Electrolyte, secondary battery, battery module, battery pack, and electric device

Abstract

An electrolyte, a secondary battery, a battery module, a battery pack, and an electrical device are provided. The electrolyte includes an organic solvent and an additive. The organic solvent includes a first organic solvent as shown in formula (1), and the additive includes a first additive selected from one or more compounds shown in formulas (2A) and (2B). In formula (1), R1 and R2 are independently one of C1-C3 alkyl and C1-C3 haloalkyl, respectively; in formula (2A), R... 21 R 22 R 23 R 24 Each is independently a single bond or a methylene group; in formula (2B), R 31 R 32 R 33 R 34 Each of the following is independently represented by a single bond or a methylene group, and R4 is one of a single bond, -O-, C1-C3 alkylene group, C1-C3 haloalkylene group, or C1-C3 oxaalkylene group. The secondary battery not only has a long cycle life and storage life, but also excellent fast-charging performance.

Description

Technical Field

[0001] This application belongs to the field of secondary battery technology, specifically relating to an electrolyte, a secondary battery, a battery module, a battery pack, and an electrical device. Background Technology

[0002] Compared to traditional gasoline-powered cars, which can be refueled quickly and readily, electric vehicles often have longer charging times because they are typically charged at a lower rate. This issue not only causes range anxiety for consumers but also limits the rapid adoption of electric vehicles. Summary of the Invention

[0003] The purpose of this application is to provide an electrolyte, a secondary battery, a battery module, a battery pack, and an electrical device, which aims to enable the battery to have a long cycle life and storage life while also having good fast charging performance.

[0004] This application provides an electrolyte comprising an organic solvent and an additive. The organic solvent comprises a first organic solvent as shown in Formula 1, wherein R1 and R2 are independently selected from C1-C3 alkyl and C1-C3 haloalkyl groups, respectively. The additive comprises a first additive selected from one or more compounds shown in Formula 2A and Formula 2B, wherein in Formula 2A, R... 21 R 22 R 23 R 24 Each is independently a single bond or a methylene group; in formula 2B, R... 31 R 32 R 33 R 34 Each of the following can be independently represented by a single bond or a methylene group, and R4 can be one of a single bond, -O-, C1~C3 alkylene, C1~C3 haloalkylene, or C1~C3 oxaalkylene.

[0005] Formula 1

[0006] Formula 2A Formula 2B

[0007] By using the first additive in combination with the first organic solvent, the battery can maintain good cycle performance and storage performance while fully leveraging the effect of the first organic solvent in improving the conductivity of the electrolyte.

[0008] In any embodiment of this application, in Formula 1, R1 and R2 are each independently one of methyl, ethyl, propyl, fluoromethyl, fluoroethyl, and fluoropropyl. By selecting a suitable first organic solvent, the viscosity of the electrolyte can be maintained within a suitable range, thus the electrolyte has higher conductivity and the battery has better fast-charging performance.

[0009] In any embodiment of this application, the first organic solvent is selected from one or more of the following compounds:

[0010] Compound 1-1, Compounds 1-2,

[0011] Compounds 1-3, Compounds 1-4,

[0012] Compounds 1-5, Compounds 1-6.

[0013] Choosing the above-mentioned compounds as the first organic solvent can make the electrolyte have a moderate viscosity and higher conductivity.

[0014] In any embodiment of this application, the first organic solvent is selected from one or two of the following compounds:

[0015] Compound 1-1, Compounds 1-2.

[0016] Compounds 1-1 and 1-2 have lower viscosity and a more significant effect on improving the conductivity of the electrolyte.

[0017] In any embodiment of this application, in formula 2A, R 21 R 22 R 23 R 24 Each is independently one of a single bond or a methylene group.

[0018] Optionally, R 21 R 22 R 23 R 24 They are not both single keys.

[0019] More specifically, R 21 R 22 One or both of them are methylene, R 23 R 24 One or both of them are methylene.

[0020] In any embodiment of this application, in formula 2B, R31 R 32 R 33 R 34 Each is independently a single bond or a methylene group, and R 31 R 32 R 33 R 34 They are not both single keys.

[0021] In any embodiment of this application, in Formula 2B, R4 is one of a single bond, -O-, methylene, ethylene, propylene, fluoromethylene, fluoroethylene, fluoropropylene, methyleneoxy, ethoxy, and propoxy.

[0022] Optionally, R4 is one of a single bond, methylene, ethylene, or propylene.

[0023] The first additive with substituents within the above range can form a dense and stable interfacial film on the surface of the negative electrode active material, blocking the direct contact between the first organic solvent and the negative electrode active material. Therefore, it can further improve the reversibility of active ions intercalating and deintercalating between the positive and negative electrode sheets, and improve the discharge capacity and cycle performance of the battery.

[0024] In any embodiment of this application, when R4 is a single bond, R 31 R 32 One or two of them are methylene groups, and the rest are single bonds.

[0025] In any embodiment of this application, when R4 is a single bond, R 33 R 34 One or two of them are methylene groups, and the rest are single bonds.

[0026] In any embodiment of this application, when R4 is a single bond, R 31 R 32 One of them is methylene, R 33 R 34 One of them is a methylene group, and the rest are single bonds.

[0027] In any embodiment of this application, when R4 is a single bond, R 31 R 32 All are methylene, R 33 R 34 One of them is a methylene group, and the rest are single bonds.

[0028] In any embodiment of this application, when R4 is a single bond, R 33 R 34 All are methylene, R 31 R 32 One of them is a methylene group, and the rest are single bonds.

[0029] In any embodiment of this application, when R4 is a single bond, R 31 R 32 R 33 R 34 All are methylene.

[0030] In any embodiment of this application, the first additive is selected from one or more of the following compounds:

[0031] Compound 2-1, Compound 2-2,

[0032] Compounds 2-3, Compounds 2-4,

[0033] Compounds 2-5, Compounds 2-6,

[0034] Compounds 2-7, Compounds 2-8.

[0035] The aforementioned first additive can form a stable and durable interfacial film on the surface of the negative electrode active material, further improving the battery's cycle performance and storage performance.

[0036] Optionally, in any embodiment of this application, the first additive is selected from one or more of the following compounds:

[0037] Compounds 2-3, Compounds 2-4,

[0038] Compounds 2-5, Compounds 2-8.

[0039] In any embodiment of this application, the mass percentage of the first organic solvent is w1, based on the total mass of the organic solvent, and w1 ranges from 20% to 80%. Optionally, w1 ranges from 30% to 70%. Controlling the mass percentage of the first organic solvent within a suitable range can improve the battery's fast charging performance while also giving the battery good cycle performance and storage performance.

[0040] In any embodiment of this application, based on the total mass of the electrolyte, the mass percentage of the first additive is w2, and w2 ranges from 0.1% to 10%. Optionally, w2 ranges from 0.5% to 5%. Controlling the mass percentage of the first additive within a suitable range enables the battery to have good fast charging performance, cycle performance, and storage performance.

[0041] In any embodiment of this application, the additive further includes a second additive, which contains one or more of the following: unsaturated cyclic carbonate compounds, halogen-substituted cyclic carbonate compounds, sulfate compounds, sulfite compounds, sulfonyl lactone compounds, disulfonic acid compounds, nitrile compounds, aromatic compounds, isocyanate compounds, phosphonitrile compounds, cyclic anhydride compounds, phosphite compounds, phosphate compounds, borate ester compounds, and carboxylic acid ester compounds. These second additives can form a denser and more stable interfacial film on the surface of the positive electrode active material and / or the negative electrode active material, which helps to further improve the cycle performance and storage performance of the battery.

[0042] In any embodiment of this application, the second additive comprises one or two of the following compounds:

[0043] Compound 3-1, Compound 3-2.

[0044] When the electrolyte contains one or both of the above two compounds, the cycle performance and storage performance of the battery can be further enhanced.

[0045] In any embodiment of this application, based on the total mass of the electrolyte, the mass percentage of the second additive is w3, and the range of w3 is ≤10%. Optionally, the range of w3 is ≤5%. Controlling the mass percentage of the second additive within a suitable range can further enhance the cycle performance of the battery.

[0046] In any embodiment of this application, the organic solvent further includes a second organic solvent, which comprises one or more cyclic carbonate compounds and chain carbonate compounds. Optionally, the second organic solvent comprises a cyclic carbonate compound, or a combination of cyclic carbonate compounds and chain carbonate compounds. The inclusion of the aforementioned second organic solvent in the organic solvent enables the battery containing the electrolyte to have good fast-charging performance.

[0047] In any embodiment of this application, the second organic solvent includes one or more of ethylene carbonate, propylene carbonate, 1,2-butenyl carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate. The inclusion of a second organic solvent composed of the above-mentioned compounds in the electrolyte can give the battery containing the electrolyte better fast-charging performance.

[0048] In any embodiment of this application, based on the total mass of the organic solvent, the mass percentage of the cyclic carbonate compound is w4, and w4 ranges from 20% to 80%. Optionally, w4 ranges from 20% to 50%. The cyclic carbonate compound has a high dielectric constant, which is beneficial for the dissociation of lithium salt. Controlling the mass percentage of the cyclic carbonate compound within a suitable range enables the battery containing this electrolyte to have better fast-charging performance.

[0049] In any embodiment of this application, the electrolyte further includes a lithium salt, said lithium salt including LiN(C) x F 2x+1 SO2)(C y F 2y+1 The electrolyte contains one or more of the following lithium salts: SO2, LiPF6, LiBF4, LiBOB, LiDFOB, LiPO2F2, LiDFOP, LiTFOP, LiAsF6, Li(FSO2)2N, LiCF3SO3, and LiClO4, where x and y are positive integers. Including these lithium salts in the electrolyte helps form a uniform, dense, and low-resistance interfacial film on the surface of the battery's negative electrode active material, effectively improving the battery's fast-charging performance and cycle performance.

[0050] In any embodiment of this application, the conductivity of the electrolyte is ≥12 mS / cm. Optionally, the conductivity of the electrolyte is ≥13 mS / cm. Controlling the conductivity of the electrolyte within a suitable range enables the battery to have good fast charging performance, cycle performance, storage performance, and safety performance.

[0051] In any embodiment of this application, the conductivity of the electrolyte is 12 mS / cm to 24 mS / cm. Optionally, the conductivity of the electrolyte is 13 mS / cm to 20 mS / cm.

[0052] A second aspect of this application provides a secondary battery that includes the electrolyte of the first aspect of this application.

[0053] The secondary battery of this application includes the electrolyte of the first aspect of this application. The secondary battery has good fast charging performance, as well as excellent cycle performance and storage performance.

[0054] In any embodiment of this application, the secondary battery includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. The ratio H / Dv50 of the thickness H of the single-sided negative electrode film layer to the volume average particle size Dv50 of the negative electrode active material satisfies ≥3. Optionally, H / Dv50 satisfies ≥3.5. More specifically, the range of H / Dv50 satisfies 4≤H / Dv50≤9. A suitable value for H / Dv50 can further improve the fast-charging performance of the secondary battery while ensuring a high volumetric energy density.

[0055] In any embodiment of this application, the thickness H of the single-sided negative electrode film layer is ≥60μm. Optionally, the thickness H of the single-sided negative electrode film layer is ≥65μm. A thickness H of the single-sided negative electrode film layer within a suitable range can further improve the energy density of the battery.

[0056] In any embodiment of this application, the volume average particle size Dv50 of the negative electrode active material satisfies ≤18μm. Optionally, the volume average particle size Dv50 of the negative electrode active material satisfies 14μm≤Dv50≤18μm. When the volume average particle size Dv50 of the negative electrode active material is within a suitable range, it can both improve the diffusion coefficient of active ions and reduce the contact area between the negative electrode film and the electrolyte, enabling the battery to simultaneously possess good fast-charging performance, cycle performance, and storage performance.

[0057] In any embodiment of this application, the compaction density of the negative electrode film is 1.4 g / cm³. 3 ~1.85g / cm 3 Optionally, the compaction density of the negative electrode film is 1.6 g / cm³. 3 ~1.8g / cm 3 When the compaction density of the negative electrode film is within a suitable range, the battery can possess both high energy density and good fast-charging performance.

[0058] In any embodiment of this application, the secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes one or more of lithium transition metal oxides, lithium phosphates with olivine structures, and their respective modified compounds.

[0059] In any embodiment of this application, the olivine-structured lithium phosphate includes one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their modified compounds. Using these positive electrode active materials in the positive electrode film layer can improve the battery's rate performance and energy density while simultaneously enhancing its cycle performance and storage performance.

[0060] A third aspect of this application provides a battery module that includes the secondary battery of the second aspect of this application.

[0061] The fourth aspect of this application provides a battery pack, which includes one of the secondary battery of the second aspect of this application and the battery module of the third aspect.

[0062] The fifth aspect of this application provides an electrical device that includes at least one of the secondary battery of the second aspect of this application, the battery module of the third aspect, and the battery pack of the fourth aspect.

[0063] The battery module, battery pack, and power device of this application include the secondary battery provided in this application, and therefore have at least the same advantages as the secondary battery. Attached Figure Description

[0064] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some implementation methods of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0065] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0066] Figure 2 This is an exploded view of one embodiment of the secondary battery of this application.

[0067] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0068] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0069] Figure 5 yes Figure 4 The exploded diagram.

[0070] Figure 6 This is a schematic diagram of one embodiment of the electrical device that uses a secondary battery as a power source according to this application. Detailed Implementation

[0071] To make the inventive objectives, technical solutions, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of this application.

[0072] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0073] In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" include the number itself, and "several" in "one or several" means two or more.

[0074] In this description, unless otherwise stated, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0075] It should be understood that relational terms such as “first,” “second,” etc., are used only to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations.

[0076] The foregoing description of this invention is not intended to describe every disclosed embodiment or implementation. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are merely representative and should not be construed as exhaustive.

[0077] [Rechargeable Battery]

[0078] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0079] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, also positioned between the positive and negative electrodes, mainly serves to conduct active ions.

[0080] Electrolyte

[0081] Secondary batteries include electrolytes, which act as a bridge for the passage of active ions in the battery. They play a crucial role in transporting active ions between the positive and negative electrodes, and are essential for the battery's fast charging performance, specific capacity, cycle efficiency, and safety performance.

[0082] The inventors discovered that one of the key factors affecting the fast-charging performance of batteries is the conductivity of the electrolyte. Adding carboxylic acid esters to the electrolyte can improve its conductivity and the battery's fast-charging performance. This is because carboxylic acid esters have advantages such as low viscosity and high dielectric constant, which improve the ionic conductivity of the electrolyte. However, carboxylic acid esters are incompatible with the negative electrode. The α-H on the carboxylic acid ester readily reacts with the active lithium obtained from the reduction at the negative electrode, causing the loss of active lithium and affecting the battery's cycle performance and storage performance, especially at high temperatures. Furthermore, carboxylic acid esters have poor oxidation resistance and are prone to oxidative decomposition during high-charge storage, further affecting the battery's storage performance. To reduce the negative impact of carboxylic acid esters on battery cycle performance and storage performance, existing technologies have reported the addition of cyclic sulfate esters to the electrolyte. Cyclic sulfate esters can form an interfacial film on the surfaces of both the positive and negative electrode active materials, blocking direct contact between the positive and negative electrode active materials and the electrolyte, and inhibiting the continuous reaction between the negative electrode and the carboxylic acid ester in the electrolyte. However, conventional cyclic sulfates also generate gas during the formation of the interfacial film. These continuously generated gases accumulate at the interface between the positive electrode, negative electrode and separator, forming macroscopic bubbles. These bubbles block the transport of active ions, thus affecting the battery's cycle performance and storage performance.

[0083] The inventors conducted further extensive research and ingeniously added the first additive shown in Formula 2A and / or Formula 2B to the electrolyte containing carboxylic acid esters, breaking through the aforementioned bottleneck. The electrolyte of this application can fully utilize the effect of carboxylic acid esters in improving electrolyte conductivity and battery fast-charging performance while ensuring good cycle performance and storage performance of the battery, especially ensuring good cycle performance and storage performance of the battery even under high-temperature environments.

[0084] Specifically, the electrolyte of this application includes an organic solvent and an additive, wherein the organic solvent includes a first organic solvent as shown in Formula 1, and the additive includes a first additive selected from one or more compounds shown in Formula 2A and Formula 2B. Specifically, in some embodiments, the first additive is selected from one or more compounds shown in Formula 2A; in some embodiments, the first additive is selected from one or more compounds shown in Formula 2B; in some embodiments, the first additive simultaneously includes compounds shown in Formula 2A and compounds shown in Formula 2B.

[0085] Formula 1

[0086] In Formula 1, R1 and R2 are independently one of C1-C3 alkyl and C1-C3 haloalkyl, respectively. R1 and R2 can be the same or different. Alkyl and haloalkyl can be straight-chain or branched-chain structures. The number of halogen atoms in a haloalkyl can be one or more; when multiple halogen atoms are present in a haloalkyl, these halogen atoms can be the same or different.

[0087] Formula 2A Formula 2B

[0088] In equation 2A, R 21 R 22 R 23 R 24 Each can be independently either a single bond or a methylene group (-CH2-). R 21 R 22 R 23 R 24 They can be the same or different.

[0089] In equation 2B, R 31 R 32 R 33 R 34 Each of the following can be independently represented by a single bond or a methylene group: R4 can be a single bond, -O-, a C1-C3 alkylene group, a C1-C3 haloalkylene group, or a C1-C3 oxaalkylene group. Alkylenes, haloalkylenes, and oxaalkylenes can be straight-chain or branched. A haloalkylene group can contain one or more halogen atoms; when multiple halogen atoms are present in a haloalkylene group, these halogen atoms can be the same or different. An oxaalkylene group can contain one or more oxygen atoms.

[0090] When R 31 R 32 R 33 R 34When it is a single bond, it means that R4 is directly bonded to R. 31 R 32 R 33 R 34 Adjacent -O- are bonded by single bonds. R 31 R 32 R 33 R 34 They can be the same or different.

[0091] The electrolyte of this application incorporates a first additive with a high reduction potential. During charging, it can accept electrons from the negative electrode and undergo self-reduction. It preferentially forms a dense and stable sulfur-containing organic interface film on the surface of the negative electrode active material, inhibiting the reaction between the first organic solvent and the active lithium obtained from the reduction at the negative electrode. The first additive exhibits high thermal stability, producing no gas during the formation of the sulfur-containing organic interface film, thus not affecting the battery's cycle performance and storage performance, especially at high temperatures. Furthermore, the first additive preferentially forms an interface film on the surface of the positive electrode active material, inhibiting the oxidative decomposition of the first organic solvent at the positive electrode. It can also coordinate with transition metals on the surface of the positive electrode active material to form complexes, making the interface film formed on the positive electrode active material more dense and stable, effectively preventing direct contact between the organic solvent (especially the first organic solvent) and the positive electrode active material.

[0092] By combining the first additive with the first organic solvent, the effect of the first organic solvent in improving the electrolyte conductivity can be fully utilized while ensuring that the battery has good cycle performance and storage performance. Therefore, the electrolyte of this application can enable the battery to have both excellent fast charging performance and good cycle performance and storage performance.

[0093] Without being bound by any theoretical limitations, the inventors discovered for the first time during their research that the first additive added to the electrolyte has a far superior effect on inhibiting the reaction between the first organic solvent and the negative electrode, and on ensuring that the battery has good cycle performance and storage performance compared to conventional cyclic sulfates (e.g., vinyl sulfate DTD) used in the prior art.

[0094] In some embodiments, in Formula 1, R1 and R2 can each be independently one of methyl, ethyl, propyl, fluoromethyl, fluoroethyl, or fluoropropyl. R1 and R2 can be the same or different. The number of fluorine atoms can be one or more. When R1 and R2 are selected from the above-mentioned groups, the viscosity of the electrolyte can be kept within a suitable range, thus the electrolyte has higher conductivity and the battery has better fast-charging performance.

[0095] In some embodiments, the first organic solvent may be selected from one or more of the following compounds:

[0096] Compound 1-1, Compounds 1-2,

[0097] Compounds 1-3, Compounds 1-4,

[0098] Compounds 1-5, Compounds 1-6.

[0099] The inventors discovered that when the electrolyte includes one or more of the above-mentioned compounds, the electrolyte has a moderate viscosity and higher conductivity, thereby significantly improving the fast charging performance of the battery.

[0100] In some embodiments, the first organic solvent may be selected from one or two of the following compounds:

[0101] Compound 1-1, Compounds 1-2.

[0102] Through in-depth research, the inventors discovered that compounds 1-1 and 1-2 have lower viscosity, thus having a more significant effect on improving the conductivity of the electrolyte, thereby enabling the battery to have better fast charging performance.

[0103] In some embodiments, the mass percentage of the first organic solvent is w1, based on the total mass of the organic solvent, and w1 can range from 20% to 80%. For example, w1 can range from 25% to 80%, 25% to 75%, 30% to 70%, 30% to 60%, 35% to 65%, 35% to 60%, 40% to 60%, or 50% to 60%. Taking into full account the effect of the first organic solvent on improving the conductivity of the electrolyte and its negative impact on the battery's cycle performance and storage performance, the inventors have controlled the mass percentage of the first organic solvent within a suitable range, which can improve the battery's fast-charging performance while ensuring good cycle performance and storage performance.

[0104] In some implementations, in formula 2A, R 21 R 22 R 23 R 24 Not both are single keys. Optionally, R 21 R 22 One or both of them are methylene, R 23 R 24 One or both of them are methylene.

[0105] In some implementations, R 21 R 23 For methylene, R 22 R 24 It is a single key.

[0106] In some implementations, R 21 R 23 For methylene, R 22 R 24 One of them is a methylene group, and the rest are single bonds.

[0107] In some implementations, R 21 R 22 R 23 R 24 All are methylene.

[0108] In some implementations, in Equation 2B, R 31 R 32 R 33 R 34 It can be independently either a single bond or a methylene group, and R 31 R 32 R 33 R 34 They are not both single keys.

[0109] In some implementations, in Equation 2B, R 31 R 32 R 33 R 34 At least two of them are methylene groups.

[0110] In some embodiments, in Formula 2B, R4 can be one of a single bond, O-, methylene, ethylene, propylene, fluoromethylene, fluoroethylene, fluoropropylene, methyleneoxy, ethoxy, and propoxy. Optionally, R4 can be one of a single bond, methylene, ethylene, and propylene. These substituents can be either straight-chain or branched. The number of fluorine atoms can be one or more.

[0111] When these substituents fall within the above-mentioned range, the first additive can form a dense and stable interface film on the surface of the positive and negative active materials, blocking the direct contact between the first organic solvent and the positive and negative active materials, reducing the loss of active lithium, thereby further improving the reversibility of active ions intercalation and deintercalation between the positive and negative electrode sheets, and improving the discharge capacity and cycle performance of the battery.

[0112] In some implementations, when R4 is a single bond, R 31 R 32 One or two of them are methylene groups, and the rest are single bonds.

[0113] In some implementations, when R4 is a single bond, R 33 R 34 One or two of them are methylene groups, and the rest are single bonds.

[0114] In some implementations, when R4 is a single bond, R 31 R 32 One of them is methylene, R 33 R 34 One of them is a methylene group, and the rest are single bonds.

[0115] In some implementations, when R4 is a single bond, R 31 R 32 All are methylene, R 33 R 34 One of them is a methylene group, and the rest are single bonds.

[0116] In some implementations, when R4 is a single bond, R 33 R 34 All are methylene, R 31 R 32 One of them is a methylene group, and the rest are single bonds.

[0117] In some implementations, when R4 is a single bond, R 31 R 32 R 33 R 34 All are methylene.

[0118] In some embodiments, the first additive may be selected from one or more of the following compounds:

[0119] Compound 2-1, Compound 2-2,

[0120] Compounds 2-3, Compounds 2-4,

[0121] Compounds 2-5, Compounds 2-6,

[0122] Compounds 2-7, Compounds 2-8.

[0123] The inventors discovered that using one or more of the above-mentioned compounds as the first additive can form a more stable and durable interface film on the surface of the positive and negative electrode active materials; even after long-term charge and discharge, the interface film can still effectively prevent organic solvents (especially the first organic solvent) from directly contacting the positive and negative electrode active materials, thus further improving the cycle performance and storage performance of the battery.

[0124] In some embodiments, the first additive is selected from one or more of the following compounds:

[0125] Compounds 2-3, Compounds 2-4,

[0126] Compounds 2-5, Compounds 2-8.

[0127] In some embodiments, the first additive is selected from one or two of the following compounds:

[0128] Compounds 2-4, Compounds 2-5.

[0129] In some embodiments, the mass percentage of the first additive is w2, based on the total mass of the electrolyte, and w2 can be ≤10%. For example, the range of w2 can be 0.05% ~ 10%, 0.1% ~ 10%, 0.5% ~ 10%, 0.5% ~ 8%, 0.5% ~ 5%, 1% ~ 5%, or 2% ~ 5%. Within a suitable range, the synergistic effect of the first additive and the first organic solvent can be fully utilized. A larger mass percentage of the first additive results in a thicker film on the surface of the negative electrode active material, which may affect the transport rate of active ions at the negative electrode interface and may not significantly improve the battery's fast charging performance. A smaller mass percentage of the first additive cannot effectively inhibit the continuous reaction between the first organic solvent and the negative electrode, and may not significantly improve the battery's cycle performance and storage performance. Through inventive effort, the inventors have selected a range of mass percentages for the first additive, thereby enabling the battery to possess good fast charging performance, cycle performance, and storage performance.

[0130] In some embodiments, the additive may further include a second additive. The second additive may include one or more of the following: cyclic carbonate compounds containing unsaturated bonds, halogen-substituted cyclic carbonate compounds, sulfate compounds, sulfite compounds, sulfonyl lactone compounds, disulfonic acid compounds, nitrile compounds, aromatic compounds, isocyanate compounds, phosphonitrile compounds, cyclic anhydride compounds, phosphite compounds, phosphate compounds, borate ester compounds, and carboxylic acid ester compounds. These second additives can form a denser and more stable interfacial film on the surface of the positive electrode active material and / or the negative electrode active material, which helps to further improve the cycle performance and storage performance of the battery.

[0131] In some embodiments, the second additive may include one or two of the following compounds:

[0132] Compound 3-1, Compound 3-2.

[0133] When the second additive contains one or both of the above two compounds, it can further enhance the battery's cycle performance and storage performance.

[0134] In some embodiments, the mass percentage of the second additive is w3 based on the total mass of the electrolyte, and w3 can range from ≤10%. For example, the range of w3 can be ≤9%, ≤8%, ≤7%, ≤6%, ≤5%, ≤4%, ≤3%, ≤2%, or ≤1%.

[0135] In some embodiments, the mass percentage w3 of the second additive, based on the total mass of the electrolyte, can be 1%~10%, 1%~8%, 1%~7%, 1%~5%, 1%~4%, 1%~3%, or 1%~2%.

[0136] When the mass percentage of the second additive is within a suitable range, it can further enhance the battery's cycle performance and storage performance.

[0137] In some embodiments, the organic solvent may further include a second organic solvent, which may include one or more of cyclic carbonate compounds and chain carbonate compounds. Optionally, the second organic solvent may include cyclic carbonate compounds, or a combination of cyclic carbonate compounds and chain carbonate compounds.

[0138] This application does not specifically limit the types of chain carbonate compounds or cyclic carbonate compounds, and they can be selected according to actual needs. In some embodiments, the second organic solvent may include one or more of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butenyl carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). When the organic solvent of this application also includes these second organic solvents, the battery can have good fast charging performance.

[0139] In some embodiments, the mass percentage of the second organic solvent may range from 20% to 80% based on the total mass of the organic solvent. Optionally, the mass percentage of the second organic solvent may range from 20% to 75%, 25% to 75%, 30% to 70%, 40% to 70%, 35% to 65%, 40% to 65%, 40% to 60%, or 40% to 50%.

[0140] In some embodiments, the mass percentage of the cyclic carbonate compound is w4 based on the total mass of the organic solvent, and w4 can range from 20% to 80%. For example, w4 can range from 20% to 50%, 25% to 50%, 25% to 45%, 25% to 40%, 25% to 35%, 30% to 50%, 30% to 45%, or 30% to 40%.

[0141] Cyclic carbonate compounds have a high dielectric constant, which is beneficial for the dissociation of lithium salts. When the mass percentage of cyclic carbonate compounds is controlled within a suitable range, batteries containing this electrolyte can exhibit superior fast-charging performance.

[0142] In some embodiments, the mass percentage of the chain carbonate compound may range from 0% to 50%, 0% to 40%, 0% to 30%, 0% to 25%, 0% to 20%, 10% to 50%, 10% to 40%, 10% to 30%, or 10% to 20%, based on the total mass of the organic solvent.

[0143] In some embodiments, the electrolyte further includes a lithium salt. This application does not specifically limit the type of lithium salt, which can be selected according to actual needs. As an example, the lithium salt may include LiN(C) x F 2x+1 SO2)(C y F 2y+1The electrolyte contains one or more of the following lithium salts: SO2, LiPF6, LiBF4, LiBOB, LiDFOB, LiPO2F2, LiDFOP, LiTFOP, LiAsF6, Li(FSO2)2N, LiCF3SO3, and LiClO4, where x and y are positive integers. When the electrolyte includes the above lithium salts, it can help form a uniform, dense, and low-resistance interfacial film on the surface of the negative electrode active material, effectively improving the battery's fast charging performance and cycle performance.

[0144] In some embodiments, the conductivity of the electrolyte may be ≥12 mS / cm. For example, the conductivity of the electrolyte may be ≥12 mS / cm, ≥13 mS / cm, ≥14 mS / cm, ≥15 mS / cm, ≥16 mS / cm, ≥17 mS / cm, ≥18 mS / cm, ≥19 mS / cm, or ≥20 mS / cm.

[0145] When the conductivity of the electrolyte is within a suitable range, the battery can have good fast charging performance, cycle performance, storage performance, and safety performance.

[0146] In some embodiments, the conductivity of the electrolyte may be 12 mS / cm to 24 mS / cm. For example, the conductivity of the electrolyte may be 12 mS / cm to 23 mS / cm, 12 mS / cm to 22 mS / cm, 12 mS / cm to 21 mS / cm, 12 mS / cm to 20 mS / cm, or 13 mS / cm to 20 mS / cm.

[0147] [Negative electrode plate]

[0148] A secondary battery includes a negative electrode sheet, which typically includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and including a negative electrode active material.

[0149] The ratio H / Dv50, which is the thickness H of a single-sided negative electrode film to the volume average particle size Dv50 of the negative electrode active material, can be used to characterize the number of longitudinal particles per unit negative electrode film.

[0150] The inventors discovered that the higher the number of longitudinal particles per unit negative electrode film layer containing negative electrode active material, the higher the diffusion coefficient of active ions, and the better the battery's fast charging performance. However, a higher number of longitudinal particles per unit negative electrode film layer also increases the contact area between the negative electrode film layer and the electrolyte, leading to increased side reactions of the electrolyte on the surface of the negative electrode active material particles, which can negatively impact the battery's cycle performance and storage performance to some extent. Conversely, a lower number of longitudinal particles per unit negative electrode film layer results in poorer fast charging performance, but improved cycle performance and storage performance.

[0151] The inventors conducted extensive research and selected a suitable range for H / Dv50. Specifically, in the negative electrode sheet of the secondary battery of this application, the ratio H / Dv50 of the thickness H of the single-sided negative electrode film layer to the volume average particle size Dv50 of the negative electrode active material satisfies ≥3. For example, H / Dv50 satisfies ≥4, ≥5, ≥6, ≥7, ≥8, or ≥9. A suitable range for H / Dv50 can further improve the fast-charging performance of the secondary battery while ensuring a high volumetric energy density.

[0152] In some embodiments, the ratio H / Dv50 of the thickness H of the single-sided negative electrode film to the volume average particle size Dv50 of the negative electrode active material can satisfy 4 ≤ H / Dv50 ≤ 9. By limiting the ratio H / Dv50 of the thickness H of the single-sided negative electrode film to the volume average particle size Dv50 of the negative electrode active material to a suitable range, and combining it with the electrolyte of this application, a secondary battery with excellent fast charging performance, long service life, and high energy density can be obtained.

[0153] In some embodiments, the thickness H of the single-sided negative electrode film can be ≥60 μm. Optionally, the thickness of the single-sided negative electrode film can be ≥65 μm. More specifically, the thickness H of the single-sided negative electrode film can be ≥70 μm. Controlling the thickness H of the single-sided negative electrode film within a suitable range can further improve the battery energy density.

[0154] In some embodiments, the volume average particle size Dv50 of the negative electrode active material can be ≤18μm. Optionally, the volume average particle size Dv50 of the negative electrode active material can be 14μm≤Dv50≤18μm. With a fixed thickness H of the single-sided negative electrode film, the smaller the volume average particle size Dv50 of the negative electrode active material, the higher the diffusion coefficient of the active ions; however, the volume average particle size Dv50 of the negative electrode active material should not be too small, as this would increase the contact area between the negative electrode film and the electrolyte, thus affecting the battery's cycle performance and storage performance. When the volume average particle size Dv50 of the negative electrode active material is within a suitable range, it can both improve the diffusion coefficient of active ions and reduce the contact area between the negative electrode film and the electrolyte. Therefore, the battery can simultaneously possess good fast-charging performance, cycle performance, and storage performance.

[0155] In some embodiments, the compaction density of the negative electrode film is 1.4 g / cm³. 3 ~1.85g / cm 3 Optionally, the compaction density of the negative electrode film is 1.6 g / cm³. 3 ~1.8g / cm 3By controlling the compaction density of the negative electrode film within a suitable range, the negative electrode active material particles in the film can be brought into close contact, increasing the content of negative electrode active material per unit volume, thereby improving the energy density of the battery.

[0156] In the secondary battery of this application, the type of negative electrode active material is not specifically limited, and any negative electrode active material known in the art for use in secondary batteries may be used. As examples, the negative electrode active material may include one or more of graphite, soft carbon, hard carbon, mesophase carbon microspheres, carbon fibers, carbon nanotubes, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide, and tin alloys. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0157] In the secondary battery of this application, the negative electrode film typically comprises a negative electrode active material, an optional binder, an optional conductive agent, and other optional additives. The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these. The type and content of the conductive agent and binder are not specifically limited and can be selected according to actual needs. As an example, the conductive agent may include one or more of superconducting carbon, carbon black (e.g., acetylene black, Ketjen black, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. As an example, the binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). Other optional additives may include thickeners (e.g., sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0158] In the secondary battery of this application, the negative electrode film layer can be disposed on one side of the negative electrode current collector, or it can be disposed on both sides of the negative electrode current collector. For example, the negative electrode current collector has two opposite sides in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the opposite sides of the negative electrode current collector.

[0159] In the secondary battery of this application, the type of negative electrode current collector is not specifically limited and can be selected according to actual needs.

[0160] In the secondary battery of this application, the negative electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, the negative electrode current collector can be copper foil. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material can be selected from one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer material base layer can be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0161] It should be noted that the parameters of each negative electrode film layer (such as thickness, compaction density, etc.) given in this application refer to the parameters of the negative electrode film layer on one side of the negative electrode current collector. When the negative electrode film layer is disposed on both sides of the negative electrode current collector, if the parameters of the negative electrode film layer on either side meet the requirements of this application, it is considered to fall within the protection scope of this application. Furthermore, the ranges of negative electrode film layer thickness, compaction density, etc., mentioned in this application refer to the parameters of the negative electrode film layer after cold pressing and compaction and used for assembling the battery.

[0162] Furthermore, in the secondary battery of this application, the negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application may also include a conductive undercoat layer (e.g., composed of a conductive agent and a binder) disposed between the negative electrode current collector and the negative electrode film layer. In other embodiments, the negative electrode sheet of this application also includes a protective layer covering the surface of the negative electrode film layer.

[0163] In this application, the volume average particle size Dv50 of the negative electrode active material is the particle size corresponding to the cumulative volume distribution percentage of the negative electrode active material reaching 50%, which can be determined by laser diffraction particle size analysis. For example, it can be determined using a laser particle size analyzer (e.g., Malvern Master Size 3000) in accordance with standard GB / T19077.1-2016.

[0164] In this application, the thickness of the negative electrode film layer has a meaning known in the art and can be tested using methods known in the art, such as using a micrometer (e.g., Mitutoyo 293-100 type, with an accuracy of 0.1 μm).

[0165] In this application, the compaction density of the negative electrode film layer has a meaning known in the art and can be tested using methods known in the art. The compaction density of the negative electrode film layer = the areal density of the negative electrode film layer / the thickness of the negative electrode film layer. The areal density of the negative electrode film layer has a meaning known in the art and can be tested using methods known in the art. For example, take a negative electrode sheet that is coated on one side and cold-pressed (if it is a double-sided coated negative electrode sheet, the negative electrode film layer on one side can be wiped off first), cut it into a small circular piece with an area of ​​S1, weigh it, and record its weight as M1; then wipe off the negative electrode film layer of the weighed negative electrode sheet, weigh the negative current collector, and record it as M0; the areal density of the negative electrode film layer = (weight of the negative electrode sheet M1 - weight of the negative current collector M0) / S1.

[0166] It should be noted that the above-mentioned tests on various parameters of the negative electrode film or negative electrode active material can be conducted by sampling during the battery manufacturing process or by sampling from the prepared secondary battery.

[0167] When the test sample is taken from the prepared secondary battery, as an example, the sampling can be carried out according to the following steps (1) to (3).

[0168] (1) Discharge the secondary battery (for safety reasons, the battery is generally in a fully discharged state); after removing the battery, take out the negative electrode sheet and soak it in dimethyl carbonate (DMC) for a certain period of time (e.g., 2 to 10 hours); then take out the negative electrode sheet and dry it at a certain temperature and time (e.g., 60°C, 4h), and take out the negative electrode sheet after drying. At this time, samples can be taken from the dried negative electrode sheet to test the parameters related to the negative electrode film layer mentioned above in this application. (2) Bake the negative electrode sheet dried in step (1) at a certain temperature and time (e.g., 400°C, 2h), and select a region in the baked negative electrode sheet to sample the negative electrode active material (a blade can be used to scrape the powder for sampling). (3) The negative electrode active material collected in step (2) is sieved (e.g., sieved through a 200-mesh sieve) to finally obtain a sample that can be used to test the parameters of the negative electrode active material mentioned above in this application.

[0169] [Positive electrode plate]

[0170] In the secondary battery of this application, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0171] In some embodiments, the positive electrode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. In the secondary battery of this application, the modified compounds of the above-mentioned positive electrode active materials may be used to modify the positive electrode active material by doping, surface coating, or doping and surface coating.

[0172] As examples, lithium transition metal oxides may include one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. As examples, olivine-structured lithium phosphates may include one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their modified compounds. These positive electrode active materials may be used alone or in combination of two or more.

[0173] In some embodiments, the positive electrode active material may include one or more of olivine-structured lithium phosphates and their modified compounds. In other embodiments, the positive electrode active material may be one or more of olivine-structured lithium phosphates and their modified compounds. Using these positive electrode active materials in the positive electrode film can improve the battery's cycle performance and storage performance, while also enhancing the battery's rate performance. Batteries using these positive electrode active materials have a low operating voltage, typically ≤4.3V. Within this voltage range, the first organic solvent and the first additive work better together, thus further improving the battery's cycle performance and storage performance.

[0174] In the secondary battery of this application, the positive electrode film layer typically comprises a positive electrode active material, an optional binder, and an optional conductive agent. The positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto. The type and content of the conductive agent and binder are not specifically limited and can be selected according to actual needs. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0175] In the secondary battery of this application, the positive electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, the positive electrode current collector can be aluminum foil. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material can be selected from one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer material base layer can be selected from polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.

[0176] [Isolation membrane]

[0177] The secondary battery of this application also includes a separator. The separator is disposed between the positive and negative electrode plates, serving as a separator. The type of separator is not specifically limited; any known porous separator with good chemical and mechanical stability can be selected. In some embodiments, the material of the separator can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, but is not limited to these. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different. In some embodiments, a ceramic coating or a metal oxide coating may also be provided on the separator.

[0178] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0179] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0180] In some implementations, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as one or more of polypropylene, polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0181] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1 This is an example of a square-structured secondary battery 5.

[0182] In some implementations, refer to Figure 2The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. Positive electrode sheets, negative electrode sheets, and a separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0183] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module.

[0184] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0185] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0186] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0187] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0188] Electrical appliances

[0189] A second aspect of this application provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0190] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0191] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0192] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0193] Example

[0194] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0195] In the following examples and comparative examples, the artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) used in the negative electrode sheet are all commercially available. The lithium iron phosphate positive electrode active material, binder polyvinylidene fluoride (PVDF), conductive agent acetylene black, and solvent N-methylpyrrolidone (NMP) used in the positive electrode sheet are all commercially available. The LiPF6, first organic solvent, second organic solvent, first additive, second additive, and vinyl sulfate (DTD) used in the electrolyte are all commercially available. The polypropylene membrane used in the separator is commercially available.

[0196] Example 1

[0197] Preparation of negative electrode sheet

[0198] Artificial graphite (anode active material), acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) (thickener) are dissolved in deionized water at a mass ratio of 95:2:2:1 and thoroughly mixed to prepare a cathode slurry. The cathode slurry is then uniformly coated onto copper foil (anode current collector), and subsequently dried, cold-pressed, and slit to obtain the cathode sheet.

[0199] Preparation of positive electrode sheet

[0200] Lithium iron phosphate, a positive electrode active material, polyvinylidene fluoride (PVDF) binder, and acetylene black, a conductive agent, are dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 97:2:1. The mixture is stirred and mixed thoroughly to prepare a positive electrode slurry. The positive electrode slurry is then uniformly coated onto an aluminum foil current collector, and subsequently dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0201] Preparation of electrolyte

[0202] In an argon-atmospheric glove box (H2O content <0.1ppm, O2 content <0.1ppm), compounds 1-2, ethylene carbonate (EC), and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 30:30:40 to prepare an organic solvent. A certain amount of LiPF6 and a certain amount of compound 2-4 were dissolved in the above organic solvent and stirred uniformly to obtain an electrolyte. The mass percentage of compound 2-4 in the electrolyte was 2%, and the conductivity of the electrolyte was 13.5 mS / cm.

[0203] Separating membrane

[0204] Polypropylene film is used as the separator.

[0205] Preparation of secondary batteries

[0206] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrodes are then wound to form an electrode assembly. This assembly is placed in outer packaging, dried, and then injected with electrolyte. After formation and settling processes, a secondary battery is obtained. The secondary battery has a length of 194 mm, a width of 70 mm, and a height of 112 mm.

[0207] Examples 2-26 and Comparative Examples 1-3

[0208] The preparation methods of Examples 2-26 and Comparative Examples 1-3 are similar to those of Example 1, except that the relevant parameters of the electrolyte were adjusted. Specific electrolyte parameters are detailed in Table 1. In Comparative Example 3, the first additive used in the electrolyte was compound 2-9.

[0209] Compounds 2-9

[0210] Test section

[0211] (1) Battery fast charging performance test

[0212] At 25°C, the batteries of the above embodiments and comparative examples were charged and discharged for the first time at a current of 0.33C (where 1C represents the current value corresponding to the complete discharge of the theoretical capacity of the battery within 1 hour). The specific steps included: charging the battery at a constant current of 0.33C to a voltage of 3.65V, and then charging it at a constant voltage of 3.65V until the current ≤0.05C; letting the battery stand for 5 minutes, and then discharging it at a constant current of 0.33C to a voltage of 2.5V, and recording the actual discharge capacity of the battery as C0.

[0213] The battery was charged sequentially at different charging rates: 0.5C0, 0.8C0, 1.2C0, 1.5C0, 2.0C0, 2.5C0, 3.0C0, 4.0C0, and 5.0C0, using a constant current until the battery charging cutoff voltage of 3.65V or the negative electrode potential dropped to 0V (whichever comes first). After each charging cycle, the battery was discharged at 0.33C0 until the battery discharge cutoff voltage of 2.5V. The negative electrode potential corresponding to charging the battery to 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% SOC (SOC represents the battery's state of charge) at different charging rates was recorded.

[0214] Plot the charge rate-negative electrode potential curves for different states of charge (SOCs). Linearly fit these curves to obtain the charge rate corresponding to a negative electrode potential of 0V under different SOCs. This charge rate is the charging window for that SOC. The charging windows for different SOCs are denoted as C. 10%SOC C 20%SOC C 30%SOC C 40%SOC C 50%SOC C 60%SOC C 70%SOC C 80%SOC According to the formula (60 / C) 20%SOC + 60 / C 30%SOC + 60 / C 40%SOC + 60 / C 50%SOC + 60 / C 60%SOC+ 60 / C 70%SOC +60 / C 80%SOC The charging time T is calculated by multiplying the current state of charge (SOC) by 10% to obtain the charging time T from 10% SOC to 80% SOC. The shorter the charging time T, the better the battery's fast charging performance.

[0215] (2) Battery 60℃ Cyclic Performance Test

[0216] At 60°C, the batteries of the above embodiments and comparative examples were charged at a constant current of 1C to a voltage of 3.65V, then charged at a constant voltage of 3.65V until the current ≤0.05C, and then discharged at a constant current of 1C to a voltage of 2.5V. This constitutes one charge-discharge cycle, and the discharge capacity at this point is recorded as the discharge capacity of the battery in its first cycle. This charge-discharge cycle was repeated, and the capacity retention rate of the battery after 500 cycles was calculated.

[0217] The capacity retention rate (%) of the battery after 500 cycles at 60℃ = (discharge capacity of the battery in the 500th cycle / discharge capacity of the battery in the first cycle) × 100%.

[0218] (3) Gas production test of battery at 60℃

[0219] At 25°C, the batteries of the above embodiments and comparative examples were charged at a constant current of 0.33C to a voltage of 3.65V, then charged at a constant voltage of 3.65V until the current ≤0.05C. The batteries were then discharged at a constant current of 0.33C to a voltage of 2.5V, and the actual discharge capacity of the battery was recorded as C0. At 25°C, the batteries were continued to be charged at a constant current of 0.33C0 to a voltage of 3.65V, then charged at a constant voltage of 3.65V until the current ≤0.05C0. At this point, the battery was fully charged, and the volume of the battery was measured and recorded as the volume before storage. The fully charged batteries were stored in a constant temperature chamber at 60°C for 30 days. After storage, the batteries were removed from the constant temperature chamber and their volume was measured.

[0220] Gas production (ml / Ah) of a battery stored at 60℃ for 30 days = (Volume of battery after 30 days of storage - Volume of battery before storage) / Rated capacity of battery.

[0221] (4) Battery storage capacity retention test at 60°C

[0222] At 25°C, the batteries of the above embodiments and comparative examples were charged at a constant current of 0.33C to a voltage of 3.65V, and then charged at a constant voltage of 3.65V until the current ≤0.05C. The batteries were then discharged at a constant current of 0.33C to a voltage of 2.5V, and the actual discharge capacity of the battery was recorded as C0. At 25°C, the batteries were continued to be charged at a constant current of 0.33C0 to a voltage of 3.65V, and then charged at a constant voltage of 3.65V until the current ≤0.05C0. At this point, the batteries were in a fully charged state. The fully charged batteries were stored in a constant temperature chamber at 60°C for 60 days, and then the batteries were taken out for capacity testing.

[0223] The capacity retention rate of a battery after 60 days of storage at 60°C is calculated as follows: (Discharge capacity of the battery after 60 days of storage / Actual discharge capacity of the battery C0) × 100%.

[0224] The electrolyte parameters for Examples 1-26 and Comparative Examples 1-3 are detailed in Table 1, and the test results are detailed in Table 2.

[0225]

[0226] Table 2

[0227]

[0228] The test results in Table 2 show that using the first organic solvent in the electrolyte can improve the battery's fast-charging performance. However, due to the poor compatibility between the first organic solvent and the negative electrode, it deteriorates the battery's cycle performance and storage performance, especially under high-temperature conditions. The test results from Comparative Example 2 and Comparative Example 1 show that adding an appropriate amount of DTD to the electrolyte does not significantly improve the battery's cycle performance and storage performance. This is mainly because DTD forms a stable interfacial film on both the positive and negative electrode active materials, inhibiting the continuous reaction between the negative electrode and the first organic solvent. However, DTD also generates gas during the formation of the interfacial film. This continuously generated gas accumulates at the interfaces of the positive electrode, negative electrode, and separator, forming macroscopic bubbles that block lithium-ion transport.

[0229] As can be seen from the test results in Table 2, the batteries of Examples 1 to 26 can significantly improve the cycle performance and storage performance of the batteries by using the first additive instead of DTD, especially the high-temperature cycle performance and high-temperature storage performance of the batteries; at the same time, the batteries of Examples 1 to 26 still maintain good fast charging performance.

[0230] The comparison of the test results of Comparative Example 3 with those of Examples 1-26 shows that the batteries of Examples 1-26 have better cycle performance and storage performance.

[0231] The comparison of the test results in Examples 1 and 2 shows that changing the type of the second organic solvent will affect the battery's fast charging performance, cycle performance, and storage performance, but these changes are all within a reasonable range and will not produce excessively large variations. Therefore, this application does not impose any particular restrictions on the type of the second organic solvent.

[0232] The comparison of test results from Examples 1 and 3-8 shows that increasing the content of the first organic solvent decreases the battery charging time T, increases the gas production during high-temperature storage, and reduces both the high-temperature storage capacity retention rate and the high-temperature cycle capacity retention rate. This is mainly because increasing the content of the first organic solvent increases the number of α-H atoms, leading to increased loss of active lithium within the battery, thus reducing the capacity retention rate after high-temperature storage. Furthermore, the first organic solvent has poor oxidation resistance and is prone to oxidative decomposition during storage under high charge conditions, which also increases the gas production during high-temperature storage.

[0233] The comparison of the test results of Examples 1 and 9-15 shows that the change in the type of the first additive will also change the fast charging performance, cycle performance and storage performance of the battery, but all within a reasonable range and will not produce excessive changes.

[0234] The comparison of the test results of Examples 1 and 16-18 shows that the change in the type of the first organic solvent will also change the fast charging performance, cycle performance and storage performance of the battery, but all within a reasonable range and will not produce excessive changes.

[0235] The comparison of test results from Examples 19-26 shows that as the content of the first additive increases, the amount of gas generated during high-temperature storage decreases, the battery charging time initially decreases and then increases, and the battery high-temperature storage capacity retention rate and high-temperature cycle capacity retention rate initially increase and then decrease. This may be because the first additive has a higher reduction potential, allowing it to preferentially form a dense and stable sulfur-containing organic interface film on the surface of the negative electrode active material before the first organic solvent, thus inhibiting the continuous reaction between the first organic solvent and the negative electrode, thereby reducing the amount of gas generated during high-temperature storage. However, the first additive has a cyclic structure; as its content increases, the film thickness on the surface of the negative electrode active material increases, and the film resistance slightly increases, affecting the lithium-ion transport speed at the negative electrode interface. Therefore, the battery charging time will increase to some extent, and the battery high-temperature storage capacity retention rate and high-temperature cycle capacity retention rate will decrease to some extent.

[0236] Example 27

[0237] Preparation of negative electrode sheet

[0238] Artificial graphite (volume average particle size Dv50 of 17 μm), acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) (thickener) were dissolved in deionized water at a mass ratio of 95:2:2:1 and thoroughly mixed to prepare a negative electrode slurry. The negative electrode slurry was then uniformly coated onto both surfaces of a copper foil current collector. After drying, cold pressing, and slitting, the negative electrode sheet was obtained. The dried negative electrode slurry formed a negative electrode film with a single-sided thickness of 60 μm and a compaction density of 1.65 g / cm³. 3 .

[0239] Preparation of positive electrode sheet

[0240] Lithium iron phosphate, a positive electrode active material, polyvinylidene fluoride (PVDF) binder, and acetylene black, a conductive agent, are dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 97:2:1. The mixture is stirred and mixed thoroughly to prepare a positive electrode slurry. The positive electrode slurry is then uniformly coated onto an aluminum foil current collector, and subsequently dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0241] Preparation of electrolyte

[0242] In an argon-atmospheric glove box (H2O content <0.1ppm, O2 content <0.1ppm), compounds 1-2, ethylene carbonate (EC), and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 30:30:40 to prepare an organic solvent. A certain amount of LiPF6 and a certain amount of the first additive compound 2-4 were dissolved in the above organic solvent and stirred evenly to obtain an electrolyte. The mass percentage of compound 2-4 in the electrolyte was 2%, and the conductivity of the electrolyte was 13.5 mS / cm.

[0243] Separating membrane

[0244] Polypropylene film is used as the separator.

[0245] Preparation of secondary batteries

[0246] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrodes are then wound to form an electrode assembly. This assembly is placed in outer packaging, dried, and then injected with electrolyte. After formation and settling processes, a secondary battery is obtained. The secondary battery has a length of 194 mm, a width of 70 mm, and a height of 112 mm.

[0247] Examples 28-37

[0248] The preparation methods of Examples 28-37 are similar to those of Example 27, except that the relevant parameters of the negative electrode sheet are adjusted. For details of the parameters, please refer to Table 3.

[0249] Test section

[0250] (1) Battery volumetric energy density test

[0251] At 25°C, the batteries of the above embodiments and comparative examples were charged at a constant current of 0.33C to a voltage of 3.65V, and then charged at a constant voltage of 3.65V until the current ≤0.05C. The batteries were then discharged at a constant current of 0.33C to a voltage of 2.5V, and the discharge energy Q was obtained. The length, width, and height of the battery casing were measured using vernier calipers, and the volume V of the battery was calculated.

[0252] The volumetric energy density of a battery = discharge energy Q / battery volume V. The unit of volumetric energy density is Wh / L.

[0253] The negative electrode parameters and battery performance test results of Examples 27-37 are detailed in Table 3.

[0254] Table 3

[0255]

[0256] As shown in Table 3, the test results indicate that as the thickness H of the single-sided negative electrode film increases, the volumetric energy density of the battery increases, but the charging time T increases. With a fixed thickness H, as the volume average particle size Dv50 of the negative electrode active material decreases, the diffusion path of active ions shortens, and the charging time T decreases. However, the volume average particle size Dv50 of the negative electrode active material should not be too small, as this increases the contact area between the negative electrode film and the electrolyte, increasing side reactions of the electrolyte on the surface of the negative electrode active material particles, thus affecting the battery's cycle performance and storage performance. Therefore, limiting the ratio H / Dv50 of the single-sided negative electrode film thickness to the volume average particle size Dv50 of the negative electrode active material to a suitable range, combined with the electrolyte of this application, enables the battery to possess good fast-charging performance, long service life, and high energy density.

[0257] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An electrolyte comprising an organic solvent and additives, in, The organic solvent includes the first organic solvent shown in Formula 1. Formula 1, In Formula 1, R1 and R2 are each independently selected from C1 to C3 alkyl groups; The additive includes a first additive selected from compounds of formula 2B. Equation 2B In equation 2B, R 31 R 32 One is a methylene group, and the other is a single bond; R 33 R 34 One of them is a methylene group, and the other is a single bond; R4 is a single bond, one of the C1-C3 alkylene groups; Based on the total mass of the organic solvent, the mass percentage of the first organic solvent is w1, and w1 ranges from 30% to 70%; based on the total mass of the electrolyte, the mass percentage of the first additive is w2, and w2 ranges from 1% to 5%.

2. The electrolyte according to claim 1, wherein, R 31 R 32 R 33 R 34 R4 also satisfies: R4 is a single bond, R 31 R 32 One of them is methylene, R 33 R 34 One of them is a methylene group, and the rest are single bonds.

3. The electrolyte according to claim 1, wherein, The first organic solvent is selected from one or more of the following compounds: Compound 1-1, Compounds 1-2, Compounds 1-3.

4. The electrolyte according to claim 3, wherein, The first organic solvent is selected from one or two of the following compounds: Compound 1-1, Compounds 1-2.

5. The electrolyte according to claim 1, wherein, The first additive is selected from one or more of the following compounds: Compounds 2-4, Compounds 2-5, Compounds 2-8.

6. The electrolyte according to claim 5, wherein, The first additive is selected from one or more of the following compounds: Compounds 2-4, Compounds 2-5.

7. The electrolyte according to claim 1, wherein, The additive further includes a second additive, which comprises one or more of the following: cyclic carbonate compounds containing unsaturated bonds, halogen-substituted cyclic carbonate compounds, sulfate compounds, sulfite compounds, sulfonyl lactone compounds, disulfonic acid compounds, nitrile compounds, aromatic compounds, isocyanate compounds, phosphonitrile compounds, cyclic anhydride compounds, phosphite compounds, phosphate compounds, borate ester compounds, and carboxylic acid ester compounds.

8. The electrolyte according to claim 7, wherein, The second additive includes one or two of the following compounds: Compound 3-1, Compound 3-2.

9. The electrolyte according to claim 7 or 8, wherein, Based on the total mass of the electrolyte, the mass percentage of the second additive is w3, and the range of w3 is ≤10%.

10. The electrolyte according to claim 9, wherein, The range of w3 is ≤5%.

11. The electrolyte according to claim 1, wherein, The organic solvent also includes a second organic solvent, which includes one or more of cyclic carbonate compounds and chain carbonate compounds.

12. The electrolyte according to claim 11, wherein, The second organic solvent includes cyclic carbonate compounds or a combination of cyclic carbonate compounds and chain carbonate compounds.

13. The electrolyte according to claim 1, wherein, The organic solvent further includes a second organic solvent, which includes one or more of ethylene carbonate, propylene carbonate, 1,2-butenyl carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

14. The electrolyte according to claim 11 or 12, wherein, Based on the total mass of the organic solvent, the mass percentage of the cyclic carbonate compound is w4, and w4 ranges from 20% to 80%.

15. The electrolyte according to claim 14, wherein, The range of w4 is 20% to 50%.

16. The electrolyte according to claim 1, wherein, The electrolyte also includes a lithium salt, which includes LiN(C) x F 2x+1 SO2)(C y F 2y+1 One or more of the following: SO2), LiPF6, LiBF4, LiBOB, LiDFOB, LiPO2F2, LiDFOP, LiTFOP, LiAsF6, Li(FSO2)2N, LiCF3SO3, and LiClO4, where x and y are positive integers.

17. The electrolyte according to claim 1, wherein, The conductivity of the electrolyte is ≥12 mS / cm.

18. The electrolyte according to claim 17, wherein, The conductivity of the electrolyte is ≥13 mS / cm.

19. The electrolyte according to claim 17, wherein, The conductivity of the electrolyte is 12 mS / cm ~ 24 mS / cm.

20. The electrolyte according to claim 18, wherein, The conductivity of the electrolyte is 13 mS / cm ~ 20 mS / cm.

21. A secondary battery comprising the electrolyte according to any one of claims 1 to 20.

22. The secondary battery according to claim 21, wherein, The secondary battery includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and including a negative electrode active material. The ratio H / Dv50 of the thickness H of the single-sided negative electrode film layer to the volume average particle size Dv50 of the negative electrode active material satisfies ≥3.

23. The secondary battery according to claim 22, wherein, The ratio of the thickness H of the single-sided negative electrode film to the volume average particle size Dv50 of the negative electrode active material satisfies: 4≤H / Dv50≤9.

24. The secondary battery according to claim 21, wherein, The thickness H of the single-sided negative electrode film layer satisfies ≥60μm; and / or The volume average particle size Dv50 of the negative electrode active material is ≤18μm.

25. The secondary battery according to claim 24, wherein, The thickness H of the single-sided negative electrode film layer satisfies ≥65μm; and / or The volume average particle size Dv50 of the negative electrode active material satisfies 14μm≤Dv50≤18μm.

26. The secondary battery according to claim 21, wherein, The compaction density of the negative electrode film is 1.4 g / cm³. 3 ~1.85g / cm 3 .

27. The secondary battery according to claim 26, wherein, The compaction density of the negative electrode film is 1.6 g / cm³. 3 ~1.8g / cm 3 .

28. The secondary battery according to claim 21, wherein, The secondary battery includes a positive electrode sheet, which includes a positive electrode active material, which includes one or more of lithium transition metal oxides, lithium phosphates with olivine structures, and their respective modified compounds.

29. The secondary battery according to claim 28, wherein, The lithium phosphates with the olivine structure include one or more of lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate.

30. The secondary battery according to claim 28, wherein, The modified compounds containing lithium phosphates with olivine structures include one or more of the following: lithium iron phosphate and carbon composites, lithium manganese phosphate and carbon composites, and lithium manganese iron phosphate and carbon composites.

31. A battery module comprising a secondary battery according to any one of claims 21 to 30.

32. A battery pack comprising a secondary battery according to any one of claims 21 to 30 and a battery module according to claim 31.

33. An electrical device comprising at least one of the following: a secondary battery according to any one of claims 21 to 30, a battery module according to claim 31, and a battery pack according to claim 32.

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