Electrolyte additive, electrolyte and battery

Abstract

The invention discloses an electrolyte additive, an electrolyte and a battery. The electrolyte additive comprises a first additive and a second additive; the first additive comprises organic lithium borate, and the organic lithium borate comprises at least one of the following components; the second additive comprises at least one of vinylene carbonate, fluoroethylene carbonate and vinylethylene carbonate; the mass ratio of the first additive to the second additive is 0.03-6.67. When the electrolyte additive provided by the invention is applied to an electrolytic tank, the battery impedance can be reduced, and the battery performance can be improved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to an electrolyte additive, an electrolyte, and a battery. Background Technology

[0002] Lithium-ion batteries, due to their advantages such as high energy density, high charging efficiency, and long cycle life, coupled with increasing market demand and policy guidance in recent years, have been vigorously promoted. As lithium-ion batteries are widely used in drones, mobile phones, new energy vehicles, and vehicle start-stop systems, the performance requirements for batteries are constantly increasing. An important component of lithium-ion batteries is the electrolyte, which conducts lithium ions between the positive and negative electrodes. Electrolytes typically consist of a composition of lithium salt electrolyte, organic solvents, and additives. Film-forming additives are a particularly important type of electrolyte additive.

[0003] Film-forming additives can typically form an SEI film on the negative electrode. This film is ion-conducting and electron-insulating, preventing direct contact between the electrolyte and electrode materials, slowing down interfacial reactions between them, and improving battery stability.

[0004] However, existing film-forming additives on the market, such as VC (ethylene carbonate), FEC (fluoroethylene carbonate), and VEC (ethylene ethylene carbonate) and their derivatives, all have drawbacks in forming SEI films, including high impedance and poor high-temperature stability, which negatively impact battery performance. This is especially true for power batteries, which place higher demands on fast charging and low-temperature performance. Therefore, research is needed on how to reduce battery impedance and further improve battery performance. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one object of this invention is to provide an electrolyte additive, an electrolyte, and a battery. This electrolyte additive reduces battery impedance and improves battery performance.

[0006] The first aspect of this application provides an electrolyte additive, comprising a first additive and a second additive;

[0007] The first additive includes lithium organoborate, which includes:

[0008]

[0009] At least one of Formula 3;

[0010] The second additive includes at least one of vinylene carbonate (“Vinylene Carbonate”, abbreviated as VC), fluoroethylene carbonate (“Fluoroethylene Carbonate”, abbreviated as FEC), and ethylene ethylene carbonate (“4-Vinyl-1,3-dioxolan-2-one”, abbreviated as VEC);

[0011] The mass ratio of the first additive to the second additive is 0.03 to 6.67.

[0012] The electrolyte additive provided in this application, through the synergistic effect of the first and second additives, constructs a stable SEI film with good ionic conductivity, reducing impedance and improving battery performance. When the electrolyte additive provided in this application is applied to a battery electrolyte, on the one hand, the organoborate lithium of the first additive readily loses an electron, forming a free radical. This free radical can react with the second additive in the electrolyte, forming a series of polycarbonate-like oligomers and polymers on the electrode surface. Furthermore, the fluorine atoms in these oligomers / polymers can be further replaced by other oxygen-containing substances, such as alcohols, alkanes, and carbonates. The fluorine atoms then react with Li+ to form LiF components. These additional reactions can produce three-dimensional polymerization products, thereby forming a relatively robust and thin passivation layer on the electrode surface. This can increase the chemical energy barrier for the self-polymerization of the second additive, inhibiting further decomposition of the carbonate solvent and LiPF6 salt, improving ionic conductivity while reducing interfacial impedance. In other words, the BO bonds are easily broken, participating in the polymerization reaction of the second additive, jointly constructing a more stable, mechanically elastic film with more Li+. + The organic polymer SEI film in the transmission channel suppresses excessive consumption of the second additive during battery formation, solving the problem of high initial impedance. Simultaneously, the remaining second additive can continuously repair the SEI film damaged by volume changes during long-term cycling. On the other hand, the inorganic components such as lithium oxide, lithium fluoride, and LiBO2 formed during the formation process of the first additive (organo-lithium borate) effectively isolate the organic polymer layer from direct contact with the highly active negative electrode material layer (such as the graphite layer). These materials have a wide electrochemical window and high Li... + Electrical conductivity is beneficial for protecting the electrode interface and facilitating rapid Li transport. + Furthermore, it can effectively suppress the growth of Li dendrites and the occurrence of other parasitic reactions on the electrode surface (such as lithium hexafluorophosphate decomposition and transition metal dissolution), thereby achieving excellent cycle performance.

[0013] The electrolyte additive provided in this application has a mass ratio of 0.03 to 6.67 between the first additive and the second additive. Meeting this condition promotes the synergistic effect of the first and second additives. If the mass ratio of the first additive to the second additive is too low, it is not conducive to the first additive providing sufficient Li. + The transmission channel increases impedance and affects fast charging performance; if the mass ratio of the first additive to the second additive is too high, it is not conducive to the complete dissolution of the first additive in the electrolyte, causing the electrolyte to become turbid and increasing the cost of battery use.

[0014] In some embodiments of this application, the mass ratio of the first additive to the second additive is 0.05 to 2.

[0015] In some embodiments of this application, the first additive is And / or, the second additive is vinylene carbonate.

[0016] In some embodiments of this application, a third additive is also included, which includes at least one of sulfonate additives, sulfate additives, borate additives, phosphate additives, acid anhydride additives, and nitrile additives.

[0017] In some embodiments of this application, the third additive satisfies at least one of the following:

[0018] (i) Sulfonate additives include at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone and methanedisulfonate methylene ester;

[0019] (ii) Sulfate additives include vinyl sulfate and At least one of them;

[0020] (iii) Boron ester additives include tris(trimethylsilane)boron esters;

[0021] (iv) Phosphate ester additives include at least one of tris(trimethylsilane) phosphate and tripropenyl phosphate;

[0022] (v) Anhydride additives include at least one of succinic anhydride, maleic anhydride, citrate anhydride, butyric anhydride and heptafluorobutyric anhydride;

[0023] (vi) Nitrile additives include at least one of butadionitrile, adiponitrile, 1,3,6-hexanetrionitrile, transbutenedionitrile, 1,2-bis(cyanoethoxy)ethane and 1,2,3-tris(2-cyanoethoxy)propane.

[0024] A second aspect of this application provides an electrolyte comprising the electrolyte additives described above.

[0025] The electrolyte provided in the second aspect of this application contains the aforementioned additives. Through the synergistic effect of the first and second additives, a stable SEI film is constructed, which has good ionic conductivity, can reduce impedance, and improve battery performance.

[0026] In some embodiments of this application, the mass percentage of the first additive is 0.1% to 3% based on the total mass of the electrolyte.

[0027] In some embodiments of this application, the mass percentage of the second additive is 0.1% to 5% based on the total mass of the electrolyte.

[0028] In some embodiments of this application, the mass percentage of the third additive is 0.1% to 5% based on the total mass of the electrolyte.

[0029] In some embodiments of this application, lithium salts and non-aqueous solvents are also included;

[0030] Optionally, the lithium salt includes at least one of LiPF6, LiAsF6, LiClO4, LiSO3CF3, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2 and LiPF4C2O4;

[0031] Optionally, the non-aqueous organic solvent is a cyclic organic solvent and / or a chain organic solvent.

[0032] A third aspect of this application provides a battery comprising the electrolyte described above.

[0033] The battery proposed in the third aspect of this application includes the electrolyte of the second aspect, and has low impedance, good low-temperature discharge performance and high-temperature storage performance, exhibiting good fast-charging performance.

[0034] In some embodiments of this application, positive electrode active material and negative electrode active material are also included;

[0035] Optionally, the positive electrode active material includes LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, and Li 1+a Mn 1- x M x O2, LiCo 1-x M x O2, LiFe 1-x M x PO4, Li2Mn 1-xAt least one of O4, wherein M includes at least one selected from Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, 0≤a≤0.2, 0≤x<1;

[0036] Optionally, the negative electrode active material includes at least one of graphite, silicon-carbon composite material, silicon material, lithium metal, and lithium titanate.

[0037] 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

[0038] Figure 1 This is the dQ / dV diagram provided in the embodiments of this application. Detailed Implementation

[0039] The embodiments of the present invention are described in detail below, and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0040] Currently, film-forming additives can typically form an SEI film on the negative electrode. This film is ion-conducting but electronically insulating, preventing direct contact between the electrolyte and electrode materials, slowing down interfacial reactions, and improving battery stability. However, existing film-forming additives such as VC, FEC, and VEC derivatives are prone to free radical polymerization, forming an SEI film rich in organic matter. This type of film composition has drawbacks such as uneven film surface thickness, poor high-temperature stability, and high impedance, which adversely affect the battery's high-temperature long lifespan, fast charging, and high-rate discharge.

[0041] Therefore, the first aspect of the embodiments of this application proposes an electrolyte additive, including a first additive and a second additive;

[0042] The first additive includes lithium organoborate, which includes:

[0043]

[0044] At least one of Formula 3;

[0045] The second additive includes at least one of vinylene carbonate, fluoroethylene carbonate and ethylene ethylene carbonate;

[0046] The mass ratio of the first additive to the second additive is 0.03 to 6.67.

[0047] The CAS number of the organoborate lithium shown in Formula 1 is 291541-84-9; the CAS number of the organoborate lithium shown in Formula 2 is 263880-01-9; and the CAS number of the organoborate lithium shown in Formula 3 is 220836-34-0.

[0048] The electrolyte additives provided in this application embodiment, through the synergistic effect of the first and second additives, construct a stable SEI film with good ionic conductivity, reducing impedance and improving battery performance. When applied to battery electrolytes, the first additive, lithium organoborate, readily loses an electron to form a free radical. This free radical can react with the second additive in the electrolyte, forming a series of polycarbonate-like oligomers and polymers on the electrode surface. Furthermore, the fluorine atoms in these oligomers / polymers can be further replaced by other oxygen-containing substances, such as alcohols, alkanes, and carbonates. The fluorine atoms then react with Li+ to form LiF components. These additional reactions can generate three-dimensional polymerization products, thereby forming a relatively robust and thin passivation layer on the electrode surface. This increases the chemical energy barrier for the self-polymerization of the second additive, inhibits further decomposition of the carbonate solvent and LiPF6 salt, and improves ionic conductivity while reducing interfacial impedance. In other words, the BO bonds are easily broken, participating in the polymerization reaction of the second additive to jointly construct a more stable, mechanically elastic film with more Li+. + The organic polymer SEI film in the transmission channel suppresses excessive consumption of the second additive during battery formation, solving the problem of high initial impedance. Simultaneously, the remaining second additive can continuously repair the SEI film damaged by volume changes during long-term cycling. On the other hand, the organoborate lithium of the first additive also forms inorganic components such as lithium oxide, lithium fluoride, and LiBO2 on the positive and negative electrode surfaces during formation, isolating the organic polymer layer from direct contact with the highly active negative electrode material layer (such as a graphite layer). These materials have a wide electrochemical window and high Li... + Electrical conductivity is beneficial for protecting the electrode interface and facilitating rapid Li transport. + Furthermore, it can effectively suppress the growth of Li dendrites and the occurrence of other parasitic reactions on the electrode surface (such as lithium hexafluorophosphate decomposition and transition metal dissolution), thereby achieving excellent cycle performance.

[0049] The electrolyte additives provided in this application have a mass ratio of 0.03 to 6.67 between the first additive and the second additive. Meeting this condition promotes the synergistic effect of the first and second additives and prevents the mass ratio from being too low, which would be detrimental to the first additive providing sufficient Li. +Increasing the impedance of the transmission channel is detrimental to improving fast charging performance and reduces the overall battery performance improvement effect. On the other hand, an excessively high mass ratio of the first additive to the second additive is also problematic, as it hinders the complete dissolution of the first additive in the electrolyte, causing electrolyte turbidity, which in turn reduces the overall battery performance improvement effect and increases battery usage costs. In specific examples, the mass ratios of the first and second additives are 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1. 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.61, 6.62, 6.63, 6.64, 6.65, 6.66, 6.67, etc.

[0050] In some embodiments of this application, the mass ratio of the first additive to the second additive is 0.05 to 2.

[0051] In this embodiment, the mass ratio of the first additive and the second additive satisfies the above conditions, which facilitates the synergistic effect of the first and second additives, constructing a stable SEI film with good ionic conductivity, reducing impedance, and improving battery performance. In specific examples, the mass ratio of the first additive and the second additive is 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, etc.

[0052] In some embodiments of this application, the first additive is And / or, the second additive is vinylene carbonate.

[0053] In this embodiment of the application, the first additive is It can decompose on the surface of the battery negative electrode to form a sufficiently stable SEI film containing boron and fluorine elements. This can effectively reduce the consumption of irreversible lithium ions in the battery, effectively weaken the transport resistance of lithium ions at low temperatures, increase the migration rate of lithium ions in the SEI film, and significantly reduce the free radicals at active sites in the electrolyte, thereby reducing the negative impact of free radicals at active sites and achieving excellent low-temperature discharge and cycle performance.

[0054] In this embodiment, the second additive is vinylene carbonate, which, as a negative electrode film-forming additive, can effectively suppress solvent molecule intercalation and battery gas expansion, thereby improving the battery's cycle performance and lifespan.

[0055] In some embodiments of this application, a third additive is also included, which includes at least one of sulfonate additives, sulfate additives, borate additives, phosphate additives, acid anhydride additives, and nitrile additives.

[0056] In this embodiment, while the first and second additives are used together as electrolyte additives, the addition of a third additive can further enhance the battery's performance under extreme environments (such as high temperature and high voltage). Based on the combined use of the first and second additives, the combined use of sulfonate and sulfate additives can further form S-containing inorganic lithium salts (such as lithium sulfate or alkyl sulfonate LiiOSO2-R) at the negative electrode interface, improving high-temperature performance; the combined use of borate and phosphate additives can avoid the influence of trace amounts of water in the electrolyte on the electrolyte, reducing the formation of HF and its damage to the interface film; the combined use of anhydride additives can further assist in film formation on the positive electrode surface, optimizing the composition of the CEI film; the combined use of nitrile additives can provide functional groups, complexing dissolved transition metals, reducing the deposition of dissolved transition metal ions on the negative electrode, and maintaining the overall stability of the battery.

[0057] Sulfonate additives, such as 1,3-propanesulfonate lactone and methanedisulfonate methylene ester, can form a stable CEI film (short for "Cathode Electrolyte Interphase") at the positive electrode, reducing the electrode / electrolyte interface impedance and improving the cycle stability and high-temperature performance of the battery.

[0058] Sulfate ester additives: such as vinyl sulfate (DTD) and A stable SEI film can be formed preferentially by a reduction reaction on the surface of the negative electrode, thereby improving the high-temperature characteristics and cycle characteristics of the battery.

[0059] Borate additives, such as tris(trimethylalkyl)borate (TMSB), form a protective film on the positive electrode surface, improving the battery's cycle stability and high-temperature and high-pressure resistance.

[0060] Phosphate ester additives, such as tris(trimethylalkyl) phosphate (TMSP), can form a uniform SEI film on the negative electrode, significantly improving coulombic efficiency and battery cycle stability.

[0061] Anhydride additives, such as succinic anhydride (SA), can construct a robust cathode-electrolyte interface (CEI) film on the electrode surface, effectively capturing HF / H2 and improving the high-temperature stability of the battery.

[0062] Nitrile additives, such as succinate (SN) and adiponitrile (ADN), can form a stable CEI film on the positive electrode, enhance the electrolyte's resistance to positive electrode oxidation, and improve the battery's high-voltage cycle life.

[0063] In some embodiments of this application, the third additive satisfies at least one of the following:

[0064] (i) Sulfonate additives include at least one of 1,3-propane sulfonate lactone (“1,3-Propane Sultone”, abbreviated as PS), 1,3-propene sulfonate lactone (“1,3-Propene sultone”, abbreviated as PST) and methylene methanedisulfonate (“Methylene Methanedisulfonate”, abbreviated as MMDS);

[0065] (ii) Sulfate ester additives include At least one of diethylene glycosulfate (DTD);

[0066] (iii) Boronate additives include tris(trimethylsilyl)borate (abbreviated as TMSB);

[0067] (iv) Phosphate additives include at least one of tris(trimethylsilyl) phosphate (TMSP) and triallyl phosphate (TAP);

[0068] (v) Anhydride additives include at least one of the following: succinic anhydride (SA), maleic anhydride (MA), citraconic anhydride (CA), butyric anhydride (BA), and heptafluorobutyric anhydride (HFBA);

[0069] (vi) Nitrile additives include at least one of the following: succinonitrile (SN), adiponitrile (ADN), 1,3,6-hexanetricarbonitrile (HTCN), fumaronitrile (Fumaronitrile), 1,2-bis(cyanoethoxy)ethane (DENE), and 1,2,3-tris(2-cyanoethoxy)propane (TCEP).

[0070] In this embodiment of the application, while the first additive and the second additive are used together as electrolyte additives, the addition of the third additive can further enhance the performance of the battery under extreme environments (such as high temperature and high voltage).

[0071] A second aspect of this application provides an electrolyte that includes the electrolyte additives proposed in the first aspect.

[0072] The electrolyte provided in the second aspect of this application contains the above-mentioned additives. Through the synergistic effect of the first and second additives, a stable SEI film is constructed, which has good ionic conductivity, can reduce impedance, and improve battery performance.

[0073] In some embodiments of this application, the mass percentage of the first additive is 0.1% to 3% based on the total mass of the electrolyte. Specific examples show that the mass percentage of the first additive is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, etc. In electrolytes, appropriately increasing the content of the primary additive is beneficial for improving the coulombic efficiency and cycle stability of the battery under different ambient temperatures. However, if its addition exceeds the upper limit of its solubility in the electrolyte, it may adversely affect the performance of the electrolyte, thereby impacting the improvement of battery performance. By controlling the content of the primary additive to meet the given range, it is beneficial to further avoid the risk of the primary additive exceeding its solubility limit in the electrolyte, allowing the electrolyte to achieve a better improvement effect on battery performance with a lower amount of primary additive. This, in turn, is beneficial for further improving the coulombic efficiency and cycle stability of the battery under different ambient temperatures.

[0074] Furthermore, based on the total mass of the electrolyte, the mass percentage of the first additive is 0.1% to 1%.

[0075] In some embodiments of this application, the mass percentage of the second additive is 0.1% to 5% based on the total mass of the electrolyte. Specifically, the mass percentage of the second additive is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2 ... The recommended dosages are 0.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, and 5%. Controlling the amount of the second additive within the given range not only helps to improve the interfacial stability and room-temperature cycling performance of the negative electrode while maintaining a lower total additive dosage, but also helps to further reduce the risk of a larger SEI film thickness and the resulting increase in interfacial impedance and decrease in ion transport performance caused by excessive carbonate additives.

[0076] Furthermore, based on the total mass of the electrolyte, the mass percentage of the second additive is 0.3% to 2%.

[0077] In some embodiments of this application, the mass percentage of the third additive is 0.1% to 5% based on the total mass of the electrolyte. Specifically, the mass percentage of the third additive is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2 ... The electrolyte concentrations are 0.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, and 5%. This contributes to the battery's excellent electrochemical performance. Simultaneously, it further reduces the risk that excessive additives might diminish the electrolyte's effectiveness in improving battery cycle performance and high / low temperature performance, thus lowering electrolyte costs.

[0078] Furthermore, based on the total mass of the electrolyte, the mass percentage of the third additive is 0.3% to 2%.

[0079] In some embodiments of this application, lithium salts and non-aqueous solvents are also included.

[0080] The electrolyte provided in this application embodiment also includes lithium salt and non-aqueous solvent.

[0081] In some embodiments of this application, the lithium salt may be a lithium salt known in the art for use in batteries. As an example, the lithium salt includes at least one of LiPF6, LiAsF6, LiClO4, LiSO3CF3, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2, and LiPF4C2O4.

[0082] In some embodiments of this application, the non-aqueous volume may employ non-aqueous volumes known in the art for use in batteries. As an example, the non-aqueous organic solvent is a cyclic organic solvent and / or a chain organic solvent.

[0083] In some embodiments of this application, the mass percentage of lithium salt is 8% to 20% based on the total mass of the electrolyte. Specific examples show that the mass percentage of lithium salt is 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc.

[0084] In some embodiments of this application, the mass percentage of non-aqueous volume is 65% to 91.8% based on the total mass of the electrolyte. Specific examples show that the mass percentage of non-aqueous volume is 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 91.6%, etc.

[0085] In some embodiments of this application, the cyclic organic solvent includes at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone, sulfolane, and fluoroethylene carbonate.

[0086] In some embodiments of this application, the chain organic solvent includes at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and 2,2-difluoroethyl acetate.

[0087] A third aspect of this application provides a battery comprising the electrolyte described in the second aspect.

[0088] The battery proposed in the third aspect of the embodiments of this application includes the electrolyte of the second aspect, has low impedance, good low-temperature discharge performance and high-temperature storage performance, and exhibits good fast-charging performance.

[0089] In some embodiments of this application, positive electrode active materials and negative electrode active materials are also included.

[0090] In some embodiments of this application, the positive electrode active material may be a known positive electrode active material for batteries. As examples, positive electrode active materials include LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, and Li... 1+ a Mn 1-x M x O2, LiCo 1-x M x O2, LiFe 1-x M x PO4, Li2Mn 1-x At least one of O4, wherein M includes at least one selected from Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, 0≤a≤0.2, 0≤x<1;

[0091] In some embodiments of this application, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material includes at least one of graphite, silicon-carbon composite materials, silicon materials, lithium metal, and lithium titanate.

[0092] In some embodiments of this application, the battery further includes a positive electrode, a negative electrode, and a separator.

[0093] Furthermore, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector. The positive active material layer includes a positive active material, a conductive agent, and a binder. Optionally, the positive current collector includes aluminum foil.

[0094] Furthermore, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector. The negative active material layer includes a negative active material, a conductive agent, and a binder. Optionally, the negative current collector includes copper foil.

[0095] Furthermore, the conductive agents and binders in both the positive and negative electrode active material layers can be conventional materials in this field.

[0096] Furthermore, the separator is a separator known in the art that can be used in batteries and is stable to the electrolyte used, and may include at least one of polyolefin, aromatic polyamide, polytetrafluoroethylene and polyethersulfone, which may be configured as needed.

[0097] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the invention in any way. The reagents used in the embodiments are all from Aladdin Biochemical Technology Co., Ltd.

[0098] Example 1

[0099] (1) Preparation of electrolyte: Under a dry environment with a water content of less than 5 ppm, lithium salt and the first additive are added to a non-aqueous organic solvent and stirred evenly to obtain a mixed solution; then, the second additive and the third additive are added to the above mixed solution and mixed evenly to obtain the electrolyte.

[0100] Based on the total mass of the electrolyte, the lithium salt content is 12.5%, the first additive content is 0.5%, the second additive content is 2%, the third additive content is 0%, and the non-aqueous volume content is 85% (based on the total mass of the electrolyte, the EC content is 32%, the PC content is 4%, and the EMC content is 49%, with a mass ratio of EC / PC / EMC = 32:4:49). The lithium salt is lithium hexafluorophosphate (LiPF6), the first additive is the compound shown in Formula 1, the second additive is vinylene carbonate (VC), and the non-aqueous organic solvent is a combination of ethylene carbonate (EC), propylene carbonate (PC), and methyl ethyl carbonate (EMC).

[0101] (3) The positive electrode material LiFePO4, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were dispersed in the solvent N-methylpyrrolidone (NMP) at a mass ratio of 96:2:2 to obtain a positive electrode active material layer slurry; the positive electrode active material layer slurry was uniformly coated on both sides of the positive electrode current collector aluminum foil, with an areal density of 40 mg / cm³. 2 After drying, rolling, baking, slitting and spot welding of tabs, the positive electrode sheet is obtained, with a total thickness of 190μm.

[0102] (4) Preparation of negative electrode sheet: The negative electrode active material graphite, the conductive agent conductive carbon black (super-p), and the binder styrene-butadiene latex (SBR) are dispersed in deionized water at a mass ratio of 96:2:2 and stirred evenly to obtain a negative electrode active material layer slurry; the negative electrode active material layer slurry is uniformly coated on both sides of the negative electrode current collector copper foil, with an areal density of 18 mg / cm³. 2 After drying, rolling, baking, slitting and spot welding of the tabs, the negative electrode sheet is obtained, with a total thickness of 123μm.

[0103] (5) Battery preparation: The above-mentioned positive electrode, separator and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode to provide isolation. Then, the cells are wound to obtain a bare cell, which is placed in an outer packaging shell, dried, and then injected with the electrolyte prepared in step (2). After vacuum sealing, standing, formation, aging and capacity testing, the battery preparation is completed, with a rated capacity of 1.6 Ah.

[0104] Examples 2-33

[0105] Examples 2-33 use the same method as Example 1, but the electrolyte composition and positive electrode active material are different, as detailed in Tables 1-1, 1-2, 2-1 and 2-2.

[0106] Comparative Examples 1-8

[0107] Comparative Examples 1-8 were conducted using the same method as in Example 1, but the electrolyte composition and positive electrode active material differed, as detailed in Tables 1-1, 1-2, 2-1, and 2-2.

[0108] The electrolytes and positive electrode active materials of Examples 1-33 and Comparative Examples 1-8 are different, as detailed in Tables 1-1, 1-2, 2-1 and 2-2.

[0109] Table 1-1

[0110]

[0111] Table 1-2

[0112]

[0113] Table 2-1

[0114]

[0115] Table 2-2

[0116]

[0117] Note: In Tables 1-1 and 1-2:

[0118] The compound shown in Formula 1 is: The compound shown in Formula 2 is:

[0119] The compound shown in Formula 3 is: The third additive used in Example 26 is:

[0120]

[0121] In Tables 2-1 and 2-2:

[0122] EC: Abbreviation for Ethylene Carbonate; PC: Abbreviation for Propylene Carbonate; EMC: Abbreviation for Ethyl Methyl Carbonate; DEC: Abbreviation for Diethyl Carbonate.

[0123] Performance testing

[0124] I. Testing Method:

[0125] 1. Initial DCIR test: Charge the battery at 1C to the upper voltage limit at room temperature after capacity grading, let it rest for 5 minutes, then discharge it at 1C for 30 minutes, let it rest for 1 hour, and then discharge it at 2C for 10 seconds. Calculate the DCIR of the battery at 50% SOC.

[0126] 2. Low-temperature DCIR test: After capacity grading, charge the battery at 1C to the upper voltage limit at room temperature, let it stand for 5 minutes, then discharge it at 1C for 30 minutes, then transfer the battery to a low temperature of -20℃ and let it stand for 240 minutes, then discharge it at 2C for 10 seconds, and calculate the DCIR of the battery at 50% SOC.

[0127] 3. Low-Temperature Discharge Performance Test: After capacity grading, the battery is charged at room temperature (25℃) with a constant current of 1C to the upper voltage limit, then charged at the upper voltage limit to the cutoff current of 0.05C. The battery is then discharged at a constant current of 1C, and the discharge capacity is recorded as B1. At room temperature (25℃), the battery is charged at a constant current of 1C to the upper voltage limit, then charged at the upper voltage limit to the cutoff current of 0.05C. The battery is then transferred to a low temperature of -20℃ and left to stand for 240 minutes. It is then discharged at a constant current of 0.5C, and the discharge capacity is recorded as B2. The capacity retention rate at -20℃ is η3 = B2 / B1 * 100%.

[0128] 4. High-Temperature Storage Performance Test: After capacity grading, the battery is charged at room temperature (25℃) with a constant current of 1C to the upper voltage limit, then charged at the upper voltage limit to the cutoff current of 0.05C. The battery is then discharged at a constant current of 1C, and the discharge capacity is recorded as A1. At room temperature (25℃), the battery is charged at a constant current of 1C to the upper voltage limit, then charged at the upper voltage limit to the cutoff current of 0.05C. The battery is then transferred to a high temperature of 60℃ and stored for 30 days. It is then discharged at room temperature with a constant current of 1C, and the discharge capacity is recorded as A2. The capacity retention rate at 60℃ = A2 / A1*100%.

[0129] 5. 3C Room Temperature Cycling Performance Test: The battery is charged at 3C constant current to the upper voltage limit at room temperature (25℃), then charged at the upper voltage limit to the cutoff current of 0.05C. The battery is then discharged at 1C. This charge-discharge cycle is repeated for 3 weeks, and the discharge capacity is recorded as D3. After 1000 cycles, the discharge capacity is recorded as D. 1000 Room temperature cycle retention rate = D 1000 / D3*100%.

[0130] II. Test Results:

[0131] The battery performance test results of Examples 1-33 and Comparative Examples 1-8 are shown in Tables 3-1 and 3-2.

[0132] Table 3-1

[0133]

[0134] Table 3-2

[0135]

[0136] Results and conclusions:

[0137] 1. First, let's take the lithium iron phosphate battery system as an example:

[0138] (1) Compared with Comparative Examples 1-3, which did not add any additives or only added one of the first additive or the second additive, the technical solutions provided in this application (including the solutions of the combination of the first additive and the second additive as shown in Examples 1-21, and the solutions of the combination of the first additive, the second additive and the third additive as shown in Examples 22-30) reduce battery impedance and improve the high and low temperature performance of the battery and the stability of room temperature fast charging cycle.

[0139] (2) As shown in Examples 1-21, the first additive can suppress the excessive consumption of the second additive during the initial cycle, which could lead to an excessively thick SEI film and excessive impedance. Introducing the first and second additives into the electrolyte is beneficial for improving the battery's high and low temperature performance and its stability during room-temperature fast-charge cycling. Among these,

[0140] (3) Among them, as the ratio of the first additive to the second additive in the electrolyte increases, the overall improvement effect on the high and low temperature performance and room temperature fast charging performance of the battery shows a trend of first increasing and then decreasing. This is because if the mass ratio of the first additive to the second additive is too low, it will not be conducive to the first additive providing sufficient Li. + Increasing the impedance of the transmission channel is detrimental to improving fast charging performance and reduces the overall performance improvement effect on the battery. On the other hand, preventing the mass ratio of the first additive and the second additive from being too high is not conducive to the complete dissolution of the first additive in the electrolyte, causing the electrolyte to become turbid, which in turn reduces the overall performance improvement effect on the battery and increases the cost of battery use.

[0141] As shown in Comparative Example 4, when the ratio of the first additive to the second additive is too low, and as shown in Comparative Example 5, when the ratio of the first additive to the second additive is too high, both exhibit problems such as increased impedance, reduced high and low temperature performance of the battery, and decreased stability of fast charging cycle at room temperature. Therefore, controlling the ratio of the first additive to the second additive in the electrolyte to be between 0.03 and 6.67 can achieve a better overall improvement effect.

[0142] (4) Compared with Example 1, the solutions provided in Examples 22-30 add a third additive, that is, the third additive and the first additive are used in combination with the second additive, which can further improve the effect and enhance the high temperature performance and cycle life of the battery.

[0143] 2. Secondly, the electrolyte composition of the above embodiments is not only applicable to battery systems with low operating voltage such as lithium iron phosphate and lithium manganese iron phosphate, but also to battery systems with high operating voltage such as nickel cobalt manganese system and lithium cobalt oxide system, as shown in Examples 31-33.

[0144] 3. Finally, such as Figure 1 The figure shows the dQ / dV graph for Example 1. It can be seen that the first additive is preferentially reduced before VC, forming a film on the negative electrode first. This suppresses excessive consumption of the second additive during battery formation and solves the problem of high initial impedance.

[0145] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is 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. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0146] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An electrolyte additive, characterized in that, Includes the first additive and the second additive; The first additive includes lithium organoborate, wherein the lithium organoborate comprises: At least one of Formula 3; The second additive includes at least one of vinylene carbonate, fluoroethylene carbonate, and ethylene ethylene carbonate; The mass ratio of the first additive to the second additive is 0.03 to 6.

67.

2. The electrolyte additive according to claim 1, characterized in that, The mass ratio of the first additive to the second additive is 0.05 to 2.

3. The electrolyte additive according to claim 1, characterized in that, The first additive is And / or, the second additive is vinylene carbonate.

4. The electrolyte additive according to claim 1, characterized in that, It also includes a third additive, which includes at least one of sulfonate additives, sulfate additives, borate additives, phosphate additives, acid anhydride additives, and nitrile additives.

5. The electrolyte additive according to claim 4, characterized in that, The third additive satisfies at least one of the following: (i) The sulfonate additives include at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone and methanedisulfonate methylene ester; (ii) The sulfate ester additives include vinyl sulfate and At least one of them; (iii) The borate ester additives include tris(trimethylsilane)boronic esters; (iv) The phosphate ester additives include at least one of tris(trimethylsilane) phosphate and tripropenyl phosphate; (v) The acid anhydride additives include at least one of succinic anhydride, maleic anhydride, citrate anhydride, butyric anhydride and heptafluorobutyric anhydride; (vi) The nitrile additives include at least one of butadionitrile, adiponitrile, 1,3,6-hexanetrionitrile, transbutenedionitrile, 1,2-bis(cyanoethoxy)ethane, and 1,2,3-tris(2-cyanoethoxy)propane.

6. An electrolyte, characterized in that, Includes the electrolyte additive as described in any one of claims 1 to 5.

7. The electrolyte according to claim 6, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the first additive is 0.1% to 3%.

8. The electrolyte according to claim 6 or 7, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the second additive is 0.1% to 5%.

9. The electrolyte according to claim 6, characterized in that, Based on the total mass of the electrolyte, the third additive accounts for 0.1% to 5% of the total mass.

10. The electrolyte according to claim 6, characterized in that, It also includes lithium salts and non-aqueous solvents; Optionally, the lithium salt includes at least one of LiPF6, LiAsF6, LiClO4, LiSO3CF3, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2, and LiPF4C2O4; Optionally, the non-aqueous organic solvent is a cyclic organic solvent and / or a chain organic solvent.

11. A battery, characterized in that, Includes the electrolyte as described in any one of claims 6 to 10.

12. The battery according to claim 11, characterized in that, It also includes positive electrode active materials and negative electrode active materials; Optionally, the positive electrode active material includes LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, and Li 1+a Mn 1- x M x O2, LiCo 1-x M x O2, LiFe 1-x M x PO4, Li2Mn 1-x At least one of O4, wherein M includes at least one selected from Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, 0≤a≤0.2, 0≤x<1; Optionally, the negative electrode active material includes at least one of graphite, silicon-carbon composite material, silicon material, lithium metal, and lithium titanate.

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