Negative electrode active material, battery, and electric device

Abstract

A negative electrode active material, a battery, and an electric device, relating to the field of batteries. The particle size Dv50 of the negative electrode active material is a μm, and the specific surface area of the negative electrode active material is b m2 / g, wherein 20≤2.5×a+b≤40. The battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte; the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector; and the negative electrode active material layer contains the negative electrode active material. According to the negative electrode active material, the battery, and the electric device, the low-temperature discharge capacity of the battery can be improved, and the low-temperature discharge capacity retention rate can be increased.

Description

Negative electrode active material, battery and electrical device

[0001] This application claims priority to the Chinese patent application with application number 202310980528.9 filed with the China Patent Office on August 4, 2023, entitled “Negative Electrode Active Material, Negative Electrode Sheet, Battery and Electrical Device,” the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of batteries, and in particular to a negative electrode active material, a battery, and an electrical device. Background Art

[0003] At present, as the ambient temperature drops, the internal polarization of lithium-ion battery cells increases, and the high-rate discharge capability of 10C and above gradually decreases. However, some electrical devices such as power tools and drones need to continue to work at low temperatures, so they have strict requirements for low-temperature high-rate discharge capability. The conventional method is to improve the low-temperature discharge capability by reducing the internal resistance of the battery cell (such as thin coating of the electrode), but this method often causes a loss of energy density, resulting in insufficient endurance of electrical equipment such as power tools and drones.

[0004] Summary of the Invention

[0005] In view of the above problems, the present application provides a negative electrode active material, a battery and an electrical device, which can improve the low-temperature discharge capability of the battery and enhance the low-temperature discharge capacity retention rate.

[0006] In the first aspect, the present application provides a negative electrode active material having a particle size Dv50 of a μm and a specific surface area BET of bm 2 / g, 20≤2.5×a+b≤40.

[0007] In the technical solution of the embodiment of the present application, the particle size and specific surface area of ​​the negative electrode active material satisfy the relationship: 20≤2.5×a+b≤40. The particles of the negative electrode active material that meet this condition can be tightly stacked, and electrons can be conducted between the particles, that is, the functions of ion diffusion and electronic conductive network can be taken into account, thereby providing a good conductive network, reducing the charge conduction impedance, and thus improving the low-temperature discharge capability of the battery, thereby improving the low-temperature high-rate discharge capability of the battery and improving the low-temperature discharge capacity retention rate.

[0008] In some embodiments, 25≤2.5×a+b≤35. This can further improve the low-temperature discharge capacity retention rate of the battery.

[0009] In some embodiments, 2≤a≤10; alternatively, 2≤a≤8. The negative electrode active material has a small particle size, and the particles can be densely packed, so that the battery has a high low-temperature discharge capacity retention rate.

[0010] In some embodiments, 10≤b≤25; alternatively, 13≤b≤20. The negative electrode active material has a large specific surface area, and electrons can be rapidly conducted inside and on the surface of the particles, thereby improving the low-temperature discharge capability of the battery.

[0011] In some embodiments, the tap density of the negative electrode active material is T g / cm 3 , 0.3≤T-0.05×a≤1.0; optionally, 0.5≤T-0.05×a≤0.8. The particle size and tap density of the negative electrode active material also satisfy the relationship: 0.3≤T-0.05×a≤1.0. The negative electrode active material can have a small particle size and good tap density, thereby improving the electronic conductivity between the particles and enhancing the low-temperature discharge capacity retention rate.

[0012] In some embodiments, 0.5≤T≤1.4; alternatively, 0.9≤T≤1.2. The negative electrode active material has a high tap density, which can further enhance electron conduction between particles and improve the low-temperature discharge capability of the battery.

[0013] In some embodiments, the negative electrode active material has a degree of graphitization of G%, 94.0 ≤ G ≤ 98.5, and optionally, 95.0 ≤ G ≤ 97.5. A high degree of graphitization of the negative electrode active material provides good electronic conductivity. Furthermore, a high degree of graphitization results in softer particles, allowing for a higher compaction density even with a small particle size, further improving the battery's low-temperature discharge capability.

[0014] In some embodiments, the compacted density of the negative electrode active material is P g / cm 3 , 1.75≤P≤2.20; optionally, 1.90≤P≤2.10. The negative electrode active material has a high compaction density, which can enhance electron conduction between particles and further improve the low-temperature discharge capability of the battery.

[0015] In some embodiments, the negative electrode active material has a Raman Id / Ig range of 0.1 to 0.35. The negative electrode active material has a good degree of graphitization, and its particle surface Raman Id / Ig range of 0.1 to 0.35, allowing electrons to conduct rapidly within and on the particle surface, thereby improving the low-temperature discharge capability of the battery.

[0016] In some embodiments, the negative electrode active material includes a sheet-like structure material, and the sheet-like structure material accounts for 90% to 100% of the negative electrode active material by weight. The sheet-like structure material has a large specific surface area, complete crystals, and good conductivity within and between particles, thereby improving the battery's low-temperature discharge capability and increasing the battery's low-temperature discharge capacity retention rate.

[0017] In some embodiments, the negative electrode active material comprises at least one of artificial graphite, natural graphite, a silicon-carbon material, or a silicon-oxygen material. Alternatively, the negative electrode active material comprises graphite having a soft or hard carbon surface. Alternatively, the negative electrode active material comprises flake graphite having a soft or hard carbon surface. The flake graphite having a soft or hard carbon surface has complete crystal growth, a high degree of graphitization, few surface defects, and rapid electron conduction within the particles. Furthermore, the high specific surface area ensures good contact between particles, resulting in a good electronic conductive network for the entire electrode.

[0018] In the second aspect, the present application provides a battery comprising a positive electrode plate, a negative electrode plate and an electrolyte, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on the surface of at least one side of the negative electrode current collector, and the negative electrode active material layer contains the negative electrode active material in the above embodiment. The battery using the negative electrode active material in the above embodiment has good kinetic performance, low impedance, and can continuously discharge at a high rate at low temperature.

[0019] In some embodiments, the negative electrode sheet has an electrical conductivity of 1 S / cm to 10 S / cm under a load of 25 MPa, and optionally, an electrical conductivity of 5 S / cm to 10 S / cm. The negative electrode active material has good electronic conductivity, and the formed negative electrode sheet also has an excellent electronic conductive network.

[0020] In some embodiments, the OI value of the negative electrode plate ranges from 11 to 21.

[0021] In a third aspect, the present application provides an electrical device, which includes the battery in the above embodiment, and the battery is used to provide electrical energy.

[0022] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0024] FIG1 is a SEM image of the negative electrode active material of Example 1-1. DETAILED DESCRIPTION

[0025] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0027] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0028] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0029] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0030] In the description of the embodiments of the present application, the orientations or positional relationships indicated by technical terms such as "inside" and "outside" are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the embodiments of the present application.

[0031] In the description of the embodiments of this application, unless otherwise expressly specified or limited, technical terms such as "installation," "connection," and "fixation" should be understood in a broad sense. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the embodiments of this application based on specific circumstances.

[0032] Currently, market developments indicate that power batteries are becoming increasingly widely used. They are not only used in energy storage systems such as hydropower, thermal, wind, and solar power plants, but are also widely used in electric vehicles like electric bicycles, electric motorcycles, and electric vehicles, as well as in military equipment and aerospace. As power battery applications continue to expand, market demand is also growing.

[0033] The high-rate discharge capability of a secondary battery at low temperatures depends on its polarization. When the polarization voltage falls below the lower discharge voltage, the secondary battery cannot be discharged. Existing lithium-ion secondary batteries have poor low-temperature high-rate discharge capability. As the ambient temperature drops, the internal polarization of the battery increases, and the high-rate discharge capability gradually decreases. However, some electrical devices, such as power tools and drones, require continuous operation at low temperatures, placing strict requirements on the battery's low-temperature high-rate discharge capability.

[0034] The conventional method to improve the low-temperature, high-rate discharge capability of a battery is to reduce its internal resistance (such as by thinly coating the electrodes). However, this method often results in a loss of energy density in the battery, which in turn results in insufficient battery life for electrical equipment such as power tools and drones, as well as increased manufacturing costs.

[0035] In order to improve the problem of low low-temperature discharge capability of the battery, the applicant has found that the charge conduction impedance (1s DCR) caused by low temperature is one of the key factors affecting the low-temperature discharge of the battery. Specifically screened negative electrode active materials can be used to form the electrode sheet to provide a good conductive network for the electrode sheet, reduce the charge conduction impedance, thereby improving the low-temperature discharge capability of the battery and improving the low-temperature discharge capacity retention rate.

[0036] The battery cells disclosed in the embodiments of this application can be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft. A power supply system comprising the battery cells and batteries disclosed in this application can be used to alleviate and automatically regulate deterioration in cell expansion, replenish electrolyte consumption, and improve battery performance stability and battery life.

[0037] The present invention provides an electric device that uses a battery as a power source. The electric device may be, but is not limited to, a mobile phone, a tablet, a laptop computer, an electric toy, an electric tool, a battery-powered vehicle, an electric car, a ship, a spacecraft, etc. The electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc. The spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, etc.

[0038] For the convenience of description, the following embodiments are described by taking a battery according to an embodiment of the present application as an example.

[0039] According to some embodiments of the present application, the present application provides a negative electrode active material, the particle size Dv50 of the negative electrode active material is a μm, the specific surface area BET is bm 2 / g, 20≤2.5×a+b≤40.

[0040] The particle size Dv50 and specific surface area BET of the negative electrode active material are characteristic parameters of the particle collection. Dv50 refers to the particle size (particle size) corresponding to 50% of the cumulative volume in the volume-based particle size distribution of the negative electrode active material, measured from the smallest particle size. a refers to the value of the particle size Dv50 in μm. The specific surface area BET refers to the total area of ​​the particles per unit mass, and b refers to the specific surface area BET in m 2 / g value.

[0041] The value of a of the particle size Dv50 of the negative electrode active material of the present application and the value of b of the specific surface area satisfy the relationship: 20≤2.5×a+b≤40. The negative electrode active material can take into account the functions of ion diffusion and electronic conductive network, thereby providing a good conductive network, improving the low-temperature discharge capability of the battery, and improving the low-temperature discharge capacity retention rate. According to some embodiments of the present application, 25≤2.5×a+b≤35 can further improve the low-temperature discharge capacity retention rate of the battery. As an example, the relationship between the particle size Dv50 and the specific surface area BET of the negative electrode active material 2.5×a+b can take values ​​of 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, 38, 40 or an intermediate value between any two values.

[0042] According to some embodiments of the present application, 2≤a≤10; alternatively, 2≤a≤8. The negative electrode active material has a small particle size, which allows the particles to be densely packed, improving electron conduction and enabling the battery to have a high low-temperature discharge capacity retention rate. The Dv50 particle size of the material can be controlled by controlling crushing parameters, for example. As an example, the particle size Dv50 of the negative electrode active material can be 2μm, 4μm, 6μm, 8μm, 10μm, or an intermediate particle size between any two numerical particle sizes.

[0043] According to some embodiments of the present application, 10≤b≤25; optionally, 13≤b≤20. The negative electrode active material has the characteristic of a large specific surface area, and electrons can be quickly conducted inside and on the surface of the particles, thereby improving the low-temperature discharge capability of the battery. The specific surface area BET of the material can be controlled by shaping parameters and controlling graphitization process parameters. As an example, the specific surface area BET of the negative electrode active material can be 10m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g、15m 2 / g、16m 2 / g、18m 2 / g, 20m 2 / g、22m 2 / g、24m 2 / g, 25m 2 / g or the intermediate specific surface area between any two numerical specific surface areas.

[0044] According to some embodiments of the present application, the tap density of the negative electrode active material is T g / cm 3 , 0.3≤T-0.05×a≤1.0; optionally, 0.5≤T-0.05×a≤0.8. This shows that even when the particle size of the negative electrode active material is small, it can have both a large specific surface area and a good tap density. During the electrode coating process, the particles of the negative electrode active material can be tightly stacked, thereby improving the lithium insertion capacity of the electrode, and making the electronic conductivity between the particles good, and the battery has a high low-temperature discharge capacity retention rate. As an example, T-0.05×a can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 or an intermediate value between any two values. The tap density refers to the average density of all particles after tapping.

[0045] According to some embodiments of the present application, 0.5≤T≤1.4; alternatively, 0.9≤T≤1.2. The negative electrode active material has the characteristic of high tap density, which can further improve the electron conduction between particles and improve the low-temperature discharge capability of the battery. The tap density of the material can be controlled by shaping and other methods. As an example, the tap density of the negative electrode active material can be 0.5g / cm 3 , 0.6g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.4g / cm 3 Or the tap density intermediate between any two numerical tap densities.

[0046] According to some embodiments of the present application, the degree of graphitization of the negative electrode active material is G%, 94.0≤G≤98.5, optionally, 95.0≤G≤97.5. The negative electrode active material has a high degree of graphitization and has good electronic conductivity. The high degree of graphitization makes the particles softer, and even if the material particle size is small, it can have a high compaction density, further improving the low-temperature discharge capability of the battery. The degree of graphitization of the material can be controlled by controlling the graphitization process parameters during material processing. As an example, the degree of graphitization of the negative electrode active material can be 94%, 94.5%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98.5% or an intermediate value between any two values.

[0047] According to some embodiments of the present application, the compacted density of the negative electrode active material is P g / cm 3 , 1.75≤P≤2.20; alternatively, 1.90≤P≤2.10. The test tonnage of the compacted density of the negative electrode active material is 5.0 tons. The negative electrode active material has a higher compacted density, which can improve the electronic conduction between particles, shorten the transmission path of active ions, and further improve the low-temperature discharge capability of the battery. As an example, P g / cm 3 The acceptable value is 1.75g / cm 3 , 1.80g / cm 3 、1.90g / cm 3 , 1.95g / cm 3 , 2.00g / cm 3 , 2.05g / cm 3 , 2.10g / cm 3 , 2.20g / cm 3 Or any value halfway between any two values.

[0048] According to some embodiments of the present application, the Raman Id / Ig ratio of the negative electrode active material ranges from 0.1 to 0.35, indicating high particle crystallinity, low defects, and rapid electron conduction within and on the particle surface, thereby improving the battery's low-temperature discharge capability. The Raman Id / Ig ratio of the material can be controlled by controlling graphitization process parameters and coating parameters during material processing. For example, the Raman Id / Ig ratio of the negative electrode active material can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or any value intermediate between these two values.

[0049] According to some embodiments of the present application, the negative electrode active material includes a sheet structure material, and the mass proportion of the sheet structure material in the negative electrode active material is 90% to 100%. The sheet structure material has a large specific surface area, complete crystals, and good conductivity within and between particles, which can enable the negative electrode active material to meet the above-mentioned relationship conditions, thereby improving the low-temperature discharge capability of the battery and improving the low-temperature discharge capacity retention rate of the battery. As an example, the mass proportion of the sheet structure material can be 90%, 92%, 95%, 98%, 99%, 99.99% or an intermediate value between any two values. The sheet structure material refers to a sheet-like negative electrode active material having two opposing surfaces with a small thickness difference between the two surfaces.

[0050] According to some embodiments of the present application, the negative electrode active material includes but is not limited to at least one of carbon materials (artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microbeads, carbon fiber, carbon nanotubes, graphene, etc.), titanium oxide-based materials (lithium titanate, titanium dioxide, etc.), alloyed negative electrode materials (silicon-based materials (silicon-oxygen materials and / or silicon-carbon materials), tin-based materials, germanium-based materials, etc.), and conversion-type negative electrode materials (transition metal oxides, phosphides, sulfides, nitrides, etc.); optionally, the negative electrode active material includes graphite having soft carbon or hard carbon on the surface, and the mass proportion of soft carbon or hard carbon is between 3% and 5% based on the mass of graphite; optionally, the negative electrode active material includes flake graphite having soft carbon or hard carbon on the surface.

[0051] According to some embodiments of the present application, the present application provides a method for preparing a negative electrode active material, which includes the following steps:

[0052] S1: providing a raw material for a negative electrode active material. For example, flake graphite with a purity of 90% or more is used as the raw material.

[0053] S2: Crushing the raw materials to a particle size Dv50 of a'μm.

[0054] S3: The crushed raw material is shaped to a specific surface area of ​​b'm 2 / g, the tap density is T'g / cm3 , and satisfy 20≤2.5×a'+b'≤40, and 0.3≤T'-0.05×a'≤1.0 is optional.

[0055] S4: The raw material obtained in S3 is mixed with the coating agent in proportion and heat-treated in a reactor.

[0056] As an embodiment, the heat treatment temperature is 400°C to 700°C, and the heat treatment time is 2h to 8h; illustratively, the heat treatment temperature is 400°C, 500°C, 600°C, 700°C or an intermediate temperature between any two temperatures, and the heat treatment time is 2h, 3h, 4h, 5h, 6h, 7h, 8h or an intermediate time between any two times.

[0057] As an embodiment, the coating agent can be an asphalt-based coating agent; the mixing ratio of the raw material and the coating agent is 90% to 98%: 10% to 2%, for example, 90%:10%, 93%:7%, 95%:5%, 98%:2% or an intermediate ratio between any two ratios.

[0058] S5: The sample obtained in S4 is graphitized to make its crystal growth more complete, so as to control the graphitization degree of the treated sample to G%, and the Raman Id / Ig value.

[0059] As an embodiment, the graphitization treatment temperature is 2000°C to 3000°C, and the graphitization treatment time is 20h to 40h. Exemplarily, the graphitization treatment temperature is 2000°C, 2200°C, 2400°C, 2600°C, 2800°C, 3000°C or between any two temperatures, and the graphitization treatment time is 20h, 24h, 28h, 30h, 32h, 34h, 36h, 38h, 40h.

[0060] S6: The sample in S5 is screened to remove magnetism and obtain the negative electrode active material.

[0061] Since the parameters of the negative electrode active material (particle size Dv50, specific surface area and tap density) vary less than the relevant parameters of the raw materials, the parameters of the negative electrode active material can be made to meet the above conditions by controlling the parameters of the raw materials. Specifically, the particle size Dv50 of the prepared negative electrode active material is aμm, the specific surface area is bm 2 / g, tap density is Tg / cm 3 , and satisfy 20≤2.5×a+b≤40, and 0.3≤T-0.05×a≤1.0 is optional.

[0062] According to some embodiments of the present application, a battery is provided, comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode active material described in any of the above embodiments. The battery of the present application has good kinetic performance, low impedance, and is capable of sustained high-rate discharge at low temperatures.

[0063] The negative electrode plate uses the aforementioned negative electrode active material, which has good electronic conductivity, and can be made with little or no additional conductive agent. Exemplarily, the negative electrode plate does not contain a conductive agent (such as carbon black, acetylene black, Ketjen black, superconducting carbon, carbon dots, carbon nanotubes, carbon fibers, graphene, or any combination thereof).

[0064] In some embodiments, the negative electrode current collector may be any material suitable for use as a negative electrode current collector for lithium-ion secondary batteries. The negative electrode current collector may be a metal foil or a composite current collector. Optionally, the negative electrode current collector includes copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0065] In some embodiments, the negative electrode active material layer further comprises a binder, which includes but is not limited to polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber, epoxy resin, nylon, or any combination thereof.

[0066] In some embodiments, the negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0067] According to some embodiments of the present application, the negative electrode sheet has a conductivity of 1 S / cm to 10 S / cm under a load of 25 MPa, and optionally, a conductivity of 5 S / cm to 10 S / cm. As an example, the conductivity of the negative electrode sheet may be 1 S / cm, 2 S / cm, 3 S / cm, 4 S / cm, 5 S / cm, 6 S / cm, 7 S / cm, 8 S / cm, 9 S / cm, 10 S / cm, or an intermediate conductivity between two values.

[0068] According to some embodiments of the present application, the OI value of the negative electrode plate is 11 to 21. As an example, the OI value of the negative electrode plate can be 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 or an intermediate value between two values.

[0069] According to some embodiments of the present application, a method for preparing a negative electrode sheet includes the following steps: mixing the negative electrode active material, binder, and thickener in a weight ratio of 95-98:1-3:1-3, and then thoroughly stirring and mixing in an appropriate amount of deionized water to form a uniform negative electrode slurry; applying the slurry to a current collector, drying, and cold pressing to obtain the negative electrode sheet. In some embodiments, the conductivity and OI value of the negative electrode sheet can be controlled by selecting the negative electrode active material, and the conductivity and OI value of the negative electrode sheet can also be controlled by controlling the compaction of the sheet. Higher compaction results in higher conductivity and higher OI value.

[0070] According to some embodiments of the present application, the battery includes a secondary battery, which may be the aforementioned battery cell or battery pack. According to some embodiments of the present application, the battery includes but is not limited to: a lithium-ion battery or a sodium-ion battery.

[0071] In order to enable a clearer understanding of the technical solution of the present application, the embodiments of the present application are mainly described using lithium-ion batteries. Other types of batteries can be appropriately adjusted according to the battery type and will not be described in detail.

[0072] A lithium-ion battery includes a positive electrode sheet, the aforementioned negative electrode sheet and a separator, and an electrolyte.

[0073] [Positive electrode]

[0074] According to some embodiments of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material, a binder and a conductive agent.

[0075] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0076] In some embodiments, the positive electrode active material includes at least one of lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganese oxide, spinel lithium nickel manganese oxide, and lithium titanate.

[0077] In some embodiments, the binder comprises an adhesive polymer, such as at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane. In some embodiments, the polyolefin binder comprises at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0078] In some embodiments, the conductive agent includes a carbon-based material, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black or carbon fiber; a metal-based material, such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; a conductive polymer, such as a polyphenylene derivative; or a mixture thereof.

[0079] [Isolation film]

[0080] The present application has no particular limitation on the material and shape of the isolation membrane, which may be any material disclosed in the prior art.

[0081] In some embodiments, the isolation film includes a polymer or inorganic material formed of a material that is stable to the electrolyte of the present application. For example, the isolation film may include a substrate layer and a surface treatment layer.

[0082] The substrate layer is a non-woven fabric, film, or composite film having a porous structure. The material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric, or polypropylene-polyethylene-polypropylene porous composite film can be used.

[0083] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of aluminum oxide, 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, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0084] [Electrolyte]

[0085] The electrolyte conducts ions between the positive electrode and the negative electrode.

[0086] The electrolyte of the present application may be an electrolyte known in the prior art.

[0087] In some embodiments, the electrolyte includes an organic solvent, a lithium salt and an optional additive. The organic solvent in the electrolyte of the present application may be any organic solvent known in the prior art that can be used as a solvent for the electrolyte. There is no restriction on the electrolyte used in the electrolyte according to the present application, and it may be any electrolyte known in the prior art. The additive of the electrolyte according to the present application may be any additive known in the prior art that can be used as an electrolyte additive. In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, methyl propionate, propyl propionate, or ethyl propionate. In some embodiments, the organic solvent includes an ether solvent, for example, including at least one of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME). In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate) LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one of fluoroethylene carbonate, succinonitrile, glutaronitrile, 1,3-propane sultone, and adiponitrile.

[0088] According to some embodiments of the present application, the above-mentioned negative electrode plates without conductive agent are assembled into a battery, which has good kinetic performance, low impedance, and can be continuously discharged at a high rate at low temperatures: the battery can be discharged at a high rate of 10C at -20°C, and its capacity retention rate is as high as 80% or more compared to the 10C high rate discharge at 25°C, which fully improves the battery's low-temperature endurance.

[0089] According to some embodiments of the present application, the present application further provides an electrical device, which includes the battery described in any of the above embodiments, and the battery is used to provide electrical energy to the electrical device.

[0090] The power-consuming device may be any of the aforementioned battery-applying devices or systems, including but not limited to laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0091] Next, one or more embodiments will be described in more detail with reference to the following examples. Of course, these examples do not limit the scope of one or more embodiments.

[0092] Example 1-1

[0093] Preparation of negative electrode active materials

[0094] 1) Crushing 95% pure flake graphite to a particle size Dv50 of about 6 μm;

[0095] 2) Shape the crushed flake graphite for 20 minutes (the specific surface area of ​​flake graphite is b'm 2 / g, the tap density is T'g / cm 3 );

[0096] 3) Mix the above sample with the asphalt coating agent at a mixing ratio of 98%:2%, place the mixed sample in a reactor, and heat treat at 500°C for 2 hours to achieve coating;

[0097] 4) The heat-treated sample was further graphitized at a temperature of 2500° C. for 24 h (the graphitization degree of the treated sample was G%, and the Raman Id / Ig value).

[0098] 5) The sample after graphitization treatment is sieved and demagnetized to obtain the negative electrode active material.

[0099] Scanning electron microscope (SEM) test: The scanning electron microscope used in the examples of the present application is the JEOL JSM-6360LV model and its supporting X-ray spectrometer to analyze the sample morphology and structure and observe the morphological characteristics of the sample.

[0100] The SEM image of the negative electrode active material prepared in this example is shown in FIG1 . As can be seen from FIG1 , the negative electrode active material has a small particle-like flake morphology.

[0101] Preparation of lithium-ion batteries

[0102] Negative electrode sheet: The prepared negative electrode active material, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are mixed in a weight ratio of 97.4:1.2:1.4, and then stirred and mixed with an appropriate amount of deionized water to form a uniform negative electrode slurry; this slurry is coated on the current collector Cu foil, dried, and cold pressed to obtain the negative electrode sheet (the conductivity of the negative electrode sheet is 1S / cm to 10S / cm, and the OI value is 11 to 21).

[0103] Positive electrode: Ni 0.83 Co 0.07 Mn 0.1 The positive electrode active material is mixed with the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) in a weight ratio of 96.3:2.2:1.5 in an appropriate amount of N-methylpyrrolidone (NMP) solvent to form a uniform positive electrode slurry; the slurry is coated on the current collector Al foil, dried and cold pressed to obtain a positive electrode sheet.

[0104] Electrolyte: In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP), and ethyl propionate (EP) were mixed in a mass ratio of EC:PC:PP:EP = 4:3:2:1. Fluorinated ethylene carbonate and 1,3-propane sultone were then added, dissolved, and thoroughly stirred. Lithium salt LiPF6 was added and mixed until uniformly distributed to obtain an electrolyte. The mass percentage of LiPF6 was 12.5%, the mass percentage of fluoroethylene carbonate was 3%, and the mass percentage of 1,3-propane sultone was 2%. The mass percentages of each substance were calculated based on the mass of the electrolyte.

[0105] Lithium-ion battery: The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to act as an isolate. The electrode assembly is wound and placed in an outer packaging aluminum-plastic film. After dehydration at 80°C, the above-mentioned electrolyte is injected and packaged. After the formation, degassing, and trimming processes, a lithium-ion battery is obtained.

[0106] Experiment 1: Based on Example 1-1, the crushing particle size, shaping time, asphalt coating ratio, heat treatment temperature and time, and graphitization treatment temperature and time during the preparation of the negative electrode active material were adjusted. The specific process parameters are shown in Table 1, and Examples 1-2 to 1-9 and Comparative Examples 1-1 to 1-2 were obtained. The specific test result parameter data are shown in Table 4.

[0107] Table 1 Preparation process parameters of Experiment 1

[0108] Experiment 2: Based on Example 1-1, the crushing particle size, shaping time, asphalt coating ratio, heat treatment temperature and time, and graphite temperature and time during the preparation of the negative electrode active material were adjusted. The specific process parameters are shown in Table 2, and Examples 2-1 to 2-6 were obtained. The specific parameter data are shown in Table 5.

[0109] Table 2 Preparation process parameters of Experiment 2

[0110] Experiment 3: Based on Example 1-1, the crushing particle size, shaping time, asphalt coating ratio, heat treatment temperature and time, and graphite temperature and time during the preparation of the negative electrode active material were adjusted. The specific process parameters are shown in Table 3. The particle size Dv50 (aμm), specific surface area (bm) and specific surface area of ​​the negative electrode active material of each example were obtained. 2 / g) are the same, the tap density (Tg / cm 3 ) are the same, and the specific parameter data are shown in Table 6.

[0111] Table 3 Preparation process parameters of Experiment 3

[0112] Test Method

[0113] The lithium-ion battery was discharged at a constant current of 1C to a voltage of 3.0V. After disassembly, the negative electrode was removed and soaked in dimethyl carbonate (DMC) for 20 minutes. It was then rinsed with DMC and acetone in sequence. The negative electrode was then placed in an oven and baked at 80°C for 12 hours to obtain the treated negative electrode. The powder on the negative electrode was scraped off with a scraper and heat-treated in a tube furnace at 400°C for 4 hours under argon protection to obtain the negative electrode active material.

[0114] The negative electrode active material and negative electrode sheet obtained above were tested as follows:

[0115] 1. Particle size test

[0116] The particle size test method for negative electrode active materials refers to GB / T 19077-2016. The specific process is to weigh 1g of sample and mix it evenly with 20mL of deionized water and a trace amount of dispersant. After placing it in an ultrasonic device for 5 minutes, the solution is poured into the sampling system Hydro 2000SM for testing. The testing equipment used is the Mastersizer 3000 produced by Malvern. During the test, when the laser beam passes through the dispersed particle sample, the particle size measurement is completed by measuring the intensity of the scattered light. The data is then used to analyze and calculate the particle size distribution that forms the scattering spectrum. The test is set to a refractive index of 1.8. A sample is tested three times, and the particle size is finally measured as the average of the three tests to obtain Dv50.

[0117] 2. Specific surface area test

[0118] The specific surface area test method refers to GB / T 19587-2017. The specific process is to weigh 1g to 8g of negative electrode active material (the negative electrode active material weighs at least 1 / 3 of the volume of the sphere) and place it in a 1 / 2-inch long tube with a bulb (the diameter of the spherical part is 12mm). After pre-treatment at 200°C for 2h, it is placed in the test equipment TriStar3030 (Machinery, USA) for testing. The adsorption gas used is N2 (purity: 99.999%). The test conditions are carried out at 77K, and the specific surface area is calculated using the BET method.

[0119] 3. Tap density test

[0120] The test method of GB / T 5162-2006 "Determination of tap density of metal powders" was adopted, using a McMurritics GeoPyc1365 instrument, weighing 3±0.1g of negative electrode active material, and a consolidation force of 85N.

[0121] 4. Graphitization degree test

[0122] The national standard JJS K 0131-1996 "General Rules for X-ray Diffraction Analysis" was adopted. The instrument model was Bruker D8 ADVANCE, a Cu Kα target was used, a voltage and current of 40 kV / 40 mA, a test angle of 52° to 58°, and a scanning test was conducted on the negative electrode active material containing a carbon-silicon ratio of C:Si = 5:1 (mass ratio). The duration per step was 0.3 s.

[0123] 5. Compaction density test

[0124] The compaction density test standard refers to GB / T 24533-2009, "Graphite-Based Anode Materials for Lithium-Ion Batteries." The specific test method involves weighing 1.0000±0.0500g of the anode active material and placing it in a test mold (CARVER #3619 (13mm)). The anode active material is then placed in a 5.0-ton Sansi Zongheng UTM7305 test apparatus. The compaction density is calculated as follows: Compaction density = Mass of anode active material / Load-bearing area of ​​anode active material / Thickness of anode active material.

[0125] 6. Id / Ig (Raman test surface defect) test

[0126] A laser microconfocal Raman spectrometer (Raman, HR Evolution, HORIBA Scientific Instruments Division) was used to scan and test the negative electrode active material. A scanning area of ​​100 μm × 100 μm was arbitrarily selected. The particles within the area were scanned to obtain the D peak and G peak of all particles within the area. The data was processed using LabSpec software to obtain the peak intensities of the D peak and G peak of each particle, which are Id and Ig, respectively. The laser wavelength of the Raman spectrometer can be in the range of 532 nm to 785 nm. The Id / Ig value in this application is the average of the Id and Ig ratios of all particles measured within this range.

[0127] 7. Negative electrode conductivity test

[0128] Reference standard: GB / T 30385-2014 "Carbon-composite lithium iron phosphate cathode material for lithium-ion batteries". Test procedure: Weigh the negative electrode and place it on an electronic pressure platform. Then increase the pressure at a rate of 5 mm / min to a load of 25 MPa, maintain the pressure for 60 seconds, and then release the pressure to 0 to obtain the electrode conductivity.

[0129] 8. Negative electrode OI value test

[0130] The national standard JJS K 0131-1996 "General Rules for X-ray Diffraction Analysis" was used, instrument model: Bruker D8ADVANCE, Cu Kα target, 40KV / 40mA voltage and current were used to scan the negative electrode piece to obtain C004 peak and C110 peak data. The OI value of the negative electrode piece was obtained by calculating the C004 / C110 ratio.

[0131] The lithium-ion battery obtained above was subjected to the following performance tests:

[0132] 1. Lithium-ion battery 1s DCR test

[0133] At -20°C, charge the lithium-ion battery at a constant current of 1C to 4.25V. Then, charge it at a constant voltage of 4.25V to 0.05C and let it rest for 30 minutes. Discharge it at 0.1C for 10 seconds, recording the voltage as U1. Discharge it at 1C for 360 seconds, recording the voltage as U2. Repeat this charge and discharge process five times. "1C" is the current value required to fully discharge the lithium-ion battery in one hour.

[0134] The DC resistance R of a lithium-ion battery at 25°C is calculated using the following formula:

[0135] R = (U2-U1) / (1C-0.1C).

[0136] Unless otherwise specified, the DCR described in this application refers to the direct current resistance (DCR) of a lithium-ion battery at 50% state of charge (SOC).

[0137] 2. Lithium-ion battery capacity retention test

[0138] Place the lithium-ion battery in a high and low temperature box, adjust the ambient temperature to 25℃, charge it to 4.25V at a constant current rate of 0.2C, then charge it to 0.05C at a constant voltage of 4.25V, let it stand for 5 minutes, and then discharge it to 3V at a rate of 0.2C to obtain the 25℃ 0.2C capacity.

[0139] Repeat the charging steps, charge to 4.25V at a constant current rate of 0.2C, then charge to 0.05C at a constant voltage rate of 4.25V, adjust the ambient temperature to -20℃, let it stand for 30 minutes, and then discharge to 3V at a rate of 10C to obtain the -20℃ 10C capacity. The 10C discharge capacity retention rate of lithium-ion batteries is as follows:

[0140] -20°C 10C capacity retention rate = (-20°C 10C discharge capacity / 25°C 0.2C discharge capacity) × 100%.

[0141] The test results are shown in Tables 4 to 6:

[0142] Table 4 Test results of Experiment 1

[0143] Table 4 shows that compared with Comparative Examples 1-1 to 1-2, the particle size Dv50 (a μm) and specific surface area BET (bm 2 / g) satisfies 20≤2.5×a+b≤40, the lithium-ion battery made with this negative electrode active material has a low 1s DCR, can discharge even at temperatures as low as -20°C, and can improve the low-temperature 10C discharge capacity retention rate. Negative electrode active material particles that meet this condition have complete crystal growth, few surface defects, and can conduct electrons quickly within the particles. Furthermore, the high specific surface area ensures good contact between particles, giving the entire electrode a good electronic conductive network. At low temperatures, this good conductive network can reduce the discharge polarization of lithium-ion batteries at low temperatures and high rates, thereby reducing the 1s DCR of lithium-ion batteries and improving the low-temperature 10C discharge capacity retention rate.

[0144] According to Examples 1-1 to 1-7, 2≤a≤10, 10≤b≤25, and 20≤2.5×a+b≤40, the 1s DCR of the lithium-ion battery is significantly reduced, and the low-temperature 10C discharge capacity retention rate is significantly improved.

[0145] Table 5 Test results of Experiment 2

[0146] Table 5 shows that compared with Example 1-1, the particle size (a μm) and tap density T (g / cm 3 ) satisfies 0.3≤T-0.05×a≤1.0, which can improve the low-temperature, high-rate discharge capability of lithium-ion batteries. Negative electrode active material particles that meet this condition can be densely packed together during coating, resulting in a negative electrode sheet with a low OI value. This improves the conductivity and lithium-ion diffusion properties of the negative electrode sheet, thereby enhancing the low-temperature, high-rate discharge capability of the lithium-ion battery.

[0147] According to Examples 2-1 to 2-4, 0.5≤T≤1.4, and 0.3≤T-0.05×a≤1.0 are satisfied at the same time, the 1s DCR of the lithium-ion battery is reduced, and the low-temperature 10C discharge capacity retention rate is significantly improved.

[0148] Table 6 Test results of Experiment 3

[0149] As can be seen from Table 6, compared with Example 1-1, when the degree of graphitization of the negative electrode active materials of Examples 3-1 to 3-7 is higher, the Id / Ig value is lower, the Id / Ig defects on the particle surface are fewer, the particle crystal growth is more complete, the electron conduction in the particle is better, the conductivity of the negative electrode sheet is improved, the electrons can also be conducted at low temperatures, the voltage polarization caused by low-temperature high-rate discharge inside the lithium-ion battery is reduced, and the discharge capacity of the lithium-ion battery is improved.

[0150] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A negative electrode active material, characterized in that: The particle size Dv50 of the negative electrode active material is a μm, and the specific surface area is bm 2 / g, 20≤2.5×a+b≤40.

2. The negative electrode active material according to claim 1, characterized in that 25≤2.5×a+b≤35.

3. The negative electrode active material according to claim 1 or 2, characterized in that: 2≤a≤10; optionally, 2≤a≤8.

4. The negative electrode active material according to any one of claims 1 to 3, characterized in that 10≤b≤25; optionally, 13≤b≤20.

5. The negative electrode active material according to any one of claims 1 to 4, characterized in that The tap density of the negative electrode active material is T g / cm 3 , 0.3≤T-0.05×a≤1.0; optionally, 0.5≤T-0.05×a≤0.

8.

6. The negative electrode active material according to claim 5, characterized in that 0.5≤T≤1.4; optionally, 0.9≤T≤1.

2.

7. The negative electrode active material according to any one of claims 1 to 6, characterized in that The graphitization degree of the negative electrode active material is G%, 94.0≤G≤98.5, optionally, 95.0≤G≤97.

5.

8. The negative electrode active material according to any one of claims 1 to 7, characterized in that The compaction density of the negative electrode active material is P g / cm 3 , 1.75≤P≤2.20; optionally, 1.90≤P≤2.

10.

9. The negative electrode active material according to any one of claims 1 to 8, characterized in that The Id / Ig of the negative electrode active material is 0.1 to 0.

35.

10. The negative electrode active material according to any one of claims 1 to 9, characterized in that The negative electrode active material includes a sheet-like structural material, and the mass proportion of the sheet-like structural material in the negative electrode active material is 90% to 100%.

11. The negative electrode active material according to any one of claims 1 to 10, characterized in that The negative electrode active material includes a carbon material; optionally, the negative electrode active material includes flake graphite with a carbon coating layer.

12. A battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, characterized in that: The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer includes the negative electrode active material according to any one of claims 1 to 11.

13. The battery according to claim 12, characterized in that The negative electrode plate has an electrical conductivity of 1 S / cm to 10 S / cm under a load of 25 MPa. Optionally, the electrical conductivity is 5 S / cm to 10 S / cm.

14. The battery according to claim 12 or 13, characterized in that: The OI value of the negative electrode plate is 11 to 21.

15. An electrical device, characterized in that: It comprises the battery according to any one of claims 12 to 14.

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