Electrochemical device and electronic device comprising the same

Abstract

The application provides an electrochemical device and an electronic device comprising the same, wherein the electrochemical device comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, and the negative electrode active material layer comprises a negative electrode active material; the length L of the negative electrode current collector and the width W of the negative electrode current collector satisfy 8≤L / W≤40 and 40mm≤W≤145mm; and the R value of the negative electrode active material is 0.1-0.4. The ratio of the length L of the negative electrode current collector to the width W and the R value of the negative electrode active material are simultaneously regulated in the above range, so that the high-temperature storage performance of the electrochemical device is effectively improved.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to an electrochemical device and an electronic device comprising the electrochemical device. Background Technology

[0002] Secondary batteries, such as lithium-ion batteries, are widely used in electric vehicles, outdoor equipment, and solar energy equipment due to their high energy density and long cycle life. With the rapid development of these fields, the market is placing increasingly higher demands on the long-term high-temperature resistance of lithium-ion batteries.

[0003] However, the storage performance of existing lithium-ion batteries is significantly affected when continuously stored at temperatures above 80°C. Therefore, improving the high-temperature storage performance of electrochemical devices has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] The purpose of this application is to provide an electrochemical device and an electronic device comprising the electrochemical device, so as to improve the high-temperature storage performance of the electrochemical device.

[0005] It should be noted that while this application uses lithium-ion batteries as an example of an electrochemical device to explain the invention, the electrochemical device described herein is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0006] The first aspect of this application provides an electrochemical device comprising a negative electrode, the negative electrode comprising a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer comprising a negative active material; the length L and width W of the negative current collector satisfy: 8 ≤ L / W ≤ 40, 40 mm ≤ W ≤ 145 mm; preferably, 18 ≤ L / W ≤ 40; the R value of the negative active material is 0.1 to 0.4, preferably 0.15 to 0.30; the R value is the average value of the peak intensity ratio I(D) / I(G) of the D peak and G peak of the negative active material particles in any region of size 100 μm × 100 μm on the negative active material layer using Raman spectroscopy; the D peak is the Raman spectrum of the negative active material particles with a shift range of 1300 cm⁻¹. -1 Up to 1400cm -1 The peak, G, is the Raman spectrum of the negative electrode active material particles with a shift range of 1530 cm⁻¹. -1 Up to 1630cm -1 The peak. By simultaneously controlling the ratio of the length L to the width W of the negative electrode current collector and the R value of the negative electrode active material within the above range, the high-temperature storage performance of the electrochemical device is effectively improved.

[0007] In one embodiment of this application, the impedance of the electrochemical device is 30 mΩ to 60 mΩ. By adjusting the impedance within the above range, the electrochemical device is placed in a more stable system. When the electrochemical device is stored at high temperatures, the phenomenon of gas generation from the electrolyte reaction is alleviated, thereby reducing the risk of expansion of the electrochemical device and improving its high-temperature storage performance.

[0008] In one embodiment of this application, the conductivity σ of the negative electrode sheet satisfies: 15S / cm ≤ σ ≤ 35S / cm, preferably 25S / cm ≤ σ ≤ 30S / cm. By controlling the conductivity σ of the negative electrode sheet within the above range, the current density at the interface between the negative electrode sheet and the electrolyte can be effectively controlled, thereby alleviating lithium plating on the negative electrode sheet and improving the high-temperature storage performance of the electrochemical device.

[0009] In one embodiment of this application, the areal density of the negative electrode active material layer is 0.05 mg / mm². 2 Up to 0.11 mg / mm 2 By controlling the areal density of the negative electrode active material layer within the aforementioned range, it is more beneficial to improve the high-temperature storage performance of the electrochemical device.

[0010] In one embodiment of this application, the compaction density of the negative electrode active material layer is 1.6 g / cm³. 3 Up to 1.8 g / cm 3 By controlling the compaction density of the negative electrode active material layer within the aforementioned range, it is possible to improve the energy density of the electrochemical device while simultaneously enhancing its high-temperature storage performance.

[0011] In one embodiment of this application, when the state of charge (SOC) of the electrochemical device is 0%, the lattice index OI of the negative electrode active material satisfies: 8 ≤ OI ≤ 20. By controlling the lattice index OI of the negative electrode active material within the above range, it is more beneficial to improve the high-temperature storage performance of the electrochemical device.

[0012] In one embodiment of this application, the electrochemical device includes an electrolyte comprising ethylene carbonate (also known as ethylene carbonate, abbreviated EC); based on the mass of the electrolyte, the mass percentage of ethylene carbonate is 8% to 30%, preferably 15% to 25%. By controlling the mass percentage of EC within the range of this application, it is more conducive to passivating the interface between the negative electrode and the electrolyte, thereby alleviating lithium plating and suppressing gas generation in the electrolyte, thus further improving the high-temperature storage performance of the electrochemical device.

[0013] In one embodiment of this application, the electrolyte comprises a lithium salt, which includes at least one selected from LiPF6, lithium bis(fluorosulfonyl)imide (LiFSI), or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); the concentration of the lithium salt in the electrolyte is from 0.9 mol / L to 1.5 mol / L. By selecting the above-mentioned types of lithium salt and controlling the concentration of the lithium salt in the electrolyte within the above range, it is more beneficial to reduce the rise in electrolyte acidity, mitigate the impact of transition metal dissolution in the positive electrode active material, and thus improve the high-temperature storage performance of the electrochemical device.

[0014] A second aspect of this application provides an electronic device that includes the electrochemical device described in any of the foregoing embodiments.

[0015] This application provides an electrochemical device and an electronic device comprising the electrochemical device, wherein the electrochemical device includes a negative electrode plate, the negative electrode plate 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; the length L and width W of the negative electrode current collector satisfy: 8≤L / W≤40, 40mm≤W≤145mm; the R value of the negative electrode active material is 0.1 to 0.4; the R value is the average value of the peak intensity ratio I(D) / I(G) of the D peak and G peak of the negative electrode active material particles in any region of size 100μm×100μm on the negative electrode active material layer using Raman testing; the D peak is the Raman spectrum of the negative electrode active material particles with a shift range of 1300cm. -1 Up to 1400cm -1 The peak, G, is the Raman spectrum of the negative electrode active material particles with a shift range of 1530 cm⁻¹. -1 Up to 1630cm -1 The peak value was determined by simultaneously controlling the ratio of the length L to the width W of the negative electrode current collector and the R value of the negative electrode active material within the aforementioned range, thereby effectively improving the high-temperature storage performance of the electrochemical device.

[0016] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these accompanying drawings.

[0018] Figure 1 This is a negative current collector in one embodiment of this application;

[0019] Figure 2 The images show the Raman spectra of the negative electrode active materials in Examples 1-4. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the embodiments and accompanying drawings. 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 the embodiments in this application are within the scope of protection of this application.

[0021] It should be noted that, in the specific embodiments of this application, a lithium-ion battery is used as an example of an electrochemical device to explain this application; however, the electrochemical device of this application is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0022] A first aspect of this application provides an electrochemical device comprising 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; such as Figure 1 As shown, the length L and width W of the negative electrode current collector 10 satisfy: 8 ≤ L / W ≤ 40, 40 mm ≤ W ≤ 145 mm; preferably, 18 ≤ L / W ≤ 40; the R value of the negative electrode active material is 0.1 to 0.4, preferably 0.15 to 0.30; the R value is the average value of the peak intensity ratio I(D) / I(G) of the D peak and G peak of the negative electrode active material particles in any region with a size of 100 μm × 100 μm on the negative electrode active material layer, measured by Raman spectroscopy; the D peak is the peak with a shift range of 1300 cm⁻¹ in the Raman spectrum of the negative electrode active material particles. -1 Up to 1400cm -1 The peak G is the Raman spectrum of the negative electrode active material particles with a shift range of 1530 cm⁻¹. -1 Up to 1630cm -1 The peak.

[0023] For example, the value of L / W can be 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, or any value within any two of the above ranges. W can be 40mm, 45.8mm, 50mm, 60mm, 66.4mm, 70mm, 80mm, 90mm, 100mm, 110mm, 120mm, 130mm, 140mm, 145mm, or any value within any two of the above ranges. When the value of L / W is too small (e.g., less than 8), the width W of the negative electrode is larger; when the value of L / W is too large (e.g., greater than 40), the length L of the negative electrode is larger. A larger width W or a larger length L of the negative electrode will affect the initial impedance of the electrochemical device, causing the initial impedance to be outside the reasonable range. This reduces the system stability of the electrochemical device, and the impedance increases sharply during charge-discharge cycles, thereby increasing the thickness expansion rate of the electrochemical device. By adjusting the L / W value within the range specified in this application, the length L and width W of the negative electrode current collector are more coordinated, resulting in a reasonable initial impedance of the electrochemical device. This leads to higher system stability and a slower increase in impedance during charge-discharge cycles, thus reducing the thickness expansion rate of the electrochemical device. Further adjusting the L / W value within the preferred range further enhances the system stability of the electrochemical device, resulting in an even slower increase in impedance during charge-discharge cycles and a further reduction in the thickness expansion rate.

[0024] The R value can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, or any value within any two of the above ranges. The R value characterizes the crystallinity of the surface of the negative electrode active material. If the R value is too small (e.g., less than 0.1), the kinetics of the negative electrode active material are poor, resulting in high initial impedance, which continues to increase after high-temperature storage, ultimately affecting the system stability of the electrochemical device. If the R value is too large (e.g., greater than 0.4), the surface of the negative electrode active material is too active, leading to violent surface reactions, which is not conducive to long-term high-temperature storage of the electrochemical device. Adjusting the R value within the range specified in this application indicates that the surface crystallinity of the negative electrode active material is low, and the kinetic performance of the negative electrode active material is good. This ensures that the relative impedance of the electrochemical device remains low after long-term half-charge storage at temperatures above 80°C, indicating good kinetic performance of the electrochemical device. The lithium plating phenomenon after charging the electrochemical device is suppressed and alleviated. Adjusting the R value within the preferred range specified in this application further improves the kinetic performance of the electrochemical device after long-term half-charge storage at temperatures above 80°C. The lithium plating phenomenon after charging the electrochemical device is further suppressed and alleviated.

[0025] In this application, the R value can be adjusted by selecting different types of negative electrode active materials, etc. This application does not impose any special restrictions on this, as long as the R value is adjusted within the range of this application.

[0026] Therefore, by simultaneously controlling the ratio of the length L to the width W of the negative electrode current collector (L / W) and the R value of the negative electrode active material within the above range, a synergistic effect is achieved between the ratio of the length L to the width W of the negative electrode current collector (L / W) and the R value of the negative electrode active material, thereby effectively improving the high-temperature storage performance of the electrochemical device.

[0027] By simultaneously controlling the ratio of the length L to the width W of the negative electrode current collector (L / W) and / or the R value of the negative electrode active material within the aforementioned preferred range, the high-temperature storage performance of the electrochemical device is further effectively improved.

[0028] In this application, "at least one surface of the negative electrode current collector" refers to one or both surfaces along the thickness direction of the negative electrode current collector itself. A "surface" can be the entire area of ​​the negative electrode current collector or only a portion thereof; this application does not impose any particular limitation, and those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved. This application does not impose any particular limitation on the type of negative electrode current collector, as long as it achieves the purpose of this application. For example, the negative electrode current collector can include copper foil, copper alloy foil, nickel foil, titanium foil, nickel foam, or copper foam, etc. This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector can be 6 μm to 10 μm.

[0029] In one embodiment of this application, the impedance of the electrochemical device is between 30 mΩ and 60 mΩ. For example, the impedance can be 30 mΩ, 35 mΩ, 40 mΩ, 45 mΩ, 50 mΩ, 55 mΩ, 60 mΩ, or any value between any two of the above ranges. If the impedance is too small (e.g., less than 30 mΩ) or too large (e.g., greater than 60 mΩ), the stability of the electrochemical device system decreases, and the increase in impedance during the charging and discharging process of the electrochemical device increases, which will affect the high-temperature storage performance of the electrochemical device. By adjusting the impedance within the above range, the electrochemical device is placed in a more stable system. When the electrochemical device is stored at high temperatures, the phenomenon of electrolyte reaction and gas production is alleviated, thereby reducing the risk of expansion of the electrochemical device and improving the high-temperature storage performance of the electrochemical device. It should be noted that "impedance" in this application should be understood as direct current impedance (DCR).

[0030] In one embodiment of this application, the conductivity σ of the negative electrode sheet satisfies: 15S / cm ≤ σ ≤ 35S / cm, preferably 25S / cm ≤ σ ≤ 30S / cm. For example, the conductivity σ of the negative electrode sheet can be 15S / cm, 25S / cm, 28S / cm, 30S / cm, 35S / cm, or any value between any two of the above ranges. By adjusting the conductivity σ of the negative electrode sheet within the above range, the current density at the interface between the negative electrode sheet and the electrolyte can be effectively controlled, thereby alleviating the lithium plating phenomenon of the negative electrode sheet and improving the high-temperature storage performance of the electrochemical device. By adjusting the conductivity σ of the negative electrode sheet within the above preferred range, the current density at the interface between the negative electrode sheet and the electrolyte can be further effectively controlled, thereby effectively alleviating the lithium plating phenomenon of the negative electrode sheet and further improving the high-temperature storage performance of the electrochemical device.

[0031] In this application, the conductivity σ of the negative electrode sheet can be controlled by adjusting the type of negative electrode active material, the compaction density of the negative electrode active material layer, etc. This application does not impose any special restrictions on this, as long as the conductivity σ of the negative electrode sheet is controlled within the range of this application.

[0032] In one embodiment of this application, the areal density of the negative electrode active material layer is 0.05 mg / mm². 2 Up to 0.11 mg / mm 2 For example, the areal density of the negative electrode active material layer can be 0.05 mg / mm². 2 0.07 mg / mm 2 0.09 mg / mm 2 0.11 mg / mm 2 Or any value between any two of the above ranges. The areal density of the negative electrode active material layer is too low (e.g., less than 0.05 mg / mm²). 2 This can easily affect the adhesion between the negative electrode active material layer and the negative electrode current collector. An excessively high areal density of the negative electrode active material layer (e.g., greater than 0.11 mg / mm²) can also negatively impact adhesion. 2 This can easily affect lithium-ion transport, leading to lithium plating in electrochemical devices and impacting their high-temperature storage performance. Controlling the areal density of the negative electrode active material layer within the aforementioned range further improves the high-temperature storage performance of the electrochemical device.

[0033] In one embodiment of this application, the compaction density of the negative electrode active material layer is 1.6 g / cm³. 3 Up to 1.8 g / cm 3 For example, the compaction density of the negative electrode active material layer can be 1.6 g / cm³. 3 1.65g / cm 3 1.7g / cm 3 1.75g / cm 31.8g / cm 3 Or any value between any two of the above ranges. By controlling the compaction density of the negative electrode active material layer within the above range, it is possible to improve the energy density of the electrochemical device while leaving sufficient pores in the negative electrode active material layer, thus mitigating the expansion of the negative electrode active material during the charging and discharging process of the electrochemical device, thereby reducing the risk of expansion of the electrochemical device and improving the high-temperature storage performance of the electrochemical device.

[0034] In this application, the compaction density of the negative electrode active material layer can be controlled by adjusting the size of the roller gap and the preset pressure value of the cold press. This application does not impose any special restrictions on this, as long as the compaction density of the negative electrode active material layer is controlled within the range of this application.

[0035] In one embodiment of this application, when the state of charge of the electrochemical device is 0%, the lattice index OI of the negative electrode active material satisfies: 8 ≤ OI ≤ 20. For example, the lattice index OI of the negative electrode active material can be 8, 10, 12, 14, 16, 18, 20, or any value between any two of the above ranges. By controlling the lattice index OI of the negative electrode active material within the above range, the negative electrode active material can have better kinetics while ensuring its structural stability, thereby further improving the high-temperature storage performance of the electrochemical device.

[0036] This application does not impose any particular limitation on the type of negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, at least one of artificial graphite, natural graphite, or hard carbon.

[0037] This application does not impose any particular restrictions on the preparation method of the negative electrode active material, as long as it can achieve the purpose of this application.

[0038] In one embodiment of this application, the electrochemical device includes an electrolyte comprising EC; based on the mass of the electrolyte, the mass percentage of EC is 8% to 30%, preferably 15% to 25%. For example, the mass percentage of EC can be 8%, 12%, 15%, 17%, 20%, 25%, 30%, or any value between any two of the above ranges. If the mass percentage of EC is too low (e.g., below 8%), it is not easy to passivate the interface between the negative electrode and the electrolyte. If the mass percentage of EC is too high (e.g., above 30%), the viscosity of the electrolyte increases at low temperatures, and gas generation is more likely to occur at high voltages, increasing the expansion rate of the electrochemical device. By controlling the mass percentage of EC within the range of this application, it is more conducive to passivating the interface between the negative electrode and the electrolyte, thus alleviating lithium plating and suppressing gas generation in the electrolyte, thereby improving the high-temperature storage performance of the electrochemical device. By controlling the mass percentage of EC within the preferred range of this application, it is more conducive to further passivating the interface between the negative electrode and the electrolyte, thereby further alleviating the lithium plating phenomenon and further suppressing the gas generation phenomenon of the electrolyte, thus further improving the high-temperature storage performance of the electrochemical device.

[0039] In one embodiment of this application, the electrolyte includes a lithium salt, which includes at least one of LiPF6, LiFSI, or LiTFSI; the concentration of the lithium salt in the electrolyte is from 0.9 mol / L to 1.5 mol / L. For example, the concentration of the lithium salt in the electrolyte can be 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.3 mol / L, 1.5 mol / L, or any value between any two of the above ranges. Lithium salts have poor thermal stability at high temperatures and are prone to decomposition, leading to an increase in electrolyte acidity. By selecting the above-mentioned types of lithium salts and controlling the concentration of lithium salts in the electrolyte within the above-mentioned ranges, it is more beneficial to reduce the increase in electrolyte acidity, mitigate the impact of transition metal dissolution in the positive electrode active material, and thus improve the high-temperature storage performance of the electrochemical device.

[0040] The electrolyte of this application includes non-aqueous solvents. This application does not have particular limitations on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, the non-aqueous solvent may include at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (EMC). The aforementioned cyclic carbonate compounds may include, but are not limited to, at least one of propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). The aforementioned fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, or propyl propionate. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvents mentioned above may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphate esters. Based on the mass of the electrolyte, the mass percentage of the above non-aqueous solvents is 5% to 70%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any value between any two of the above ranges.

[0041] The electrochemical device of this application includes a positive electrode sheet. This application does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet includes a positive current collector and a positive active material layer. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application. For example, the positive current collector may include aluminum foil or aluminum alloy foil. The positive active material layer of this application includes a positive active material. This application does not impose any particular limitation on the type of positive active material, as long as it achieves the purpose of this application. For example, the positive active material may include 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 (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. In this application, the positive active material may also include non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, and sulfur, which can further improve the stability of the positive active material. In this application, there are no particular limitations on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. The thickness of the single-sided positive electrode active material layer is 30 μm to 120 μm. In this application, the positive electrode active material layer can be disposed on one surface or on two surfaces in the thickness direction of the positive electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the positive electrode current collector or a part of the positive electrode current collector; there are no particular limitations in this application, as long as the purpose of this application can be achieved. Optionally, the positive electrode sheet may also include a conductive layer, which is located between the positive electrode current collector and the positive electrode active material layer. The composition of the conductive layer is not particularly limited and can be a conductive layer commonly used in the art.

[0042] This application does not impose any particular restrictions on the preparation method of the positive electrode active material, as long as it achieves the purpose of this application. For example, the preparation method of the positive electrode active material includes the following steps:

[0043] (1) Precursor: Prepare a mixed salt solution with a molar concentration of 1 mol / L to 3 mol / L by mixing nickel sulfate (or nickel chloride), cobalt sulfate (or cobalt chloride), and manganese sulfate (or manganese chloride) in the ratio of n(Ni):n(Co):n(Mn) = (0.4-0.6):(0.1-0.3):0.3. Prepare an alkaline solution with a molar concentration of 3 mol / L to 5 mol / L by mixing sodium hydroxide. Use ammonia water with a concentration of 3 mol / L to 5 mol / L as a complexing agent. All prepared solutions must be filtered to remove solid impurities before proceeding to the next step. Add the filtered salt solution, alkaline solution, and complexing agent to the reactor at a flow rate of 20 L / h to 40 L / h, and control the stirring rate of the reactor at 20 r·min. -1 to 40r·min -1The reaction slurry is kept at room temperature and pH 10 to 13, which allows the salt and alkali to undergo a neutralization reaction to generate ternary precursor crystal nuclei that gradually grow. When the average particle size reaches 2.5 μm to 4.5 μm, the reaction slurry is filtered, washed, and dried to obtain the ternary precursor.

[0044] (2) Primary mixing: The lithium source Li2CO3 and the precursor are mixed in a Li / M (M = Ni, Co, Mn) molar ratio of (1.01-1.10):1 and then placed in a high-speed mixer and added to a sagger for the next primary sintering process;

[0045] (3) First sintering: The material mixed evenly in step (2) and loaded into the sagger is placed in the kiln and first pre-fired in the air atmosphere at a heating rate of 4℃ / min to 6℃ / min to the first sintering temperature of 680℃ to 720℃. Then, it is calcined in the air atmosphere at the first sintering temperature for 11 to 13 hours to obtain the first sintered material.

[0046] (4) Mechanical crushing and air jet milling: After cooling the primary sintered material obtained in step (3), mechanical crushing, air jet milling and grading are performed.

[0047] (5) Secondary sintering and coating: The primary sintering material after crushing and grading in step (4) is mixed with the coating additive at a mass ratio of (90-110):0.5 in a high-speed mixer, and then placed in a sagger and placed in a kiln. After calcination in air atmosphere for 5 to 7 hours, the obtained material is mechanically pulverized, graded, demagnetized, and sieved to obtain the positive electrode active material. This application does not have any particular restrictions on the type of coating additive mentioned above, as long as it can achieve the purpose of this application.

[0048] The electrochemical device of this application includes a diaphragm. This application does not impose any particular limitation on the diaphragm, as long as it achieves the purpose of this application. For example, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure. The material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, at least one surface of the substrate layer is provided with a surface treatment layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. The inorganic particles are not particularly limited, and may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The adhesive is not particularly limited and may include, for example, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0049] The electrochemical device described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In some embodiments, the electrochemical device may include, but is not limited to, lithium metal secondary batteries, lithium-ion batteries, sodium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0050] The fabrication process of electrochemical devices is well known to those skilled in the art, and this application does not impose any particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a packaging shell; injecting electrolyte into the packaging shell and sealing it to obtain the electrochemical device; or stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a packaging shell; injecting electrolyte into the packaging shell and sealing it to obtain the electrochemical device. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the packaging shell as needed to prevent pressure rise and overcharging / discharging inside the electrochemical device.

[0051] A second aspect of this application provides an electronic device that includes the electrochemical device described in any of the foregoing embodiments. Therefore, the beneficial effects of the electrochemical device described in any of the foregoing embodiments can be obtained.

[0052] There are no particular limitations on the electronic devices covered by this application, which may include, but are not limited to, the following: laptops, pen-based 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, large household batteries, and lithium-ion capacitors, etc.

[0053] Example

[0054] 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.

[0055] Test methods and equipment:

[0056] R-value testing:

[0057] An area of ​​100 μm × 100 μm was selected on the negative electrode active material layer. 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 and G peaks of all negative electrode active material particles within this area were obtained. The data were processed using LabSpec software to obtain the peak intensities of the D and G peaks for each negative electrode active material particle, denoted as I(D) and I(G), respectively. The laser wavelength of the Raman spectrometer can be in the range of 532 nm to 785 nm. The R value, I(D) / I(G), is the average value of the I(D) to I(G) ratio of all negative electrode active material particles measured within this range.

[0058] Peak D: Displacement range is 1300 cm -1 Up to 1400cm -1 Caused by the radial breathing mode of the symmetric stretching vibration of sp2 carbon atoms in the aromatic ring (structural defect); G peak: displacement range 1530 cm⁻¹ -1 Up to 1630cm -1 It is caused by the stretching vibration between sp2 carbon atoms, which corresponds to the vibration of the E2g optical phonon at the center of the Brillouin zone (in-plane vibration of carbon atoms).

[0059] DCR testing:

[0060] Take five lithium-ion batteries prepared in each of the embodiments and comparative examples, place each lithium-ion battery in a constant temperature chamber at 25°C for 5 minutes, charge at a constant current rate of 1C to 4.2V, then charge at a constant voltage until the current is less than or equal to 0.05C, let stand for 30 minutes, discharge at a current of 0.1C for 10 seconds, and record the corresponding voltage value U1. Then discharge at a current of 1C for 360 seconds and record the corresponding voltage value U2. Repeat the above discharge steps until the battery voltage is less than 3.0V. "1C" is the current value that completely discharges the capacity of each lithium-ion battery within 1 hour.

[0061] After each of the above-mentioned discharge steps (i.e., once each at a current of 0.1C for 10 seconds and once at a current of 1C for 360 seconds), the DC resistance (DCR) of the lithium-ion battery after the corresponding discharge step at 25°C was calculated using the following formula: R = (U1 - U2) / (1C - 0.1C), in milliohms (mΩ). The DCR of each lithium-ion battery after the 5th discharge step was taken, and the corresponding average value was calculated. This average value was then used as the DCR measured in the embodiments and comparative examples of this application (as shown in Tables 1-3).

[0062] Unless otherwise specified, the DCR mentioned in this application refers to the average DCR of each lithium-ion battery after the 5th discharge step.

[0063] Testing the conductivity σ of the negative electrode:

[0064] The conductivity σ of the negative electrode is measured using an electrode resistance meter. The formula is R = ρ × l / S, and σ = 1 / ρ, therefore σ = l / (R × S). In this formula, R is the resistance of the negative electrode, ρ is the resistivity of the negative electrode, and S is the measured area of ​​the negative electrode.

[0065] Testing of the areal density of the negative electrode active material layer:

[0066] The areal density Q of the negative electrode active material layer is calculated using the formula: Q = 1540.25 m / Ar. In the formula, m is the mass of the negative electrode active material layer (g), and Ar is the area of ​​the negative electrode active material layer (mm²). 2 .

[0067] Testing the compaction density of the negative electrode active material layer:

[0068] The compaction density Pa of the negative electrode active material layer is calculated using the formula: Pa = Ma / Va. In the formula, Ma is the mass of the negative electrode active material layer (g), and Va is the volume of the negative electrode active material layer (cm³). 3 Wherein, the volume Va is the product of the area Sa of the negative electrode active material layer and the thickness of the negative electrode active material layer.

[0069] Testing of the lattice index (OI):

[0070] The lattice index OI value of the negative electrode active material was tested using an X-ray (XRD) diffractometer: The negative electrode active material layer was placed in the XRD diffractometer, and the crystal plane areas of the (004) and (110) peaks were measured to be C(004) and C(110), respectively. The OI value was calculated according to the following formula: OI value = C(004) / C(110).

[0071] High-temperature storage performance testing:

[0072] Ten lithium-ion batteries were tested in each embodiment or comparative example, and the average value was taken as the final result. At 25°C, the lithium-ion batteries were left to stand for 30 minutes, then charged at a constant current of 0.7C to 3.65V, and then charged at a constant voltage of 3.65V to 0.05C. After standing for 5 minutes, the thickness of the lithium-ion batteries was measured and recorded as the thickness before storage. Then, after storing for 1008 hours at 85% humidity, 80°C, and 3.65V, the thickness of the lithium-ion batteries was measured and recorded as the thickness after storage. The thickness expansion rate of the lithium-ion batteries was then calculated using the following formula: Thickness expansion rate = [(Thickness after storage / Thickness before storage) - 1] × 100%.

[0073] The number of passes refers to the number of lithium-ion batteries with a thickness expansion rate of less than or equal to 12% out of 10 lithium-ion batteries tested in each embodiment or comparative example.

[0074] Example 1-1

[0075] <Preparation of Electrolyte>

[0076] In a dry argon-atmospheric glove box, EC, PC, and DEC were mixed to obtain an organic solvent. Lithium salt LiPF6 was then added to the organic solvent, dissolved, and mixed thoroughly. Finally, fluoroethylene carbonate and adiponitrile were added to obtain the electrolyte. The concentration of LiPF6 in the electrolyte was 1.0 mol / L. Based on the mass of the electrolyte, the mass percentages of EC, fluoroethylene carbonate, and adiponitrile were 8%, 3%, and 3%, respectively; the remainder consisted of PC and DEC in a mass ratio of 1:2.

[0077] <Preparation of Negative Electrode Sheets>

[0078] Graphite, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95:2:3, and deionized water was added. The mixture was stirred evenly under vacuum to obtain a negative electrode slurry with a solid content of 75 wt%. The negative electrode slurry was uniformly coated onto one surface of a 12 μm thick copper foil current collector. The copper foil was dried at 120°C to obtain a single-sided negative electrode sheet with a 1.5 μm coating thickness of the negative electrode active material layer. The above steps were repeated on the other surface of the copper foil to obtain a double-sided negative electrode sheet with a negative electrode active material layer. After drying, cold pressing, cutting, and slitting, a negative electrode sheet with dimensions of 87.6 mm × 700.8 mm (length L = 700.8 mm, width W = 87.6 mm) was obtained. The lattice index OI of the negative electrode active material was 18, the R value was 0.15, and the areal density of the negative electrode active material layer was 0.08 mg / mm². 2 The compacted density is 1.7 g / cm³. 3 The conductivity σ of the negative electrode is 15 S / cm.

[0079] <Preparation of Positive Electrode Active Materials>

[0080] (1) Precursors: Nickel sulfate, cobalt sulfate, and manganese sulfate were prepared into a mixed salt solution with a molar concentration of 2 mol / L according to the ratio of n(Ni):n(Co):n(Mn) = 0.5:0.2:0.3. Sodium hydroxide was prepared into an alkaline solution with a molar concentration of 4 mol / L. Ammonia water with a concentration of 4 mol / L was used as a complexing agent. All prepared solutions were filtered to remove solid impurities before proceeding to the next step. The filtered mixed salt solution, alkaline solution, and complexing agent were added to the reactor at a flow rate of 30 L / h, and the stirring rate of the reactor was controlled at 30 r·min. -1 The reaction slurry is kept at room temperature and pH 11.5 to allow the salt and alkali to neutralize and generate ternary precursor crystal nuclei, which gradually grow. When the average particle size reaches 3.5 μm, the reaction slurry is filtered, washed, and dried to obtain the ternary precursor.

[0081] (2) Primary mixing: The lithium source Li2CO3 and the precursor are mixed according to n(Li):n(Ni):n(Co):n(Mn)=1.05:0.5:0.2:0.3 and then placed in a high-speed mixer and added to a sagger for the next primary sintering process;

[0082] (3) First sintering: The material that was mixed evenly in step (2) and loaded into the sagger is placed in the kiln and first pre-fired in the air atmosphere at a heating rate of 5℃ / min to the first sintering temperature of 700℃. Then, it is calcined in the air atmosphere at the first sintering temperature for 12 hours to obtain the first sintered material.

[0083] (4) Mechanical crushing and air jet milling: After cooling the primary sintered material obtained in step (3), mechanical crushing, air jet milling and grading are performed.

[0084] (5) Secondary sintering and coating: The primary sintering material after crushing and grading in step (4) is mixed with the coating additive alumina at a mass ratio of 100:0.5 and then mixed evenly in a high-speed mixer. After being placed in a sagger and placed in a kiln, it is calcined in an air atmosphere for 6 hours. The obtained material is then mechanically pulverized, graded, demagnetized, and sieved to obtain the positive electrode active material.

[0085] <Preparation of the positive electrode>

[0086] The prepared positive electrode active materials lithium nickel cobalt manganese oxide, acetylene black, and polyvinylidene fluoride were mixed at a mass ratio of 96:2:2, and N-methylpyrrolidone (NMP) was added. The mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated onto one surface of a 12 μm thick aluminum foil for positive electrode current collectors. The aluminum foil was dried at 120 °C to obtain a positive electrode sheet with a single-sided coating of positive electrode active material. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode active material. After drying, cold pressing, cutting, and slitting, a positive electrode sheet with a size of 86 mm × 698.8 mm was obtained.

[0087] <Preparation of the diaphragm>

[0088] A porous polyethylene film with a thickness of 7μm (supplied by Celgard) is used.

[0089] <Preparation of Lithium-ion Batteries>

[0090] The positive electrode, separator, and negative electrode prepared above are stacked in sequence, with the separator positioned between the positive and negative electrode to act as a separator. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, degassing, and edge trimming, a lithium-ion battery is obtained.

[0091] Examples 1-2 to Examples 1-9

[0092] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0093] Examples 2-1 to 2-8

[0094] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-1.

[0095] Examples 3-1 to 3-7

[0096] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-1.

[0097] Comparative Examples 1 to 6

[0098] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0099] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0100] Table 1

[0101]

[0102]

[0103] As can be seen from Examples 1-1 to 1-9 and Comparative Examples 1 to 6, the high-temperature storage performance of lithium-ion batteries varies with the ratio of the length L to the width W of the negative electrode current collector (L / W) and the R value of the negative electrode active material. Lithium-ion batteries with both L / W and R values ​​within the scope of this application exhibit a larger DCR (as relative to Comparative Example 1), a smaller thickness expansion rate, and a higher number of passes, indicating that the lithium-ion batteries have better high-temperature storage performance.

[0104] As can be seen from Examples 1-1 to 1-9 and Comparative Examples 3 to 6, lithium-ion batteries with L / W and R values ​​within the scope of this application (such as Examples 1-1 to 1-9) have a smaller thickness expansion rate and a higher number of passes compared to lithium-ion batteries with L / W or R values ​​outside the scope of this application (such as Comparative Examples 3 to 6), indicating that lithium-ion batteries have better high-temperature storage performance.

[0105] Figure 2 Raman spectra of the negative electrode active materials of Examples 1-4 are shown, as follows: Figure 2 As shown in the figure, the displacement range is 1300cm. -1 Up to 1400cm -1 The D peak and displacement range are in the range of 1530 cm. -1 Up to 1630cm -1 The G peak has an R value of 0.30.

[0106] Table 2

[0107]

[0108] The mass percentage of EC in the electrolyte typically affects the high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-1 to 2-5, the lithium-ion batteries within the scope of this application with an EC mass percentage in the electrolyte exhibit a larger DCR, a lower thickness expansion rate, and a higher number of passes, thus demonstrating good high-temperature storage performance.

[0109] The type of lithium salt typically affects the high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 2-4, 2-6, and 2-7, the lithium salt used in the lithium-ion batteries within the scope of this application exhibits a larger DCR, a lower thickness expansion rate, and a higher number of passes, thus demonstrating good high-temperature storage performance.

[0110] The concentration of lithium salt in the electrolyte typically affects the high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 2-4 and 2-8, the lithium salt concentration in the electrolyte within the scope of this application results in lithium-ion batteries with a large DCR, low thickness expansion rate, and high throughput, i.e., good high-temperature storage performance.

[0111] Table 3

[0112]

[0113] The conductivity σ of the negative electrode typically affects the high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 3-1 to 3-3, the conductivity σ of the negative electrode in the lithium-ion battery within the scope of this application has a large DCR, a low thickness expansion rate, and a high number of passes, i.e., it has good high-temperature storage performance.

[0114] The areal density of the negative electrode active material layer typically affects the high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 3-4, and 3-5, the lithium-ion battery with an areal density of negative electrode active material layer within the scope of this application has a large DCR, a low thickness expansion rate, and a high number of passes, thus exhibiting good high-temperature storage performance.

[0115] The compaction density of the negative electrode active material layer typically affects the high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 3-6, and 3-7, the lithium-ion batteries within the scope of this application exhibit a large DCR (Displacement Rate), a low thickness expansion rate, and a high number of passes, thus demonstrating good high-temperature storage performance.

[0116] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. An electrochemical device comprising a negative electrode sheet, the negative electrode sheet comprising 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 comprising a negative electrode active material; The length L of the negative electrode current collector and the width W of the negative electrode current collector satisfy: 10≤L / W≤40, 40mm≤W≤145mm; The R value of the negative electrode active material is 0.1 to 0.4; The R value is the average value of the peak intensity ratio I(D) / I(G) of the D peak and G peak of the negative electrode active material particles in any region with a size of 100μm×100μm on the negative electrode active material layer using Raman testing. The D peak represents the Raman spectrum of the negative electrode active material particles with a shift range of 1300 cm⁻¹. -1 Up to 1400cm -1 The peak, G, is the Raman spectrum of the negative electrode active material particles with a shift range of 1530 cm⁻¹. -1 Up to 1630cm -1 The peak.

2. The electrochemical device according to claim 1, wherein, The impedance of the electrochemical device is 30 mΩ to 60 mΩ.

3. The electrochemical device according to claim 1, wherein, The conductivity σ of the negative electrode sheet satisfies: 15S / cm≤σ≤35S / cm.

4. The electrochemical device according to claim 1, wherein, The areal density of the negative electrode active material layer is 0.05 mg / mm². 2 Up to 0.11 mg / mm 2 .

5. The electrochemical device according to claim 1, wherein, The compaction density of the negative electrode active material layer is 1.6 g / cm³. 3 Up to 1.8 g / cm 3 .

6. The electrochemical device according to claim 1, wherein, When the state of charge of the electrochemical device is 0%, the lattice index OI of the negative electrode active material satisfies: 8≤OI≤20.

7. The electrochemical device according to claim 3, wherein it satisfies at least one of the following features (1) to (3): (1) The length L of the negative electrode current collector and the width W of the negative electrode current collector satisfy: 18≤L / W≤40; (2) The value of R is between 0.15 and 0.30; (3) The conductivity σ of the negative electrode sheet satisfies: 25S / cm≤σ≤30S / cm.

8. The electrochemical device according to claim 1, wherein, The electrochemical device includes an electrolyte, which includes ethylene carbonate. Based on the mass of the electrolyte, the mass percentage of ethylene carbonate is 8% to 30%.

9. The electrochemical device according to claim 8, wherein, Based on the mass of the electrolyte, the mass percentage of ethylene carbonate is 15% to 25%.

10. The electrochemical device according to claim 8, wherein, The electrolyte includes a lithium salt, which includes at least one of LiPF6, lithium bis(fluorosulfonyl)imide, or lithium bis(trifluoromethanesulfonyl)imide. The concentration of the lithium salt in the electrolyte is from 0.9 mol / L to 1.5 mol / L.

11. An electronic device comprising the electrochemical device according to any one of claims 1 to 10.

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