Battery

Abstract

The present invention relates to the technical field of batteries, and specifically relates to a battery. The battery comprises a battery cell, an electrolyte solution and a case, wherein the battery cell and the electrolyte solution are located in an accommodating space formed by the case; the case comprises a first side in the thickness direction, a second side in the width direction and a third side in the height direction, the second side and the third side form a first face of the case, and the first face is the face having the largest area among all the faces of the case; and the electrolyte solution comprises a linear carboxylic ester. The battery meets both of the following relational expressions: 0.025≤S3 / a≤0.4, and 150≤a / d≤450, wherein a is the area of the first face, with the unit thereof being cm2; d is the thickness of the first face, with the unit thereof being mm; and S3 is the weight content of the linear carboxylic ester in the electrolyte solution, with the unit thereof being %. The battery can meet the requirement of startup at low temperatures while improving the wettability of the electrolyte solution at low temperatures, which enhances the kinetic performance of the battery, thereby improving the low-temperature cycle performance of the battery.

Description

A type of battery Technical Field

[0001] This disclosure relates to the field of battery technology, specifically to a battery. Background Technology

[0002] Compared with traditional batteries, lithium-ion batteries have advantages such as high energy density, long cycle life, no pollution, and high operating voltage, making them an excellent energy storage medium. They can be used for industrial energy storage and outdoor energy storage. When there is an excess of energy from water, wind, and solar power, lithium-ion batteries can convert that energy into chemical energy for storage, and then provide power when cities, homes, and base stations are short of electricity.

[0003] Lithium iron phosphate batteries offer advantages in safety and cost compared to ternary lithium batteries, resulting in a significant market share for both home and outdoor storage. However, outdoor storage batteries require additional heating equipment to reach 0°C before starting in low winter temperatures, leading to significant time waste and higher costs. Therefore, there is a strong demand for batteries capable of starting at low temperatures. Summary of the Invention

[0004] Research has found that existing outdoor storage batteries have high volumetric energy density, large individual cells, and thick electrodes. However, at low temperatures, the electrolyte has insufficient wettability, which easily leads to severe lithium plating and results in poor cycle performance at low temperatures.

[0005] To address the issue of low cycle performance of batteries at low temperatures, this disclosure provides a battery. This battery can meet the requirements for starting at low temperatures while improving the wettability of the electrolyte at low temperatures, thus improving the battery's kinetic performance and consequently its low-temperature cycle performance. Simultaneously, it can suppress cell expansion and reduce the battery's expansion rate.

[0006] To achieve the above objectives, this disclosure provides a battery comprising a battery cell, an electrolyte, and a casing. The battery cell and the electrolyte are located within a containment space formed by the casing. The casing includes a first side along the thickness direction, a second side along the width direction, and a third side along the height direction. The second side and the third side form a first surface of the casing, which is the surface with the largest area among all surfaces of the casing. The electrolyte comprises a linear carboxylic acid ester. The battery simultaneously satisfies the following relationships: 0.025 ≤ S³ / a ≤ 0.4, 150 ≤ a / d ≤ 450, where a is the area of ​​the first surface in cm². 2 d is the thickness of the first surface in mm, and S3 is the weight content of the linear carboxylic acid ester in the electrolyte in %.

[0007] Compared with the prior art, the present disclosure has at least the following advantages through the above technical solution:

[0008] The electrolyte disclosed herein includes a linear carboxylic acid ester, which can meet the requirements of low-temperature start-up batteries and improve the wettability of the electrolyte to the electrodes at low temperatures, thereby improving the low-temperature cycle performance of the battery. However, due to the structural characteristics of linear carboxylic acid esters, they are prone to gas generation, leading to an increased battery expansion rate. This disclosure, by controlling the ratio of the weight content of linear carboxylic acid ester in the electrolyte to the area of ​​the first surface, can prevent excessive expansion of the battery cell while maintaining high low-temperature cycle performance. Simultaneously, by controlling the ratio of the area to the thickness of the first surface, the compressive strength of the casing is controlled within a suitable range, which can suppress cell expansion, further reduce the battery's thickness expansion rate, and prevent the battery's energy density from being affected by excessive casing thickness.

[0009] Other features and advantages of this disclosure will be described in detail in the following detailed description section.

[0010] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0011] Figure 1 shows one of the schematic diagrams of the casing of the battery disclosed herein.

[0012] Figure 2 shows a second schematic diagram of the casing of the battery disclosed herein.

[0013] Figure 3 shows a third schematic diagram of the casing of the battery disclosed herein. Detailed Implementation

[0014] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of this disclosure. Unless otherwise specified herein, the data range includes endpoints.

[0015] It should be noted that the numerical designations such as "first" and "second" in this disclosure are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0016] This disclosure provides a battery comprising a battery cell, an electrolyte, and a casing. The battery cell and the electrolyte are located within a containment space formed by the casing. The casing includes a first side along the thickness direction, a second side along the width direction, and a third side along the height direction. The second side and the third side form a first surface of the casing, which is the surface with the largest area among all surfaces of the casing. The electrolyte comprises a linear carboxylic acid ester. The battery simultaneously satisfies the following relationships: 0.025 ≤ S3 / a ≤ 0.4 (e.g., 0.025, 0.05, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or 0.4), 150 ≤ a / d ≤ 450 (e.g., 150, 180, 200, 230, 250, 280, 300, 330, 350, 380, 400, 430, or 450), where a is the area of ​​the first surface in cm². 2 d is the thickness of the first surface in mm, and S3 is the weight content of the linear carboxylic acid ester in the electrolyte in %.

[0017] As shown in Figure 1, the outer shell includes a first side 3 along the thickness direction X, a second side 1 along the width direction Y, and a third side 2 along the height direction Z. The second side 1 and the third side 2 form the first surface 12 of the outer shell. The outer shell includes two first surfaces located on either side of the third side. In this disclosure, the thickness direction X is the thickness direction of the outer shell, the width direction Y is the width direction of the outer shell, and the height direction Z is the height direction of the outer shell.

[0018] Because linear carboxylic acid esters have relatively low viscosity and melting point, adding them to the electrolyte can reduce the overall viscosity of the electrolyte, allowing for better wetting of the electrodes at low temperatures and rapid lithium ion transport, thus improving the battery's kinetic performance and low-temperature cycle performance. However, due to the structural characteristics of linear carboxylic acid esters, the ester groups have a strong electron-withdrawing inductive effect, causing α-H to easily be lost at the negative electrode, leading to a reduction reaction in the battery, resulting in gas production and increased battery expansion rate. Research has shown that the area of ​​the first surface (the largest surface among all surfaces of the casing) is comparable to the area of ​​the largest surface of the electrode. By controlling the ratio of the weight content of linear carboxylic acid esters in the electrolyte to the area of ​​the first surface, the amount of linear carboxylic acid esters in the electrolyte in contact with a unit area of ​​the cell can be controlled, ensuring a moderate content of linear carboxylic acid esters in the electrolyte in contact with a unit area of ​​the cell. This ensures the low-temperature performance of the battery while avoiding excessive expansion. When the ratio of the weight content of linear carboxylic acid esters in the electrolyte to the area of ​​the first surface is small (e.g., below 0.025), the contact area between the linear carboxylic acid esters and the electrode is small, which is not conducive to ion transport and affects the low-temperature performance of the battery. When the ratio of the weight content of linear carboxylic acid esters in the electrolyte to the area of ​​the first surface is large (e.g., above 0.4), the amount of linear carboxylic acid esters in the electrolyte in contact with the cell per unit area is excessive, resulting in excessive gas production by linear carboxylic acid esters and excessive expansion of the battery. In order to further reduce the expansion rate of the battery, and at the same time control the ratio of the area to the thickness of the first surface, the compressive strength of the casing is kept within a suitable range, thereby suppressing the expansion of the cell and further reducing the expansion rate of the battery, while avoiding the impact of excessive casing thickness on the energy density of the battery.

[0019] In this disclosure, by adding a linear carboxylic acid ester to the electrolyte and simultaneously controlling the weight ratio of the linear carboxylic acid ester to the area of ​​the first surface and the ratio of the area of ​​the first surface to its thickness, a battery can achieve both high low-temperature cycling performance and low thickness expansion rate compared to existing technologies. To further improve the effect, one or more of these technical features can be further optimized.

[0020] In one example, the battery simultaneously satisfies the following relationships: 0.05 ≤ S³ / a ≤ 0.3, 200 ≤ a / d ≤ 300, where a is the area of ​​the first surface in cm². 2 d is the thickness of the first surface in mm, and S3 is the weight content of the linear carboxylic acid ester in the electrolyte in %.

[0021] In one example, the area of ​​the first face is 150 cm². 2 -300cm 2 (For example, 150cm) 2 160cm 2170cm 2 180cm 2 190cm 2 200cm 2 210cm 2 220cm 2 230cm 2 240cm 2 250cm 2 260cm 2 270cm 2 280cm 2 290cm 2 Or 300cm 2 ).

[0022] In one example, the thickness of the first surface is 0.45mm-0.95mm (e.g., 0.45mm, 0.5mm, 0.55mm, 0.6mm, 0.65mm, 0.7mm, 0.75mm, 0.8mm, 0.85mm, 0.9mm or 0.95mm).

[0023] In one example, the linear carboxylic acid ester in the electrolyte contains 5%-70% by weight (e.g., 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%).

[0024] In one example, the linear carboxylic acid ester in the electrolyte contains 10%-50% by weight.

[0025] According to a specific implementation, a is 150-300, d is 0.45-0.95, S3 is 5-70, and the battery simultaneously satisfies the following relationships: 0.025≤S3 / a≤0.4, 150≤a / d≤450, where a is the area of ​​the first surface in cm². 2 d is the thickness of the first surface in mm, and S3 is the weight content of the linear carboxylic acid ester in the electrolyte in %.

[0026] According to a specific implementation, a is 150-300, d is 0.45-0.95, S3 is 10-50, and the battery simultaneously satisfies the following relationships: 0.05≤S3 / a≤0.3, 200≤a / d≤300, where a is the area of ​​the first surface in cm². 2 d is the thickness of the first surface in mm, and S3 is the weight content of the linear carboxylic acid ester in the electrolyte in %.

[0027] In one example, the linear carboxylic acid ester comprises one or more of the following compounds, either fluorinated or unsubstituted: ethyl acetate, methyl propionate, propyl formate, ethyl propionate, methyl acetate, ethyl formate, methyl formate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, ethyl fluoroacetate, ethyl difluoroacetate, and ethyl trifluoroacetate.

[0028] In one example, the electrolyte further includes cyclic carbonates and linear carbonates.

[0029] In one example, the cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate, and butene carbonate. The cyclic carbonate has a high dielectric constant, enabling it to dissociate from lithium salts, thus separating lithium ions from anions in the electrolyte. This results in an electrolyte containing lithium salt solvent that forms a solution with a certain conductivity. Furthermore, the cyclic carbonate can form a film on the negative electrode, protecting the negative electrode interface and maintaining the battery's high-temperature long-cycle performance and high-temperature storage performance.

[0030] In one example, the cyclic carbonate in the electrolyte contains 5% to 40% by weight (e.g., 5%, 10%, 15%, 20%, 25%, 30%, 35%, or 40%).

[0031] In one example, the cyclic carbonate in the electrolyte contains 10%-35% by weight.

[0032] In one example, the linear carbonate comprises one or more of the following compounds, either fluorinated or unsubstituted: diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, 2,2-difluoroethyl methyl carbonate, and 2-fluoroethyl ethyl carbonate. The linear carbonate has a low viscosity; adding it to the electrolyte can reduce the overall viscosity of the electrolyte, improve its fluidity, and thus enhance the lithium-ion transport rate.

[0033] In one example, the linear carbonate in the electrolyte contains 0.01% to 70% by weight (e.g., 0.01%, 0.05%, 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%).

[0034] In one example, the linear carbonate content in the electrolyte is 5%-50% by weight.

[0035] In one example, the weight ratio of the linear carboxylic acid ester to the linear carbonate is 0.1-20 (e.g., 0.1, 0.5, 1, 3, 5, 8, 10, 13, 15, 18, or 20). Both linear carboxylic acid esters and linear carbonates have low viscosity. Adding them to the electrolyte can further reduce the overall viscosity of the electrolyte, improve its fluidity, and, compared to linear carbonates, the linear carboxylic acid ester has a lower melting point and lower viscosity, which can improve the wettability of the electrolyte at low temperatures and increase the lithium-ion transport rate. Controlling the weight ratio of the linear carboxylic acid ester to the linear carbonate within the above range can further improve the wettability of the electrolyte at low temperatures, further improve the lithium-ion transport rate, and thus further improve the low-temperature cycle performance of the battery.

[0036] In one example, the weight ratio of the linear carboxylic acid ester to the linear carbonate is 0.5-10.

[0037] According to one specific embodiment, the cyclic carbonate in the electrolyte has a weight content of 5%-40%, the linear carbonate in the electrolyte has a weight content of 0.01%-70%, and the weight ratio of the linear carboxylic acid ester to the linear carbonate is 0.5-20.

[0038] According to one specific embodiment, the cyclic carbonate in the electrolyte has a weight content of 10%-35%, the linear carbonate in the electrolyte has a weight content of 5%-50%, and the weight ratio of the linear carboxylic acid ester to the linear carbonate is 0.5-10.

[0039] In one example, the electrolyte also includes additives and an electrolyte lithium salt.

[0040] In one example, the additives include cyclic carbonate additives, heteroatom-containing organic additives, and lithium salt additives. Adding these additives to the electrolyte can improve the interface quality of the negative electrode, prevent the reduction reaction of linear carboxylic esters at the negative electrode, reduce gas production, and thus reduce the battery's thickness expansion rate.

[0041] In one example, the carbonate additive includes one or more of vinylene carbonate, vinyl ethylene carbonate, and fluoroethylene carbonate.

[0042] In one example, the heteroatom-containing organic additive includes one or more of tris(trimethylsilane)phosphate, tris(trimethylsilane)borate, vinyl sulfate, methylene disulfonate, and 1,3-propane sulpholactone.

[0043] In one example, the heteroatoms in the heteroatom-containing organic additive include one or more of N, S, P, B, Si, and F. The heteroatom-containing organic additive can generate an interface with low impedance, preventing the linear carboxylic acid ester from undergoing reductive decomposition on the negative electrode, reducing gas production, and lowering the battery's thickness expansion rate. Furthermore, the organic additive containing heteroatoms P can generate Li3PO4 at the interface, which can lower the desolvation energy of lithium ions. The presence of multiple Li atoms in the structure of Li3PO4 allows for rapid lithium ion transport. The organic additive containing heteroatoms S can generate Li2SO3 near the negative electrode interface, which can also rapidly transport lithium ions, thus reducing the battery's impedance.

[0044] In one example, the lithium salt additive includes one or more of lithium difluorophosphate, lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium difluorodi(oxalato)phosphate, lithium tetrafluorooxalatophosphate, lithium tetrafluoroborate, and lithium nitrate.

[0045] In one example, the weight content S4 of the cyclic carbonate additive is 0.5%-5% (e.g., 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%) based on the total weight of the electrolyte.

[0046] In one example, the heteroatom-containing organic additive has a weight content of 0.01%-3% (e.g., 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5% or 3%) based on the total weight of the electrolyte.

[0047] In one example, the lithium salt additive has a weight content of 0.01%-3% (e.g., 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5% or 3%) based on the total weight of the electrolyte.

[0048] In one example, the electrolyte lithium salt includes inorganic lithium salts and organic lithium salts.

[0049] In one example, the inorganic lithium salt comprises lithium hexafluorophosphate and / or lithium tetrafluoroborate.

[0050] In one example, the organic lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium bis(pentafluoroethyl)sulfonylimide, lithium bis(hexafluoroisopropyl)sulfonylimide, lithium difluorooxalateborate, and lithium difluorodioxalate phosphate.

[0051] In one example, based on the total weight of the electrolyte, the weight content L1 of the inorganic lithium salt is 5%-20% (e.g., 5%, 8%, 10%, 13%, 15%, 18%, or 20%). Controlling L1 within the above range allows the electrolyte to passivate the positive electrode aluminum current collector, forming an Al2O3 passivation layer and preventing the aluminum in the positive electrode from dissolving in the electrolyte.

[0052] In one example, based on the total weight of the electrolyte, the weight content L2 of the organic lithium salt is 0.01%-20% (e.g., 0.01%, 0.05%, 0.1%, 0.5%, 1%, 3%, 5%, 8%, 10%, 13%, 15%, 18%, or 20%). Organic lithium salts have large anionic groups, enabling better dissociation. By controlling the weight content of inorganic lithium salts in the electrolyte within the above range, higher conductivity and electromobility number can be achieved in the electrolyte, thereby reducing impedance and increasing the lithium-ion transport rate.

[0053] In one example, the battery satisfies the following relationship: 8 ≤ L1 + L2 ≤ 20 (e.g., 8, 10, 13, 15, 18, or 20), where L1 is the weight content of the inorganic lithium salt in the electrolyte (%), and L2 is the weight content of the organic lithium salt in the electrolyte (%). Controlling the battery to satisfy the above relationship enables an effective combination of organic and inorganic lithium salts. On the one hand, this increases the electromobility number of the electrolyte, resulting in higher conductivity and electromobility. On the other hand, it passivates the positive electrode current collector, preventing the electrolyte from decomposing at the positive electrode current collector.

[0054] In one example, the battery satisfies the following relationship: 10 ≤ L1 + L2 ≤ 18, where L1 is the weight content of the inorganic lithium salt in the electrolyte (%), and L2 is the weight content of the organic lithium salt in the electrolyte (%).

[0055] According to one specific embodiment, L1 is 5-50, L2 is 0.01-20, and the battery satisfies the following relationship: 8≤L1+L2≤20, where L1 is the weight content of the inorganic lithium salt in the electrolyte (%), and L2 is the weight content of the organic lithium salt in the electrolyte (%).

[0056] According to one specific embodiment, L1 is 5-50, L2 is 0.01-20, and the battery satisfies the following relationship: 10≤L1+L2≤18, where L1 is the weight content of the inorganic lithium salt in the electrolyte (%), and L2 is the weight content of the organic lithium salt in the electrolyte (%).

[0057] In one example, the battery cell includes a negative electrode sheet, which includes a negative current collector and a negative active layer. The negative active layer includes a negative active material, which includes a graphite substrate and soft carbon coated on the surface of the graphite substrate. The graphite substrate includes artificial graphite and / or natural graphite. The aforementioned negative active material exhibits low-temperature fast-charging performance. Incorporating this negative active material into the battery of this disclosure improves the battery's low-temperature long-cycle performance. Furthermore, because the negative active material includes a soft carbon coating layer, it can suppress the expansion of the graphite substrate, reduce the expansion rate of the negative electrode sheet, and thus further reduce the battery's thickness expansion rate. Simultaneously, the soft carbon is anisotropic; coating the graphite substrate with soft carbon increases the number of lithium intercalation sites, allowing lithium ions to intercalate into the negative active material from all directions, thereby improving the battery's fast-charging performance.

[0058] In one example, the weight content of the soft carbon in the negative electrode active material is 1%-5% (e.g., 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%).

[0059] In one example, in the Raman spectrum of the negative electrode, the average value I of the ratio of the intensity of the D peak to the intensity of the G peak, Id / Ig, is 0.1-0.8 (e.g., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or 0.8). A higher I value indicates more defects and more active sites in the negative electrode active material, resulting in better low-temperature performance of the battery. However, more defects in the negative electrode active material lead to greater electrolyte consumption, affecting the battery's cycle performance. Excessive electrolyte consumption can negatively impact cycle performance and even cause the battery to experience a rapid decline in performance. Therefore, it is necessary to control the I value within a suitable range. By controlling the I value within the aforementioned range, the battery can achieve both good low-temperature cycle performance and high cycle performance.

[0060] In this disclosure, the average value I of the ratio of the intensity of the D peak to the intensity of the G peak, Id / Ig, refers to the value of Id / Ig calculated by randomly selecting 100 points of the D peak and G peak intensity distribution map obtained by Raman spectroscopy of the negative electrode active material, and taking the average value of 100 Id / Ig values ​​as I.

[0061] In one example, in the intensity distribution maps of the D and G peaks obtained by Raman spectroscopy of the negative electrode sheet, the numerical distributions satisfying 0.3 ≤ Id / Ig ≤ 0.6 are ≥90%, where Id is the intensity of the D peak in the Raman spectrum of the negative electrode active material, and Ig is the intensity of the G peak in the Raman spectrum of the negative electrode active material. In this disclosure, the statement that in the intensity distribution maps of the D and G peaks obtained by Raman spectroscopy of the negative electrode sheet, the numerical distributions satisfying 0.3 ≤ Id / Ig ≤ 0.6 are ≥90% means that, in the intensity distribution maps of the D and G peaks obtained by Raman spectroscopy of the negative electrode active material, if 100 D and G peaks are randomly selected and the Id / Ig value is calculated, the percentage of points satisfying 0.3 ≤ Id / Ig ≤ 0.6 is ≥90% of the 100 points.

[0062] In one example, the battery satisfies the following relationship: 4 ≤ I / S4 ≤ 100 (e.g., 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100), where I is the average value of the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material, Id / Ig, and S4 is the weight content of the cyclic carbonate additive in the electrolyte, in percent. Cyclic carbonates can cover defects on the surface of the negative electrode active material and prevent electrolyte gas generation. When the I value is large, there are more defects on the surface of the negative electrode active material, and more cyclic carbonates are needed to cover the excess defects and prevent electrolyte gas generation. When the I value is small, there are fewer defects on the surface of the negative electrode active material, and a small amount of cyclic carbonates is needed. However, too little cyclic carbonate will increase the battery impedance and deteriorate the low-temperature performance. Therefore, I / S4 needs to be controlled within the above range to achieve a high degree of compatibility between the two, so that the battery has both good low-temperature performance and low thickness expansion rate.

[0063] In one instance, the battery satisfies the following relationship: 10 ≤ I / S4 ≤ 50.

[0064] According to a specific embodiment, I is 0.1-0.8, S4 is 0.5-5, and the battery satisfies the following relationship: 4≤I / S4≤100, where I is the average value of the ratio of the intensity of the D peak to the intensity of the G peak (Id / Ig) in the Raman spectrum of the negative electrode active material, and S4 is the weight content of the cyclic carbonate additive in the electrolyte (in %).

[0065] According to a specific embodiment, I is 0.1-0.8, S4 is 0.5-5, and the battery satisfies the following relationship: 10≤I / S4≤50, where I is the average value of the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material, Id / Ig, and S4 is the weight content of the cyclic carbonate additive in the electrolyte, in units of %.

[0066] In one example, the average particle size of the negative electrode active material is 5 μm-15 μm (e.g., 5 μm, 8 μm, 10 μm, 13 μm, or 15 μm). Controlling the average particle size of the negative electrode active material within this range shortens the transport distance of lithium ions within the particles of the negative electrode active material, preventing lithium ion accumulation and deposition on the particle surface of the negative electrode active material under low-temperature charging conditions.

[0067] In this disclosure, the average particle size can be obtained by testing using the following method: Taking the average particle size of the negative electrode active material as an example, the surface of the negative electrode active layer is observed using a scanning electron microscope (S-3400N manufactured by Hitachi, Ltd.). For particle size, a square or rectangle with the smallest area completely surrounding a particle of the negative electrode active material is drawn on the obtained image; that is, a square or rectangle is drawn where the end of the particle is connected to the four sides of the square or rectangle. In the case of a square, the length of one side is taken as the particle size; in the case of a rectangle, the length of the long side (major axis diameter) is taken as the particle size. For any 100 particles of the negative electrode active material, the particle size of each particle is measured, and the average of these values ​​is taken as the average particle size. It should be noted that if more than 100 particles are observed in the captured image, the average number of any 100 particles in that image is taken as the average particle size of the negative electrode active material; if no 100 particles are observed in the image, multiple images are captured, and the average number of the total 100 particles is taken as the average particle size.

[0068] In one example, the particle size distribution Dv90 / Dv10 of the negative electrode active material is 2.3-3.5 (e.g., 2.3, 2.5, 2.8, 3, 3.3, or 3.5), and Dv10 ≥ 1 μm. By controlling the particle size distribution of the negative electrode active material, lithium ions can be uniformly intercalated into the negative electrode active material at low temperatures.

[0069] In this disclosure, Dv90 is the particle size of the negative electrode active material when the cumulative particle size distribution percentage reaches 90% in the volume distribution curve of the negative electrode active material. Dv10 is the particle size of the negative electrode active material when the cumulative particle size distribution percentage reaches 10% in the volume distribution curve of the negative electrode active material.

[0070] In one example, the negative electrode active layer further includes a negative electrode binder.

[0071] In one example, the negative electrode binder includes one or more of polyacrylate, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, and polyvinylidene fluoride.

[0072] In one example, the polyacrylic acid is a lithium-ionized polyacrylic acid ester. Lithium-ionized polyacrylic acid ester is beneficial for improving the low-temperature performance of the negative electrode. The lithium-ionized polyacrylic acid ester contains a -CO2Li structure (lithiumized ester group), which can capture lithium ions in the electrolyte, enabling rapid desolvation of the lithium ions and thus rapid transport to the negative electrode, thereby improving low-temperature performance.

[0073] In one example, the lithium-ionized polyacrylate comprises lithium and side chains containing ester groups.

[0074] In one example, based on the total weight of the lithium-ionized polyacrylate, the weight content of lithium is 1.5%-4% (e.g., 1.5%, 2%, 2.5%, 3%, 3.5%, or 4%), and the weight content of the ester-containing side chains is 10%-45% (e.g., 10%, 15%, 20%, 25%, 30%, 35%, 40%, or 45%).

[0075] In one example, the negative electrode is at 2000 cm -1 -2500cm -1 (For example, 2000cm) -1 2100cm -1 2200cm -1 2300cm -1 2400cm -1 Or 2500cm -1 Infrared characteristic peaks are present.

[0076] In one example, the glass transition temperature of the lithium-ionized polyacrylate is 50°C-120°C (e.g., 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, or 120°C).

[0077] In one example, the negative electrode active layer is located on one or both sides of the negative electrode current collector.

[0078] In one example, the negative electrode active layer further includes a negative electrode conductive agent.

[0079] In one example, the negative electrode conductive agent includes one or more of acetylene black, conductive carbon black, carbon nanotubes, Ketjen black, conductive graphite, and conductive carbon fiber.

[0080] In one example, based on the total weight of the negative electrode active layer, the weight content of the negative electrode active material is 94%-98% (e.g., 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, or 98%), the weight content of the negative electrode binder is 0.5%-3% (e.g., 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%), and the weight content of the negative electrode conductive agent is 0.5%-3% (e.g., 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%).

[0081] In one example, the thickness of one side of the negative electrode active layer is 40μm-100μm (e.g., 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm or 100μm).

[0082] In one example, the thickness of the negative electrode active layer on one side is 50 μm-80 μm.

[0083] In this disclosure, the single-sided thickness of the negative electrode active layer refers to the thickness of the negative electrode active layer on one side of the negative electrode current collector (i.e., the side with the negative electrode active layer); when there are negative electrode active layers on both sides of the negative electrode current collector, the thicknesses of the negative electrode active layers on both sides are equal, and the single-sided thickness of the negative electrode active layer is the thickness of the negative electrode active layer on either side.

[0084] In one example, the areal density of the negative electrode is 7 mg / cm³. 2 -13mg / cm 2 (For example, 7 mg / cm) 2 8mg / cm 2 9mg / cm 2 10mg / cm 2 11mg / cm 2 12mg / cm 2 Or 13mg / cm 2 In this disclosure, the areal density of the negative electrode sheet is the areal density of one side. When there is a negative electrode active layer on one side of the negative electrode current collector, the areal density of the negative electrode sheet is the areal density of the negative electrode active layer on that side (i.e., the side with the negative electrode active layer). When there are negative electrode active layers on both sides of the negative electrode current collector, the areal densities of the negative electrode active layers on both sides are equal, and the areal density of the negative electrode sheet is the areal density of the negative electrode active layer on either side.

[0085] In one example, the compaction density of the negative electrode is 1.3 mg / cm³. 3 -1.8mg / cm 3 (For example, 1.3 mg / cm) 31.4 mg / cm 3 1.5 mg / cm 3 1.6 mg / cm 3 1.7 mg / cm 3 Or 1.8 mg / cm 3 ).

[0086] According to one specific embodiment, the areal density of the negative electrode sheet is 7 mg / cm³. 2 -13mg / cm 2 The compaction density of the negative electrode sheet is 1.3 mg / cm³. 3 -1.8mg / cm 3 Research has shown that the higher the areal density and compaction density of the negative electrode, the higher the energy density of the battery, but the worse the low-temperature performance of the battery. This is because when the compaction density and areal density increase, the wettability of the electrolyte is insufficient, which will cause concentration polarization during low-temperature charge and discharge, resulting in lithium plating. Therefore, controlling the areal density and compaction density of the negative electrode within the above-mentioned range, and using the electrolyte described in this disclosure, can achieve both high energy density and good low-temperature performance.

[0087] In one example, the battery cell further includes a positive electrode sheet, which includes a positive current collector and a positive active layer, the positive active layer including a positive active material, the positive active material including lithium iron phosphate material.

[0088] In one example, the lithium iron phosphate material comprises carbon, lithium, iron, and phosphorus.

[0089] In one example, based on the total weight of the lithium iron phosphate material, the weight content of carbon is 1%-1.5% (e.g., 1%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%), the weight content of lithium is 1%-10% (e.g., 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%), the weight content of iron is 25%-40% (e.g., 25%, 28%, 30%, 33%, 35%, 38%, or 40%), and the weight content of phosphorus is 10%-20% (e.g., 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%).

[0090] In one example, the lithium iron phosphate material has an average particle size of 0.5 μm to 1.5 μm (e.g., 0.5 μm, 0.8 μm, 1 μm, 1.3 μm or 1.5 μm).

[0091] In one example, the specific surface area of ​​the lithium iron phosphate material is 5 m². 2 / g-20m 2 / g (e.g., 5m 2 / g、8m 2 / g, 10m 2 / g、13m 2 / g, 15m 2 / g、18m 2 / g or 20m 2 / g).

[0092] In one example, the positive electrode active layer is located on one or both sides of the surface of the positive electrode current collector.

[0093] In one example, the positive electrode active layer further includes a positive electrode conductive agent and a positive electrode binder.

[0094] In one example, the positive electrode conductive agent includes one or more of acetylene black, conductive carbon black, carbon nanotubes, Ketjen black, conductive graphite, and conductive carbon fiber.

[0095] In one example, the positive electrode binder includes one or more of polyvinylidene fluoride, acrylic acid-modified polyvinylidene fluoride, carboxylic acid-modified polyvinylidene fluoride, polyacrylic acid, polyacrylic acid copolymer, polymethyl methacrylate, and polyimide.

[0096] In one example, based on the total weight of the positive electrode active layer, the weight content of the lithium iron phosphate material is 94%-98% (e.g., 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, or 98%), the weight content of the positive electrode conductive agent is 0.5%-3% (e.g., 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%), and the weight content of the positive electrode binder is 0.5%-3% (e.g., 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%).

[0097] In one example, the thickness of one side of the positive electrode active layer is 50 μm-100 μm (e.g., 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm or 100 μm).

[0098] In one example, the thickness of the positive electrode active layer on one side is 60 μm-90 μm.

[0099] In this disclosure, the single-sided thickness of the positive electrode active layer refers to the thickness of the positive electrode active layer on the side where the positive electrode current collector is located (i.e., the side with the positive electrode active layer); when there are positive electrode active layers on both sides of the positive electrode current collector, the thicknesses of the positive electrode active layers on both sides are equal, and the single-sided thickness of the positive electrode active layer is the thickness of the positive electrode active layer on either side.

[0100] In one example, the ratio of the single-sided thickness of the positive electrode active layer to the single-sided thickness of the negative electrode active layer is 1:(0.8-5) (e.g., 1:0.8, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, or 1:5). Controlling the single-sided thicknesses of the positive and negative electrode active layers within these ranges, while using a low-viscosity linear carboxylic acid ester, can improve the wettability of the electrolyte to the electrode sheets and prevent lithium plating at low temperatures.

[0101] In one example, the ratio of the thickness of one side of the positive electrode active layer to the thickness of one side of the negative electrode active layer is 1:(1-3).

[0102] In one instance, the outer casing is made of aluminum.

[0103] In one example, the width of the outer shell is 12cm-20cm (e.g., 12cm, 13cm, 14cm, 15cm, 16cm, 17cm, 18cm, 19cm or 20cm).

[0104] In one example, the height of the outer casing is 8cm-15cm (e.g., 8cm, 9cm, 10cm, 11cm, 12cm, 13cm, 14cm or 15cm).

[0105] In one example, the thickness of the outer shell is 3cm-7cm (e.g., 3cm, 4cm, 5cm, 6cm or 7cm).

[0106] In one example, the battery is a square aluminum-cased battery, and the cell includes a wound structure or a stacked structure.

[0107] In one example, an explosion-proof valve is provided on the surface of the housing.

[0108] In one instance, at least one (e.g., one, two, three, four, five, or six) explosion-proof valve is provided on the surface of the housing.

[0109] In one example, the explosion-proof valve is located on at least one of the following surfaces of the housing: a top surface, a side surface, and a bottom surface. As shown in Figures 1 and 3, a width 1 and a thickness 3 form the top surface 131 and the bottom surface 132 of the housing. The top surface 131 includes a positive terminal 51 and a negative terminal 52, and the bottom surface is located opposite the top surface. A thickness 3 and a height 2 form the side surface 23 of the housing. The housing also includes one top surface, one bottom surface, and two side surfaces.

[0110] In one example, the explosion-proof valve includes an explosion-proof disc, the shape of which includes one or more of the following: circular, elliptical (as shown in Figure 3), racetrack-shaped (as shown in Figure 2), square, triangular, and rectangular.

[0111] In one example, the projected area of ​​the explosion-proof valve on the surface of the housing is 50 mm². 2 -2000mm 2 (For example, 50mm) 2 100mm 2 300mm 2 500mm 2 800mm 2 1000mm 2 1300mm 2 1500mm 2 1800mm 2 Or 2000mm 2 ).

[0112] In one example, the battery cell further includes a separator. The separator is an aqueous separator. The separator includes a carrier layer and an adhesive layer located on one or both surfaces of the carrier layer.

[0113] In one example, the carrier layer includes a base film and an optional ("optional" means that it may or may not be present) ceramic layer located on one or both surfaces of the base film.

[0114] In one example, the base film comprises one or more of polyethylene (PE), polypropylene (PP), and PE and PP composite structures.

[0115] In one example, the ceramic layer comprises inorganic particles, which include one or more of aluminum oxide (Al2O3), aluminum hydroxide, magnesium oxide, alumina, zirconium oxide, titanium oxide, and silicon oxide.

[0116] The adhesive layer can be a conventional spray-applied adhesive layer, for example, the adhesive layer includes one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylic acid resin, polymethyl acrylate, butyl acrylate-acrylonitrile copolymer, polyacrylonitrile, ethylene-acrylic acid copolymer, ethyl polyacrylate or sodium carboxymethyl cellulose.

[0117] In one example, the battery is a lithium-ion rechargeable battery.

[0118] The present disclosure will be described in detail below through embodiments. The embodiments described in this disclosure are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0119] The following examples illustrate the battery of this disclosure.

[0120] Example 1

[0121] (1) Electrolyte

[0122] In an argon-filled glove box with a water content of <0.1 ppm and an oxygen content of <0.1 ppm, cyclic carbonates, linear carbonates, and linear carboxylic acids were mixed evenly. Thoroughly dried inorganic and organic lithium salts were added and stirred to dissolve. Heteroatom-containing organic additives and lithium salt additives were then added and stirred until homogeneous. After passing physical property testing, the electrolyte was obtained. The electrolyte composition was as follows: linear carboxylic acid ester: ethyl acetate (EA), 30 parts by weight; cyclic carbonate: ethylene carbonate, 25 parts by weight; linear carbonate: methyl ethyl carbonate, 25 parts by weight; cyclic carbonate additive: vinylene carbonate, 2.5 parts by weight; heteroatom-containing organic additive: ethylene sulfate, 1.5 parts by weight; lithium salt additive: lithium difluorophosphate (LiPO2F2), 1 part by weight; inorganic lithium salt: lithium hexafluorophosphate (LiPF6), 10 parts by weight; organic lithium salt: lithium bis(fluorosulfonyl)imide (LiFSI), 5 parts by weight. The weight ratio of linear carboxylic acid ester to linear carbonate is 1.2, and L1+L2=10+5=15.

[0123] (2) Negative electrode sheet

[0124] A negative electrode active material (graphite substrate coated with soft carbon (commercially purchased), wherein the soft carbon content of the negative electrode active material is 2% by weight), a negative electrode binder (styrene-butadiene rubber and lithium-ionized polyacrylate (lithium content of 2% by weight and ester-containing side chain content of 30% by weight), wherein the weight ratio of styrene-butadiene rubber to lithium-ionized polyacrylate is 1:1), and a positive electrode conductive agent (acetylene black) are added to a vacuum mixer in a mass ratio of 96.5:1:1:1.5. Deionized water is added, and the mixture is thoroughly mixed under vacuum to form a uniform, free-flowing negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry is then uniformly coated on both sides of a 6 μm thick copper foil to form a negative electrode active layer. The single-sided thickness of the negative electrode active layer is 92.3 μm, and the single-sided surface density is 9.6 mg / cm². 2 The material is dried, rolled, and die-cut to obtain the negative electrode sheet. The average value of the ratio of the D peak intensity to the G peak intensity, Id / Ig, is 0.5, and I / S4 = 0.5 / 2.5% = 20. In the Raman spectroscopy of the negative electrode active material, the intensity distribution of the D and G peaks, obtained from surface scanning, satisfies the condition 0.3 ≤ Id / Ig ≤ 0.6, with a distribution value ≥ 90%.

[0125] (3) Positive electrode plate

[0126] Lithium iron phosphate powder, positive electrode binder (polyvinylidene fluoride), and positive electrode conductive agent (1.5 parts by weight of acetylene black and 0.5 parts by weight of carbon nanotubes) were added to a vacuum mixer in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) was added, and the mixture was thoroughly mixed under vacuum until a uniform, free-flowing positive electrode slurry with a solid content of 55 wt% was formed. The positive electrode slurry was then uniformly coated onto both sides of a 12 μm thick carbon-coated aluminum foil to form a positive electrode active layer. The single-sided thickness of the positive electrode active layer was 75.1 μm, and the single-sided surface density was 20 mg / cm². 2 The cathode is obtained by drying, rolling, slitting, and punching.

[0127] (5) Lithium-ion batteries

[0128] The positive electrode obtained in step (3), the negative electrode obtained in step (2), and the separator (PP) are wound together to obtain a bare cell. The bare cell is then welded with tabs and placed in a battery casing. The electrolyte prepared in step (1) is injected into the dried and qualified cell. After processes such as settling, aging, formation, venting, aging, and sorting, a lithium-ion secondary battery is obtained. The first side of the casing along the thickness direction has a length of 49.9 mm, the second side along the width direction has a length of 160 mm, the third side along the height direction has a length of 112.75 mm, and the area a of the first surface is 180.4 cm². 2 The thickness d of the first surface is 0.65 mm. S3 / a = 30 / 180.4 = 0.166, a / d = 180.4 / 0.65 = 277.5. The ratio of the single-sided thickness of the negative electrode active layer to the single-sided thickness of the positive electrode active layer is 1:1.2. The projected area of ​​the explosion-proof valve on the outer shell surface is 802.6 mm². 2 .

[0129] Example 2

[0130] (1) Electrolyte

[0131] The experiment was conducted in accordance with Example 1, except that: linear carboxylic acid ester: ethyl acetate (EA), 20 parts by weight; cyclic carbonate: ethylene carbonate, 40 parts by weight; linear carbonate: methyl ethyl carbonate, 20 parts by weight; cyclic carbonate additive: vinylene carbonate, 4 parts by weight; heteroatom-containing organic additive: ethylene sulfate, 2 parts by weight; lithium salt additive: lithium difluorophosphate (LiPO2F2), 2 parts by weight; inorganic lithium salt: lithium hexafluorophosphate (LiPF6), 9 parts by weight; organic lithium salt: lithium bis(fluorosulfonyl)imide (LiFSI), 8 parts by weight. The weight ratio of the linear carboxylic acid ester to the linear carbonate was 1.33, and L1 + L2 = 9 + 8 = 17.

[0132] (2) Negative electrode sheet

[0133] The experiment was conducted in accordance with Example 1, except that the single-sided thickness of the negative electrode active layer was 94.8 μm, the average value of the ratio of the intensity of the D peak to the intensity of the G peak (Id / Ig) was 0.3, I / S4 = 0.3 / 4% = 7.5, the weight content of lithium in the lithium polyacrylate was 3%, and the weight content of the side chain containing ester groups was 20%.

[0134] (3) Positive electrode plate

[0135] The same procedure was performed as in Example 1, except that the thickness of the positive electrode active layer on one side was 55.3 μm.

[0136] (4) Lithium-ion batteries

[0137] The procedure is carried out with reference to Embodiment 1, except that the length of the first side of the outer shell along the thickness direction is 50.1 mm, the length of the second side of the outer shell along the width direction is 140.2 mm, the length of the third side of the outer shell along the height direction is 109 mm, and the area 'a' of the first surface is 152.8 cm². 2 The thickness d of the first surface is 0.8 mm, S3 / a = 20 / 152.8 = 0.131, a / d = 152.8 / 0.65 = 191, the ratio of the single-sided thickness of the negative electrode active layer to the single-sided thickness of the positive electrode active layer is 1:1.7, and the projected area of ​​the explosion-proof valve on the outer shell surface is 1532.3 mm². 2 .

[0138] Example 3 Group

[0139] This set of examples illustrates the effects of changing the weight ratio of linear carboxylic acid esters to linear carbonates.

[0140] This embodiment group is based on Example 1, except that the weight ratio of linear carboxylic acid ester to linear carbonate ester is changed, as detailed in Table 1-1.

[0141] Example 4 group

[0142] This set of examples illustrates the effects of changes in the weight content of cyclic carbonates in the electrolyte.

[0143] This embodiment group is based on Example 1, except that the weight content of cyclic carbonates in the electrolyte is changed, as detailed in Table 1-1.

[0144] Table 1-1 - indicates that it does not exist.

[0145] Example 5 group

[0146] This set of examples illustrates the effects of changes in the weight content of carbonate additives in the electrolyte.

[0147] This embodiment group is based on Example 1, except that the weight content of carbonate additives in the electrolyte is changed, as detailed in Tables 1-2.

[0148] Example 6 group

[0149] This set of examples illustrates the effects that occur when L1+L2 changes.

[0150] This embodiment group is based on embodiment 1, except that L1+L2 is changed, as detailed in Table 1-2.

[0151] Table 1-2 - indicates that it does not exist.

[0152] Example 7 group

[0153] This set of examples illustrates the effects of changes in a / d.

[0154] This set of embodiments is based on Embodiment 1, except that a / d is changed, as detailed in Tables 1-3. Specifically, the energy density of the battery in Embodiment 7a is 180.6 Wh / kg; the energy density of the battery in Embodiment 7b is 181.7 Wh / kg; the energy density of the battery in Embodiment 7c is 184.3 Wh / kg; and the energy density of the battery in Embodiment 7d is 175.1 Wh / kg.

[0155] Example 8 group

[0156] This set of examples illustrates the effects of changes in I / S4.

[0157] This embodiment group is based on Embodiment 1, except that I / S4 is changed, as detailed in Tables 1-3.

[0158] Table 1-3

[0159] Example 9 group

[0160] This set of examples illustrates the effects of changes in lithium-ionized polyacrylate.

[0161] This embodiment group is based on Example 1, except that the lithium-ionized polyacrylate is changed, as detailed in Tables 1-4.

[0162] Example 10 group

[0163] This set of examples illustrates the effects of changing the ratio of the single-sided thickness of the negative electrode active layer to the single-sided thickness of the positive electrode active layer.

[0164] This embodiment group is based on Embodiment 1, except that the ratio of the single-sided thickness of the negative electrode active layer to the single-sided thickness of the positive electrode active layer is changed, as detailed in Tables 1-4.

[0165] Table 1-4

[0166] Comparative Example 1

[0167] The procedure was carried out in accordance with Example 1, except that no linear carboxylic acid esters were added to the electrolyte, as detailed in Tables 1-5.

[0168] Comparative Example 2

[0169] The procedure was carried out in accordance with Example 1, except that S3 / a > 0.4, as detailed in Tables 1-5.

[0170] Comparative Example 3

[0171] The procedure was carried out in accordance with Example 1, except that S3 / a < 0.025, as detailed in Tables 1-5.

[0172] Table 1-5

[0173] Test case

[0174] The batteries prepared in the examples and comparative examples were tested as follows:

[0175] (1) Low temperature cycling performance test

[0176] a) At -10℃, charge the battery after capacity testing to 3.65V using a constant current and constant voltage of 0.2C, with a cutoff current of 0.05C. Then discharge it to 2.5V using a constant current of 0.3C, and record the initial discharge capacity C0. b) Cycle the battery according to step a) for 800 cycles. Record the discharge capacity of the 800th cycle as C1. Calculate the capacity retention rate after 800 charge-discharge cycles using the following formula:

[0177] Cyclic capacity retention rate (%) = (C1 / C0) × 100%.

[0178] (2) High-temperature storage test

[0179] At 25℃, the thickness d1 of the battery before placement was measured using vernier calipers. The battery, after capacity testing, was charged to 3.65V using a constant current and constant voltage at 0.2C, with a cutoff current of 0.05C. Then, it was discharged to 2.5V using a constant current at 0.3C, and the initial discharge capacity C1 was recorded. The battery was then charged to 3.65V again using a constant current and constant voltage at 0.2C, maintaining 100% SOC. The battery was stored at 60℃ for 180 days. During this period, the battery was charged and discharged every 30 days. The charging and discharging steps were as follows: discharge to 2.5V using a constant current at 0.3C, record the remaining capacity C2, then charge the battery to 3.65V using a constant current and constant voltage at 0.2C, and repeat this cycle once more (the cycle was: discharge to 2.5V using a constant current at 0.3C, then charge to 3.65V using a constant current and constant voltage at 0.2C), maintaining 100% SOC. After 180 days, the thickness d2 of the battery was recorded.

[0180] 180D residual capacity retention rate = (C2 / C1) × 100%

[0181] 180D battery expansion rate = [(d2-d1) / d1] × 100%

[0182] The results are recorded in Table 2.

[0183] Table 2

[0184] As can be seen from Table 2, by comparing the comparative examples and the embodiments, it can be seen that the battery of the embodiment has a significantly improved low-temperature cycle capacity retention rate, a high high-temperature storage residual capacity retention rate, and a low high-temperature storage thickness expansion rate. This indicates that by adding linear carboxylic acid esters to the electrolyte and simultaneously controlling the weight ratio of linear carboxylic acid esters in the electrolyte to the area of ​​the first surface and the ratio of the area of ​​the first surface to the thickness of the first surface, the battery achieves both high low-temperature cycle performance and low thickness expansion rate.

[0185] The preferred embodiments of this disclosure have been described in detail above; however, this disclosure is not limited thereto. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in this disclosure and are all within the protection scope of this disclosure.

Claims

1. A battery, characterized in that, The battery includes a cell, an electrolyte, and a casing. The cell and the electrolyte are located within a space formed by the casing. The casing includes a first side along the thickness direction, a second side along the width direction, and a third side along the height direction. The second side and the third side form a first surface of the casing, which is the surface with the largest area among all surfaces of the casing. The electrolyte includes a linear carboxylic acid ester. The battery simultaneously satisfies the following relationships: 0.025 ≤ S³ / a ≤ 0.4, 150 ≤ a / d ≤ 450, where a is the area of ​​the first surface in cm². 2 d is the thickness of the first surface in mm, and S3 is the weight content of the linear carboxylic acid ester in the electrolyte in %.

2. The battery according to claim 1, wherein, The battery simultaneously satisfies the following relationships: 0.05≤S3 / a≤0.3, 200≤a / d≤300; And / or, the area of ​​the first surface is 150 cm². 2 -300cm 2 ; And / or, the thickness of the first surface is 0.45mm-0.95mm; And / or, the linear carboxylic acid ester in the electrolyte has a weight content of 5%-70%, preferably 10%-50%.

3. The battery according to claim 1 or 2, wherein, The outer casing is made of aluminum metal; And / or, the length of the second side of the outer casing along the width direction is 12cm-30cm; And / or, the length of the third side of the outer casing along the height direction is 8cm-15cm; And / or, the length of the first side of the outer shell along the thickness direction is 3cm-7cm.

4. The battery according to any one of claims 1-3, wherein, The linear carboxylic acid ester includes one or more of the following compounds, either fluorinated or unsubstituted: ethyl acetate, methyl propionate, propyl formate, ethyl propionate, methyl acetate, ethyl formate, methyl formate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, ethyl fluoroacetate, ethyl difluoroacetate, and ethyl trifluoroacetate. And / or, the electrolyte further includes cyclic carbonates and linear carbonates.

5. The battery according to claim 4, wherein, The cyclic carbonates include one or more of ethylene carbonate, propylene carbonate, and butene carbonate; And / or, the linear carbonate comprises one or more of the following compounds, either fluorinated or unsubstituted: diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, 2,2-difluoroethyl methyl carbonate, and 2-fluoroethyl ethyl carbonate. And / or, the cyclic carbonate in the electrolyte contains 5%-40% by weight, preferably 10%-35%; And / or, the linear carbonate in the electrolyte has a weight content of 0.01%-70%, preferably 5%-50%; And / or, the weight ratio of the linear carboxylic acid ester to the linear carbonate is 0.1-20, preferably 0.5-10.

6. The battery according to any one of claims 1-5, wherein, The electrolyte also includes additives and electrolyte lithium salts. The additives include cyclic carbonate additives, heteroatom-containing organic additives, and lithium salt additives. The electrolyte lithium salts include inorganic lithium salts and organic lithium salts.

7. The battery according to claim 6, wherein, The carbonate additives include one or more of vinylene carbonate, vinyl ethylene carbonate, and fluoroethylene carbonate; And / or, the heteroatoms in the heteroatom-containing organic additive include one or more of N, S, P, B, Si and F, preferably, the heteroatom-containing organic additive includes one or more of tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, vinyl sulfate, methylene disulfonate and 1,3-propane sulpholactone. And / or, the lithium salt additives include one or more of lithium difluorophosphate, lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium difluorodi(oxalato)phosphate, lithium tetrafluorooxalatophosphate, lithium tetrafluoroborate, and lithium nitrate. And / or, the inorganic lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium difluorophosphate; And / or, the organic lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium bis(pentafluoroethyl)sulfonylimide, lithium bis(hexafluoroisopropyl)sulfonylimide, lithium difluorooxalateborate, and lithium difluorodioxalate phosphate.

8. The battery according to claim 6 or 7, wherein, Based on the total weight of the electrolyte, the weight content of the cyclic carbonate additive S4 is 0.5%-5%, the weight content of the heteroatom-containing organic additive is 0.01%-3%, the weight content of the lithium salt additive is 0.01%-3%, the weight content of the inorganic lithium salt L1 is 5%-20%, and the weight content of the organic lithium salt L2 is 0.01%-20%. And / or, the battery satisfies the following relationship: 8≤L1+L2≤20, where L1 is the weight content of inorganic lithium salt in the electrolyte, in %, and L2 is the weight content of organic lithium salt in the electrolyte, in %.

9. The battery according to any one of claims 1-8, wherein, The battery cell includes a negative electrode sheet, which includes a negative current collector and a negative active layer. The negative active layer includes a negative active material, which includes a graphite substrate and soft carbon coated on the surface of the graphite substrate.

10. The battery according to claim 9, wherein, The weight content of the soft carbon in the negative electrode active material is 1%-5%; And / or, in the Raman spectrum of the negative electrode, the average value of the ratio Id / Ig of the intensity of the D peak to the intensity of the G peak is 0.1-0.8; And / or, in the intensity distribution diagrams of the D peak and G peak obtained by surface scanning of the negative electrode active material using Raman, the numerical distributions satisfying 0.3≤Id / Ig≤0.6 are ≥90%, where Id is the intensity of the D peak in the Raman spectrum of the negative electrode active material, and Ig is the intensity of the G peak in the Raman spectrum of the negative electrode active material. And / or, the battery satisfies the following relationship: 4≤I / S4≤100, preferably 10≤I / S4≤50, where I is the average value of the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material, Id / Ig, and S4 is the weight content of the cyclic carbonate additive in the electrolyte.

11. The battery according to claim 9 or 10, wherein, The negative electrode active layer further includes a negative electrode binder, which includes one or more of the following: polyacrylate, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, and polyvinylidene fluoride. And / or, the particle size distribution Dv90 / Dv10 of the negative electrode active material is 2.3-3.5, and Dv10≥1μm; And / or, the negative electrode is at 2000cm -1 -2500cm -1 Infrared characteristic peaks are present.

12. The battery according to claim 11, wherein, The polyacrylate is a lithium-ionized polyacrylate, comprising lithium and ester-containing side chains. Based on the total weight of the lithium-ionized polyacrylate, the lithium content is 1.5%-4% by weight, and the ester-containing side chains contain 10%-45% by weight. And / or, the glass transition temperature of the lithium-ionized polyacrylate is 50°C-120°C.

13. The battery according to any one of claims 9-12, wherein, The thickness of the negative electrode active layer on one side is 40μm-100μm, preferably 50μm-90μm; And / or, the thickness of one side of the positive electrode active layer is 50μm-120μm, preferably 60μm-100μm; And / or, the ratio of the single-sided thickness of the positive electrode active layer to the single-sided thickness of the negative electrode active layer is 1:(0.8-5), preferably 1:(1-3).

14. The battery according to any one of claims 1-13, wherein, An explosion-proof valve is provided on the surface of the outer casing; Preferably, the projected area of ​​the explosion-proof valve on the surface of the housing is 50 mm². 2 -2000mm 2 .

15. The battery according to any one of claims 1-14, wherein, The battery is a lithium-ion rechargeable battery.

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