Negative active material, negative electrode sheet, battery, and electric device

Abstract

This application provides a negative electrode active material, a negative electrode sheet, a battery, and an electrical 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 is bm². 2 / g, 20≤2.5×a+b≤40. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer containing the aforementioned negative electrode active material. The negative electrode active material, negative electrode sheet, battery, and power device of the present application embodiments can improve the low-temperature discharge capability of the battery and enhance the low-temperature discharge capacity retention rate.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to a negative electrode active material, a negative electrode sheet, a battery, and an electrical device. Background Technology

[0002] Currently, as ambient temperature decreases, the internal polarization of lithium-ion batteries increases, and their discharge capacity at high rates of 10C and above gradually decreases. However, some power tools and drones need to operate continuously at low temperatures, thus placing strict requirements on their low-temperature, high-rate discharge capabilities. A conventional method is to improve low-temperature discharge capacity by reducing the internal resistance of the battery cell (e.g., through thinner electrode coating), but this often results in energy density loss, leading to insufficient battery life in power tools and drones. Summary of the Invention

[0003] In view of the above problems, this application provides a negative electrode active material, a negative electrode sheet, a battery and an electrical device, which can improve the low-temperature discharge capability of the battery and improve the low-temperature discharge capacity retention rate.

[0004] In a first aspect, this application provides a negative electrode active material, wherein the particle size Dv50 of the negative electrode active material is a μm and the specific surface area BET is bm. 2 / g, 20≤2.5×a+b≤40.

[0005] In the technical solution of this application embodiment, 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 satisfy this condition can be tightly packed together, and electrons can also be conducted between the particles. That is, it can take into account the role of ion diffusion and electronic conductivity network, thereby providing a good conductivity network, reducing charge conduction impedance, thereby 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.

[0006] In some embodiments, 25 ≤ 2.5 × a + b ≤ 35. This can further improve the low-temperature discharge capacity retention rate of the battery.

[0007] In some embodiments, 2 ≤ a ≤ 10; alternatively, 2 ≤ a ≤ 8. The negative electrode active material has the characteristic of small particle size, and the particles can be packed tightly together, so that the battery has a high low-temperature discharge capacity retention rate.

[0008] In some embodiments, 10 ≤ b ≤ 25; alternatively, 13 ≤ b ≤ 20. The negative electrode active material has a large specific surface area, allowing electrons to conduct rapidly inside and on the particle surface, thereby improving the battery's low-temperature discharge capability.

[0009] In some embodiments, the tap density of the negative electrode active material is T g / cm³. 3 The particle size and tap density of the negative electrode active material also satisfy the relationship: 0.3≤T-0.05×a≤1.0; optionally, 0.5≤T-0.05×a≤0.8.

[0010] In some embodiments, 0.5 ≤ T ≤ 1.4; optionally, 0.9 ≤ T ≤ 1.2. The negative electrode active material has a high tap density, which can further improve the electron conduction between particles and improve the low-temperature discharge capability of the battery.

[0011] In some embodiments, the degree of graphitization of the negative electrode active material is G%, 94.0≤G≤98.5, and optionally, 95.0≤G≤97.5. A high degree of graphitization in the negative electrode active material results in good electronic conductivity, and the higher degree of graphitization also makes the particles softer, allowing for higher compaction density even with small particle sizes, further improving the battery's low-temperature discharge capability.

[0012] In some embodiments, the compaction density of the negative electrode active material is P g / cm³. 3 1.75≤P≤2.20; optionally, 1.90≤P≤2.10. The negative electrode active material has a high compaction density, which can improve the electron conduction between particles and further improve the low-temperature discharge capability of the battery.

[0013] In some embodiments, the Raman Id / Ig ratio of the negative electrode active material ranges from 0.1 to 0.35. This negative electrode active material exhibits good graphitization, and its particle surface Raman Id / Ig ratio ranges from 0.1 to 0.35, allowing for rapid electron conduction both inside and on the particle surface, thus improving the battery's low-temperature discharge capability.

[0014] In some embodiments, the negative electrode active material comprises a sheet-like structure material, wherein the mass percentage of the sheet-like structure material in the negative electrode active material is 90%-100%. The sheet-like structure material has a large specific surface area, intact crystals, and good conductivity within and between particles, thereby improving the battery's low-temperature discharge capability and enhancing the battery's low-temperature discharge capacity retention rate.

[0015] In some embodiments, the negative electrode active material includes at least one of artificial graphite, natural graphite, silicon-carbon materials, or silicon-oxygen materials. Optionally, the negative electrode active material includes graphite with soft or hard carbon on its surface. Optionally, the negative electrode active material includes flake graphite with soft or hard carbon on its surface. The flake graphite particles with soft or hard carbon on their surface have complete crystal growth, high graphitization, few surface defects, rapid electron conduction within the particles, and a high specific surface area, resulting in good contact between particles and a good electronic conductivity network for the entire electrode.

[0016] Secondly, this application provides a negative electrode sheet, which includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, wherein the negative active material layer comprises the negative active material in the above embodiments.

[0017] In some embodiments, the negative electrode sheet has a conductivity of 1-10 S / cm under a load of 25 MPa, optionally 5-10 S / cm. The negative electrode active material exhibits good electronic conductivity, and the formed negative electrode sheet also possesses an excellent electronic conductivity network.

[0018] In some embodiments, the OI value of the negative electrode is in the range of 10-21.

[0019] Thirdly, this application provides a battery that includes the negative electrode sheet in the above embodiments. The battery has good dynamic performance, low impedance, and can continuously discharge at high rates at low temperatures.

[0020] Thirdly, this application provides a battery comprising the negative electrode sheet described in the above embodiments. When the negative electrode sheet is assembled into a secondary battery, the secondary battery exhibits good kinetic performance, low impedance, and the ability to continuously discharge at high rates at low temperatures.

[0021] Fourthly, this application provides an electrical device that includes the battery described in the above embodiments, the battery being used to provide electrical energy.

[0022] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0023] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0024] Figure 1 The image shows the SEM image of the negative electrode active material in Example 1-1. Detailed Implementation

[0025] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0027] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

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

[0029] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0030] In the description of the embodiments of this application, the technical terms "inner" and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0031] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms "installation," "connection," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0032] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0033] The high-rate discharge capability of a secondary battery at low temperatures depends on its polarization. When the polarization voltage is below the discharge lower limit voltage, the secondary battery cannot discharge. Existing lithium-ion secondary batteries have poor low-temperature high-rate discharge capability; as the ambient temperature decreases, the internal polarization of the battery increases, and the high-rate discharge capability gradually decreases. However, some power tools and drones, among other electrical devices, need to operate continuously at low temperatures, thus 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 batteries is to reduce the internal resistance of the battery (such as by thinning the electrode coating). However, this method often results in a loss of energy density in the battery, which leads to insufficient battery life for power tools, drones and other electrical devices, as well as increased manufacturing costs.

[0035] To address the issue of low low-temperature discharge capability of batteries, the applicant discovered that charge conduction impedance (1s DCR) caused by low temperature is one of the key factors affecting low-temperature discharge of batteries. By using specially selected negative electrode active materials to form electrodes, a good conductive network can be provided for the electrodes, reducing charge conduction impedance and thus improving the low-temperature discharge capability of the battery, while also improving the low-temperature discharge capacity retention rate.

[0036] The battery cells disclosed in this application can be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft. A power system for such an electrical device can be constructed using battery cells and batteries disclosed in this application. This helps to mitigate and automatically regulate the deterioration of cell expansion force, replenish electrolyte consumption, and improve the stability of battery performance and battery life.

[0037] This application provides an electrical device that uses a battery as a power source. The electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0038] For ease of explanation, the following embodiments use a battery according to an embodiment of this application as an example.

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

[0040] The particle size Dv50 and specific surface area BET of anode active materials refer to characteristic parameters of the particle aggregate. Dv50 refers to the particle size (diameter) corresponding to 50% of the cumulative volume in the volumetric particle size distribution of the anode active material, starting from the smallest particle size. 'a' refers to the value of Dv50 in μm. Specific surface area BET refers to the total surface area per unit mass of particles. 'b' refers to the specific surface area BET in m³. 2 The value at / g.

[0041] The particle size (Dv50) *a* ​​and the specific surface area (BET) of the negative electrode active material in this application satisfy the relationship: 20 ≤ 2.5 × a + b ≤ 40. This allows the negative electrode active material to simultaneously function as an ion diffusion and electronic conductivity network, thereby providing a good conductivity network, improving the battery's low-temperature discharge capability, and enhancing the low-temperature discharge capacity retention rate. According to some embodiments of this application, 25 ≤ 2.5 × a + b ≤ 35, which can further improve the battery's low-temperature discharge capacity retention rate. 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 be 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, 38, 40, or any intermediate value between two values.

[0042] According to some embodiments of this application, 2 ≤ a ≤ 10; optionally, 2 ≤ a ≤ 8. The negative electrode active material has a small particle size, allowing for close packing of particles, improving electron conduction, and enabling the battery to maintain a high low-temperature discharge capacity. The Dv50 particle size of the material can be controlled by controlling crushing parameters, etc. For example, the Dv50 particle size of the negative electrode active material can be 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, or any intermediate value between two such values.

[0043] According to some embodiments of this application, 10 ≤ b ≤ 25; optionally, 13 ≤ b ≤ 20. The negative electrode active material has a large specific surface area, allowing electrons to conduct rapidly within and on the particle surface, thereby improving the battery's low-temperature discharge capability. The specific surface area BET of the material can be controlled by shaping parameters and controlling graphitization process parameters. For example, the specific surface area BET of the negative electrode active material can be 10m². 2 / g、12m 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 median of the specific surface area between any two numerical values.

[0044] According to some embodiments of this application, the tap density of the negative electrode active material is T g / cm³. 3 0.3 ≤ T - 0.05 × a ≤ 1.0; optionally, 0.5 ≤ T - 0.05 × a ≤ 0.8. This indicates that even when the particle size of the negative electrode active material is small, it can simultaneously possess a large specific surface area and good tap density. During the electrode coating process, the particles of the negative electrode active material can be tightly stacked, improving the lithium intercalation capability of the electrode and ensuring good electronic conductivity between particles, resulting in a high low-temperature discharge capacity retention rate for the battery. 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 any value between two of these. Tap density refers to the average density of all particles after tapping.

[0045] According to some embodiments of this application, 0.5 ≤ T ≤ 1.4; optionally, 0.7 ≤ T ≤ 1.2. The negative electrode active material has a 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 methods such as shaping. For example, the tap density of the negative electrode active material can be 0.5 g / cm³.3 0.6 g / cm 3 0.7 g / cm 3 0.8 g / cm 3 0.9 g / cm 3 1.0 g / cm 3 1.1 g / cm 3 1.2 g / cm 3 Or the intermediate value of the tap density between any two numerical tap densities.

[0046] According to some embodiments of this application, the graphitization degree of the negative electrode active material is G%, 94.0≤G≤98.5, optionally 95.0≤G≤97.5. A high graphitization degree in the negative electrode active material results in good electronic conductivity, and the higher graphitization degree makes the particles softer, allowing for higher compaction density even with small particle sizes, further improving the battery's low-temperature discharge capability. The graphitization degree of the material can be controlled by adjusting the graphitization process parameters during material processing. For example, the graphitization degree of the negative electrode active material can be 94%, 94.5%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98.5%, or any intermediate value between two values.

[0047] According to some embodiments of this application, the compaction density of the negative electrode active material is P g / cm³. 3 1.75≤P≤2.20; optionally, 1.90≤P≤2.10. The test tonnage for the compaction density of the negative electrode active material is 5.0 tons. A higher compaction density in the negative electrode active material can improve electron conduction between particles, shorten the transport path of active ions, and further improve the low-temperature discharge capability of the battery. As an example, P g / cm³ 3 The possible value is 1.80 g / cm³. 3 1.90g / cm 3 1.95g / cm 3 2.00g / cm 3 2.05g / cm 3 2.10 g / cm 3 2.30g / cm 3 Or the midpoint between any two values.

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

[0049] According to some embodiments of this application, the negative electrode active material includes a sheet-like structure material, with the sheet-like structure material accounting for 90%-100% of the total mass of the negative electrode active material. The sheet-like structure material has a large specific surface area, intact crystals, and good conductivity both within and between particles, enabling the negative electrode active material to satisfy the aforementioned relationship conditions, thereby improving the battery's low-temperature discharge capability and enhancing its low-temperature discharge capacity retention rate. As an example, the mass percentage of the sheet-like structure material can be 90%, 92%, 95%, 98%, 99%, 99.99%, or any value between two of these. The sheet-like structure material refers to a negative electrode active material that is sheet-like, having two opposing surfaces with a small difference in thickness between the two surfaces.

[0050] According to some embodiments of this application, the negative electrode active material includes, but is not limited to, at least one of the following: carbon materials (artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, carbon fibers, 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 with soft carbon or hard carbon on its surface, wherein the mass percentage of soft carbon or hard carbon is between 3% and 5% based on the mass of the graphite; optionally, the negative electrode active material includes flake graphite with soft carbon or hard carbon on its surface.

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

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

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

[0054] S3: Shape the pulverized raw material to a specific surface area of ​​b'm 2 / g, tap density is T' g / cm³ 3And satisfy 20≤2.5×a'+b'≤40, and can be selected as 0.3≤T'-0.05×a'≤1.0.

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

[0056] As one implementation method, the heat treatment temperature is 400-700℃ and the heat treatment time is 2-8h; for example, the heat treatment temperature is 400℃, 500℃, 600℃, 700℃ or any intermediate temperature between two temperatures, and the heat treatment time is 2h, 3h, 4h, 5h, 6h, 7h, 8h or any intermediate time between two times.

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

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

[0059] As one implementation method, the graphitization treatment temperature is 2000-3000℃, and the graphitization treatment time is 20-40h. For example, the graphitization treatment temperature is 2000℃, 2200℃, 2400℃, 2600℃, 2800℃, 3000℃ or any two of these temperatures, and the graphitization treatment time is 20h, 24h, 28h, 30h, 32h, 34h, 36h, 38h, or 40h.

[0060] S6: The sample from S5 is sieved and demagnetized until the negative electrode active material is obtained.

[0061] Since the parameters of the negative electrode active material (particle size Dv50, specific surface area, and tap density) vary relatively little with respect to 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 a μm, and the specific surface area is b m². 2 / g, tap density is Tg / cm 3 And satisfy 20≤2.5×a+b≤40, and can be selected as 0.3≤T-0.05×a≤1.0.

[0062] According to some embodiments of this application, this application also provides a negative electrode sheet, which 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 comprises the negative electrode active material described in any of the above embodiments.

[0063] The negative electrode sheet uses the aforementioned negative electrode active material, which has good electronic conductivity. The negative electrode sheet can have little or no additional conductive agent added. For example, the negative electrode sheet does not contain conductive agents (such as carbon black, acetylene black, Ketjen black, superconducting carbon, carbon dots, carbon nanotubes, carbon fibers, and graphene or any combination thereof).

[0064] In some embodiments, the negative electrode current collector can be any material suitable for use as a negative electrode current collector in lithium-ion secondary batteries, and the negative electrode current collector can 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 includes an adhesive, which includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, 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 also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0067] According to some embodiments of this application, the negative electrode has a conductivity of 1-10 S / cm under a load of 25 MPa, optionally 5-10 S / cm. As an example, the conductivity of the negative electrode can 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 value between two values.

[0068] According to some embodiments of this application, the OI value of the negative electrode is 10-21. As an example, the negative electrode can take the value of 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 or an intermediate value between two values.

[0069] According to some embodiments of this application, the preparation method of the 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, then thoroughly mixing them in an appropriate amount of deionized water solvent to form a uniform negative electrode slurry; coating this slurry onto a current collector, drying, and cold pressing to obtain the aforementioned 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 can also be controlled by controlling the compaction of the electrode sheet; higher compaction results in higher conductivity and a higher OI value.

[0070] According to some embodiments of this application, this application also provides a battery that includes the negative electrode sheet described in any of the above embodiments.

[0071] The battery includes a secondary battery, which can be the aforementioned battery cell, battery, or battery pack. According to some embodiments of this application, the battery of this application includes, but is not limited to, lithium-ion batteries or sodium-ion batteries.

[0072] To better understand the technical solution of this application, the embodiments of this 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.

[0073] A lithium-ion battery includes a positive electrode, the aforementioned negative electrode and separator, and an electrolyte.

[0074] [Positive electrode plate]

[0075] According to some embodiments of this application, the positive electrode sheet includes a positive current collector and a positive active material layer, wherein the positive active material layer includes a positive active material, a binder, and a conductive agent.

[0076] In some embodiments, the positive current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used. Composite current collectors can be formed by forming a metallic material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate.

[0077] In some embodiments, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel manganese cobalt oxide, 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-type lithium manganese oxide, spinel-type lithium nickel manganese oxide, and lithium titanate.

[0078] In some embodiments, the adhesive comprises an adhesive polymer, such as at least one selected from polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane. In some embodiments, the polyolefin adhesive comprises at least one selected from polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0079] In some embodiments, the conductive agent includes carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, or carbon fiber; metal-based materials, such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0080] [Isolation membrane]

[0081] This application does not impose any particular restrictions on the material and shape of the separator, which can be any technology disclosed in the prior art.

[0082] In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application. For example, the separator may include a substrate layer and a surface treatment layer.

[0083] The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, polypropylene porous membrane, polyethylene porous membrane, polypropylene nonwoven fabric, polyethylene nonwoven fabric, or polypropylene-polyethylene-polypropylene porous composite membrane can be selected.

[0084] A surface treatment layer is disposed 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 mixture of polymer and inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0085] Electrolyte

[0086] The electrolyte plays a role in conducting ions between the positive and negative electrode plates.

[0087] The electrolyte used in this application can be any electrolyte known in the prior art.

[0088] In some embodiments, the electrolyte comprises an organic solvent, a lithium salt, and optional additives. The organic solvent in the electrolyte of this application may be any organic solvent known in the art that can be used as an electrolyte solvent. There are no limitations on the electrolyte used in the electrolyte according to this application; it may be any electrolyte known in the art. The additives in the electrolyte according to this application may be any additives known in the art that can be used as electrolyte additives. 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 ether solvents, such as at least one selected from 1,3-dioxane (DOL) and dimethyl glycol ether (DME). In some embodiments, the lithium salt includes at least one selected from organic lithium salts or inorganic lithium salts. 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)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one selected from fluoroethylene carbonate, succinate, glutaronitrile, 1,3-propanesulfonate lactone, and adiponitrile.

[0089] According to some embodiments of this application, the above-mentioned negative electrode sheet without conductive agent is assembled into a battery. The battery has good dynamic performance, low impedance, and can continuously discharge at high rate at low temperature. The battery can discharge at a high rate of 10C at -20℃, and its capacity retention rate is as high as 80% or more compared to a high rate of 10C discharge at 25℃, which greatly improves the battery's low-temperature endurance.

[0090] According to some embodiments of this application, this application also provides an electrical device that includes a battery as described in any of the above embodiments, and the battery is used to provide electrical energy to the electrical device.

[0091] The electrical device can be any of the aforementioned battery-powered devices or systems. This includes, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0092] The following examples will describe one or more embodiments in more detail. Of course, these examples do not limit the scope of the one or more embodiments.

[0093] Example 1-1

[0094] Preparation of negative electrode active materials

[0095] 1) Crush 95% pure flake graphite to a particle size Dv50 of about 6μm;

[0096] 2) Shape the crushed flake graphite for 20 minutes (the specific surface area of ​​the flake graphite is b'm). 2 / g, tap density is T' g / cm³ 3 );

[0097] 3) Mix the above sample with asphalt coating agent at a ratio of 98%:2%, place the mixed sample in a reaction vessel, and heat-treat at 500℃ for 2 hours to achieve coating;

[0098] 4) The heat-treated sample was further graphitized at a temperature of 2500℃ for 24 hours (the degree of graphitization of the treated sample was G%, and the Raman Id / Ig value was also measured).

[0099] 5) The graphitized sample is sieved and demagnetized to obtain the negative electrode active material.

[0100] Scanning electron microscopy (SEM) testing: The scanning electron microscope used in this embodiment is the JEOL JSM-6360LV model and its matching X-ray energy dispersive spectrometer to analyze the morphology and structure of the sample and observe its morphological characteristics.

[0101] SEM images of the negative electrode active material prepared in this embodiment are shown below. Figure 1 As shown, from Figure 1 It can be seen that the negative electrode active material has a small particle-like morphological structure.

[0102] Preparation of lithium-ion batteries

[0103] Negative electrode sheet: The prepared negative electrode active material, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC) thickener are mixed in a weight ratio of 97.4:1.2:1.4, and then thoroughly stirred with an appropriate amount of deionized water to form a uniform negative electrode slurry. This slurry is coated onto the current collector Cu foil, dried, and cold-pressed to obtain the negative electrode sheet (the conductivity of the negative electrode sheet is 1-10 S / cm, and the OI value is 11-21).

[0104] Positive electrode: Ni is selected 0.83 Co 0.07 Mn 0.1 As the positive electrode active material, it is mixed with conductive agent acetylene black and 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. This slurry is coated onto current collector Al foil, dried, and cold-pressed to obtain the positive electrode sheet.

[0105] Electrolyte: In a dry argon-atmospheric 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. Then, fluoroethylene carbonate and 1,3-propanesulfonyl lactone were added, dissolved, and thoroughly stirred. Lithium salt LiPF6 was then added and mixed evenly to obtain the electrolyte. The mass percentages of LiPF6, fluoroethylene carbonate, and 1,3-propanesulfonyl lactone were 12.5%, 3%, and 2%, respectively, calculated based on the mass of the electrolyte.

[0106] Lithium-ion battery: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound up to form an electrode assembly. The electrode assembly is placed in an outer aluminum-plastic film and dehydrated at 80°C. The electrolyte is then injected and the battery is sealed. After formation, degassing, and edge trimming processes, the lithium-ion battery is obtained.

[0107] Experiment 1: Based on Example 1-1, the particle size, shaping time, asphalt coating ratio, heat treatment temperature and time, and graphitization temperature and time were adjusted during the preparation of the negative electrode active material. The specific process parameters are shown in Table 1, resulting in Examples 1-2 to 1-9 and Comparative Examples 1-1 to 1-2. The specific test results are shown in Table 4.

[0108] Table 1. Preparation process parameters for Experiment 1

[0109]

[0110] Experiment 2: Based on Example 1-1, the particle size, shaping time, asphalt coating ratio, heat treatment temperature and time, and graphite temperature and time were adjusted to obtain Examples 2-1 to 2-6. The specific parameter data are shown in Table 5.

[0111] Table 2. Preparation process parameters for Experiment 2

[0112]

[0113] Experiment 3: Based on Examples 1-1, adjustments were made to the particle size, shaping time, pitch coating ratio, heat treatment temperature and time, and graphite temperature and time during the preparation of the negative electrode active material, resulting in Examples 3-1 to 3-7. The particle size Dv50 (aμm) and specific surface area (bm²) of the negative electrode active materials in each example were determined. 2 Same as / g), tap density (Tg / cm) 3 The parameters are the same, and the specific parameters are shown in Table 6.

[0114] Table 3. Preparation process parameters for Experiment 3

[0115]

[0116] Test methods

[0117] A fully discharged lithium-ion battery was disassembled, and the negative electrode was soaked in ethylene carbonate (DMC) for 20 min, followed by rinsing with DMC and acetone respectively. The battery was then placed in an oven and baked at 80°C for 12 h to obtain the treated negative electrode sheet. Powder was scraped off the negative electrode sheet with a scraper, and the scraped powder was heat-treated in a tube furnace at 400°C for 4 h under argon protection to obtain the negative electrode active material.

[0118] The negative electrode active material, negative electrode active material layer, and negative electrode sheet obtained above were subjected to the following tests:

[0119] 1. Particle size test

[0120] The particle size testing method for negative electrode active materials follows GB / T 19077-2016. The specific procedure is as follows: 1g of sample is weighed and mixed thoroughly with 20mL of deionized water and a trace dispersant. The mixture is then sonicated in an ultrasonic device for 5 minutes. The solution is then poured into a Hydro 2000SM sample introduction system for testing. The testing equipment used is a Mastersizer 3000 manufactured by Malvern. During the test, the particle size is measured by measuring the intensity of the scattered light as the laser beam passes through the dispersed particle sample. The data is then used to analyze and calculate the particle size distribution that forms the scattering spectrum. The refractive index is set to 1.8, and each sample is tested three times. The final particle size (Dv50) is calculated as the average of the three tests.

[0121] 2. Specific surface area test

[0122] The test method for specific surface area refers to GB / T 19587-2017. The specific procedure is as follows: weigh 1 g to 8 g of negative electrode active material (the amount of negative electrode active material should be 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 of the tube is 12 mm). After pretreatment at 200℃ for 2 h, it is placed in the TriStar3030 test equipment (McGen, Inc., USA) for testing. The adsorbed gas used is N2 (purity: 99.999%). The test conditions are 77 K, and the specific surface area is determined by the BET calculation method.

[0123] 3. Tap density test

[0124] The test method of GB / T 5162-2006 "Determination of tap density of metal powder" was adopted, and the McMurray GeoPyc1365 instrument was used. 3±0.1g of negative electrode active material was weighed, and the bonding force was 85N.

[0125] 4. Graphitization degree test

[0126] The X-ray diffraction analysis was performed using the national standard JJS K 0131-1996, with the instrument model Bruker D8ADVANCE, Cu Kα target, 40 kV / 40 mA voltage and current, and a test angle of 52° - 58°. The negative electrode active material containing a carbon-silicon ratio of C:Si = 5:1 (mass ratio) was scanned and tested, with a step time of 0.3 s.

[0127] 5. Compacted density test

[0128] The compaction density test standard refers to GB / T 24533-2009 "Graphite 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)). Then, the anode active material is placed in the testing equipment, a Sansi Zongheng UTM7305 with a testing tonnage of 5.0 tons. The formula for calculating compaction density is: Compaction density = Mass of anode active material / Area of ​​anode active material under stress / Thickness of anode active material.

[0129] 6. Raman Surface Defect Test

[0130] The negative electrode active material was scanned and tested using a laser confocal Raman spectrometer (Raman, HR Evolution, HORIBA Scientific Instruments Division). A scanning region of arbitrarily selected size (100 μm × 100 μm) was used to scan the particles within this region, obtaining the D and G peaks of all particles within that region. The data was processed using LabSpec software to obtain the peak intensities of the D and G peaks for each particle, which are denoted as Id and Ig, respectively. The laser wavelength of the Raman spectrometer can be in the range of 532 nm to 785 nm. In this application, the Id / Ig value is the average of the Id and Ig ratios of all particles measured within this range.

[0131] 7. Electrode conductivity test

[0132] Reference standard: GB / T 30385-2014 "Carbon composite lithium iron phosphate cathode material for lithium-ion batteries" Test procedure: Weigh the negative electrode sheet and place it on an electronic pressure stage. Then, increase the pressure at a rate of 5 mm / min to a load of 25 MPa, hold the pressure for 60 seconds, and then release the pressure to 0 to obtain the electrode conductivity.

[0133] 8. Electrode OI value test

[0134] The negative electrode was scanned using the national standard JJS K 0131-1996 "General Rules for X-ray Diffraction Analysis", with the instrument model Bruker D8ADVANCE, Cu Kα target, and voltage and current of 40 kV / 40 mA. The C004 peak and C110 peak data were obtained, and the OI value of the negative electrode was obtained by calculating the C004 / C110 ratio.

[0135] The lithium-ion batteries obtained above were subjected to the following performance tests:

[0136] 1. Battery 1s DCR test

[0137] At -20℃, the lithium-ion battery was charged at a constant current of 1C to 4.25V, then charged at a constant voltage of 4.25V to 0.05C, and left to stand for 30 minutes. It was then discharged at 0.1C for 10 seconds, and the voltage value was recorded as U1. Finally, it was discharged at 1C for 360 seconds, and the voltage value was recorded as U2. This charge-discharge cycle was repeated 5 times. "1C" refers to the current value required to completely discharge the lithium-ion battery within one hour.

[0138] The DC resistance R of a lithium-ion battery at 25°C can be calculated using the following formula:

[0139] R=(U2-U1) / (1C-0.1C).

[0140] Unless otherwise specified, the DCR mentioned in this application refers to the DC resistance of a lithium-ion battery at 50% state of charge (SOC).

[0141] 2. Battery capacity retention test

[0142] The lithium-ion battery was placed in a high and low temperature chamber, the ambient temperature was adjusted to 25°C, and it was charged at a constant current of 0.2C to 4.25V. Then it was charged at a constant voltage of 4.25V to 0.05C. After standing for 5 minutes, it was discharged at a rate of 0.2C to 3V, thus obtaining the 25°C 0.2C capacity.

[0143] The charging process was repeated, charging at a constant current rate of 0.2C to 4.25V, then charging at a constant voltage of 4.25V to 0.05C. The ambient temperature was adjusted to -20℃, and the battery was left to stand for 30 minutes. Finally, it was discharged at a 10C rate to 3V, yielding the -20℃ 10C capacity. The 10C discharge capacity retention rate of the lithium-ion battery is calculated using the following formula:

[0144] -20℃ 10C capacity retention rate = (-20℃ 10C discharge capacity / 25℃ 0.2C discharge capacity) × 100%.

[0145] The test results are shown in Table 4-6:

[0146] Table 4 Test results of Experiment 1

[0147]

[0148] Table 4 shows that, compared to Comparative Examples 1-1 to 1-2, the particle size Dv50 (aμm) and specific surface area BET (bm²) of the negative electrode active materials in Examples 1-1 to 1-9 are significantly different. 2When the anode active material ( / g) satisfies 20 ≤ 2.5 × a + b ≤ 40, the battery made from this material has a low 1s DCR and can discharge at temperatures as low as -20°C, while also improving the low-temperature 10C discharge capacity retention rate. The anode active material particles meeting this condition have complete crystal growth, 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 conductivity network for the entire electrode. At low temperatures, this good conductivity network reduces polarization during high-rate discharge, thereby lowering the 1s DCR and improving the low-temperature 10C discharge capacity retention rate.

[0149] According to Examples 1-1 to 1-7, 2≤a≤10, 10≤b≤25, and 20≤2.5×a+b≤40, the 1sDCR of the lithium-ion battery is significantly reduced, and the capacity retention rate at low temperature 10C discharge is significantly improved.

[0150] Table 5 Test results of Experiment 2

[0151]

[0152] Table 5 shows that, compared to Examples 1-1, the particle size (a μm) and tap density T (g / cm³) of the negative electrode active materials in Examples 2-1 to 2-6 are significantly different. 3 When 0.3 ≤ T - 0.05 × a ≤ 1.0, the low-temperature high-rate discharge capability of the battery can be improved. The negative electrode active material particles meeting this condition can be tightly packed together during coating, resulting in a low OI value for the formed negative electrode sheet. This improves the conductivity and lithium-ion diffusion performance of the negative electrode sheet, thereby enhancing the low-temperature high-rate discharge capability of the lithium-ion battery.

[0153] According to Examples 2-1 to 2-4, 0.5≤T≤1.4, and simultaneously satisfy 0.3≤T-0.05×a≤1.0, the battery 1s DCR decreases and the low-temperature 10C discharge capacity retention rate is significantly improved.

[0154] Table 6 Test results of Experiment 3

[0155]

[0156] As shown in Table 6, compared with Example 1-1, when the graphitization degree of the negative electrode active material in Examples 3-1 to 3-7 is higher, the Id / Ig value is lower, there are fewer Id / Ig defects on the particle surface, the particle crystal growth is more complete, the electron conduction within the particle is better, the conductivity of the negative electrode sheet is improved, electrons can also conduct 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.

[0157] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort 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 and 2≤a≤8; The degree of graphitization of the negative electrode active material is G%, 96.0≤G≤97.5; The compaction density of the negative electrode active material is P g / cm³. 3 , 1.90≤P≤2.10; The tap density of the negative electrode active material is T g / cm³. 3 , 0.8≤T≤1.

2.

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, characterized in that, 10≤b≤25。 4. The negative electrode active material according to claim 3, characterized in that, 13≤b≤20。 5. The negative electrode active material according to any one of claims 1-4, characterized in that, The tap density of the negative electrode active material is T g / cm³. 3 , 0.3≤T-0.05×a≤1.

0.

6. The negative electrode active material according to claim 5, characterized in that, 0.5≤T-0.05×a≤0.

8.

7. The negative electrode active material according to any one of claims 1-4, characterized in that, The Raman Id / Ig ratio of the negative electrode active material is 0.1-0.

35.

8. The negative electrode active material according to any one of claims 1-4, characterized in that, The negative electrode active material includes a sheet-like structure material, and the mass percentage of the sheet-like structure material in the negative electrode active material is 90%-100%.

9. The negative electrode active material according to any one of claims 1-4, characterized in that, The negative electrode active material includes carbon materials.

10. The negative electrode active material according to claim 9, characterized in that, The negative electrode active material includes flake graphite with a carbon coating.

11. A negative electrode sheet, characterized in that, It 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 comprises the negative electrode active material according to any one of claims 1-10.

12. The negative electrode sheet according to claim 11, characterized in that, The negative electrode has a conductivity of 1-10 S / cm under a load of 25 MPa.

13. The negative electrode sheet according to claim 12, characterized in that, The negative electrode has a conductivity of 5-10 S / cm under a load of 25 MPa.

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

15. A battery, characterized in that, It includes the negative electrode sheet as described in any one of claims 12-14.

16. An electrical appliance, characterized in that, It includes the battery as described in claim 15.

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