Batteries and their manufacturing methods, battery packs and electrical equipment

Abstract

This invention discloses a battery, its preparation method, battery pack, and electrical device. The battery includes: a negative electrode active material; and an SEI film, wherein the SEI film coats at least a portion of the surface of the negative electrode active material. The XPS spectrum of at least a portion of the SEI film adjacent to the surface of the negative electrode active material shows 45%≤C≤70%, 12%≤O≤20%, and 7%≤F≤15%. According to the battery of this invention, by limiting the content of C, O, and F in the XPS spectrum of at least a portion of the SEI film adjacent to the surface of the negative electrode active material, the layered structure and component distribution of the SEI film are controlled. This facilitates the synergistic optimization of the mechanical stability and ion transport efficiency of each portion of the SEI film, enabling the SEI film to achieve both low impedance and high interfacial stability. This helps to avoid the continuous decomposition of the electrolyte, thereby improving the kinetic performance of the battery and extending its high-temperature storage life.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a battery, its preparation method, battery pack, and electrical equipment. Background Technology

[0002] With the rapid development of new energy vehicles, energy storage systems, and other fields, the demand for high energy density, long cycle life, and low interfacial impedance in batteries is becoming increasingly urgent. As a key protective layer on the surface of the battery's negative electrode, the chemical composition and structural characteristics of the solid electrolyte interphase (SEI) directly affect the battery's initial coulombic efficiency, cycle stability, and interfacial kinetic performance.

[0003] In related technologies, the formation of the SEI film mainly depends on the reduction and decomposition of a single component in the electrolyte on the negative electrode surface. However, SEI films dominated by a single component have significant defects, namely, the SEI film is brittle and prone to cracking due to volume expansion, leading to continuous electrolyte decomposition, or the SEI film is prone to initiating side reactions and increasing interfacial impedance. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. Therefore, one objective of this invention is to provide a battery that synergistically optimizes the mechanical stability and ion transport efficiency of each SEI membrane component, helps avoid continuous electrolyte decomposition, thereby improving the battery's kinetic performance and extending its high-temperature storage life.

[0005] A battery according to a first aspect of the present invention includes: a negative electrode active material; an SEI film, the SEI film covering at least a portion of the surface of the negative electrode active material, wherein the XPS spectrum of at least a portion of the SEI film adjacent to the surface of the negative electrode active material shows 45%≤C≤70%, 12%≤O≤20%, and 7%≤F≤15%.

[0006] According to the battery of the present invention, by limiting the content of C, O and F in the XPS spectrum of a portion of the SEI film on the surface of the adjacent negative electrode active material, the layered structure and component distribution of the SEI film are regulated, which is beneficial to improve the synergistic optimization of the mechanical stability and ion transport efficiency of each part of the SEI film. This allows the SEI film to have both low impedance and high interfacial stability, which helps to avoid the continuous decomposition of the electrolyte, thereby improving the kinetic performance of the battery and extending the high-temperature storage life of the battery.

[0007] According to some embodiments of the present invention, the SEI film includes a first SEI film and a second SEI film, and the first SEI film and the second SEI film are sequentially disposed on the surface of the negative electrode active material. The first SEI film covers at least a portion of the surface of the negative electrode active material. Preferably, the first SEI film is an inorganic-organic composite SEI film, and the second SEI film is an organic SEI film.

[0008] According to some embodiments of the present invention, the thickness of the first SEI film is 5 nm to 50 nm; and / or, the thickness of the second SEI film is 30 nm to 200 nm.

[0009] According to some embodiments of the present invention, the battery further includes: an electrolyte comprising compound additives, wherein the compound additives include inorganic additives and organic additives, the inorganic additives and the organic additives forming the first SEI film in the SEI film, and the organic additives forming the second SEI film.

[0010] According to some embodiments of the present invention, the inorganic additives include water and / or fluorine-containing inorganic additives, and the organic additives include vinylene carbonate, fluoroethylene carbonate, and methane disulfonate.

[0011] According to some embodiments of the present invention, the electrolyte further includes: an electrolyte salt and a solvent, wherein the electrolyte salt comprises lithium hexafluorophosphate or a complex of lithium hexafluorophosphate and lithium difluorosulfonylimide; and / or the solvent comprises ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and ethyl acetate.

[0012] A method for preparing a battery according to a second aspect of the present invention includes the following steps: injecting an electrolyte into a battery cell and forming the battery, wherein the electrolyte includes inorganic additives and organic additives.

[0013] According to some embodiments of the present invention, the mass ratio of the inorganic additive to the organic additive is 1:(10-100); and / or, the mass percentage of the inorganic additive in the electrolyte is 0.05%-0.2%, and the mass percentage of the organic additive is 2%-5%.

[0014] According to some embodiments of the present invention, the electrolyte injection step includes a first injection and a second injection, wherein the first injection injects a first electrolyte and the second injection injects a second electrolyte, and the mass ratio of the first electrolyte to the second electrolyte is (75:25) to (85:15).

[0015] According to some embodiments of the present invention, the first electrolyte comprises, by mass percentage, 1% to 5% lithium hexafluorophosphate and 2.5% to 7.5% lithium bisfluorosulfonylimide; and / or, by mass percentage, the second electrolyte comprises 15% to 30% of the lithium hexafluorophosphate and 0% to 7.5% of the lithium bisfluorosulfonylimide.

[0016] A battery pack according to a third aspect of the present invention includes: a battery according to the first aspect of the present invention described above; or a battery prepared using the preparation method according to the second aspect of the present invention described above.

[0017] An electrical device according to a fourth aspect of the present invention includes: a battery according to the first aspect of the present invention described above; or a battery prepared using the preparation method of the second aspect of the present invention described above; or a battery pack according to the third aspect of the present invention described above.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a partial schematic diagram of a battery according to an embodiment of the present invention; Figure 2 This is a graph showing the elemental content of C in the first SEI film of a battery according to an embodiment of the present invention at different sputtering depths; Figure 3 This is a graph showing the elemental content of O in the first SEI film of a battery according to an embodiment of the present invention at different sputtering depths. Figure 4 This is a graph showing the elemental content of F in the first SEI film of a battery according to an embodiment of the present invention at different sputtering depths.

[0020] Figure label: 100: Battery; 1: Negative electrode active material; 2: SEI membrane; 21: First SEI membrane; 22: Second SEI membrane. Detailed Implementation

[0021] The following is for reference. Figures 1-4 A battery 100 according to an embodiment of the first aspect of the present invention is described.

[0022] like Figures 1-4 As shown, the battery 100 according to a first aspect embodiment of the present invention includes a negative electrode active material 1 and an SEI film 2.

[0023] Specifically, the SEI film 2 is coated on at least a portion of the surface of the negative electrode active material 1, and the XPS spectrum of at least a portion of the SEI film 2 adjacent to the surface of the negative electrode active material 1 shows that 45%≤C≤70%, 12%≤O≤20%, and 7%≤F≤15%.

[0024] For example, in Figure 1 In the example, the SEI film 2 is coated on at least part of the surface of the negative electrode active material 1. The SEI film 2 allows electrolyte lithium ions to shuttle freely and prevents the electrolyte from continuously reacting with the negative electrode active material 1, which is beneficial to improving the first coulombic efficiency, cycle stability and interfacial kinetic performance of the battery 100.

[0025] For example, in the XPS spectrum of the aforementioned partial SEI film 2, C can be any value from 45%, 50%, 55%, 60%, 65%, 70%, or a range of any combination of both. The carbon content of the aforementioned partial SEI film 2 is reasonable. The organic components in the SEI film 2 help improve the structural and performance stability of the SEI film 2, and also help improve the density of the aforementioned partial SEI film 2, thereby improving the stability of the SEI film 2 and preventing further decomposition of the electrolyte. This allows the aforementioned partial SEI film 2 to stably coat at least a portion of the surface of the negative electrode active material 1, improving the cycle life and safety of the battery 100.

[0026] For example, in the XPS spectrum of the aforementioned partial SEI film 2, O can be any value from 12%, 15%, 16%, 17%, 18%, 20%, or any combination of both. The oxygen content of the aforementioned partial SEI film 2 is reasonable, the stability of the SEI film 2 is good, and the interfacial reaction is excellent, so that the aforementioned partial SEI film 2 can be stably coated on the surface of the negative electrode active material 1.

[0027] For example, in the XPS spectrum of the aforementioned portion of the SEI membrane 2, F can be any value from 7%, 8%, 10%, 12%, 14%, 15%, or a range of any combination of both. The fluorine content in the aforementioned portion of the SEI membrane 2 is relatively reasonable, which is beneficial to increasing the proportion of inorganic components in the SEI membrane 2, promoting rapid ion transport in the SEI membrane 2, and thus reducing the interfacial impedance of the battery 100.

[0028] Therefore, the C, O and F contents of the SEI film 2 adjacent to the negative electrode active material 1 are relatively reasonable. They are interconnected and jointly reflect that the SEI film 2 has high ionic conductivity, strong corrosion resistance, low impedance, high stability and moderate flexibility, which can effectively suppress lithium dendrite growth and improve the safety and cycle life of battery 100.

[0029] At least a portion of the remaining SEI film 2 is disposed on the side of the aforementioned portion of SEI film 2 away from the negative electrode active material 1, thereby separating the electrolyte and the aforementioned portion of SEI film 2. During the operation of the battery 100, the SEI film 2 can balance the functions of electrolyte ion transport and electrolyte protection, effectively suppressing the occurrence of continuous side reactions, ensuring the long-term capacity stability of the battery 100, and improving the safety of the battery 100. Therefore, this application regulates the layered structure and component distribution of the SEI film 2, which is beneficial to improving the synergistic optimization of the mechanical stability and ion transport efficiency of each portion of the SEI film 2, so that the SEI film 2 has both low impedance and high interfacial stability, which helps to avoid the continuous decomposition of the electrolyte, thereby improving the kinetic performance of the battery 100 and extending the high-temperature storage life of the battery 100.

[0030] According to the battery 100 of the present invention, by limiting the content of C, O and F in the XPS spectrum of at least a portion of the SEI film 2 on the surface of the adjacent negative electrode active material 1, the layered structure and component distribution of the SEI film 2 are regulated, which is beneficial to improve the synergistic optimization of the mechanical stability and ion transport efficiency of each part of the SEI film 2, so that the SEI film 2 has both low impedance and high interfacial stability, which is beneficial to avoid the continuous decomposition of the electrolyte, thereby improving the kinetic performance of the battery 100 and extending the high-temperature storage life of the battery 100.

[0031] According to some embodiments of the present invention, with reference to Figure 1 The SEI film 2 includes a first SEI film 21 and a second SEI film 22. The first SEI film 21 and the second SEI film 22 are sequentially disposed on the surface of the negative electrode active material 1. The first SEI film 21 covers at least a portion of the surface of the negative electrode active material 1. The XPS spectrum of the first SEI film 21 shows 45%≤C≤70%, 12%≤O≤20%, and 7%≤F≤15%, which helps to effectively isolate the negative electrode active material 1 from the electrolyte, suppresses the excessive formation of the second SEI film 22 on the surface of the negative electrode active material 1, and thus helps to reduce the influence of the second SEI film 22. This maximizes the density of the SEI film 2 directly coated on the surface of the negative electrode active material 1, reduces interfacial impedance, and improves the stability and safety of the battery 100.

[0032] Preferably, the first SEI membrane 21 is an inorganic-organic composite SEI membrane. The first SEI membrane 21 combines the advantages of both inorganic and organic components. The inorganic components provide the first SEI membrane 21 with higher interfacial energy, stronger electrochemical stability, higher mechanical toughness, and higher ion diffusion kinetics, which are beneficial to improving the stability of the first SEI membrane 21. The organic components help to give the first SEI membrane 21 good flexibility and ion conductivity, which can promote the ion transport performance of the first SEI membrane 21. Therefore, using the inorganic-organic composite SEI membrane 21 as the first SEI membrane is beneficial to improving the structural density, rate performance, and cycle stability of the first SEI membrane 21.

[0033] The second SEI film 22 is an organic SEI film. The second SEI film 22 is composed of organic components, which makes the second SEI film 22 more flexible and able to adapt to the volume changes of the corresponding negative electrode during charging and discharging, thereby giving the battery 100 good interface stability.

[0034] The first SEI membrane 21 is disposed on the side of the second SEI membrane 22 adjacent to the negative electrode active material 1. Since the first SEI membrane 21 has both high ionic conductivity and strong flexibility, it helps to reduce the ion migration energy barrier, suppress volume deformation, effectively suppress the continuous decomposition of organic additives to form an ultra-thin and dense second SEI membrane 22, and block electrolyte penetration and side reactions.

[0035] Furthermore, the thickness of the first SEI film 21 is 5 nm to 50 nm. For example, the thickness of the first SEI film 21 can be any value from 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, and 50 nm, or a range of any combination of both. The aforementioned thickness of the first SEI film 21 is reasonable, and the first SEI film 21 is relatively complete and dense, giving it both good ion transport efficiency and stability. It can minimize the ion migration energy barrier and suppress volume deformation, and minimize the continuous decomposition of organic additives to form an ultrathin and dense second SEI film 22, thus blocking electrolyte penetration and side reactions.

[0036] The thickness of the second SEI film 22 is 30nm to 200nm. For example, the thickness of the second SEI film 22 can be any value from 30nm, 50nm, 100nm, 150nm, and 200nm, or a range of any combination of both. The thickness of the second SEI film 22 is relatively reasonable, resulting in better ion transport and facilitating the buffering of the volume expansion of the negative electrode active material 1. The second SEI film 22 is also relatively dense and uniform, leading to a more uniform current density distribution, which helps improve the safety of the battery 100.

[0037] The chemical composition of SEI film 2 can be measured by the changes in chemical composition at different depths of XPS sputtering: In actual production, the C, O, and F content in the SEI film 2 (which is only the first SEI film 21 at this time) of the negative electrode can be controlled after the formation step reaches a negative electrode potential of 1.0 V (2.55 V for a full cell 100). In its XPS spectrum, when the etching time is ≤0.3 min, the content of C, O, and F is 45%≤C≤70%, 12%≤O≤20%, and 7%≤F≤15%. The F content in the SEI film 2 (which is the first SEI film 21 and the second SEI film 22 at this time) of the negative electrode can be controlled after the formation step reaches a negative electrode potential of 0.05 V (3.8 V for a full cell 100). In its XPS spectrum, when the etching time is ≤0.3 min, the content of F is 7%≤F≤15%.

[0038] The thickness of SEI film 2 can be measured by high-resolution TEM (HRTEM): After the full cell has been formed to 3.8V, the cell is disassembled in the glove box to remove the negative electrode sheet. The negative electrode sheet is characterized using HRTEM (High-Resolution Transmission Electron Microscopy). The part attached to the surface of the negative electrode active material 1 is the first SEI film 21, and the part away from the surface of the negative electrode active material 1 is the second SEI film 22.

[0039] According to other embodiments of the present invention, the battery 100 further includes an electrolyte comprising a compound additive, wherein the compound additive comprises inorganic and organic additives, the inorganic and organic additives forming a first SEI film 21 in the SEI film 2, and the organic additives forming a second SEI film 22. The inorganic and organic additives in the electrolyte can synergistically form a film, i.e., form the first SEI film 21. Utilizing the staged decomposition characteristics of the inorganic and organic additives during the electrochemical reduction process, a first SEI film 21 rich in inorganic nanoparticles and flexible organic polymers is preferentially formed on the surface of the negative electrode active material 1. This film layer possesses both high ionic conductivity and strong flexibility, significantly reducing the ion migration barrier and suppressing volume deformation, inhibiting the continuous decomposition of the organic additives to form an ultra-thin and dense second SEI film 22, and blocking electrolyte penetration and side reactions. The aforementioned synergistic structure of the first SEI film 21 and the second SEI film 22 overcomes the performance contradiction between low impedance and high stability in traditional SEI films 2, thereby helping to extend the service life of the battery 100 and improve the power of the battery 100.

[0040] Furthermore, the inorganic additives include water and / or fluorine-containing inorganic additives (such as LiPO2F2). Water causes the electrolyte salt (e.g., LiPF6 and / or LiFSI) to hydrolyze to form hydrofluoric acid. Hydrofluoric acid, as an additive, undergoes a reduction reaction to generate lithium fluoride. This lithium fluoride, as a component of the first SEI film 21, enhances the density and structural stability of the first SEI film 21. Simultaneously, the inorganic additives can directly utilize impurities H2O within the battery cell to reduce and form inorganic SEI film structures such as LiF and Li2CO3, achieving both reduction and water removal. This method is low-cost and can appropriately reduce the energy consumption of battery cell baking. Fluorine-containing inorganic additives facilitate the formation of an inorganic SEI film component rich in lithium fluoride, increasing the inorganic content of the first SEI film 21 and improving its density and structural stability.

[0041] The organic additives include at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), and methylene disulfonate (MMDS). Vinylene carbonate (VC) exhibits excellent high and low temperature performance and anti-swelling properties, forming a stable SEI film 2 on the surface of the negative electrode active material 1, effectively inhibiting the decomposition of the electrolyte in the battery 100, thereby improving the charge-discharge efficiency and cycle life of the lithium battery 100. Fluoroethylene carbonate (FEC) also forms a stable SEI film 2, contributing to improved safety, reliability, and performance of the battery 100, significantly enhancing its rate performance, capacity retention, and low-temperature performance. Methylene disulfonate (MMDS) suppresses impedance rise, effectively improving cycle characteristics and increasing the cycle life of the battery 100. In addition, vinylene carbonate (VC), fluoroethylene carbonate (FEC), and methane disulfonate (MMDS) can all synergistically form a relatively dense first SEI film 21 with inorganic additives. At the same time, the above-mentioned organic substances have similar potentials to inorganic additives (such as water) and have high reactivity, making it easy to preferentially form the first SEI film 21 on the surface of the negative electrode active material 1 first, and then form the second SEI film 22 through the above-mentioned organic additives.

[0042] According to further embodiments of the invention, the electrolyte further includes an electrolyte salt and a solvent. The electrolyte salt provides the electrolyte ions (e.g., Li) required for the charging and discharging of the battery 100. + The solvent serves to dissolve the electrolyte salt and construct ion transport channels. The selection and ratio of the two directly determine the ionic conductivity, chemical stability, and compatibility with the electrodes of the electrolyte, thereby affecting the overall performance of the battery 100.

[0043] The electrolyte salt includes lithium hexafluorophosphate or a complex of lithium hexafluorophosphate and lithium difluorosulfonylimide. Lithium hexafluorophosphate provides a high concentration of lithium ions to meet the ion transport requirements during 100% charge and discharge of the battery, while the PF6 generated by the dissociation of lithium hexafluorophosphate... -It participates in the negative electrode surface reaction, generating LiF (a stable inorganic component in the first SEI film 21), improving the density and corrosion resistance of the SEI film 2. Lithium difluorosulfonylimide has good thermal stability, a high decomposition temperature, and can generate hydrofluoric acid through hydrolysis, with high ionic conductivity. Therefore, lithium hexafluorophosphate or a complex of lithium hexafluorophosphate and lithium difluorosulfonylimide can react with inorganic and organic additives to form a relatively stable first SEI film 21 and / or second SEI film 22.

[0044] The solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and ethyl acetate (EA). Ethyl carbonate (EC) has an extremely strong solubility for polar substances; due to its high boiling point, it can dissolve sparingly soluble substances at relatively high temperatures and is not prone to concentration changes due to volatilization, making it suitable for dissolving lithium salts and providing ion conduction channels. Ethyl methyl carbonate (EMC) has good solubility and, due to the presence of methyl and ethyl groups in its molecule, exhibits excellent compatibility with both polar solvents (such as EC) and non-polar solvents (such as EA), making it an ideal mixed solvent component. Dimethyl carbonate (DMC) has good chemical stability due to the presence of carbonate groups in its molecule. Ethyl acetate (EA) has a broad solubility spectrum, which is beneficial for meeting the needs of dissolving electrolyte salts, etc. Preferably, the above components are combined to reduce electrolyte viscosity, improve ion mobility, balance high and low temperature performance, and maintain good conductivity even at low temperatures.

[0045] The polarity, boiling point, and viscosity of the above solvents can be adjusted by mixing and compounding to meet specific process requirements.

[0046] The battery 100 also includes a housing, and the battery cells are disposed within the housing.

[0047] The method for preparing the battery 100 according to a second aspect embodiment of the present invention includes the following steps: An electrolyte is injected into the cell to form a battery 100, wherein the electrolyte includes inorganic additives and organic additives.

[0048] According to the method for preparing the battery 100 of the present invention, the preparation method is relatively simple, which makes the preparation efficiency of the battery 100 high, thereby improving the market competitiveness of the battery 100 and reducing the production cost of the battery 100.

[0049] In actual production, the C, O, and F content in the SEI film 2 (which is only the first SEI film 21 at this time) of the negative electrode can be controlled after the formation step reaches a negative electrode potential of 1.0 V (2.55 V for a full cell 100). In its XPS spectrum, when the etching time is ≤0.3 min, the content of C, O, and F is 45%≤C≤70%, 12%≤O≤20%, and 7%≤F≤15%. The F content in the SEI film 2 (which is the first SEI film 21 and the second SEI film 22 at this time) of the negative electrode can be controlled after the formation step reaches a negative electrode potential of 0.05 V (3.8 V for a full cell 100). In its XPS spectrum, when the etching time is ≤0.3 min, the content of F is 7%≤F≤15%.

[0050] Furthermore, the mass ratio of inorganic additives to organic additives is 1:(10-100). For example, the mass percentage of inorganic and organic additives can be any value from 1:10, 1:30, 1:50, 1:60, 1:80, 1:100, or any combination thereof. Therefore, the mass percentage of inorganic and organic additives is relatively reasonable, which facilitates the sufficient reaction of the inorganic and organic additives to form the first SEI film 21, and subsequently the second SEI film 22, thus improving the low impedance, high stability, and moderate flexibility of the SEI film 2, and enhancing the safety and cycle life of the battery 100.

[0051] The mass percentage of inorganic additives in the electrolyte is 0.05% to 0.2%. For example, the mass percentage of inorganic additives in the electrolyte can be any value from 0.05%, 0.07%, 0.09%, 0.1%, 0.15%, and 0.2%, or a range of any combination of both. Therefore, the mass percentage of inorganic additives in the electrolyte is relatively reasonable, which is beneficial for forming a stable and dense first SEI film 21 while avoiding a large thickness of the first SEI film 21 from significantly degrading the performance of the battery 100 in multiple dimensions such as ion transport, interfacial impedance, and cycle stability.

[0052] For example, when the content of inorganic additives, such as water, is too low, the viscosity of the electrolyte increases significantly at low temperatures, which easily increases the low-temperature impedance performance of battery 100, thus easily causing the discharge performance of battery 100 to degrade, resulting in a decrease in charge-discharge efficiency and a reduction in the cycle life of battery 100. When the content of inorganic additives, such as water, is too high, while reducing the low-temperature impedance of battery 100, it also easily affects the storage performance of the battery, thereby affecting the battery's performance and lifespan. For example, electrolytes with too low viscosity are more likely to penetrate and accelerate the destruction of SEI film 2, leading to irreversible ion consumption and accelerating battery capacity decay. In addition, both of the above situations can easily affect the percentage of C, O, and / or F in the XPS spectrum of SEI film 2 to some extent, making it difficult for battery 100 to simultaneously achieve low-temperature impedance performance and high interfacial stability, thus affecting the performance and lifespan of battery 100.

[0053] The mass percentage of organic additives is 2% to 5%. For example, the mass percentage of organic additives can be any value from 2%, 2.3%, 3%, 3.5%, 4%, 5%, or a range of any combination of both. A reasonable mass percentage of organic additives in the electrolyte facilitates the formation of a more stable and uniform second SEI film 22 after the formation of the first SEI film 21, thereby improving the ion transport efficiency of the SEI film 2.

[0054] According to some embodiments of the present invention, the electrolyte injection step includes a primary injection and a secondary injection. Dividing the injection into two separate processes allows for specific adjustments to the conditions of the primary and secondary injections, increasing the specificity of the SEI membrane 2 and thus meeting the needs of the battery 100.

[0055] The first injection injects the first electrolyte, and the second injection injects the second electrolyte.

[0056] According to some embodiments of the present invention, the mass ratio of the first electrolyte to the second electrolyte is (75:25) to (85:15). For example, the mass ratio of the first electrolyte to the second electrolyte can be any value from 75:25, 80:20, 85:15, or any range of both. Therefore, the mass ratio of the first electrolyte to the second electrolyte is reasonable, facilitating rapid wetting of the electrolyte within the cell after a single injection, promoting uniform formation of the SEI film 2, and preventing excessive electrolyte overflow.

[0057] According to some specific embodiments of the present invention, the first electrolyte comprises, by mass percentage, 1% to 5% lithium hexafluorophosphate and 2.5% to 7.5% lithium bisfluorosulfonylimide. Exemplarily, by mass percentage, the lithium hexafluorophosphate in the first electrolyte can be any value from 1%, 1.5%, 2%, 3%, 4%, 5%, or a range of any combination thereof. Exemplarily, by mass percentage, the lithium bisfluorosulfonylimide in the first electrolyte can be any value from 2.5%, 3.5%, 4%, 5%, 6%, 6.5%, 7.5%, or a range of any combination thereof.

[0058] The second electrolyte comprises, by mass percentage, 15% to 30% lithium hexafluorophosphate and 0% to 7.5% lithium bisfluorosulfonyl imide. For example, the lithium hexafluorophosphate in the second electrolyte may be any value from 15%, 18%, 20%, 24%, 28%, 30%, or any combination thereof, by mass percentage. For example, the lithium bisfluorosulfonyl imide in the second electrolyte may be any value from 0%, 2.5%, 3%, 4%, 5%, 6%, 6.5%, 7.5%, or any combination thereof, by mass percentage.

[0059] Therefore, the concentration of the first electrolyte salt in the first electrolyte and the concentration of the second electrolyte salt in the second electrolyte are relatively reasonable. This is conducive to making full use of the first electrolyte with a lower concentration of first electrolyte salt introduced in the first injection to avoid excessive hydrolysis of electrolyte salt, and the second electrolyte with a higher concentration of second electrolyte salt introduced in the second injection to compensate for electronic conductivity. The step-by-step injection realizes the advantageous utilization of water and reduces the occurrence of side reactions of electrolyte hydrolysis.

[0060] According to some specific embodiments of the present invention, the mass ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide is 1:(0.1 to 0.8). Exemplarily, the mass percentage of lithium hexafluorophosphate and lithium difluorosulfonylimide can be any value from 1:0.1, 1:0.2, 1:0.5, 1:0.7, 1:0.8, or a range of any combination thereof. Thus, the mass percentage of the two electrolyte salts in the electrolyte is relatively reasonable, resulting in better power characteristics of the electrolyte. The addition of an appropriate amount of lithium difluorosulfonylimide can significantly improve the conductivity and ion transport number of the electrolyte, improve the reversibility of the electrode ion insertion / extraction reaction, and reduce the electrode interface impedance. A reasonable ratio of lithium hexafluorophosphate and lithium difluorosulfonylimide can improve the stability of the battery 100 under high-temperature conditions, reduce thermal decomposition and gas generation, extend the high-temperature cycle life of the battery 100, and further help reduce energy loss during the charging and discharging process of the battery 100, thereby improving the charging and discharging efficiency of the battery 100.

[0061] In actual production, for example, the specific preparation method of battery 100 includes the following steps: (1) Moisture control: The initial water content of the battery cell is controlled by baking the battery cell, or the corresponding water content is introduced directly into the first electrolyte of the first injection. (2) First electrolyte injection: The cell is injected with electrolyte once, the amount of which is 75% of the total electrolyte, and aged at 45°C for 36 hours; (3) Formation: The cell is formed by charging with a small current to form a film, and the formation is stopped at 40% SOC; (4) Secondary electrolyte injection: The battery cell is injected with electrolyte twice, with the amount of electrolyte being 25% of the total electrolyte volume. Then it is fully charged, aged, and tested for capacity.

[0062] In summary, the battery 100 of the first aspect of this application, or the battery 100 prepared by the above-described preparation method, has the following technical effects: (1) By synergistically forming an organic / inorganic additive system with complementary reactivity, an organic and inorganic composite first SEI film 21 is formed, and the continuous decomposition of organic additives is inhibited to form an ultrathin and dense organic second SEI film 22, thus taking into account both low impedance and high stability. (2) The inorganic additives directly use the impurities H2O in the battery cell to reduce and form inorganic SEI film structures such as LiF and Li2CO3, while achieving reduction and water removal. This is low-cost and can appropriately reduce the energy consumption of battery cell baking. (3) The first electrolyte with a lower concentration of LiPF6 is introduced in the first injection to avoid excessive hydrolysis of electrolyte salts. The second electrolyte with a higher concentration of LiPF6 is introduced in the second injection to compensate for electronic conductivity. The step-by-step injection realizes the advantageous utilization of water and avoids side reactions of electrolyte hydrolysis. Thus, the present invention achieves targeted regulation of the microstructure of SEI film 2, taking into account both long lifetime and low impedance.

[0063] A battery pack (not shown) according to a third aspect embodiment of the present invention includes: the battery 100 of the first aspect embodiment of the present invention described above; or the battery 100 prepared by the preparation method of the second aspect embodiment of the present invention described above.

[0064] According to the battery pack of the present invention, by using the battery 100 described above, the reliability of the battery pack can be effectively improved, the cycle life of the battery pack can be improved, the temperature adaptability and rate tolerance of the battery pack can be improved, and the safety of the battery pack can be enhanced, reducing the risk of thermal runaway.

[0065] An electrical device (not shown) according to a fourth aspect embodiment of the present invention includes: a battery 100 of the first aspect embodiment of the present invention described above; or a battery 100 prepared by the preparation method of the second aspect embodiment of the present invention described above; or a battery pack of the third aspect embodiment of the present invention described above.

[0066] Electrical equipment can include vehicles, aircraft, ferries, computers, energy storage cabinets, etc.

[0067] According to the embodiments of the present invention, the use of the above-mentioned battery 100 or battery pack in the electrical equipment is beneficial to extending the battery life and service life of the electrical equipment, reducing replacement costs, and also helps to optimize the operating condition adaptability of the electrical equipment and broaden the application scenarios.

[0068] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known to others. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0069] Example 1 In this example, a lithium iron phosphate-graphite system cell with a water content of 0.15% relative to the electrolyte mass was subjected to a first electrolyte injection. The composition of the first electrolyte injection was 2% LiPF6, 6.8% LiFSI, 3% VC, and EC:EMC:DMC:EA = 30:20:20:30. After aging at 45℃ for 36 hours to reach 40% SOC, a second electrolyte injection was performed. The LiPF6 content in the second electrolyte injection was 25%. After being fully charged a second time, the lithium-ion battery 100 was produced after aging, capacity testing, and self-discharge testing.

[0070] Example 2 In this example, a lithium iron phosphate-graphite system cell with a water content of 0.2% relative to the electrolyte mass was subjected to a first electrolyte injection. The composition of the first electrolyte injection was 2% LiPF6, 6.8% LiFSI, 2% VC, and EC:EMC:DMC:EA = 30:20:20:30. After aging at 45℃ for 36 hours to reach 40% SOC, a second electrolyte injection was performed. The LiPF6 content in the second electrolyte injection was 25%. After being fully charged a second time, the cell underwent aging, capacity testing, and self-discharge testing before being produced as a lithium-ion battery 100.

[0071] Example 3 In this example, a lithium iron phosphate-graphite system cell with a water content of 0.2% relative to the electrolyte mass was subjected to a first electrolyte injection. The composition of the first electrolyte injection was 2% LiPF6, 6.8% LiFSI, 5% VC, and EC:EMC:DMC:EA = 30:20:20:30. After aging at 45℃ for 36 hours to reach 40% SOC, a second electrolyte injection was performed. The LiPF6 content in the second electrolyte injection was 25%. After being fully charged a second time, the cell underwent aging, capacity testing, and self-discharge testing before being produced as a lithium-ion battery 100.

[0072] Example 4 In this example, a lithium iron phosphate-graphite system cell with a water content of 0.05% relative to the electrolyte mass was subjected to a first electrolyte injection. The composition of the first electrolyte injection was 2% LiPF6, 6.8% LiFSI, 5% VC, and EC:EMC:DMC:EA = 30:20:20:30. After aging at 45℃ for 36 hours to reach 40% SOC, a second electrolyte injection was performed. The LiPF6 content in the second electrolyte injection was 25%. After being fully charged a second time, the cell underwent aging, capacity testing, and self-discharge testing before being produced as a lithium-ion battery 100.

[0073] Example 5 In this example, a lithium iron phosphate-graphite system cell with a water content of 0.05% relative to the electrolyte mass was subjected to a first electrolyte injection. The composition of the first electrolyte injection was 2% LiPF6, 6.8% LiFSI, 2% VC, and EC:EMC:DMC:EA = 30:20:20:30. After aging at 45℃ for 36 hours to reach 40% SOC, a second electrolyte injection was performed. The LiPF6 content in the second electrolyte injection was 25%. After being fully charged a second time, the lithium-ion battery 100 was produced after aging, capacity testing, and self-discharge testing.

[0074] Example 6 In this example, a lithium iron phosphate-graphite system cell with a water content of 0.15% relative to the electrolyte mass was subjected to a first electrolyte injection. The composition of the first electrolyte injection was 5% LiPF6, 5% LiFSI, 3% VC, and EC:EMC:DMC:EA = 30:20:20:30. After aging at 45℃ for 36 hours to reach 40% SOC, a second electrolyte injection was performed. The LiPF6 content in the second electrolyte injection was 22%. After being fully charged a second time, the lithium-ion battery 100 was produced after aging, capacity testing, and self-discharge testing.

[0075] Comparative Example 1 A lithium iron phosphate-graphite system cell with a water content ≤0.001% relative to the electrolyte mass was first injected with electrolyte. The composition of the first-injection electrolyte was 3% LiPF6, 6% LiFSI, 3% VC, and EC:EMC:DMC:EA = 30:20:20:30. After aging at 45℃ for 36 h to reach 40% SOC, a second-injection electrolyte was performed, with a LiPF6 content of 25%. After being fully charged a second time, the lithium-ion battery 100 was produced after aging, capacity testing, and self-discharge testing.

[0076] Comparative Example 2 A lithium iron phosphate-graphite system cell with a water content of 0.3% relative to the electrolyte mass was first injected with electrolyte. The composition of the first-injection electrolyte was 5% LiPF6, 5% LiFSI, 1.5% VC, and EC:EMC:DMC:EA = 30:20:20:30. After aging at 45℃ for 36 h to reach 40% SOC, a second-injection electrolyte was performed, with a LiPF6 content of 22%. After being fully charged a second time, the lithium-ion battery 100 was produced after aging, capacity testing, and self-discharge testing.

[0077] Comparative Example 3 A lithium iron phosphate-graphite system cell with a water content of 0.2% relative to the electrolyte mass was injected with electrolyte containing 8% LiPF6, 5% LiFSI, 2% VC, and EC:EMC:DMC:EA = 30:20:20:30. After aging at 45℃ for 36 h, the cells were formed and fully charged. Following aging, capacity testing, and self-discharge testing, the resulting lithium-ion battery 100 was produced.

[0078] Performance testing (1) Element content detection in the first SEI film 21 and the second SEI film 22: The negative electrode interface in the cell after the battery is taken off the production line was tested by XPS according to GB / T 28893-2024. The cell was formed until the negative electrode potential was 1.0V and then the cell was disassembled in the glove box to remove the negative electrode. After cleaning with anhydrous DMC solvent, a 1×1cm electrode sheet was cut and the element content in the first SEI film 21 was tested by XPS. Another cell was formed until it was fully charged. The cell was disassembled in the glove box to remove the negative electrode. After cleaning with anhydrous DMC solvent, a 1×1cm electrode sheet was cut and the element content in the second SEI film 22 was tested by XPS. The formula for calculating the content of each element in the SEI is: Ni=Ci / (C1+C2+C3+Ci+……+Cn), that is, the percentage of element i in the total mass of all elements.

[0079] (2) Low temperature impedance test at -10℃ After the lithium-ion battery 100 is discharged and charged to 50% SOC at room temperature, it is then placed in a -10℃ constant temperature chamber for 6 hours and discharged at 1.5C for 30 seconds. The voltage before the start of discharge is V1 and the voltage at the end of the 30 seconds of discharge is V2. The impedance DCIR = (V1-V2) / I is calculated.

[0080] (3) 168D retention rate during high-temperature storage at 60℃ At 25℃, the cells were fully charged to 3.8V using a constant current and voltage of 0.33C. After resting, they were discharged to 2V using a constant current of 0.33C. This process was repeated three times. Then, the cells were fully charged to 3.8V using a constant current and voltage of 0.33C. The capacity of the third discharge cycle was recorded as C0. The cells were then stored in a 60℃ forced-air drying oven. Every 28 days, the cells were taken out and subjected to three charge-discharge tests following the above steps. The capacity of the third discharge cycle after 168 days of storage was recorded as C. The capacity retention rate R was calculated as R = C / C0 × 100%.

[0081] Table 1. Parameters of the Examples and Comparative Examples

[0082] Table 2 Test results of the examples and comparative examples

[0083] Test Result Analysis Referring to Tables 1 and 2, compared with Comparative Examples 1 and 3, Examples 1-6 have better low-temperature impedance performance at -10℃, and at the same time, they have better capacity recovery rate at 60℃ for 168D storage. Therefore, when the XPS spectrum of the first SEI film 21 shows 45%≤C≤70%, 12%≤O≤20%, and 7%≤F≤15%, it helps the battery 100 to have both lower low-temperature impedance performance and higher capacity recovery rate.

[0084] Other configurations and operations of the battery 100, battery pack, and electrical equipment according to embodiments of the present invention are known to those skilled in the art and will not be described in detail here.

[0085] Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0086] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0087] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A battery, characterized in that, include: Negative electrode active material; The SEI film covers at least a portion of the surface of the negative electrode active material, and the XPS spectrum of at least a portion of the SEI film adjacent to the surface of the negative electrode active material shows 45%≤C≤70%, 12%≤O≤20%, and 7%≤F≤15%.

2. The battery according to claim 1, characterized in that, The SEI film includes a first SEI film and a second SEI film. The first SEI film and the second SEI film are sequentially disposed on the surface of the negative electrode active material. The first SEI film covers at least a portion of the surface of the negative electrode active material. Preferably, the first SEI membrane is an inorganic-organic composite SEI membrane, and the second SEI membrane is an organic SEI membrane.

3. The battery according to claim 2, characterized in that, The thickness of the first SEI film is 5 nm to 50 nm; and / or, The thickness of the second SEI film is 30nm to 200nm.

4. The battery according to claim 2 or 3, characterized in that, Also includes: An electrolyte comprising compounded additives, wherein the compounded additives include inorganic additives and organic additives, wherein the inorganic additives and the organic additives form the first SEI membrane in the SEI membrane, and the organic additives form the second SEI membrane.

5. The battery according to claim 4, characterized in that, The inorganic additives include water and / or fluorine-containing inorganic additives. The organic additives include at least one of vinylene carbonate, fluoroethylene carbonate, and methane disulfonate.

6. The battery according to claim 4, characterized in that, The electrolyte also includes: electrolyte salt and solvent. The electrolyte salt comprises lithium hexafluorophosphate or a complex of lithium hexafluorophosphate and lithium difluorosulfonylimide; and / or, Solvents include ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and ethyl acetate.

7. A method for preparing a battery according to any one of claims 1-6, characterized in that, Includes the following steps: The battery is prepared by injecting an electrolyte into a cell and forming it, wherein the electrolyte includes inorganic additives and organic additives.

8. The preparation method according to claim 7, characterized in that, The mass ratio of the inorganic additive to the organic additive is 1:(10-100); and / or, The inorganic additive in the electrolyte has a mass percentage of 0.05% to 0.2%, and the organic additive has a mass percentage of 2% to 5%.

9. The preparation method according to claim 7, characterized in that, The electrolyte injection step includes a primary injection and a secondary injection. The first injection injects the first electrolyte, and the second injection injects the second electrolyte. The mass ratio of the first electrolyte to the second electrolyte is (75:25) to (85:15).

10. The preparation method according to any one of claims 7-9, characterized in that, The first electrolyte comprises, by weight percentage, 1%–5% lithium hexafluorophosphate and 2.5%–7.5% lithium bis(fluorosulfonyl)imide; and / or, The second electrolyte comprises, by mass percentage, 15% to 30% of the lithium hexafluorophosphate and 0% to 7.5% of the lithium difluorosulfonylimide.

11. A battery pack, characterized in that, include: The battery according to any one of claims 1-6; or the battery prepared by the preparation method according to any one of claims 7-10.

12. An electrical appliance, characterized in that, include: The battery according to any one of claims 1-6; or the battery prepared by the preparation method according to any one of claims 7-10; Or the battery pack as described in claim 11.

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