Prismatic lithium-ion battery

Abstract

A prismatic lithium-ion battery. The prismatic lithium-ion battery comprises a battery housing, and a battery cell assembly and a non-aqueous electrolyte which are accommodated in the battery housing. The battery cell assembly comprises a positive electrode sheet, a negative electrode sheet, and a separator. The non-aqueous electrolyte comprises a first additive, a lithium salt, and a non-aqueous organic solvent. The first additive comprises at least one of compound 1 to compound 5. The non-aqueous organic solvent comprises a short-chain carboxylate having 2 to 5 carbon atoms. The prismatic lithium-ion battery satisfies the following conditions: 0.16≤σ≤1.35, 0.01≤a≤2, 24≤b≤56, 10≤c≤40, and 85≤d≤93.

Description

A square lithium-ion battery

[0001] This application claims priority to Chinese Patent Application No. 202510323281.2, filed on March 19, 2025, entitled "A Square Lithium-ion Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application belongs to the field of secondary lithium-ion batteries, and particularly relates to a square lithium-ion battery. Background Technology

[0003] Lithium-ion batteries boast significant advantages such as high energy density, long cycle life, and no memory effect. The increasing demands for driving range and fast charging in new energy vehicles are driving cell manufacturers to develop lithium-ion power batteries that balance energy density and fast charging performance. Phosphate batteries, due to their relatively good safety performance, long cycle life, and low cost, have seen a continuous increase in market share in the new energy vehicle sector. However, phosphate materials themselves have poor kinetic properties, resulting in relatively poor fast-charging capabilities. To improve the fast-charging performance of phosphate batteries, low-resistance additives can be added to the electrolyte to reduce the interfacial impedance of the electrodes; low-viscosity solvents can be used to improve the mass transfer capacity of the electrolyte. However, these strategies sacrifice the battery's high-temperature performance, potentially leading to thermal runaway. Summary of the Invention

[0004] Based on this, the purpose of this application is to provide a square lithium-ion battery to solve the problem that square batteries are prone to overheating and runaway.

[0005] To achieve the above objectives, this application adopts the following technical solution.

[0006] This application provides a square lithium-ion battery, including a battery casing and a cell assembly and a non-aqueous electrolyte contained within the battery casing. The cell assembly includes a positive electrode, a negative electrode, and a separator.

[0007] The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector;

[0008] The non-aqueous electrolyte comprises a first additive, a lithium salt, and a non-aqueous organic solvent, wherein the first additive comprises at least one of the following compounds:

[0009] The non-aqueous organic solvent includes short-chain carboxylic acid esters with 2 to 5 carbon atoms, and the short-chain carboxylic acid esters include at least one of ethyl acetate, ethyl propionate, or methyl acetate.

[0010] The square lithium-ion battery meets the following conditions:

[0011] Safety factor It satisfies 0.16≤σ≤1.35, 0.01≤a≤2, 24≤b≤56, 10≤c≤40, 85≤d≤93;

[0012] Where a is the mass percentage of the first additive in the non-aqueous electrolyte, in %;

[0013] b represents the mass percentage of short-chain carboxylic acid esters in the non-aqueous electrolyte, in %;

[0014] c represents the porosity of the negative electrode material layer, in percentage (%).

[0015] d represents the group margin of a square lithium-ion battery cell, expressed as a percentage.

[0016] The risk of thermal runaway in lithium-ion batteries stems from exothermic reactions within the battery. Even during normal charging and discharging, lithium-ion batteries generate Joule heat. As the internal temperature gradually increases, the chemical properties of the battery materials become more reactive. The development of thermal runaway mainly involves steps such as the decomposition of the interfacial film, separator collapse, large-scale internal short circuits, reactions between the electrodes and the electrolyte, and electrolyte combustion. When the decomposition of the interfacial film reaches a certain level, the positive and negative electrodes come into direct contact with the electrolyte and react, continuously increasing exothermic reactions. Lithium salts (such as LiPF6) are also more prone to decomposition under high temperature and high voltage conditions, further promoting heat generation. All these reactions increase the internal pressure and temperature of the battery, leading to a serious risk of thermal runaway. Considering the initial stage of thermal runaway, constructing a thermally stable SEI (Sediment Injection Interchange) is an effective means to reduce the risk of battery thermal runaway.

[0017] The square lithium-ion battery provided in this application uses at least one of compounds 1 to 5 as a first additive and a short-chain carboxylic acid ester as a non-aqueous organic solvent. Through extensive research, the inventors discovered that the safety factor of a square lithium-ion battery can be defined by the mass percentage (a) of the first additive in the non-aqueous electrolyte, the mass percentage (b) of the non-aqueous organic solvent, the porosity (c) of the negative electrode material layer in the square lithium-ion battery, and the group margin (d) of the cell in the square lithium-ion battery. When the following conditions are met: 0.16≤σ≤1.35, 0.01≤a≤2, 24≤b≤56, 10≤c≤40, and 85≤d≤93, square batteries can achieve both high energy density and high safety performance. Short-chain carboxylic esters, as non-aqueous organic solvents, are highly polar and can provide higher conductivity, while having lower viscosity and freezing point, significantly improving the battery's fast-charging capability. However, this also degrades high-temperature performance, further leading to thermal runaway. To address this issue, on the one hand, introducing excellent positive and negative electrode film-forming additives into the electrolyte can form a protective film with excellent thermal stability on the positive and negative electrode surfaces, preventing corrosion and oxidation of the electrode materials at high temperatures and reducing the continuous temperature rise during charging and discharging, thereby reducing the risk of thermal runaway. On the other hand, by controlling the battery's group margin and the porosity of the negative electrode material layer, sufficient space is provided for the heat generated during charging and discharging to dissipate and conduct in a timely manner.

[0018] In summary, electrolyte additives, solvents, and various battery design parameters collectively influence the overall performance of a battery. The primary additive provides an interfacial film with excellent thermal stability, and the higher its content, the higher the safety performance of the resulting interfacial film; that is, there is a positive correlation between battery safety performance and the content of the primary additive. However, excessively high levels of the primary additive increase the battery's interfacial impedance, which is detrimental to fast-charging performance. Appropriate amounts of short-chain carboxylic esters can circumvent the negative effects of increased impedance from the primary additive. By introducing short-chain carboxylic esters into the electrolyte, the electrolyte's conductivity is improved, further enhancing the battery's fast-charging performance while maintaining a high cell margin. However, short-chain carboxylic esters themselves have low flash points and low chemical stability, making them prone to decomposition at high temperatures, increasing the risk of thermal runaway. From the perspective of compatibility between the electrolyte and the positive and negative electrode materials, stronger protective effects are needed to prevent the short-chain carboxylic ester solvent from degrading battery safety performance. Furthermore, a suitable negative electrode porosity ensures good electrolyte wettability, which helps the additive form a uniform interfacial film at the negative electrode interface. It also addresses the issue of electrolyte difficulty in wetting the battery cell after increasing the cell's group margin. Higher porosity also facilitates heat dissipation and consumes more of the primary additive in the negative electrode film formation. Considering the combined effects of increasing the primary additive content and negative electrode porosity on battery performance, as well as the interaction between increasing the short-chain carboxylic acid ester content in the electrolyte and the cell group margin, defining the battery safety factor σ between 0.16 and 1.35 allows for the full utilization of the synergistic effect between the primary additive, short-chain carboxylic acid ester solvent, negative electrode porosity, and the cell group margin design. This enables square batteries to possess high energy density, fast charging capability, and high safety performance. Specifically, the safety factor σ is selected from 0.16, 0.17, 0.18, 0.19, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.15, 1.2, 1.25, 1.31, 1.35, or any combination of these values. Preferably, the safety factor σ is selected from 0.2 to 1.0.

[0019] The first additive is a high-performance film-forming additive for both positive and negative electrodes. During the first charge and discharge of the battery, it can form a uniform, moderately thick, and thermally stable interfacial film on the surfaces of the positive and negative electrodes, thereby suppressing the temperature rise of the battery during charge and discharge. When the mass percentage a% of the first additive in the non-aqueous electrolyte is too low, a dense interfacial film that completely covers the surface of the negative electrode cannot be formed, and the positive and negative electrode interfaces cannot be effectively protected. When the mass percentage a% of the first additive is too high, the resulting interfacial film is thicker, and the cell interface impedance increases simultaneously, which is not only detrimental to the rate performance of the battery but also generates more Joule heat. Specifically, the mass percentage a% of the first additive in the non-aqueous electrolyte is 0.01%, 0.03%, 0.05%, 0.07%, 0.09%, 0.1%, 0.3%, 0.3%, 0.5%, 0.7%, 0.9%, 1%, 1.3%, 1.5%, 1.7%, 1.9%, 2%, or any combination of these values. Preferably, the mass percentage (a%) of the first additive in the non-aqueous electrolyte is 0.1% to 1%.

[0020] In non-aqueous electrolytes, short-chain carboxylic esters, as non-aqueous organic solvents, can avoid the negative effect of increased impedance caused by the first additive. Short-chain carboxylic esters are highly polar, providing higher conductivity, while having lower viscosity and freezing point, significantly improving the battery's fast-charging capability. If the mass percentage b% of short-chain carboxylic esters is too low, the electrolyte will have difficulty wetting the battery cell; if the mass percentage b% is too high, although the electrolyte can easily wet the battery cell, it reduces the cell's energy density, increasing the risk of thermal runaway. Specifically, the mass percentage b% of short-chain carboxylic esters in the non-aqueous electrolyte is 24%, 26%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 54%, 55%, 56%, or any combination of these values; preferably, the mass percentage b% of short-chain carboxylic esters in the non-aqueous electrolyte is 30% to 50%.

[0021] Specifically, in some embodiments of this application, the porosity (c%) of the negative electrode material layer of the square lithium-ion battery is 10% to 40%. If the negative electrode porosity is too low, the heat generated during battery charging and discharging is difficult to dissipate and conduct; conversely, if the negative electrode porosity is too high, the contact between the negative electrode active material particles decreases, the battery energy density decreases, and the wettability of the electrolyte also decreases. By controlling the negative electrode porosity between 10 ≤ c ≤ 40, good safety performance and high energy density can be balanced. Specifically, the porosity (c%) of the negative electrode material layer of the square lithium-ion battery is 10%, 12%, 15%, 18%, 20%, 21%, 23%, 25%, 27%, 29%, 30%, 31%, 33%, 35%, 38%, 40%, or any combination of these values; preferably, the porosity (c%) of the negative electrode material layer of the square lithium-ion battery is 15% to 30%.

[0022] For prismatic batteries, a higher cell margin increases the risk of thermal runaway. Conversely, a low cell margin makes it difficult to meet the requirements for high energy density. Cell margin refers to the ratio of the cell assembly size to the internal space size of the battery casing, also known as "fill rate." In some embodiments of this application, the cell margin (d%) of the prismatic lithium-ion battery is 85%–93%, which can balance battery energy density and safety performance to a certain extent. A higher cell margin makes it more difficult for the electrolyte to wet the entire cell during electrolyte injection, leading to difficulties in electrolyte filling and potentially increasing energy density. However, it also makes it difficult to conduct heat generated during charging and discharging, increasing the risk of thermal runaway. Conversely, a low cell margin makes it difficult to meet the requirements for high energy density. Specifically, the group margin d% of the square lithium-ion battery is 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, or any combination of these values; preferably, the group margin d% of the square lithium-ion battery is 88% to 92%.

[0023] Specifically, in some embodiments of this application, the battery can be tested by measuring the thickness d1 of the cell and the thickness d2 of the internal space of the battery casing, and the battery's group margin d% = d1 / d2 × 100%.

[0024] Specifically, in some embodiments of this application, the selected carboxylic esters contain only a main chain, and the number of carbon atoms in the main chain is ≤5. The shorter the main chain of the carboxylic ester, the higher the conductivity and the lower the viscosity, which is more beneficial for improving the conductivity and wettability of the electrolyte. When the number of carbon atoms in the main chain exceeds 5, its viscosity and conductivity no longer have a significant advantage compared to chain carbonates, making it difficult to meet the requirements of high conductivity and low viscosity. Applying it to battery systems can significantly improve the battery's fast charging capability, but it also degrades high-temperature performance, further leading to thermal runaway.

[0025] In some preferred embodiments of this application, the short-chain carboxylic acid ester includes at least ethyl acetate. Compared to other carboxylic acid ester compounds, ethyl acetate not only has a lower viscosity, which reduces the resistance to lithium-ion movement and helps improve the ionic conductivity of the electrolyte, but also helps stabilize the cathode structure. Therefore, while improving the fast-charging performance of lithium-ion batteries, it can also improve their high-temperature performance, thereby improving the overall performance of the electrochemical device.

[0026] Specifically, in some embodiments of this application, the non-aqueous electrolyte further includes auxiliary additives, which include at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and nitrile compounds.

[0027] In some preferred embodiments, the cyclic sulfate compound includes at least one of 4-methyl vinyl sulfate, vinyl sulfate, and propylene sulfate.

[0028] In some preferred embodiments, the sulfonyl lactone compound includes at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone.

[0029] In some preferred embodiments, the cyclic carbonate compound includes at least one of vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and a compound represented by structural formula 1 below:

[0030] In the structural formula 1 shown, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group.

[0031] In some preferred embodiments, the compound of structural formula 1 includes at least one of the compounds shown in compounds 1-1 to 1-6 below:

[0032] In some preferred embodiments, the phosphate ester compound includes at least one of the compounds represented by structural formula 2:

[0033] In structural formula 2, R 31 R 32 R 33Each is independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, where m is a natural number from 1 to 3; more preferably, the compound represented by structural formula 2 includes at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, triargylpropyl phosphate, diargylpropylmethyl phosphate, diargylpropylethyl phosphate, diargylpropylpropyl phosphate, diargylpropyltrifluoromethyl phosphate, diargylpropyl-2,2,2-trifluoroethyl phosphate, diargylpropyl-3,3,3-trifluoropropyl phosphate, diargylpropylhexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

[0034] In some preferred embodiments, the borate ester compound includes at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate.

[0035] In some preferred embodiments, the nitrile compound includes at least one selected from succinic anhydride, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octanilide, nonadionitrile, and sebacate.

[0036] Specifically, in some embodiments of this application, the content of the auxiliary additive is 0.01% to 10% based on the total mass of the non-aqueous electrolyte as 100%. Preferably, the content is 0.1% to 5%. More preferably, the content is 0.1% to 2%. Specifically, the content of any optional substance in the auxiliary additive can be 0.01%, 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, or any combination of these values.

[0037] Specifically, in some embodiments of this application, the lithium salt includes LiPF6, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, LiPO2F2, LiBF4, LiBOB, LiSbF6, LiAsF6, LiCF3SO3, LiDFOB, LiDFOP, LiN(SO2CF3)2, LiC(SO2CF3)3, LiN(SO2C2F5)2, LiCl, LiBr, LiI, LiClO4, and LiB 10 Cl 10 At least one of LiAlCl4, lithium chloroborane, and lithium tetraphenylborate.

[0038] Specifically, in some embodiments of this application, the positive electrode sheet includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material includes a phosphate material; the phosphate material includes lithium iron phosphate and lithium manganese iron phosphate. More specifically, the phosphate material includes LiFePO4 and LiFe 0.4 Mn 0.6 PO4, LiFe 0.3 Mn 0.7 PO4, LiFe 0.2 Mn 0.8 PO4, LiFe 0.6 Mn 0.4 PO4, LiFe 0.8 Mn 0.2 PO4, LiFe 0.1 Mn 0.9 One or more of PO4.

[0039] Specifically, in some embodiments of this application, the positive electrode sheet further includes a positive current collector, and the positive electrode material layer is disposed on the surface of the positive current collector. The positive current collector includes a metallic material capable of conducting electrons. Preferably, the positive current collector includes one or more of aluminum, nickel, tin, copper, and stainless steel.

[0040] Specifically, in some embodiments of this application, the positive electrode sheet further includes a positive electrode binder and a positive electrode conductive agent. The positive electrode binder includes one or more of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber. The positive electrode conductive agent includes one or more of the following: conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0041] Specifically, in some embodiments of this application, the negative electrode sheet includes a negative electrode material layer; the negative electrode material layer includes a negative electrode active material; the negative electrode active material includes at least one of a silicon-based negative electrode and a carbon-based negative electrode; the silicon-based negative electrode includes at least one of a silicon material, a silicon oxide, a silicon-carbon composite material, and a silicon alloy material. Preferably, the silicon material is a nano-silicon material. Preferably, the silicon oxide material is SiO₂. xThe material, wherein 0 ≤ x < 2. Preferably, the silicon-carbon material is: a silicon-based material containing silicon and carbon materials, and / or containing SiO2. y The silicon-based material is a carbon material, wherein 0 ≤ y < 2. Preferably, the silicon alloy material is a Mg2Si alloy material and / or an Fe2Si alloy material. The carbon material is selected from one or more of artificial graphite, natural graphite, composite graphite, graphene, hard carbon, soft carbon, and mesophase carbon microspheres; preferably, the carbon material is an artificial graphite material.

[0042] Specifically, in some embodiments of this application, the carbon-based negative electrode includes at least one of graphite, hard carbon, soft carbon, graphene, and mesophase carbon microspheres.

[0043] The silicon-based material is selected from one or more of silicon materials, silicon oxide materials, silicon carbon materials, and silicon alloy materials. Specifically, in some embodiments of this application, the negative electrode material layer further includes a negative electrode binder, a negative electrode conductive agent, and a negative electrode current collector. The material of the negative electrode current collector can be the same as that of the positive electrode current collector, and will not be described again here. The negative electrode binder and the negative electrode conductive agent can be the same as those of the positive electrode binder and the positive electrode conductive agent, respectively, and will not be described again here.

[0044] Specifically, in some embodiments of this application, the square lithium-ion battery further includes a separator located between the positive electrode and the negative electrode.

[0045] The diaphragm is a conventional diaphragm, selected from one or more of ceramic diaphragms, polymer diaphragms, non-woven fabrics, and inorganic-organic composite diaphragms. For example, a single-layer polypropylene (PP) diaphragm, a single-layer polyethylene (PE) diaphragm, a double-layer PP / PE diaphragm, a double-layer PP / PP diaphragm, or a triple-layer PP / PE / PP diaphragm.

[0046] Specifically, in some embodiments of this application, the battery casing includes one selected from steel casing, aluminum casing, polypropylene (PP) plastic casing, polycarbonate (PC) plastic casing, or carbon fiber composite casing.

[0047] The prismatic lithium-ion battery provided in this application comprehensively considers electrolyte additives, solvents, and battery design. It incorporates a first additive and a short-chain carboxylic acid ester into the non-aqueous electrolyte. By adjusting the relationship between the mass percentage of the first additive (a), the mass percentage of the short-chain carboxylic acid ester (b), the porosity of the negative electrode material layer (c), and the group margin (d) of the prismatic lithium-ion battery cell, the safety factor σ can be controlled. This fully leverages the synergistic effect between the first additive, the short-chain carboxylic acid ester solvent, the negative electrode porosity, and the battery's group margin design, enabling the prismatic battery to possess high energy density, high fast-charging capability, and high safety performance. The presumed reason is that using a short-chain carboxylic acid ester as a non-aqueous organic solvent provides higher conductivity due to its strong polarity, while also offering lower viscosity and freezing point, significantly improving the battery's fast-charging capability. However, this also degrades high-temperature performance, potentially leading to thermal runaway. To address this issue, on the one hand, introducing superior positive and negative electrode film-forming additives into the electrolyte can form a protective film with excellent thermal stability on the surface of the positive and negative electrodes, preventing corrosion and oxidation of the electrode materials at high temperatures and reducing the continuous rise in temperature during charging and discharging, thereby reducing the risk of thermal runaway. On the other hand, by controlling the battery's mass margin and the porosity of the negative electrode material layer, sufficient space is provided for the heat generated by the battery during charging and discharging to dissipate and be conducted in a timely manner. Detailed Implementation

[0048] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments in this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of this application.

[0049] Example 1

[0050] The method for preparing a square lithium-ion battery in this embodiment includes the following steps:

[0051] (1) Positive electrode preparation: Lithium iron phosphate, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96:2:2, and then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on both sides of an aluminum foil current collector, and after drying, rolling, and vacuum drying, aluminum leads were welded on using an ultrasonic welding machine to obtain a positive electrode sheet.

[0052] (2) Anode Preparation: Artificial graphite (anode active material), Super-P conductive carbon black, styrene-butadiene rubber (SBR) binder, and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95:1:1.5:2.5. These were then dispersed in deionized water to obtain anode slurry. The anode slurry was coated onto both sides of a copper foil, dried, calendered, vacuum dried, and then nickel leads were welded on using an ultrasonic welder to obtain the anode sheet. The porosity of the anode material layer was 20%.

[0053] (3) Preparation of non-aqueous electrolyte: Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and ethyl acetate (EA) were mixed, and additive 1 (compound 1), vinylene carbonate (VC), and fluoroethylene carbonate (FEC) were added. Then, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1.05 mol / L. Based on the total weight of the non-aqueous electrolyte (100%), the content of ethyl acetate (EA) was 50%, the content of compound 1 was 0.5%, the content of VC was 2%, and the content of FEC was 0.5%.

[0054] (4) Separator preparation: A three-layer separator membrane of polypropylene, polyethylene and polypropylene with a thickness of 20μm is used.

[0055] (5) Battery assembly: A three-layer separator with a thickness of 20 μm is placed between the positive and negative plates. Then, the sandwich structure composed of the positive plate, negative plate, and separator is wound or stacked. The cell is then placed in a square casing, the tabs are welded, and the casing is sealed to obtain the cell to be injected with electrolyte. The electrolyte prepared above is injected into the cell by cutting the opening. After standing for 1 hour, the cell is sealed. After sealing, the battery is aged at 45°C for 48 hours. Then, the first charge is carried out according to the following steps: 0.05C constant current charging for 2 hours, 0.1C constant current charging for 1 hour, and 0.2C constant current charging for 1 hour.

[0056] The group margin of the square lithium-ion battery cell obtained in this embodiment is 91%.

[0057] Examples 2 to 27 and Comparative Examples 1 to 17

[0058] This embodiment and comparative example are used to illustrate the square lithium-ion battery disclosed in this application. They include most of the operating steps in the above embodiment 1. The difference lies in the composition of the non-aqueous electrolyte and the content of each component, the porosity of the negative electrode material, the group margin and safety factor σ of the square lithium-ion battery cell, as shown in Tables 1 to 4.

[0059] The following performance tests were performed on the square lithium-ion batteries prepared in each embodiment and comparative example:

[0060] (1) 150℃ hot box test:

[0061] The fully charged battery was placed in the GX-3020-BL40 thermal shock test chamber. The chamber operated according to the set program of "heating from 25°C to 150°C at a rate of 5°C / min and then holding for 30 minutes". At the same time, the temperature and voltage channels of the "data acquisition instrument" panel began to record real-time data of the cell surface.

[0062] Thermal shock test pass rate: Before testing, the battery was charged to a full charge voltage of 3.65V at a constant current of 0.5C, with a cutoff current of 0.05C. After charging, the battery was left to stand for 4 hours. The fully charged battery was then placed in a GX-3020-BL40 thermal shock test chamber, which operated according to the set program of "heating from 25℃ to 150℃ at a rate of 5℃ / min and holding for 30 minutes". If the battery valve opened, caught fire, or exploded, the test was considered a failure; if the battery valve did not open, did not catch fire, and did not explode, the test was considered a success. 20 batteries were tested for each example and comparative example. The pass rate = number of successful batteries / 20.

[0063] (2) High-temperature cycle performance test under high-rate charging:

[0064] At 45°C, the battery was discharged at a constant current and voltage of 4C to 3.65V, with a cutoff current of 0.05C, and then discharged at a constant current of 1C to 2.5V. The discharge capacity of the first discharge and the discharge capacity of the 1000th discharge were recorded.

[0065] Calculate the capacity retention during high-temperature cycling using the following formula:

[0066] Capacity retention rate (%) = Discharge capacity of the 1000th discharge / Discharge capacity of the 1st discharge × 100%.

[0067] Test Results

[0068] Table 1 shows the parameters of the square lithium-ion batteries prepared in Examples 1 to 17 and Comparative Examples 3 to 14; the difference between Examples 2 to 17 and Comparative Examples 3 to 14 and Example 1 is the relevant parameters in Table 1.

[0069] Table 1

[0070] The test results from Examples 1 to 17 and Comparative Examples 3 to 14 show that the square lithium-ion battery provided in this application uses at least one of Compound 1 to Compound 5 as the first additive and a short-chain carboxylic acid ester as the non-aqueous organic solvent. Furthermore, the safety factor of the lithium-ion battery is defined by limiting the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the non-aqueous organic solvent, the porosity c of the negative electrode material layer in the square lithium-ion battery, and the group margin d of the cell in the square lithium-ion battery. When the following conditions are met, such that 0.16≤σ≤1.35, 0.01≤a≤2, 30≤b≤60, 10≤c≤40, and 85≤d≤93, square batteries can have both high safety performance and fast charging performance.

[0071] As can be seen from the test results of Example 1 and Comparative Examples 3 to 14, when any one of the following parameters does not meet the range, or when the mass percentage of the first additive in the non-aqueous electrolyte (a), the mass percentage of the non-aqueous organic solvent (b), the porosity of the negative electrode material layer in the square lithium-ion battery (c), or the group margin of the cell in the square lithium-ion battery (d), or when the safety factor σ of the lithium-ion battery defined by the above parameters is too large or too small, it will be impossible to guarantee the formation of a protective film with excellent thermal stability on the positive and negative electrode surfaces of the battery. This will cause corrosion and oxidation of the electrode material, or during the charging and discharging process of the battery, there will not be enough space to dissipate and conduct heat, thus leading to thermal runaway of the battery.

[0072] When the mass percentage of the first additive (a), the mass percentage of the non-aqueous organic solvent (b), the porosity of the negative electrode material layer in the square lithium-ion battery (c), the group margin of the cell in the square lithium-ion battery (d), and the safety factor (σ) further satisfy 0.2≤σ≤1.0, 0.1≤a≤1, 30≤b≤50, 15≤c≤30, and 88≤d≤92, the square battery can combine high energy density, high fast charging capability, and high safety performance.

[0073] Within this range, the first additive can provide an interfacial film with excellent thermal stability. An appropriate content of carboxylic acid esters can avoid the negative effect of increased additive impedance, while simultaneously ensuring the cell's group margin. Furthermore, within this range, the negative electrode porosity ensures good electrolyte wettability, helping the first additive to form a uniform interfacial film at the negative electrode interface, while also addressing the problem of electrolyte difficulty in wetting the cell after increasing the cell's group margin. Considering the interplay of various design parameters, by controlling the battery's safety factor σ between 0.16 and 1.35, the synergistic effect between additives, solvents, negative electrode materials, and cell group margin design can be fully utilized, enabling the square battery to possess high energy density, high fast-charging capability, and high safety performance. It can generate an interfacial film with excellent thermal stability on the positive and negative electrode surfaces, better preventing electrode material corrosion and oxidation at high temperatures, and allowing sufficient space for heat dissipation during charging and discharging, ensuring timely heat dissipation and conduction.

[0074] Table 2 shows the parameters of the square lithium-ion batteries prepared in Examples 1 and 18 to 19; the difference between Examples 18 to 19 and Example 1 lies in the relevant parameters in Table 2.

[0075] Table 2

[0076] As shown in Table 2, when the mass percentage of the first additive (a) in the non-aqueous electrolyte, the mass percentage of the non-aqueous organic solvent (b), the porosity of the negative electrode material layer (c) in the square lithium-ion battery, the cell margin (d) in the square lithium-ion battery, and the safety factor σ of the lithium-ion battery meet the relevant requirements, using any one of compounds 1 to 5 as the first additive can prevent the electrode material from corroding and oxidizing at high temperatures. Furthermore, it allows sufficient space for heat dissipation during charging and discharging, ensuring that the generated heat is dissipated and conducted in a timely manner. This results in the square battery possessing high energy density, fast charging capability, and high safety performance. This demonstrates that the battery system of this application is universally applicable to different first additives.

[0077] Table 3 shows the parameters of the lithium-ion batteries prepared in Examples 1, 21 to 26, and Comparative Examples 15 to 17; the difference between Examples 21 to 26 and Comparative Examples 15 to 17 and Example 1 lies in the relevant parameters in Table 3.

[0078] Table 3

[0079] Table 3 shows that when the mass percentages of the first additive (a) in the non-aqueous electrolyte, the mass percentage of the non-aqueous organic solvent (b), the porosity of the negative electrode material layer (c) in the square lithium-ion battery, the cell margin (d) in the square lithium-ion battery, and the safety factor σ of the lithium-ion battery meet the relevant requirements, using different short-chain carboxylic esters as solvents can prevent the electrode materials from corroding and oxidizing at high temperatures. Furthermore, it allows sufficient space for heat dissipation during charging and discharging, enabling the generated heat to be dissipated and conducted in a timely manner. This gives the square battery high energy density, fast charging capability, and high safety performance. This demonstrates the universality of the battery system in this application for different solvents.

[0080] The results from Examples 1, 21-22 and Comparative Examples 15-17 show that when long-chain carboxylic esters are used as solvents, their viscosity and conductivity no longer have a significant advantage over chain carbonates, making it difficult to meet the requirements of high conductivity and low viscosity. Although the use of long-chain carboxylic esters can significantly improve the battery's fast charging capability, it also degrades high-temperature performance and further leads to thermal runaway.

[0081] Table 4 shows the parameters of the lithium-ion batteries prepared in Examples 1, 27-28, and Comparative Examples 1-2; the difference between Examples 27-28 and Comparative Examples 1 and Example 2 and Example 1 lies in the relevant parameters in Table 4.

[0082] Table 4

[0083] Note: " / " in the table indicates that the item does not exist.

[0084] Table 4 shows that when the mass percentages of the first additive (a) in the non-aqueous electrolyte, the mass percentage of the non-aqueous organic solvent (b), the porosity of the negative electrode material layer (c) in the square lithium-ion battery, the cell margin (d) in the square lithium-ion battery, and the safety factor σ of the lithium-ion battery meet the relevant requirements, adding different types of auxiliary additives can prevent the electrode materials from corroding and oxidizing at high temperatures. Furthermore, it allows sufficient space for heat dissipation during charging and discharging, enabling the generated heat to be dissipated and conducted in a timely manner, thus giving the square battery high energy density, fast charging capability, and high safety performance. However, without the first additive and only auxiliary additives are added, an interface film with excellent thermal stability cannot be formed, which is detrimental to the battery's rate performance and generates more Joule heat, increasing the risk of thermal runaway.

[0085] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A square lithium-ion battery, wherein, The battery includes a battery casing and a cell assembly and a non-aqueous electrolyte contained within the battery casing. The cell assembly includes a positive electrode, a negative electrode, and a separator. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector; The non-aqueous electrolyte comprises a first additive, a lithium salt, and a non-aqueous organic solvent, wherein the first additive comprises at least one of the following compounds: The non-aqueous organic solvent includes short-chain carboxylic acid esters with 2 to 5 carbon atoms, and the short-chain carboxylic acid esters include at least one of ethyl acetate, ethyl propionate, or methyl acetate. The square lithium-ion battery meets the following conditions: Safety factor It satisfies 0.16≤σ≤1.35, 0.01≤a≤2, 24≤b≤56, 10≤c≤40, 85≤d≤93; Where a is the mass percentage of the first additive in the non-aqueous electrolyte, in %; b represents the mass percentage of short-chain carboxylic acid esters in the non-aqueous electrolyte, in %; c represents the porosity of the negative electrode material layer, in percentage (%). d represents the group margin of the square lithium-ion battery, expressed as a percentage.

2. The square lithium-ion battery according to claim 1, wherein, The safety factor of the square lithium-ion battery satisfies: 0.2≤σ≤1.

0.

3. The square lithium-ion battery according to claim 1, wherein, The mass percentage (a%) of the first additive in the non-aqueous electrolyte is 0.1% to 1%.

4. The square lithium-ion battery according to claim 1, wherein, The mass percentage (b%) of short-chain carboxylic acid esters in the non-aqueous electrolyte is 30% to 50%.

5. The square lithium-ion battery according to claim 1, wherein, The porosity (c%) of the negative electrode material layer is 15% to 30%.

6. The square lithium-ion battery according to claim 1, wherein, The group margin (d%) of the square lithium-ion battery is 88% to 92%.

7. The square lithium-ion battery according to claim 1, wherein, The non-aqueous electrolyte also includes auxiliary additives, which include at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and nitrile compounds.

8. The square lithium-ion battery according to claim 7, wherein, Based on the total mass of the non-aqueous electrolyte as 100%, the content of the auxiliary additives is 0.01% to 10%.

9. The square lithium-ion battery according to claim 7, wherein: The non-aqueous electrolyte satisfies at least one of the following conditions: (1) The cyclic sulfate compounds include at least one of 4-methyl vinyl sulfate, vinyl sulfate, and propylene sulfate; (2) The sulfonyl lactones include at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone. (3) The cyclic carbonate compounds include at least one of the following: vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and a compound represented by structural formula 1: In the structural formula 1 shown, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group; (4) The phosphate ester compounds include at least one of the compounds shown in structural formula 2: In structural formula 2, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, where m is a natural number from 1 to 3; (5) The borate esters include at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate; (6) The nitrile compounds include at least one of butadionitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octadionitrile, nonadionitrile and sebaconitol.

10. The square lithium-ion battery according to claim 1, wherein, The non-aqueous organic solvent also includes one or more of cyclic carbonates or chain carbonates.

11. The square lithium-ion battery according to claim 1, wherein, The non-aqueous electrolyte satisfies at least one of the following conditions: (1) The cyclic carbonates include one or more of vinylene carbonate, propylene carbonate, ethylene carbonate, and butene carbonate; (2) The chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl trifluoroethyl carbonate and bis(2,2,2-trifluoroethyl) carbonate.

12. The square lithium-ion battery according to claim 1, wherein, The positive electrode sheet includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material includes a phosphate material; The negative electrode material layer includes a negative electrode active material, which includes at least one of silicon-based negative electrode and silicon-carbon negative electrode.

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