1,1,4,4-butanetetracarboxylon, or 1,1,6,6-hexanetetracarboxylon. Using the above-mentioned types of nitrile additives can help improve the high-temperature stability of secondary batteries, which already have good cycle dynamics performance.

[0017] In one embodiment of this application, the mass percentage of nitrile additives is 5% to 8% based on the mass of the electrolyte. Controlling the mass percentage of nitrile additives within this range is beneficial for further improving the high-temperature stability of the secondary battery, building upon its already good cycle kinetic performance.

[0018] In one embodiment of this application, the organic solvent further includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, or tetrahydrofuran; the mass percentage of the organic solvent is 60% to 80% based on the mass of the electrolyte. Further selection of the above-mentioned organic solvents and controlling the mass percentage of the organic solvent within the above range is beneficial for enabling the secondary battery to have good cycle dynamics performance and high-temperature stability.

[0019] A second aspect of this application provides an electrical device comprising the secondary battery described in any of the foregoing embodiments. Therefore, the electrical device exhibits good performance.

[0020] The beneficial effects of this application are:

[0021] This application provides a secondary battery and an electrical device. The secondary battery, by adjusting the coating weight of the negative electrode active material layer, the coating weight relationship between the positive and negative electrode active material layers, the Dv99 of the positive and negative electrode active materials, and the composition and content of the electrolyte within the scope of this application, achieves a good synergistic effect among these factors. This results in shorter transport paths for lithium ions within the positive / negative electrode active materials, lower transport tortuosity, and shorter transport distances within the positive / negative electrode sheets. This reduces concentration polarization and electrochemical polarization in the secondary battery, protects the positive and negative electrode sheets, and reduces side reactions between the electrolyte and the positive / negative electrode sheets. Therefore, it improves the cycle dynamics performance of the secondary battery while also ensuring its high-temperature stability. Attached Figure Description

[0022] The accompanying drawings, which are provided to further understand this application and constitute a part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0023] Figure 1 The image shows the Raman spectrum of the negative electrode in Example 3-3. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0025] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries, and can also be used for secondary batteries such as sodium-ion batteries.

[0026] The first aspect of this application provides a secondary battery, wherein the secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The positive electrode includes a positive active material layer, and the positive active material layer includes a positive active material. The negative electrode includes a negative active material layer, and the negative active material layer includes a negative active material. The coating weight of the positive active material layer is W. z The coating weight of the negative electrode active material layer is W. f W z and W f The following conditions must be met: 1.6Wf ≤W z ≤2.2W f 3.25 mg / cm 2 ≤W f ≤5.84mg / cm 2 The Dv99 of the positive electrode active material is 27 μm to 33 μm, and the Dv99 of the negative electrode active material is 23 μm to 28 μm. The electrolyte includes an organic solvent, a lithium salt, and nitrile additives. The organic solvent includes a chain carboxylic acid ester, and the chain carboxylic acid ester has a mass percentage content of 6% to 56% based on the mass of the electrolyte. The nitrile additives have a mass percentage content of 0.01% to 10%.

[0027] For example, W f 3.25 mg / cm 2 3.5 mg / cm 2 3.75 mg / cm 2 4mg / cm 2 4.25 mg / cm 2 4.5 mg / cm 2 4.75 mg / cm 2 5mg / cm 2 5.25 mg / cm 2 5.5 mg / cm 2 5.84 mg / cm 2 Or any value between any two of the above ranges. The coating weight of the positive electrode active material layer is less than 1.6W. f The coating weight of the negative electrode active material layer is too large compared to the coating weight of the positive electrode active material layer. When the potential of the secondary battery is reached, the delithiation rate of the positive electrode increases significantly, resulting in a very high actual potential of the positive electrode and easy structural damage. The positive electrode decays rapidly, causing the secondary battery to fail to cycle normally; the coating weight of the positive electrode active material layer is greater than 2.2W. f If the coating weight of the positive electrode active material layer is too large compared to the negative electrode active material layer, excessive lithium ions will be released. The negative electrode cannot fully accept all the lithium ions released from the positive electrode, and these lithium ions cannot be properly intercalated into the negative electrode sheet, leading to lithium plating and affecting the cycle kinetics performance of the secondary battery. The coating weight of the negative electrode active material layer should be less than 3.25 mg / cm³. 2 The energy density of secondary batteries decreases, their lifespan is reduced, and they are difficult to meet the process requirements for secondary batteries; the coating weight of the negative electrode active material layer is greater than 5.84 mg / cm³. 2 As the transport distance of lithium ions inside the positive and / or negative electrode increases, the impedance of the secondary battery increases.

[0028] For example, the Dv99 of the positive electrode active material can be 27μm, 28μm, 29μm, 30μm, 31μm, 32μm, 33μm, or any value between any two of the above ranges. If the Dv99 of the positive electrode active material is less than 27μm, it indicates that the particle size of the positive electrode active material is too small. During the preparation of the positive electrode slurry, the particles are prone to agglomeration, making it extremely difficult for the positive electrode active material to be uniformly dispersed in the slurry. This results in uneven particle distribution within the formed positive electrode active material layer, affecting the processing stability of the positive electrode sheet and causing uneven coating during the coating process. Furthermore, the specific surface area of ​​the positive electrode active material particles will be too large, leading to uneven adhesion between the particles and the substrate. Increased electrolyte contact interfaces exacerbate side reactions, especially in the high-kinetic electrolyte system of super-fast charging, where side reactions become more severe, accelerating electrolyte consumption and the formation of by-products, thus deteriorating the cycle performance and high-temperature stability of the secondary battery. Furthermore, a Dv99 greater than 33 μm in the positive electrode active material results in an excessively long transport path for lithium ions within the positive electrode particles and excessive tortuosity during transport within the positive electrode sheet. This leads to excessive concentration polarization within the secondary battery, increasing its internal resistance and reducing its cycle kinetic performance.

[0029] For example, the Dv99 of the negative electrode active material can be 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, or any value within any two of these ranges. If the Dv99 of the negative electrode active material is less than 23μm, it indicates that the particle size of the negative electrode active material is too small. During the preparation of the negative electrode slurry, the particles are prone to agglomeration, making it extremely difficult for the negative electrode active material to be uniformly dispersed in the slurry. This results in uneven particle distribution within the formed negative electrode active material layer, affecting the processing stability of the negative electrode sheet and causing uneven coating during the coating process. Furthermore, the specific surface area of ​​the negative electrode active material particles will be too large, leading to uneven particle size distribution. Increased electrolyte contact interfaces exacerbate side reactions, especially in the high-kinetic electrolyte system of super-fast charging, where side reactions become more severe, accelerating electrolyte consumption and the formation of side reaction products, thus deteriorating the cycle performance and high-temperature stability of the secondary battery. Furthermore, a negative electrode active material with a Dv99 greater than 28 μm results in an excessively long lithium-ion transport path within the particles and excessive tortuosity during transport within the negative electrode sheet. This leads to excessive concentration polarization within the secondary battery, increasing its internal resistance and reducing its cycle kinetic performance.

[0030] For example, based on the mass of the electrolyte, the mass percentage of the chain carboxylic acid ester can be 6%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 56%, or any value within any two of the above ranges. Chain carboxylic acid esters possess high conductivity, low viscosity, and facilitate lithium-ion transport, giving the electrolyte high kinetic properties. If the mass percentage of the chain carboxylic acid ester is less than 6%, the amount in the electrolyte is too small to fully utilize its properties; if the mass percentage of the chain carboxylic acid ester is greater than 56%, the amount in the electrolyte is too large, resulting in a decrease in the content of lithium salts and additives. Insufficient lithium salt content will affect the charge-discharge performance of the secondary battery, and insufficient additive content will hinder the additives from functioning effectively, affecting the corresponding performance of the secondary battery and the additives.

[0031] For example, based on the mass of the electrolyte, the mass percentage of nitrile additives can be 0.01%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value within any two of the above ranges. Nitrile additives can complex with transition metal ions in the positive electrode active material to form a protective positive electrode electrolyte interface film (CEI) on the surface of the positive electrode, improving the structural stability of the positive electrode and reducing side reactions between the positive electrode active material and the electrolyte, thereby improving the high-temperature stability of the secondary battery. If the mass percentage of nitrile additives in the electrolyte is less than 0.01%, the amount is too small to exert its effect, and the improvement on the high-temperature stability of the secondary battery is not significant; if the mass percentage of nitrile additives in the electrolyte is greater than 10%, the amount is too high, which will reduce the mass percentage of other components in the electrolyte, such as organic solvents, lithium salts, and other additives, affecting the performance of the secondary battery.

[0032] Overall, this application improves the surface activity of both positive and negative electrode active materials by controlling the Dv99 of the positive and negative electrode active materials within the aforementioned range. This shortens the lithium-ion transport path within the positive / negative electrode active materials and reduces the transport tortuosity within the positive / negative electrode sheets, thereby reducing concentration polarization in the secondary battery and resulting in good cycle kinetics. Furthermore, by controlling the coating weight of the negative electrode active material layer and the relationship between the coating weights of the positive and negative electrode active material layers within the aforementioned range, using lower coating weights for the positive and negative electrode active material layers reduces their thickness and increases their porosity. This, in turn, reduces ohmic and concentration polarization in the positive and negative electrode sheets, shortens the transport distance of lithium ions and electrons within the positive and negative electrode sheets, and ultimately improves the charging rate of the secondary battery. This application controls the mass percentage of chain carboxylic acid esters and nitrile additives in the electrolyte within the aforementioned range, resulting in an electrolyte with low viscosity. This allows for faster lithium-ion transport within the electrolyte, reducing electrochemical and concentration polarization in the secondary battery, lowering its impedance, and reducing the charging temperature rise and charging time during super-fast charging. Consequently, the secondary battery exhibits excellent cycle dynamics. Furthermore, by maintaining a suitable content of nitrile additives, the positive and negative electrode plates are protected while preserving high kinetics, reducing side reactions between the electrolyte and the positive and negative electrode plates, thereby improving the high-temperature stability of the secondary battery. This application combines the coating weight of the negative electrode active material layer, the relationship between the coating weights of the positive and negative electrode active material layers, the Dv99 of the positive and negative electrode active materials, and the composition and content of the electrolyte to achieve a good synergistic effect among these factors. This allows for the improvement of the cycle dynamics performance of the secondary battery while also ensuring its high-temperature stability.

[0033] In this application, Dv99 refers to the particle size that, from the smallest particle size side, reaches 99% of the total volumetric particle size distribution. The aforementioned "particles" in this application can be particles of positive electrode active material or particles of negative electrode active material. This application does not impose any particular limitation on the method of controlling the Dv99 of the positive and negative electrode active materials, as long as the purpose of this application can be achieved. For example, it can be achieved by directly purchasing positive and negative electrode active materials whose Dv99 falls within the scope of this application, or by methods such as crushing, grinding, or ball milling.

[0034] In one embodiment of this application, 6.49 mg / cm 2 ≤Wz ≤11.69mg / cm 2 For example, W z It is 6.49 mg / cm³ 2 7mg / cm 2 7.5 mg / cm 2 8mg / cm 2 8.5 mg / cm 2 9mg / cm 2 9.5 mg / cm 2 10mg / cm 2 10.5 mg / cm 2 11mg / cm 2 11.69 mg / cm 2 Or any value between any two of the above ranges. By adjusting the coating weight of the positive electrode active material layer within the range of this application, this application can shorten the transport distance of lithium ions and electrons on the positive electrode sheet, which is beneficial to reducing the ohmic polarization and concentration polarization of the secondary battery, thereby reducing the impedance of the secondary battery and enabling the secondary battery to have good cycle dynamics performance while taking into account high temperature stability.

[0035] In one embodiment of this application, 3.90 mg / cm 2 ≤W f ≤5.19mg / cm 2 For example, W f 3.90 mg / cm 2 4.00 mg / cm 2 4.25 mg / cm 2 4.50 mg / cm 2 4.75 mg / cm 2 5.00 mg / cm 2 5.19 mg / cm 2 Or any value between any two of the above ranges. W f Within the aforementioned range, the coating weight of the negative electrode active material layer is more optimized, which is beneficial for the secondary battery to further improve its cycle dynamics performance while taking into account high-temperature stability.

[0036] In one embodiment of this application, 7.80 mg / cm 2 ≤W z ≤10.38mg / cm 2 For example, W z It is 7.80 mg / cm 2 8.20 mg / cm 2 8.50 mg / cm 2 8.80 mg / cm 29.00 mg / cm 2 9.25 mg / cm 2 9.50 mg / cm 2 9.70 mg / cm 2 10.00 mg / cm 2 10.38 mg / cm 2 Or any value between any two of the above ranges. W z Within the aforementioned range, the coating weight of the positive electrode active material layer is more optimal, which is beneficial for the secondary battery to further improve its cycle dynamics performance while taking into account high-temperature stability.

[0037] In one embodiment of this application, 3.90 mg / cm 2 ≤W f ≤5.19mg / cm 2 7.80 mg / cm 2 ≤W z ≤10.38mg / cm 2 For example, W f 3.90 mg / cm 2 4.00 mg / cm 2 4.25 mg / cm 2 4.50 mg / cm 2 4.75 mg / cm 2 5.00 mg / cm 2 5.19 mg / cm 2 Or any value between any two of the above ranges. For example, W z It is 7.80 mg / cm 2 8.20 mg / cm 2 8.50 mg / cm 2 8.80 mg / cm 2 9.00 mg / cm 2 9.25 mg / cm 2 9.50 mg / cm 2 9.70 mg / cm 2 10.00 mg / cm 2 10.38 mg / cm 2 Or any value between any two of the above ranges. W z and W f Within the aforementioned range, the coating weight ranges for both the positive and negative electrode active material layers are optimized, which is beneficial for the secondary battery to further improve its cycle dynamics performance while maintaining high-temperature stability.

[0038] In one embodiment of this application, the Dv99 of the positive electrode active material is between 28 μm and 31 μm. For example, the Dv99 of the positive electrode active material is 28 μm, 29 μm, 30 μm, 31 μm, or any value between any two of the above ranges. Controlling the Dv99 of the positive electrode active material within the above range results in a more optimal Dv99 range, which is beneficial for further improving the cycle kinetics performance and high-temperature stability of the secondary battery.

[0039] In one embodiment of this application, the Dv99 of the negative electrode active material is between 24 μm and 26 μm. For example, the Dv99 of the negative electrode active material is 24 μm, 25 μm, 26 μm, or any value between any two of the above ranges. Regulating the Dv99 of the negative electrode active material within the above range results in a more optimal Dv99 range, which is beneficial for further improving the cycle kinetics performance and high-temperature stability of the secondary battery.

[0040] In one embodiment of this application, the Dv99 of the positive electrode active material is 28 μm to 31 μm, and the Dv99 of the negative electrode active material is 24 μm to 26 μm. For example, the Dv99 of the positive electrode active material is 28 μm, 29 μm, 30 μm, 31 μm, or any value between any two of the above ranges. The Dv99 of the negative electrode active material is 24 μm, 25 μm, 26 μm, or any value between any two of the above ranges. By controlling the Dv99 of the positive and negative electrode active materials within the above ranges, a more optimal range of Dv99 for both materials is beneficial for further improving the cycle kinetics performance and high-temperature stability of the secondary battery.

[0041] In one embodiment of this application, the Dv50 of the positive electrode active material is 10 μm to 15 μm, and the Dv50 of the negative electrode active material is 7 μm to 12 μm. For example, the Dv50 of the positive electrode active material is 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or any value between any two of the above ranges. The Dv50 of the negative electrode active material is 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or any value between any two of the above ranges. By controlling the Dv50 of the positive and negative active materials within the aforementioned range, the risk of agglomeration of the positive and negative active materials in the positive slurry is reduced. This allows both the positive and negative active materials to perform their functions effectively. Furthermore, by controlling the thickness of the positive and negative active material layers within a suitable range, the risk of energy density loss due to increased thickness is reduced. This is beneficial for the secondary battery to have high energy density while maintaining good cycle dynamics and high-temperature stability.

[0042] In this application, Dv50 represents the particle size that, from the smallest particle size side, reaches 50% of the total volumetric particle size distribution. The aforementioned "particles" in this application can be either positive or negative electrode active materials. This application does not impose any particular restrictions on the method of controlling the Dv50 of the positive or negative electrode active materials, as long as the purpose of this application can be achieved. For example, it can be achieved by directly purchasing positive or negative electrode active materials with Dv50 within the scope of this application, or by methods such as crushing, grinding, or ball milling.

[0043] In one embodiment of this application, the negative electrode active material includes at least one of carbon-based, silicon-based, or tin-based materials. The carbon-based material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, or mesophase carbon microspheres. The silicon-based material includes at least one of elemental silicon, silicon-carbon materials, or silicon-oxygen materials. The tin-based material includes at least one of elemental tin, tin alloys, or tin oxides. The above-mentioned negative electrode active materials possess high surface activity. When applied in secondary batteries, they can increase the active sites for lithium ion insertion / extraction, reduce the electrochemical polarization of the secondary battery, thereby reducing the impedance of the secondary battery and enabling it to exhibit good cycle kinetic performance while maintaining high-temperature stability.

[0044] In one embodiment of this application, the peak intensity ratio I of the d-peak to the g-peak in Raman spectroscopy of the carbon-based material is... d / I g Satisfy: 0.1≤I d / I g ≤1.0. For example, I d / I g The value is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or any value within any two of the above ranges. This indicates that the carbon-based material contains amorphous carbon on its surface. The presence of amorphous carbon on the surface of the carbon-based material can enhance its electrochemical activity, facilitate lithium-ion insertion during secondary battery cycling, reduce electrochemical polarization, thereby lowering the internal impedance of the secondary battery and improving its cycle kinetics performance. The value will satisfy the above I... d / I g The application of valuable carbon-based materials in secondary batteries can help improve their cycle dynamics performance while maintaining good high-temperature stability.

[0045] In this application, the d peak represents the Raman spectrum of carbon-based material particles with a shift range of 1300 cm⁻¹. -1 Up to 1400cm -1 The peak g is the shifted peak in the Raman spectrum of carbon-based material particles, with a shift range of 1530 cm⁻¹. -1 Up to 1630cm-1 The peak.

[0046] This application relates to I d / I g There are no particular restrictions on the method of adjusting the value, as long as it achieves the purpose of this application. For example, commercially available carbon-based materials with different contents of amorphous carbon on their surface can be selected, and the I value of the carbon-based material can be determined by combining it with the "Raman test" test method in this application. d / I g Select the desired I d / I g Carbon-based materials.

[0047] This application does not impose any particular limitation on the preparation method of carbon-based materials, as long as it can achieve the purpose of this application. For example, the preparation method of carbon-based materials may include, but is not limited to: mixing carbon-based materials and amorphous carbon evenly, heating to 500°C to 1500°C and holding at that temperature for 10 to 20 hours to obtain carbon-based materials with amorphous carbon coated on the surface.

[0048] In one embodiment of this application, the positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. The chemical formula of the aforementioned "lithium-rich manganese-based material" is LiMnO·LiMO, where M may include Ni, Co, or Mn. These types of positive electrode active materials possess high surface activity. When applied in secondary batteries, they can increase the active sites for lithium ion insertion / extraction, reduce the electrochemical polarization of the secondary battery, thereby reducing the impedance of the secondary battery and enabling it to exhibit good cycle kinetic performance while maintaining high-temperature stability.

[0049] In one embodiment of this application, the positive electrode active material further includes non-metallic elements, including at least one selected from fluorine, phosphorus, boron, chlorine, silicon, or sulfur. This application does not impose any particular limitation on the content of non-metallic elements in the positive electrode active material, as long as the purpose of this application is achieved. In one embodiment, based on the mass of the positive electrode active material, the mass percentage content of the non-metallic elements is 0.1% to 10%. For example, the mass percentage content of the non-metallic elements is 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value between any two of the above ranges. Including the above-mentioned types of non-metallic elements in the positive electrode active material can further improve the stability of the positive electrode active material.

[0050] In one embodiment of this application, the chain carboxylic acid ester includes at least one of methyl formate, methyl acetate, ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, n-propyl propionate, isopropyl propionate, methyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl n-butyrate, n-propyl n-butyrate, propyl isobutyrate, n-pentyl n-butyrate, n-pentyl isobutyrate, n-butyl isobutyrate, or n-pentyl valerate. The above-mentioned chain carboxylic acid esters have high electrical conductivity and low viscosity, facilitating lithium-ion transport. Using these types of chain carboxylic acid esters enables the secondary battery to have good cycle kinetics performance and high-temperature stability.

[0051] In one embodiment of this application, the mass percentage of the chain carboxylic acid ester is 18% to 40% based on the mass of the electrolyte. For example, the mass percentage of the chain carboxylic acid ester is 18%, 20%, 25%, 30%, 35%, 40%, or any value between any two of the above ranges, based on the mass of the electrolyte. By controlling the mass percentage of the chain carboxylic acid ester within the above range, lithium ions exhibit a faster transport rate in the electrolyte, thereby further improving the cycle dynamics performance of the secondary battery while maintaining good high-temperature stability.

[0052] In one embodiment of this application, the nitrile additive includes at least one selected from malononitrile, butadionitrile, glutaronitrile, adiponitrile, heptanonitrile, octadionitrile, sebaconitol, 3,3'-oxodipropionitrile, hex-2-enadionitrile, trans-butenedionitrile, 2-pentenedionitrile, methylglutaronitrile, 4-cyanohepanilide, (Z)-but-2-enadionitrile, 2,2,3,3-tetrafluorobutadionitrile, ethylene glycol bis(propionitrile) ether, 1,3,5-pentanetricarboxylon, 1,3,6-hexanetricarboxylon, 1,2,6-hexanetricarboxylon, 1,2,3-tris(2-cyanoethoxy)propane, 1,1,3,3-propanetetracarboxylon, 2,2'-(1,4-phenylene)dipropionitrile, 1,1,5,5-pentanetetracarboxylon, 1,1,4,4-butanetetracarboxylon, or 1,1,6,6-hexanetetracarboxylon. Using the above-mentioned types of nitrile additives can help improve the high-temperature stability of secondary batteries, which already have good cycle dynamics performance.

[0053] In one embodiment of this application, the mass percentage of the nitrile additive is 5% to 8% based on the mass of the electrolyte. For example, the mass percentage of the nitrile additive is 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or any value between any two of the above ranges, based on the mass of the electrolyte. Controlling the mass percentage of the nitrile additive within the above range is beneficial for further improving the high-temperature stability of the secondary battery, while maintaining good cycle kinetic performance.

[0054] In one embodiment of this application, the organic solvent further includes at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, or tetrahydrofuran; the mass percentage of the organic solvent is 60% to 80% based on the mass of the electrolyte. For example, the mass percentage of the organic solvent is 60%, 64%, 67%, 70%, 73%, 78%, 80%, or any value between any two of the above ranges, based on the mass of the electrolyte. The aforementioned organic solvents exhibit good stability at high temperatures and fast lithium-ion transport at room temperature. Adding such organic solvents to the electrolyte can further improve the high-temperature stability, cycle dynamics, charging speed, and temperature rise of the secondary battery. Controlling the mass percentage of the organic solvent within the above range is beneficial for improving the solubility of additives and lithium salts, resulting in a lower viscosity and higher conductivity in the electrolyte, which is conducive to the migration of lithium ions in the electrolyte, thereby giving the secondary battery good cycle dynamics and high-temperature stability.

[0055] In one embodiment of this application, the mass percentage of lithium salt is 10% to 20% based on the mass of the electrolyte. For example, the mass percentage of lithium salt is 10%, 12%, 14%, 16%, 18%, 20%, or any value between any two of the above ranges. By controlling the mass percentage of lithium salt within the above range, the lithium salt has high solubility in the electrolyte, resulting in high conductivity of the electrolyte, thereby improving the cycle dynamics and high-temperature stability of the secondary battery. This application does not particularly limit the type of lithium salt, as long as it achieves the purpose of this application. For example, lithium salt includes, but is not limited to, at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate), or lithium di(fluorooxalateborate).

[0056] In one embodiment of this application, the electrolyte includes a lithium salt, an organic solvent, and additives, including nitrile additives and other additives. Based on the mass of the electrolyte, the mass percentage of the additives is 10% to 20%. This application does not particularly limit the types of other additives, as long as they achieve the purpose of this application. For example, other additives include solid electrolyte interphase (SEI) film-forming additives, flame retardant additives, overcharge protection additives, and conductive additives. Exemplarily, other additives include, but are not limited to, at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), or vinyl sulfate (DTD).

[0057] The positive electrode sheet of this application includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. In some embodiments, the positive active material layer is disposed on one surface of the positive current collector, and in other embodiments, the positive active material layer is disposed on two surfaces of the positive current collector. The aforementioned "surface" can be part or all of the surface of the positive current collector. This application does not particularly limit the type of positive current collector, as long as it achieves the purpose of this application. For example, the positive current collector may include, but is not limited to, aluminum foil or aluminum alloy foil. The positive active material layer of this application includes the positive active material described in the foregoing embodiments. In this application, there is no particular limitation on the thickness of the positive current collector and the positive active material layer, as long as it achieves the purpose of this application. For example, the thickness of the positive current collector is 5 μm to 20 μm, and further, the thickness of the positive current collector can be 6 μm to 18 μm. The thickness of the positive active material layer is 30 μm to 120 μm.

[0058] Optionally, the positive electrode active material layer may further include a positive electrode conductive agent and a positive electrode binder. This application does not impose any particular limitation on the types of positive electrode conductive agents and positive electrode binders in the positive electrode active material layer, as long as the purpose of this application is achieved. This application does not impose any particular limitation on the mass ratio of positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode active material layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved. For example, the mass ratio of positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode active material layer is (95–98):(0.5–3.5):(1.5–3.4).

[0059] The negative electrode sheet of this application includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. In some embodiments, the negative active material layer is disposed on one surface of the negative current collector, and in other embodiments, the negative active material layer is disposed on two surfaces of the negative current collector. The aforementioned "surface" can be part or all of the surface of the negative current collector. This application does not particularly limit the type of negative current collector, as long as it can achieve the purpose of this application. For example, the negative current collector includes, but is not limited to, copper foil, copper alloy foil, nickel foil, titanium foil, nickel foam, or copper foam. The negative active material layer of this application includes the negative active material described in the aforementioned embodiments. In this application, there is no particular limitation on the thickness of the negative current collector and the negative active material layer, as long as it can achieve the purpose of this application. For example, the thickness of the negative current collector is 6 μm to 10 μm, and the thickness of the negative active material layer is 30 μm to 130 μm.

[0060] Optionally, the negative electrode active material layer may further include at least one of a negative electrode conductive agent, a stabilizer, or a negative electrode binder. This application does not impose any particular limitation on the types of negative electrode conductive agents, stabilizers, and negative electrode binders in the negative electrode active material layer, as long as the purpose of this application is achieved. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, negative electrode conductive agent, stabilizer, and negative electrode binder in the negative electrode active material layer, as long as the purpose of this application is achieved. For example, the mass ratio of the negative electrode active material, negative electrode conductive agent, stabilizer, and negative electrode binder in the negative electrode active material layer is (96–98):(0.5–2):(0–1.5):(1.0–1.9).

[0061] The separator in the secondary battery of this application is not particularly limited, as long as it achieves the purpose of this application. For example, the separator includes at least one selected from polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyimide (PI), or aramid. For example, polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene. The separator of this application may have a porous structure, and this application does not particularly limit the size of the pores in the porous structure of the separator, as long as it achieves the purpose of this application. For example, the pore size may be from 0.01 μm to 1 μm. This application does not particularly limit the thickness of the separator, as long as it achieves the purpose of this application; for example, the thickness of the separator may be from 5 μm to 500 μm.

[0062] In one embodiment of this application, the secondary battery further includes a casing, in which electrode components and electrolyte are contained. This application does not impose any particular limitation on the casing, which can be any casing known in the art, as long as it can achieve the purpose of this application. For example, the casing includes, but is not limited to, aluminum-plastic film and steel casing.

[0063] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. For example, secondary batteries may include, but are not limited to: lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), sodium-ion secondary batteries (sodium-ion batteries), lithium polymer secondary batteries, and lithium-ion polymer secondary batteries.

[0064] The secondary battery of this application can be used under super-fast charging conditions, specifically, it can be used under charging rates from 5C to 15C. For example, the charging rate of the secondary battery can be 5C, 6C, 7C, 8C, 9C, 10C, 11C, 12C, 13C, 14C, 15C or any rate between any two of the above ranges.

[0065] This application does not impose any particular limitation on the preparation method of the secondary battery; any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the preparation method of the secondary battery includes, but is not limited to, the following steps: stacking the separator, positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. Alternatively, stacking the separator, positive electrode, separator, and negative electrode in sequence, fixing the four corners of the entire stacked structure to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery.

[0066] A second aspect of this application provides an electrical device comprising the secondary battery described in any of the foregoing embodiments. Therefore, the electrical device exhibits good performance.

[0067] The electrical device used in this application is not particularly limited and can be any electrical device known in the prior art. For example, the electrical device may include, but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0068] Example

[0069] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0070] Test methods and equipment:

[0071] Tests of Dv50 and Dv99:

[0072] The Dv50 and Dv99 of the positive electrode active material and the negative electrode active material were determined using a laser particle size analyzer.

[0073] Coating weight test:

[0074] (1) Coating weight W of the positive electrode active material layer z test:

[0075] The lithium-ion battery was discharged to 3.0V at 0.5C and then disassembled to obtain the positive electrode sheet. The positive electrode sheet was immersed in dimethyl carbonate (DMC) solution for 4 hours, then dried, and a piece with an area of ​​A mm was cut off. 2 The positive electrode sample was weighed on a balance and recorded as p1. Then the positive active material layer on the positive electrode was washed, and the positive current collector was weighed on a balance and recorded as p2.

[0076] If it is a positive electrode sheet with a positive electrode active material layer coated on only one side, W z = (p1-p2) / A.

[0077] If it is a positive electrode sheet with a double-sided coating of positive active material layers, W z = (p1-p2) / 2A.

[0078] (2) Coating weight W of the negative electrode active material layer f test:

[0079] The lithium-ion battery was discharged to 3.0V at 0.5C and then disassembled to obtain the negative electrode sheet. The negative electrode sheet was immersed in DMC solution for 4 hours, then dried, and a piece with an area of ​​B mm was cut off. 2 The negative electrode sample was weighed on a balance and recorded as q1. Then the negative electrode active material layer on the negative electrode was washed, and the negative electrode current collector was weighed on a balance and recorded as q2.

[0080] If it is a negative electrode sheet with a negative electrode active material layer coated on only one side, W f = (q1-q2) / B.

[0081] If it is a negative electrode sheet with a double-sided coating of negative electrode active material layers, W f = (q1-q2) / 2B.

[0082] Raman test:

[0083] The lithium-ion battery was discharged to 3.0V at 0.5C and then disassembled to obtain the negative electrode sheet. The negative electrode sheet was immersed in DMC solution for 4 hours and then dried. An area of ​​100μm × 100μm was selected on the negative electrode active material layer, and the negative electrode active material particles within this area were scanned using a laser confocal Raman spectrometer (Raman, HR Evolution, HORIBA Scientific Instruments Division). The d-peaks and g-peaks of all negative electrode active material particles within this area were obtained. The data was processed using LabSpec software to obtain the peak intensities of the d-peak and g-peak for each negative electrode active material particle, which are respectively I... d and I g The laser wavelength of the Raman spectrometer is in the range of 532 nm to 785 nm. d / I g The value of I is the I value of all negative electrode active material particles measured within this range. d and I g The average of the ratios.

[0084] Cyclic dynamic performance testing:

[0085] The lithium-ion batteries of each embodiment and comparative example were subjected to cycle kinetic performance tests at a charging rate of 10C. The specific steps are as follows:

[0086] (1) Adjust the test temperature to a constant 25℃, place the temperature sensing wire of the multi-channel temperature measuring instrument at the center of the lithium-ion battery surface, and perform the following steps: 1) 10C constant current charging to 4.2V; 2) 7C constant current charging to 4.3V; 3) 5C constant current charging to 4.45V; 4) 4.45V constant voltage charging to 0.05C; 5) Let stand for 30min; 6) 1C constant current discharge to 3.0V; 7) Let stand for 30min; End;

[0087] Charging speed: that is, the time from step 1) to step 4) in step (1);

[0088] Charging temperature rise: The difference between the maximum temperature of the process from step 1) to step 4) in step (1) of the lithium-ion battery surface temperature sensing line and the room temperature.

[0089] (2) Adjust the test temperature to a constant 25℃ and start the test: 1) Charge at a constant current of 10C to 4.2V; 2) Charge at a constant current of 7C to 4.3V; 3) Charge at a constant current of 5C to 4.45V; 4) Charge at a constant voltage of 4.45V to 0.05C; 5) Let stand for 5 minutes; 6) Discharge at a constant current of 1C to 3.0V; 7) Let stand for 5 minutes; 8) Repeat steps 1) to 7) 1000 times (cls); End.

[0090] Capacity retention rate (%) = Discharge capacity after 1000cls / First discharge capacity × 100%.

[0091] Cyclic kinetic performance is characterized by charging speed, charging temperature rise, and capacity retention. Shorter charging time and smaller charging temperature rise indicate better initial kinetic performance of lithium-ion batteries, while higher capacity retention indicates better cycle performance.

[0092] High temperature stability test:

[0093] The thickness of a lithium-ion battery is measured when it is fully manufactured; this is referred to as the initial thickness of the lithium-ion battery.

[0094] To fully charge a lithium-ion battery, follow these steps: charge at a constant current of 0.7C to 4.45V, then charge at a constant voltage of 4.45V to 0.02C.

[0095] After storing the lithium-ion battery in a 90℃ high and low temperature chamber for 8 hours, the thickness of the lithium-ion battery after storage was measured, and the test was completed.

[0096] The expansion rate of a lithium-ion battery = (thickness of the lithium-ion battery after high-temperature storage - initial thickness of the lithium-ion battery) / initial thickness of the lithium-ion battery × 100%; the expansion rate characterizes high-temperature stability, and the smaller the expansion rate, the better the high-temperature stability.

[0097] Example 1-1

[0098] <Preparation of the positive electrode>

[0099] Lithium cobalt oxide as the positive electrode active material, carbon nanotubes as the positive electrode conductive agent, and polyvinylidene fluoride (PVDF, Mw = 7 × 10⁻⁶) as the positive electrode binder are used. 6 The materials were mixed at a mass ratio of 95:3:2, with N-methylpyrrolidone (NMP) added as a solvent. The mixture was stirred under vacuum until a homogeneous positive electrode slurry with a solid content of 75 wt% was obtained. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil used as a positive electrode current collector, and dried at 95°C to obtain a positive electrode sheet with a single-sided coating of the positive electrode active material layer. This process was repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode active material layer. After cold pressing, cutting, and slitting, the slitting material was dried at 85°C under vacuum for 4 hours to obtain positive electrode sheets with dimensions of 55 mm × 1400 mm for later use. The single-layer thickness of the positive electrode active material layer was 37.3 μm, and the thickness of the positive electrode sheet was 84.6 μm. Eighteen positive electrode tabs were integrally formed in the tab area of ​​the positive electrode current collector through die-cutting. The compaction density of the positive electrode sheet was 37 g / cm³. 3 The lithium cobalt oxide has a Dv99 of 30 μm and a Dv50 of 13 μm. The coating weight W of the positive electrode active material layer... z It is 10.38 mg / cm 2 .

[0100] <Preparation of Negative Electrode Sheets>

[0101] Artificial graphite as the negative electrode active material, Super P as the negative electrode conductive agent, and sodium carboxymethyl cellulose (CMC-Na, Mw = 7 × 10⁻⁶) as the stabilizer are used. 5 ), negative electrode binder styrene-butadiene rubber (SBR, Mw = 5 × 10), 6The materials were mixed at a mass ratio of 97:1:1:1, and deionized water was added as a solvent. The mixture was stirred under vacuum until a homogeneous negative electrode slurry with a solid content of 51 wt% was obtained. The negative electrode slurry was uniformly coated onto one surface of a 7 μm thick copper foil used as a negative electrode current collector, and dried at 85°C to obtain a negative electrode sheet with a single-sided coating of the negative electrode active material layer. This process was repeated on the other surface of the same copper foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. After cold pressing, cutting, and slitting, the slitting was dried at 110°C under vacuum for 4 hours to obtain negative electrode sheets with dimensions of 58 mm × 1500 mm for later use. The single-layer thickness of the negative electrode active material layer was 58.5 μm, and the thickness of the negative electrode sheet was 124 μm. The tab area of ​​the negative electrode current collector was integrally formed into 18 negative electrode tabs through die-cutting. The compaction density of the negative electrode sheet was 1.7 g / cm³. 3 The artificial graphite has a Dv99 of 25 μm and a Dv50 of 9 μm. The coating weight W of the negative electrode active material layer... f It is 5.19 mg / cm³ 2 .

[0102] <Preparation of Electrolyte>

[0103] An electrolyte was prepared by mixing organic solvent, lithium salt, and additives in a mass ratio of 80:10:10 under an environment with a water content of less than 10 ppm. The lithium salt used was lithium hexafluorophosphate, the additives were nitrile additives such as disuccinate and other additives such as fluoroethylene carbonate (FEC), and the organic solvents were n-propyl orthocyanin, ethylene carbonate, and diethyl carbonate, with a mass ratio of n-propyl orthocyanin, ethylene carbonate, and diethyl carbonate of 40:30:30. Based on the mass of the electrolyte, the mass percentages of the chain carboxylic acid esters were W1 = 40% × 80% = 32%, ethylene carbonate W2 = 30% × 80% = 24%, diethyl carbonate W3 = 30% × 80% = 24%, and the nitrile additives were 2%, with the remainder being lithium salt and other additives (FEC).

[0104] <Preparation of the diaphragm>

[0105] A porous polyethylene membrane with a thickness of 15μm was selected as the diaphragm.

[0106] <Preparation of Lithium-ion Batteries>

[0107] The separator, positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. This is then wound to form the electrode assembly. The electrode assembly is placed in an aluminum-plastic film housing, dried, and then injected with electrolyte. Following vacuum sealing, settling, formation, capacity testing, degassing, and edge trimming, a lithium-ion battery is obtained.

[0108] Examples 1-2 to 1-33

[0109] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0110] When the mass percentage of the chain carboxylic acid ester changes, the mass percentages of ethylene carbonate and diethyl carbonate also change accordingly. When the mass percentage of the nitrile additives changes, the mass percentages of other additives also change accordingly. The mass ratio of lithium salt, organic solvent, and additives remains constant. The sum of the mass percentages of the chain carboxylic acid ester, ethylene carbonate, and diethyl carbonate, W1 + W2 + W3, equals 80%, and W2 = W3. The sum of the mass percentages of lithium salt, organic solvent, and additives is 100%.

[0111] Examples 2-1 to 2-5

[0112] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0113] Examples 2-6

[0114] Except for adjusting the mass ratio of lithium salt, organic solvent and additive to 20:60:20 in the <Preparation of Electrolyte>, the rest is the same as in Example 1-1.

[0115] Examples 2-7

[0116] Except for adjusting the mass ratio of lithium salt, organic solvent and additive to 15:70:15 in the <Preparation of Electrolyte>, the rest is the same as in Example 1-1.

[0117] Examples 2-8

[0118] Except for adjusting the mass ratio of lithium salt, organic solvent and additive to 22.5:55:22.5 in the <Preparation of Electrolyte>, the rest is the same as in Example 1-1.

[0119] Examples 2-9

[0120] Except for adjusting the mass ratio of lithium salt, organic solvent and additive to 7.5:85:7.5 in the <Preparation of Electrolyte>, the rest is the same as in Example 1-1.

[0121] Example 3-1

[0122] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-1.

[0123] Examples 3-2 to 3-4

[0124] Except for the use of artificial graphite coated with amorphous carbon as the negative electrode active material in the <Preparation of Negative Electrode Sheet>, the rest is the same as in Example 1-1. The mass ratio of artificial graphite to amorphous carbon was adjusted according to Table 3.

[0125] Examples 3-5 and 3-6

[0126] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-1.

[0127] Comparative Examples 1 to 18

[0128] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0129] When the mass percentage of the chain carboxylic acid ester changes, the mass percentages of ethylene carbonate and diethyl carbonate also change accordingly. When the mass percentage of the nitrile additives changes, the mass percentages of other additives also change accordingly. The mass ratio of lithium salt, organic solvent, and additives remains constant. The sum of the mass percentages of the chain carboxylic acid ester, ethylene carbonate, and diethyl carbonate, W1 + W2 + W3, equals 80%, and W2 = W3. The sum of the mass percentages of lithium salt, organic solvent, and additives is 100%.

[0130] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0131] Table 1

[0132]

[0133]

[0134]

[0135] Note: In Table 1, "\" indicates that there is no corresponding parameter.

[0136] As can be seen from Examples 1-1 to 1-29 and Comparative Examples 1 to 18, the secondary battery of this application embodiment, by setting the coating weight W of the positive electrode active material layer... z Coating weight W of the negative electrode active material layer f The ratio W z / W f and W fThe values ​​of the positive and negative electrode active materials, Dv99, are within the scope of this application, and the contents of chain carboxylic acid esters and nitrile additives in the electrolyte are also within the scope of this application. This results in a shorter charging time (i.e., a higher charging speed), a lower charging temperature rise, and a higher capacity retention rate at a charging rate of 10C. Furthermore, the secondary battery exhibits a lower expansion rate after being stored at 90°C for 8 hours. In other words, the secondary battery of this application embodiment can simultaneously possess a shorter charging time, a lower charging temperature rise, a higher capacity retention rate, and a lower expansion rate. This indicates that the secondary battery of this application embodiment can maintain good cycle dynamics performance while also ensuring high-temperature stability under super-fast charging conditions, meaning that the secondary battery of this application embodiment has better overall performance under super-fast charging conditions. In contrast, the secondary batteries of Comparative Examples 1 and 2 have a lower coating weight W of the negative electrode active material layer. f Not within the scope of this application; the coating weight W of the positive electrode active material layer of the secondary batteries in Comparative Examples 3 and 4 is [not specified]. z Coating weight W of the negative electrode active material layer f The ratio W z / W f The following are not within the scope of this application: In Comparative Examples 5 and 6, the negative electrode active material Dv99 is not within the scope of this application; in Comparative Examples 7 and 8, the positive electrode active material Dv99 is not within the scope of this application; in Comparative Examples 9 and 10, the content of chain carboxylic acid esters in the electrolyte is not within the scope of this application; in Comparative Examples 11 and 12, the content of nitrile additives in the electrolyte is not within the scope of this application; in Comparative Examples 13 and 14, the negative electrode active material Dv99, the positive electrode active material Dv99, and the coating weight W of the negative electrode active material layer are not within the scope of this application. f Not within the scope of this application; the secondary batteries of Comparative Examples 15 and 16, their positive electrode active material Dv99, negative electrode active material Dv99, the content of chain carboxylic acid esters in the electrolyte, and the coating weight W of the positive electrode active material layer are not included. z Coating weight W of the negative electrode active material layer f The ratio W z / W f and W f The values ​​are all outside the scope of this application; for the secondary batteries of Comparative Examples 17 and 18, the values ​​of Dv99 of the positive electrode active material, Dv99 of the negative electrode active material, the content of chain carboxylic acid esters in the electrolyte, and the coating weight W of the positive electrode active material layer are all outside the scope of this application. z Coating weight W of the negative electrode active material layer f The ratio W z / W f W fThe values ​​of W and the content of nitrile additives in the electrolyte are not within the scope of this application; the coating weight W of the positive electrode active material layer in Comparative Example 1 z Coating weight W of the negative electrode active material layer f The resulting secondary batteries exhibit lower resistance and faster charging speeds, but due to the excessively low coating weights of the positive and negative active material layers, the cost of precisely controlling the coating weight in actual industrial production is too high. This leads to a low yield rate of lithium-ion batteries in large-scale production and excessively low energy density, failing to meet the needs of actual production and making them unsuitable for industrial applications. In Comparative Examples 2 to 18, the secondary batteries cannot simultaneously meet the requirements of short charging time, low charging temperature rise, long cycle life, and low expansion rate.

[0137] Coating weight W of the negative electrode active material layer f This typically affects the cycle kinetics and high-temperature stability of secondary batteries. As can be seen from Examples 1-1 to 1-7, Comparative Example 1, and Comparative Example 2, the coating weight W of the selected negative electrode active material layer... f The secondary battery within the scope of this application simultaneously achieves a short charging time (i.e., a high charging speed), a low charging temperature rise, and a high capacity retention rate at a charging rate of 10C, and exhibits a low thickness expansion rate after storage at 90°C for 8 hours. Therefore, the secondary battery can maintain good cycle dynamics performance under super-fast charging conditions while also ensuring high-temperature stability. As mentioned above, the coating weight W of the positive electrode active material layer in Comparative Example 1 is... z Coating weight W of the negative electrode active material layer f The lower coating weight results in faster charging speed and lower impedance of the lithium-ion battery. However, due to the excessively low coating weight of the positive and negative active material layers, the cost of accurately controlling the coating weight in actual industrial production is too high. As a result, the yield rate of lithium-ion batteries obtained in large-scale production is too low, and the energy density of the lithium-ion batteries obtained is too low, which cannot meet the needs of actual production and is not suitable for industrial production applications.

[0138] Coating weight W of the positive electrode active material layer z Coating weight W of the negative electrode active material layer f The ratio W z / W f This typically affects the cycle dynamics and high-temperature stability of secondary batteries. As can be seen from Examples 1-1, 1-8, 1-9, Comparative Examples 3 and 4, the coating weight W of the selected positive electrode active material layer... z Coating weight W of the negative electrode active material layer f The ratio W z / W fThe secondary battery within the scope of this application simultaneously achieves a short charging time, low charging temperature rise, and high capacity retention at a charging rate of 10C, and exhibits low thickness expansion after storage at 90°C for 8 hours. Therefore, the secondary battery can maintain good cycle dynamics performance under super-fast charging conditions while also ensuring high-temperature stability.

[0139] The Dv99 of the negative electrode active material typically affects the cycle dynamics and high-temperature stability of secondary batteries. As can be seen from Examples 1-1, 1-10 to 1-13, Comparative Example 5, and Comparative Example 6, secondary batteries using Dv99 as the negative electrode active material, which falls within the scope of this application, can simultaneously achieve a shorter charging time, lower charging temperature rise, and higher capacity retention at a charging rate of 10C, and exhibit a lower thickness expansion rate after storage at 90°C for 8 hours. Therefore, the secondary battery can achieve good cycle dynamics under super-fast charging conditions while also maintaining high-temperature stability.

[0140] The Dv99 of the positive electrode active material typically affects the cycle kinetics and high-temperature stability of secondary batteries. As can be seen from Examples 1-1, 1-14 to 1-17, Comparative Example 7, and Comparative Example 8, secondary batteries using Dv99 as the positive electrode active material, which falls within the scope of this application, can simultaneously achieve a shorter charging time, lower charging temperature rise, and higher capacity retention at a charging rate of 10C, and exhibit a lower thickness expansion rate after storage at 90°C for 8 hours. Therefore, the secondary battery can achieve good cycle kinetics under super-fast charging conditions while also maintaining high-temperature stability.

[0141] The content of chain carboxylic acid esters in the electrolyte typically affects the cycle dynamics and high-temperature stability of secondary batteries. As can be seen from Examples 1-1, 1-18 to 1-22, Comparative Example 9, and Comparative Example 10, secondary batteries with chain carboxylic acid ester content within the range of this application simultaneously achieve shorter charging time, lower charging temperature rise, and higher capacity retention at a charging rate of 10C, and exhibit lower thickness expansion after storage at 90°C for 8 hours. Therefore, the secondary battery can achieve good cycle dynamics under super-fast charging conditions while also maintaining high-temperature stability.

[0142] The content of nitrile additives in the electrolyte typically affects the cycle dynamics and high-temperature stability of secondary batteries. As can be seen from Examples 1-1, 1-23 to 1-29, Comparative Examples 11 and 12, secondary batteries using nitrile additives in the electrolyte within the range of this application simultaneously achieve shorter charging time, lower charging temperature rise, and higher capacity retention at a charging rate of 10C, and exhibit lower thickness expansion after storage at 90°C for 8 hours. Therefore, the secondary battery can achieve good cycle dynamics under super-fast charging conditions while also maintaining high-temperature stability.

[0143] The Dv50 of the negative electrode active material typically affects the cycle dynamics and high-temperature stability of a secondary battery. As can be seen from Examples 1-1, 1-10 to 1-13, 1-30, and 1-31, secondary batteries using negative electrode active materials with Dv50 within the scope of this application simultaneously achieve shorter charging times, lower charging temperature rise, and higher capacity retention at a 10C charging rate, and exhibit lower thickness expansion after storage at 90°C for 8 hours. Therefore, the secondary battery can achieve good cycle dynamics while maintaining high-temperature stability under super-fast charging conditions. Furthermore, as can be seen from Examples 1-11 and 1-30, the cycle dynamics and high-temperature stability of the secondary battery are also affected when the negative electrode active material with the same Dv99 has different Dv50 values.

[0144] The Dv50 of the positive electrode active material typically affects the cycle dynamics and high-temperature stability of a secondary battery. As can be seen from Examples 1-1, 1-14 to 1-17, 1-32, and 1-33, secondary batteries using positive electrode active materials with Dv50 within the scope of this application simultaneously achieve shorter charging times, lower charging temperature rise, and higher capacity retention at a 10C charging rate, and exhibit lower thickness expansion after storage at 90°C for 8 hours. Therefore, the secondary battery can achieve good cycle dynamics while maintaining high-temperature stability under super-fast charging conditions. Furthermore, as can be seen from Examples 1-14 and 1-32, the cycle dynamics and high-temperature stability of the secondary battery are also affected when the same Dv99 positive electrode active material has different Dv50 values.

[0145] Table 2

[0146]

[0147]

[0148] The type of chain carboxylic acid ester typically affects the cycle dynamics and high-temperature stability of secondary batteries. As can be seen from Examples 1-1, 2-1 to 2-3, secondary batteries using chain carboxylic acid esters within the scope of this application simultaneously achieve shorter charging times, lower charging temperature rise, and higher capacity retention at a 10C charging rate, and exhibit lower thickness expansion after storage at 90°C for 8 hours. Therefore, the secondary battery can achieve good cycle dynamics under super-fast charging conditions while maintaining high-temperature stability.

[0149] The type of nitrile additives typically affects the cycle dynamics and high-temperature stability of secondary batteries. As can be seen from Examples 1-1, 2-4, and 2-5, secondary batteries using nitrile additives within the scope of this application simultaneously achieve shorter charging times, lower charging temperature rise, and higher capacity retention at a 10C charging rate, and exhibit lower thickness expansion after storage at 90°C for 8 hours. Therefore, the secondary battery can achieve good cycle dynamics under super-fast charging conditions while maintaining high-temperature stability.

[0150] The content of organic solvents in the electrolyte typically affects the cycle dynamics and high-temperature stability of secondary batteries. As can be seen from Examples 1-1, 2-6 to 2-9, secondary batteries with organic solvent content within the range of this application simultaneously achieve shorter charging time, lower charging temperature rise, and higher capacity retention at a charging rate of 10C, and exhibit lower thickness expansion after storage at 90°C for 8 hours. Therefore, the secondary battery can achieve good cycle dynamics under super-fast charging conditions while also maintaining high-temperature stability.

[0151] Table 3

[0152]

[0153]

[0154] Note: "\" in Table 3 indicates no corresponding parameter; "Mr" in Table 3 represents the mass ratio of artificial graphite to amorphous carbon.

[0155] Types of negative electrode active materials, I of carbon-based materials d / I g The value typically affects the cycle kinetics and high-temperature stability of secondary batteries. As can be seen from Examples 1-1, 3-1 to 3-4, the type of negative electrode active material selected and the I value of the carbon-based material... d / I gThe secondary battery within the scope of this application simultaneously achieves a short charging time, low charging temperature rise, and high capacity retention at a charging rate of 10C, and exhibits low thickness expansion after storage at 90°C for 8 hours. Therefore, the secondary battery demonstrates good cycle dynamics performance under super-fast charging conditions while maintaining high-temperature stability. Figure 1 The Raman spectra of Examples 3-3 are shown. Figure 1 As can be seen from the Raman spectrum of the high-kinetics anode material, its I... d / I g The high value indicates that it has good surface activity.

[0156] The type of positive electrode active material typically affects the cycle kinetics and high-temperature stability of secondary batteries. As can be seen from Examples 1-1, 3-5, and 3-6, the type of positive electrode active material selected, and the carbon-based material's I... d / I g The secondary battery within the scope of this application simultaneously achieves a short charging time, low charging temperature rise, and high capacity retention at a charging rate of 10C, and exhibits low thickness expansion after storage at 90°C for 8 hours. Therefore, the secondary battery can maintain good cycle dynamics performance under super-fast charging conditions while also ensuring high-temperature stability.

[0157] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0158] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0159] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A secondary battery, wherein, The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator film, the positive electrode sheet comprises a positive electrode active material layer, the positive electrode active material layer comprises a positive electrode active material, the negative electrode sheet comprises a negative electrode active material layer, and the negative electrode active material layer comprises a negative electrode active material. The coating weight of the positive electrode active material layer is W z , the coating weight of the negative electrode active material layer is W f , W z , and W f satisfy: 1.6W f ≤W z ≤2.2W f , 3.25 mg / cm 2 ≤W f ≤5.84 mg / cm 2 ; The Dv99 of the positive electrode active material is 27 μm to 33 μm, and the Dv99 of the negative electrode active material is 23 μm to 28 μm. The electrolyte comprises an organic solvent, a lithium salt and a nitrile additive, the organic solvent comprises a chain carboxylic acid ester, the mass percentage of the chain carboxylic acid ester is 6% to 56% based on the mass of the electrolyte, and the mass percentage of the nitrile additive is 0.01% to 10%.

2. The secondary battery according to claim 1, wherein 6.49 mg / cm 2 ≤ 11.69 mg / cm z ≤ 11.69 mg / cm 2 .

3. The secondary battery according to claim 1, wherein 3.90 mg / cm 2 ≤ W f ≤ 5.19 mg / cm 2 , and / or, 7.80 mg / cm 2 ≤ W z ≤ 10.38 mg / cm 2 .

4. The secondary battery according to claim 1, wherein The Dv99 of the positive electrode active material is 28 μm to 31 μm, and / or the Dv99 of the negative electrode active material is 24 μm to 26 μm.

5. The secondary battery according to claim 1, wherein The Dv50 of the positive electrode active material is 10 μm to 15 μm, and the Dv50 of the negative electrode active material is 7 μm to 12 μm.

6. The secondary battery according to claim 1, wherein The negative electrode active material comprises at least one of a carbon-based material, a silicon-based material or a tin-based material, the carbon-based material comprises at least one of natural graphite, artificial graphite, soft carbon, hard carbon or mesocarbon microbeads, the silicon-based material comprises at least one of elemental silicon, silicon-carbon material or silicon-oxygen material, and the tin-based material comprises at least one of elemental tin, tin alloy or tin oxide.

7. The secondary battery according to claim 6, wherein The peak intensity ratio I d / I g of the d peak and the g peak of the carbon-based material through Raman test satisfies: 0.1≤I d / I g ≤1.

0.

8. The secondary battery according to claim 1, wherein The positive electrode active material comprises at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate or lithium titanate.

9. The secondary battery according to claim 8, wherein The positive electrode active material further comprises a non-metallic element, and the non-metallic element comprises at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur.

10. The secondary battery according to claim 1, wherein The chain carboxylic acid ester comprises at least one of methyl formate, methyl acetate, ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, n-propyl propionate, isopropyl propionate, methyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl n-butanoate, n-propyl n-butanoate, propyl isobutyrate, n-pentyl n-butanoate, n-pentyl isobutyrate, n-butyl n-butanoate, isobutyl isobutyrate or n-pentyl n-pentanoate.

11. The secondary battery according to claim 1, wherein The mass percentage of the chain carboxylic acid ester is 18% to 40% based on the mass of the electrolyte.

12. The secondary battery according to claim 1, wherein The nitrile additive comprises at least one of malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, secononitrile, 3,3'-oxydipropionitrile, hex-2-enedinitrile, fumaronitrile, 2-pentenenitrile, methylglutaronitrile, 4-cyanopimelonitrile, (Z)-but-2-enedinitrile, 2,2,3,3-tetrafluorosuberonitrile, ethyleneglycolbis(propionitrile)ether, 1,3,5-pentanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,1,3,3-propanetetracarbonitrile, 2,2'-(1,4-phenylene)dimalononitrile, 1,1,5,5-pentanetetracarbonitrile, 1,1,4,4-butanetetracarbonitrile or 1,1,6,6-hexanetetracarbonitrile.

13. The secondary battery according to claim 1, wherein The mass percentage of the nitrile-based additive is 5% to 8% based on the mass of the electrolyte.

14. The secondary battery according to claim 1, wherein The organic solvent further includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone, or tetrahydrofuran; The mass percentage of the organic solvent is 60% to 80% based on the mass of the electrolyte.

15. An electric device comprising the secondary battery according to any one of claims 1 to 14.

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