A battery, a battery pack, and an electrical device.

Abstract

This application provides a battery, a battery pack, and an electrical device. The battery includes a cell and an electrolyte. The cell includes a negative electrode, a positive electrode, and a separator located between the negative electrode and the positive electrode. The negative electrode includes a negative current collector and a negative active layer present on at least one side of the negative current collector. The negative active layer includes a negative active material. The particle size D of the negative active material is... n 50 A is 6μm~13μm; the electrolyte includes an organic solvent, the organic solvent includes a carboxylic acid ester solvent, the mass ratio B of the carboxylic acid ester solvent in the electrolyte is 1.7%~14%; the capacity ratio C of the negative electrode to the positive electrode is 1.25~1.7; the battery satisfies: 0.13≤A×B×C≤3.1. This application can reduce the charge and discharge impedance of the battery under normal temperature and low temperature environments and improve the power performance of the battery.

Description

Technical Field

[0001] This application relates to the field of batteries, and more particularly to a battery, a battery pack, and an electrical device. Background Technology

[0002] Currently, high-power batteries are receiving widespread attention in the market, especially in low-temperature environments. The demand for high-power batteries in the new energy market is increasing. Existing batteries do not perform ideally in low-temperature environments due to polarization and other reasons. For example, when lithium-ion batteries operate at -10°C, their charging and discharging capabilities will drop significantly, leading to charging and discharging difficulties. When the ambient temperature drops to -40°C, the battery may be unable to charge and discharge, resulting in a "dead battery" state.

[0003] Studies have found that the main reasons for poor battery power performance include long diffusion paths of active ions such as lithium ions, high interfacial impedance between the negative electrode and the electrolyte, large concentration gradient (the concentration difference of active ions between the negative electrode and the electrolyte), and low diffusion rate of active ions. Current technologies typically optimize a single material in the battery, but this approach cannot effectively overcome the above problems, resulting in limited improvements in battery power performance. In particular, it is difficult to simultaneously reduce the charge and discharge impedance of the battery at room temperature and low temperatures, and improve the battery's power performance at these temperatures.

[0004] Therefore, how to improve the power performance of batteries, especially while also improving the power performance of batteries at room temperature and low temperature, remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This application provides a battery, a battery pack, and an electrical device that can reduce the charging and discharging impedance of the battery in normal and low temperature environments and improve the power performance of the battery in normal and low temperature environments.

[0006] In a first aspect, embodiments of this application provide a battery, including a battery cell and an electrolyte. The battery cell includes a negative electrode, a positive electrode, and a separator located between the negative electrode and the positive electrode. The negative electrode includes a negative current collector and a negative active layer present on at least one side of the negative current collector. The negative active layer includes a negative active material. The particle size D of the negative active material is... n 50 A is 6μm~13μm; the electrolyte includes an organic solvent, the organic solvent includes a carboxylic acid ester solvent, the mass ratio B of the carboxylic acid ester solvent in the electrolyte is 1.7%~14%; the capacity ratio C of the negative electrode to the positive electrode is 1.25~1.7; the battery satisfies: 0.13≤A×B×C≤3.1.

[0007] In one possible implementation, the particle size D of the negative electrode active materialn 50 represents 10μm~13μm.

[0008] In one possible implementation, the carboxylic acid ester solvent accounts for 1.7% to 11% of the mass ratio B of the electrolyte.

[0009] In one possible implementation, the capacity ratio C of the negative electrode to the positive electrode is 1.4 to 1.7.

[0010] In one possible implementation, the carboxylic acid ester solvent includes ethyl propionate and / or ethyl acetate.

[0011] In one possible implementation, the organic solvent further includes cyclic carbonates and / or chain carbonates.

[0012] In one possible implementation, the cyclic carbonate comprises ethylene carbonate and / or propylene carbonate;

[0013] And / or, the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0014] In one possible implementation, the electrolyte further includes an electrolyte salt;

[0015] Preferably, the electrolyte salt includes a lithium salt;

[0016] Preferably, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0017] In one possible implementation, the electrolyte further includes additives, which include one or more of lithium difluorosulfonylimide, vinylene carbonate, vinyl sulfate, and lithium difluorophosphate.

[0018] In one possible implementation, the battery is a lithium-ion battery.

[0019] Secondly, embodiments of this application provide a battery pack comprising at least two batteries as described above.

[0020] Thirdly, embodiments of this application provide an electrical device, including the battery or battery pack described above.

[0021] This application provides a battery, battery pack, and electrical device, which, through the control of particle size D of the negative electrode active material in the battery... nBy synergistically defining the mass ratio of carboxylic acid ester solvent to electrolyte (B), the capacity ratio of negative electrode to positive electrode (C), and the range of A×B×C, the diffusion path of active ions such as lithium ions can be shortened, thereby reducing concentration polarization and improving the insertion and extraction capabilities of active ions such as lithium ions in the negative electrode. Simultaneously, it helps reduce electrolyte consumption and forms a solid electrolyte interface film of suitable thickness on the surface of the negative electrode. Combined with a suitable capacity ratio of negative electrode to positive electrode (or N / P), concentration polarization is reduced, and lithium plating is avoided. Furthermore, the low viscosity of carboxylic acid ester solvent, when combined with a suitable mass ratio, can improve the diffusion efficiency of active ions and reduce the ohmic impedance Rs and diffusion impedance Rw of the battery. Therefore, based on the synergistic effect between the negative electrode, electrolyte, and positive electrode, this application can simultaneously reduce the charge and discharge impedance of the battery at both room temperature and low temperature environments, and improve the power performance of the battery at both temperatures. Detailed Implementation

[0022] To enable those skilled in the art to better understand the solutions of this invention, the following provides a more detailed description of this application. The specific embodiments listed below are merely descriptions of the principles and features of this invention; the examples are only for explaining the invention and are not intended to limit its scope. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0023] Existing technologies typically optimize a single material in a battery, neglecting the systematic design of synergistic effects between materials, resulting in limited improvements in battery power performance.

[0024] In view of this, embodiments of the present invention provide a battery, including a cell and an electrolyte. The cell includes a negative electrode, a positive electrode, and a separator located between the negative electrode and the positive electrode. The negative electrode includes a negative current collector and a negative active layer present on at least one side surface of the negative current collector. The negative active layer includes a negative active material. The particle size D of the negative active material is... n 50A has a diameter of 6μm to 13μm; the electrolyte includes organic solvents, including carboxylic acid ester solvents, and the mass ratio of carboxylic acid ester solvents to electrolytes is 1.7% to 14%; the capacity ratio of negative electrode to positive electrode is 1.25 to 1.7; the battery satisfies: 0.13≤A×B×C≤3.1.

[0025] According to the inventors' research, the aforementioned battery composition system can reduce the charge and discharge impedance of the battery under normal and low temperature environments, thereby improving the battery's power performance. The reason for this is attributed to the particle size D of the negative electrode active material. nWithin the range of 6μm to 13μm, the particle size of the active material can shorten the diffusion path of active ions such as lithium ions, thereby reducing concentration polarization and improving the insertion and extraction capabilities of active ions such as lithium ions in the negative electrode. Simultaneously, it helps reduce electrolyte consumption and generates a solid electrolyte interface film of suitable thickness on the surface of the negative electrode. Combined with the aforementioned capacity ratio of the negative electrode to the positive electrode (or simply N / P), concentration polarization is reduced, preventing lithium plating in the battery. Furthermore, the low viscosity of carboxylic acid ester solvents, combined with the aforementioned mass ratio of carboxylic acid ester solvents, can improve the diffusion efficiency of active ions, reducing the ohmic impedance Rs and diffusion impedance Rw of the battery. Simultaneously, the battery satisfies: 0.13 ≤ A × B × C ≤ 3.1. By synergistically limiting the particle size of the negative electrode active material, the mass ratio of carboxylic acid ester solvents to electrolyte, and the capacity ratio of the negative electrode to the positive electrode, the synergistic effect between the negative electrode active material, the organic solvent in the electrolyte, and the N / P ratio can be optimized, reducing the charge and discharge impedance of the battery under normal and low temperature environments and improving the battery's power performance.

[0026] According to further research by the inventors, smaller particle size of the negative electrode active material can achieve a shorter diffusion path for active ions such as lithium ions. The negative electrode sheet prepared using this material has a smaller active ion concentration gradient, which can effectively reduce concentration polarization. Furthermore, it typically has a high specific surface area and more active sites, thereby enhancing the insertion and extraction capabilities of active ions such as lithium ions and reducing charge transfer impedance. If the particle size D of the negative electrode active material... n If the particle size D of the negative electrode active material is greater than 13 μm, it will be detrimental to reducing concentration polarization and will increase charge transfer impedance. n If the surface area of ​​the negative electrode active material particles is too small (less than 6 μm), the specific surface area will be too large, which will easily cause more electrolyte to decompose, increase the thickness of the generated solid electrolyte interphase (SEI) film, and increase the interfacial impedance. Moreover, the porosity of the negative electrode sheet prepared by it is low, which affects the electrolyte wetting effect and also leads to an increase in impedance.

[0027] According to further research by the inventors, in the above battery composition system, the mass ratio of carboxylic acid ester solvent to electrolyte is the ratio of the mass of carboxylic acid ester solvent to the total mass of electrolyte. Carboxylic acid ester solvent is a low-viscosity solvent, which can reduce the viscosity of the electrolyte, improve the wettability of the electrolyte to the positive and negative electrodes, compensate for the low porosity of the negative electrode formed by the small-particle-size negative electrode active material, and the resulting insufficient electrolyte wetting in the negative electrode, thereby improving the ionic conductivity of the negative electrode, improving the diffusion efficiency of active ions, and reducing Rs and Rw impedances. If the mass ratio of carboxylic acid ester solvent to electrolyte is less than 1.7%, it is insufficient to react with the suitable particle size D of the negative electrode active material. nThe synergistic effect of 50 is not enough to effectively reduce battery impedance. If the mass ratio of carboxylic acid ester solvents to electrolyte is greater than 14%, the oxidation potential of carboxylic acid ester solvents is low, which leads to a decrease in the electrochemical stability of the electrolyte and will damage the negative electrode SEI film, affecting the compactness of the SEI film and thus increasing the interfacial impedance.

[0028] According to the inventors' further research, a suitable N / P ratio can reduce the local current density during charging, reduce concentration polarization, and avoid problems such as lithium plating in the battery. If the N / P ratio is higher than 1.7, the negative electrode capacity will exceed the positive electrode capacity by too much, which will waste the negative electrode active material and reduce the energy density of the battery. At the same time, with the above-mentioned negative electrode active material, the SEI film area will increase with the increase of the specific surface area of ​​the negative electrode active material, resulting in an exponential increase in interfacial impedance, which will offset the polarization reduction effect brought by N / P. If the N / P ratio is lower than 1.25, it is not conducive to reducing the local current density during charging, which may lead to problems such as lithium plating in the battery, and will also affect the battery's power performance and other electrochemical performance.

[0029] Therefore, in this embodiment of the invention, by synergistically limiting the particle size A of the negative electrode active material, the mass ratio B of the carboxylic acid ester solvent to the electrolyte, the capacity ratio C of the negative electrode sheet to the positive electrode sheet, and the range of A×B×C, it is possible to reduce the charge and discharge impedance of the battery under normal temperature and low temperature conditions and improve the power performance of the battery under normal temperature and low temperature conditions based on the synergistic effect between these conditions and their mutual compensation and balance.

[0030] For example, the particle size D of the negative electrode active material n 50 is 6μm~13μm, for example, it can be 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm or any combination thereof; the mass ratio of carboxylic acid ester solvent to electrolyte is 1.7%~14%, for example, it can be 1.7%, 2%, 4%, 6%, 8%, 10%, 11%, 12%, 14% or any combination thereof; the capacity ratio of negative electrode to positive electrode is 1.25~1.7, for example, it can be 1.25, 1.35, 1.40, 1.45, 1.55, 1.65, 1.7 or any combination thereof; the battery satisfies: 0.13≤A×B×C≤3.1, for example, it can be 0.13, 0.2, 0.5, 1.0, 1.25, 1.5, 2.0, 2.5, 2.8, 3.1 or any combination thereof.

[0031] In this embodiment of the invention, the particle size D n 50 (also known as the number median particle size) means that in the particle size distribution, 50% of the particles have a particle size smaller than this value, while 50% of the particles have a particle size greater than or equal to this value.

[0032] In this embodiment of the invention, the particle size D of the negative electrode active material n The value of 50 can be measured as follows: Take the battery described above and discharge it to an empty state, for example, to 2.8V; remove the negative electrode from the battery and dry it to remove water. Specifically, place the negative electrode in a drying oven for 12 hours to remove water. Then prepare a sample and test the cross-section of the negative electrode using a scanning electron microscope (SEM). Use the scale on the SEM to measure the particle size of the negative electrode active material in the cross-section. Measure the particle size (diameter) of 100 negative electrode active material particles and observe the median particle size, i.e., the particle size of 50% of the particles smaller than this value. Calculate the particle size D of the negative electrode active material. n 50. The magnification of the SEM should be such that the particles of the negative electrode active material can be clearly displayed, and the specific magnification can be 1000-5000.

[0033] In this embodiment of the invention, the mass ratio B of carboxylic acid ester solvent to electrolyte is determined by gas chromatography and external standard method. Specifically, the mass ratio of carboxylic acid ester solvent to electrolyte can be determined by the following method: take standard electrolyte, prepare standard solutions of different concentrations with diluent (e.g., acetone), preheat the gas chromatograph, and calibrate after the baseline stabilizes. Inject the standard solution for gas chromatography analysis, record the retention time and peak area of ​​each component, plot a standard curve (with the concentration of the standard solution as the abscissa and the chromatographic peak area as the ordinate), and fit the relationship (equation) between the peak area and the peak area of ​​carboxylic acid ester solvent. Take the battery described above, disassemble the battery, take the electrolyte as the sample to be tested, dilute the sample to 50 times with diluent, inject it into the injection port for gas chromatography analysis, record the chromatogram, perform qualitative and quantitative processing on the data in the chromatogram, obtain the retention time and peak area of ​​the carboxylic acid ester solvent, determine the composition of the carboxylic acid ester solvent, and substitute the peak area of ​​the carboxylic acid ester solvent into the above equation to calculate the mass ratio B of the carboxylic acid ester solvent to the electrolyte. The standard electrolyte can be any electrolyte with a known formulation.

[0034] In this embodiment of the invention, the capacity ratio of the negative electrode to the positive electrode is equal to the capacity of the negative electrode and the capacity of the positive electrode. The capacity of the negative electrode is equal to the reversible specific capacity of the negative active material × the weight (mass) of the negative active material in the negative electrode. The capacity of the positive electrode is equal to the reversible specific capacity of the positive active material × the weight (mass) of the positive active material in the positive electrode. The capacity ratio of the negative electrode to the positive electrode can be measured by the following method:

[0035] S1: Take the battery described above, disassemble the positive and negative electrode plates from the battery, and place the positive and negative electrode plates in a drying oven for 12 hours to remove moisture (to ensure that all moisture in the positive and negative electrode plates is removed). Use a cutting tool to cut out positive and negative electrode plates of the same area and weigh them, recording the weight as m. 正 and m 负 The positive and negative active layers are wiped away, and the weights of the positive and negative current collectors are weighed and recorded as m. 正极集流体 and m 负极集流体 Calculate the areal loading (area density) per unit area for the positive and negative electrodes: Areal loading per unit area for the positive electrode = (m² / 4) ... Calculate the areal loading per unit area for the positive and negative electrodes: Areal loading per unit area for the positive electrode = (m² / 4)² / 正 -m 正极集流体 ) / area of ​​the cut positive electrode, negative electrode unit area load = (m 负 -m 负极集流体 ) / Area of ​​the cut negative electrode sheet;

[0036] S2: Use a ruler to measure the length and width of the positive electrode active layer and the negative electrode active layer to obtain the area of ​​the positive electrode active layer and the negative electrode active layer;

[0037] S3: Reversible specific capacity of positive electrode active material: Positive electrode coin cell assembly: Place the positive electrode sheet in a drying oven to remove moisture for about 12 hours, then cut the positive electrode sheet with single-sided auxiliary material into coin cell adapter size (usually φ12-14). Assemble in a glove box in the following order: positive electrode shell → positive electrode sheet → separator → lithium sheet → electrolyte → spring sheet → gasket → negative electrode shell. Seal the coin cell and let it stand for about 4 hours. Charge at 0.1C constant current and constant voltage to 4.3V, cut off current 0.01C, let stand for 5 minutes, discharge at 0.1C constant current to 2.8V, let stand for 5 minutes, repeat the above steps 3 times, and take the capacity of the third time as the reversible specific capacity of the positive electrode active material;

[0038] S4: Reversible specific capacity of negative electrode active material: Negative electrode coin cell assembly: Place the negative electrode sheet in a drying oven to remove moisture for about 12 hours, then cut the electrode sheet with single-sided auxiliary material into coin cell adapter size (usually φ12-14). Assemble in a glove box in the following order: positive electrode shell → negative electrode sheet → separator → lithium sheet → electrolyte → spring sheet → gasket → negative electrode shell. Seal the coin cell and let it stand for about 4 hours. Discharge at a constant current of 0.05C to 0.01V, let it stand for 5 minutes, charge at a constant current of 0.1C to 1.5V, let it stand for 5 minutes, repeat the following steps 3 times, and take the capacity of the third time as the reversible specific capacity of the negative electrode active material;

[0039] S5: Positive Electrode Active Material Ratio: Disassemble the positive electrode sheet from the battery, place it in a drying oven to remove moisture for 12 hours, scrape off the positive electrode active layer, and grind it evenly. Take about 20mg and place it in the crucible of a thermogravimetric analyzer (TGA). Heat it from room temperature to 800℃ at 10℃ / min in an air or oxygen atmosphere. The positive electrode binder decomposes at 300℃-500℃, and the positive electrode conductive agent decomposes at 500℃-700℃. After 700℃, the mass remains basically unchanged. This mass is the positive electrode active material. Therefore, the positive electrode active material ratio = (mass of positive electrode active material / 20mg) × 100%;

[0040] S6: Percentage of negative electrode active material: Disassemble the negative electrode sheet from the battery, place it in a drying oven to remove moisture for 12 hours, scrape off the coating, and grind it evenly. Take about 20mg and place it in the crucible of the TGA instrument. Under a nitrogen atmosphere, heat from room temperature to 600℃ at 10℃ / min. At this time, the negative electrode binder decomposes and volatilizes. Switch the atmosphere to oxygen or air and continue heating to 800℃. At this time, the negative electrode conductive agent and graphite decompose in sequence, thus obtaining the mass of the negative electrode active material. Therefore, the percentage of negative electrode active material = mass of negative electrode active material / 20mg × 100%;

[0041] S7: N / P = Capacity of negative electrode / Capacity of positive electrode = (Area loading per unit area of ​​negative electrode × Area of ​​negative electrode active layer × Reversible specific capacity of negative electrode active material × Proportion of negative electrode active material) / (Area loading per unit area of ​​positive electrode × Area of ​​positive electrode active layer × Reversible specific capacity of positive electrode active material × Proportion of positive electrode active material). Wherein, the area of ​​the positive electrode refers to the area of ​​one side of the positive electrode, that is, the surface area of ​​one side in the thickness direction of the positive electrode; the area of ​​the negative electrode refers to the area of ​​one side of the negative electrode, that is, the surface area of ​​one side in the thickness direction of the negative electrode.

[0042] In this embodiment of the invention, the N / P ratio of the positive electrode and the negative electrode can be adjusted by conventional methods. For example, by controlling the areal density of the positive active layer in the positive electrode and the areal density of the negative active layer in the negative electrode, the capacity of the positive electrode and the negative electrode can be adjusted to achieve the preset N / P ratio. There are no particular limitations on this.

[0043] In some embodiments, the particle size D of the negative electrode active material n The thickness of 50 can be 10μm~13μm, which can further shorten the migration path of active ions, reduce electrolyte consumption, avoid the SEI film, reduce battery charge and discharge impedance, and improve battery charge and discharge performance.

[0044] In some embodiments, the mass ratio of carboxylic acid ester solvents to electrolyte can be 1.7% to 11%, which is more conducive to reducing electrolyte viscosity, improving electrolyte wettability, increasing battery ionic conductivity, reducing battery impedance, and improving battery low-temperature power performance.

[0045] In some embodiments, the capacity ratio of the negative electrode to the positive electrode can be 1.4 to 1.7, which can further improve the energy density of the battery, reduce concentration polarization, avoid lithium plating, and reduce interface impedance.

[0046] In some embodiments, the negative electrode active material may include graphite, which may include artificial graphite and / or natural graphite, which is more conducive to optimizing the above-mentioned negative electrode sheet and electrolyte system and improving the power performance of the battery.

[0047] In this embodiment of the invention, the negative electrode active material can be obtained by conventional methods, such as commercially available materials or self-made materials using conventional methods. Specifically, a negative electrode active material with the above-mentioned particle size can be obtained commercially, or the particle size D of the negative electrode active material can be controlled by conventional methods. n 50. For example, negative electrode active materials with a preset particle size can be obtained by grinding, sieving, etc.

[0048] In some embodiments, the negative electrode active layer may further include a binder and / or a conductive agent, both of which can be conventional materials in the art. For example, the conductive agent may include one or more of carbon black, conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; the binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, polyacrylic acid, and sodium polyacrylate.

[0049] Generally, in the negative electrode active layer, the mass percentage of the negative electrode active material (i.e., the ratio of the mass of the negative electrode active material to the total mass of the negative electrode active layer) can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof. The mass percentage of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof. The mass percentage of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof.

[0050] The embodiments of the present invention may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors include copper foil.

[0051] In this embodiment of the invention, the negative electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the negative electrode active layer, such as the negative electrode active material, conductive agent, and binder, can be dispersed in a solvent, such as water, to prepare a negative electrode slurry. This slurry is then coated onto the surface of the negative electrode current collector, and after drying, rolling, and other processes, the negative electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing negative electrode sheets using the coating method, and are not particularly limited thereto.

[0052] In some embodiments, carboxylic acid ester solvents include ethyl propionate (EP), which can further reduce the viscosity of the electrolyte, improve the wetting effect of the electrolyte, increase the ionic conductivity of the battery, improve the diffusion of active ions, reduce Rs and Rw impedance, and improve the charge and discharge performance of the battery.

[0053] In some embodiments, the organic solvent further includes a carbonate solvent, which includes cyclic carbonates and / or chain carbonates. Thus, the carboxylic acid ester solvent and the carboxylic acid ester solvent constitute a multi-solvent system. The carboxylic acid ester solvent is beneficial for reducing the viscosity of the electrolyte, while the carbonate solvent has a high oxidation potential, which is beneficial for improving the electrochemical stability of the electrolyte. Therefore, the multi-solvent system is more conducive to improving both the ionic conductivity and electrochemical stability of the electrolyte.

[0054] In some embodiments, cyclic carbonates include ethylene carbonate (EC) and / or propylene carbonate (PC), and chain carbonates include one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), which can further improve the electrochemical stability of the electrolyte and improve the power performance and cycle performance of the battery.

[0055] In some embodiments, the electrolyte further includes an electrolyte salt, which may include one or more of hexafluorophosphate, bis(fluorosulfonyl)imide salt, bis(trifluoromethanesulfonyl)imide salt, etc.

[0056] In some specific embodiments, the electrolyte salt includes a lithium salt, which may include one or more of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), and lithium bistrifluoromethanesulfonylimide (LiTFSI). This facilitates the dissolution of lithium salt in the electrolyte, improves the ionic conductivity of the battery, reduces the charge and discharge impedance of the battery, and further improves the power performance of the battery at room temperature and low temperature.

[0057] In some embodiments, the electrolyte further includes additives, including one or more of lithium bis(fluorosulfonyl)imide (LiFSI), vinylene carbonate (VC), vinyl sulfate (DTD), and lithium difluorophosphate (LiDFP), which are more conducive to optimizing electrolyte performance and improving the electrochemical performance of the battery, such as power.

[0058] In some embodiments, the battery described above can be a lithium-ion battery. In a lithium-ion battery, by optimizing the particle size of the negative electrode active material, the N / P ratio, the mass ratio of carboxylic acid esters in the electrolyte, and their synergistic relationship, and keeping them within the above ranges, it is beneficial to obtain a lithium-ion battery with excellent power performance.

[0059] Generally, a battery includes a cell and a casing that encapsulates the cell. Electrolyte is injected into the casing to wet the cell. The cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes. The cell can be a stacked cell, meaning it is composed of alternating layers of positive electrode, separator, and negative electrode; or it can be a wound cell, meaning it is composed of positive electrode, separator, and negative electrode layers stacked sequentially and then wound together.

[0060] In this embodiment of the invention, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited thereto.

[0061] In this embodiment of the invention, the separator is used to separate the positive electrode and the negative electrode to prevent the positive electrode and the negative electrode from short-circuiting due to contact. Conventional separators in the art can be used in this embodiment of the invention, and there are no special limitations on this.

[0062] Specifically, the diaphragm can be a polymer membrane, which can be a conventional diaphragm material in the art, for example, the diaphragm includes a polyethylene (PE) membrane.

[0063] In this embodiment of the invention, conventional positive electrode sheets in the art can be used, and there are no particular limitations. For example, the positive electrode sheet may include a positive current collector and a positive active layer located on at least one side surface of the positive current collector. Specifically, the positive active layer may be provided on one side surface of the positive current collector, or the positive active layers may be provided on both opposite sides of the positive current collector in the thickness direction (i.e., the two surfaces of the positive current collector).

[0064] Generally, the positive electrode active layer may include a positive electrode active material, a conductive agent, and a binder, all of which can be conventional materials in the art. For example, the positive electrode active material may include one or more of lithium nickel oxide, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and ternary positive electrode materials. The ternary positive electrode materials may include nickel cobalt manganese ternary materials (NCM) and / or nickel cobalt aluminum ternary materials (NCA). NCM, for example, includes NCM111 (lithium nickel cobalt manganese oxide, in which the atomic ratio of Ni, Co, and Mn elements is 1:1:1). The conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber. The binder may include one or more of polyvinylidene fluoride (PVDF), polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc.

[0065] Generally, in the positive electrode active layer, the mass percentage of the positive electrode active material (i.e., the ratio of the mass of the positive electrode active material to the total mass of the positive electrode active layer) can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof; the mass percentage of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof; and the mass percentage of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof.

[0066] The embodiments of the present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0067] In this embodiment of the invention, the positive electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the positive electrode active material, conductive agent, binder, and other components used to form the positive electrode active layer can be dispersed in a solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry. This slurry is then coated onto the surface of the positive electrode current collector, and after drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing positive electrode sheets using the coating method, and are not particularly limited thereto.

[0068] The embodiments of the present invention can assemble components such as positive electrode, separator and negative electrode into a battery using conventional methods in the art. For example, positive electrode, separator and negative electrode can be stacked in sequence to obtain a battery cell. Then the battery cell is placed in a casing (outer packaging) and after conventional battery assembly processes such as baking, liquid injection (i.e., injection of electrolyte), wetting, aging, formation and capacity testing, the battery is obtained.

[0069] This invention also provides a battery pack comprising at least two batteries as described above. This battery pack has advantages corresponding to the negative electrode or the batteries described above, which will not be elaborated further.

[0070] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0071] This invention also provides an electrical device, including the battery or battery pack described above. This electrical device has advantages corresponding to the positive electrode or battery described above, which will not be elaborated further.

[0072] The electrical equipment used in the embodiments of the present invention can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no particular limitations on this.

[0073] The present invention will be further described below through specific embodiments.

[0074] Example 1

[0075] (1) Preparation of negative electrode

[0076] 97 parts by weight of graphite and 1 part by weight of carbon black conductive agent were thoroughly mixed, deionized water was added, and then 1 part by weight of styrene-butadiene rubber (SBR) and 1 part by weight of sodium carboxymethyl cellulose (CMC) were added to prepare a negative electrode slurry. The negative electrode slurry was coated on both sides of a copper foil, and after baking and rolling, a negative electrode active layer was formed on both sides of the copper foil. After slitting, a negative electrode sheet was obtained, wherein the area of ​​the negative electrode active layer was 0.322 m². 2 Surface density is 70 g / m³ 2 .

[0077] (2) Preparation of positive electrode sheet

[0078] NCM111 (with an atomic ratio of Ni, Co, and Mn of 1:1:1), conductive agent carbon black, and binder PVDF are added sequentially to N-methylpyrrolidone. The mass ratio of NCM111, conductive agent, and binder is 93:5:2. The mixture is then homogenized using a high-speed dispersion device to prepare a positive electrode slurry. This slurry is coated onto both sides of an aluminum foil. After drying and rolling, a positive electrode active layer is formed on both sides of the aluminum foil. The resulting sheet is then slit to obtain a positive electrode plate, wherein the area of ​​the positive electrode active layer is 0.293 m². 2 The surface density is 124 g / m³ 2 .

[0079] (3) Battery assembly

[0080] The negative electrode, separator, positive electrode, and separator are stacked in sequence and then wound together using a winding machine to obtain the core (i.e., battery cell).

[0081] The battery cells are packaged in aluminum-plastic film and then assembled into lithium-ion batteries through battery assembly processes such as baking, electrolyte injection, aging, formation, and capacity testing.

[0082] The electrolyte used contains LiPF6 as the solute, EP as the carboxylic acid solvent, EC, EMC, and DMC as the carbonate solvents, and LiFSI, VC, DTD, and LiDFP as additives, which account for 8.72%, 13.63%, 17.03%, 34.06%, 20.44%, 4.62%, 0.50%, 0.50%, and 0.50% of the electrolyte by mass, respectively.

[0083] Examples 2-11, Comparative Examples 1-9: The difference from Example 1 is that the particle size D of the negative electrode active material is... n 50. The mass ratio of carboxylic acid ester solvent to electrolyte, the mass ratio of carbonate solvent DMC to electrolyte (mass ratio of carboxylic acid ester solvent to electrolyte + mass ratio of carbonate solvent DMC to electrolyte = 34.07%), the area of ​​the negative electrode active layer, the areal density of the negative electrode sheet, the area of ​​the positive electrode active layer, the areal density of the positive electrode sheet, the capacity ratio of the negative electrode sheet to the positive electrode sheet, and A×B×C are different. See Table 1 for details. Other steps and conditions are the same as in Example 1.

[0084] Example 12: The difference from Example 1 is that the carboxylic acid ester solvent in the electrolyte is EA, and the other steps and conditions are the same as in Example 1.

[0085] The particle size D of the negative electrode active material in each embodiment and comparative example n The test methods for conditions such as 50(A), the mass ratio of carboxylic acid ester solvent to electrolyte, B, and the capacity ratio of negative electrode to positive electrode, C, are as described above and will not be repeated here.

[0086] The low-temperature power and room-temperature power of the batteries in each embodiment and comparative example were tested through the following process, and the results are shown in Table 2.

[0087] (1) Low temperature power (-40℃ charge and discharge impedance) test: Take the lithium-ion battery prepared above, first discharge the battery to 2.8V at 25℃, let it stand for 600s, then charge it with 1C constant current and constant voltage, the cut-off current is 0.05C, adjust the SOC (state of charge) of the lithium-ion battery to 50%, then cool it down to -40℃ and keep it warm for 3h, and then start the test: stand for 600s, charge with 2C for 5s (the charging current is recorded as I1=2C, the voltage in the first 1s of charging is recorded as V1, and the voltage in the last 1s of charging is recorded as V2), stand for 600s, discharge with 0.1C for 100s, stand for 600s, discharge with 18C for 10s (the discharge current is recorded as I2=18C, the voltage in the first 1s of discharging is recorded as V3, and the voltage in the last 1s of discharging is recorded as V4), stand for 600s. The formula for calculating the charging impedance at -40℃ is (V2-V1) / I1×1000; the formula for calculating the discharging impedance at -40℃ is (V3-V4) / I2×1000, with the unit being mΩ.

[0088] (2) Room temperature power (charge and discharge impedance at 25℃) test: Take the lithium-ion battery prepared above, and at 25℃, first discharge the battery to 3V or 2.8V at 1C, let it stand for 600s, and then charge it with 1C constant current and constant voltage. The cutoff current is 0.05C. Adjust the SOC (state of charge) of the lithium-ion battery to 50%, and then start the test: let it stand for 600s, charge at 50C for 5s (the charging current is recorded as I1=50C, the voltage in the first 1s of charging is recorded as V1, and the voltage in the last 1s of charging is recorded as V2), let it stand for 600s, discharge at 1C for 250s to adjust the SOC (state of charge) of the battery to 50%, let it stand for 600s, discharge at 50C for 10s (the discharge current is recorded as I2=50C, the voltage in the first 1s of discharging is recorded as V3, and the voltage in the last 1s of discharging is recorded as V4), and let it stand for 600s. The formula for calculating charging impedance at 25℃ is (V2-V1) / I1×1000; the formula for calculating discharging impedance at 25℃ is (V3-V4) / I2×1000, with the unit being mΩ.

[0089] Table 1. Preparation of Lithium-ion Batteries

[0090]

[0091] Table 2 Lithium-ion battery performance test

[0092]

[0093] Compared to Comparative Examples 1-9, the particle size D of the negative electrode active material in Examples 1-12 n 50A has a thickness of 6μm to 13μm; the mass ratio of carboxylic acid ester solvent to electrolyte B is 1.7% to 14%; the capacity ratio of negative electrode to positive electrode C is 1.25 to 1.7; the battery satisfies: 0.13≤A×B×C≤3.1, which can reduce the charging and discharging impedance of the battery under normal temperature and low temperature environments and improve the power performance of the battery.

[0094] Examples 1, 4, and 6 show that as N / P increases, the cell impedance decreases and the power capability increases. However, as N / P increases to a certain extent, the power capability basically reaches saturation. Therefore, considering these factors, an N / P range of 1.4 to 1.7 is preferred.

[0095] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to what has been described above. Various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A battery, characterized in that, The battery includes a battery cell and an electrolyte, wherein the battery cell includes a negative electrode, a positive electrode, and a separator located between the negative electrode and the positive electrode; The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer present on at least one side of the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material; The particle size D of the negative electrode active material n 50 A ranges from 6 μm to 13 μm; The electrolyte includes an organic solvent, which includes carboxylic acid ester solvents, and the mass ratio B of the carboxylic acid ester solvent in the electrolyte is 1.7% to 14%. The capacity ratio C of the negative electrode to the positive electrode is 1.25~1.7; The battery satisfies: 0.13≤A×B×C≤3.

1.

2. The battery according to claim 1, characterized in that, The particle size D of the negative electrode active material n 50 represents 10μm~13μm.

3. The battery according to claim 1 or 2, characterized in that, The mass ratio B of the carboxylic acid ester solvent to the electrolyte is 1.7% to 11%.

4. The battery according to any one of claims 1-3, characterized in that, The capacity ratio C of the negative electrode to the positive electrode is 1.4 to 1.

7.

5. The battery according to any one of claims 1-4, characterized in that, The carboxylic acid ester solvents include ethyl propionate and / or ethyl acetate.

6. The battery according to any one of claims 1-5, characterized in that, The organic solvent also includes cyclic carbonates and / or chain carbonates.

7. The battery according to claim 6, characterized in that, The cyclic carbonates include ethylene carbonate and / or propylene carbonate; And / or, the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

8. The battery according to any one of claims 1-7, characterized in that, The electrolyte also includes electrolyte salts; Preferably, the electrolyte salt includes a lithium salt; Preferably, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

9. The battery according to any one of claims 1-8, characterized in that, The electrolyte also includes additives, which include one or more of lithium difluorosulfonyl imide, vinylene carbonate, vinyl sulfate, and lithium difluorophosphate.

10. The battery according to any one of claims 1-9, characterized in that, The battery is a lithium-ion battery.

11. A battery pack, characterized in that, It includes at least two batteries as described in any one of claims 1-9.

12. An electrical appliance, characterized in that, Includes the battery as described in any one of claims 1-9 or the battery pack as described in claim 11.

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