Non-aqueous electrolyte additive, non-aqueous electrolyte and lithium-ion battery

Abstract

The present disclosure provides a non-aqueous electrolyte additive, a non-aqueous electrolyte and a lithium-ion battery. The above-mentioned non-aqueous electrolyte additive is used in combination with a fluorine-containing lithium salt, and includes an additive A, an additive B and an S-containing auxiliary additive; R1≠R2 of the additive A, and R1 and R2 can be independently selected from any one of an alkane group, an alkene group, an aromatic hydrocarbon group, pyridine, pyrrole, thiophene, thiazole and imidazole; R5, R6 and R7 of the additive A can be independently selected from any one of an alkane group, an alkene group, and a halogen fluorine atom substitution. The non-aqueous electrolyte additive enables the combination of additive A, additive B and the S-containing auxiliary additive to play a good synergistic role, and can remove trace water in the non-aqueous electrolyte of the lithium-ion battery, HF, acid and by-product water generated during the cycle, so as to ensure that the lithium-ion battery has good normal temperature cycle, high temperature cycle, low temperature discharge and rate discharge performance after long-term cycling.

Description

Technical Field

[0001] The present invention relates to the technical field of non-aqueous electrolytes, and in particular to a non-aqueous electrolyte additive, a non-aqueous electrolyte and a lithium-ion battery. Background Art

[0002] With the development of renewable energy, people are increasingly demanding higher standards for energy conversion and storage. Lithium-ion batteries, with their high energy density, lack of memory effect, abundant natural lithium resources, and low cost, have rapidly captured the market for portable electronic devices, electric vehicles, and other applications.

[0003] As the gram capacity of existing lithium-ion batteries gradually increases, their high-temperature performance deteriorates severely, and long cycle life cannot be guaranteed. In particular, during long-term cyclic charge and discharge at high voltage (>4.4V), the volume of the positive electrode material will expand and cause serious cracks, causing the solvent in the electrolyte to enter the interior of the positive electrode material, destroying the structure and leading to capacity decay.

[0004] Therefore, in order to protect the positive electrode material from damage, it can usually be done in two ways: on the one hand, by changing the structure of the positive electrode material itself, such as coating, doping, etc., but these modification processes are often complicated and costly; on the other hand, by adding a small amount of additives to the electrolyte, the CEI film can be preferentially formed on the positive electrode material to achieve good protection of the positive electrode, which is not only low-cost but also easy to operate.

[0005] Electrolytes are divided into aqueous electrolytes and non-aqueous electrolytes. Non-aqueous electrolytes are mainly composed of electrolytes and non-aqueous organic solvents. Although non-aqueous electrolytes remove most of the water, they still contain trace amounts of water (usually less than 100ppm). After multiple charge and discharge cycles of lithium-ion batteries, the fluorine-containing lithium salts in the non-aqueous electrolyte will hydrolyze and produce corrosive HF. The produced HF can easily damage the density of the CEI membrane, not only causing the interfacial impedance of the CEI membrane to be larger, but also causing the non-aqueous organic solvent to penetrate into the positive electrode material and damage its structure, resulting in poor cycle performance of the lithium-ion battery. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a non-aqueous electrolyte additive, a non-aqueous electrolyte and a lithium ion battery that can remove trace water, HF, acid and by-product water generated during the circulation process in the non-aqueous electrolyte of lithium ion batteries, so as to ensure that the lithium ion battery has good room temperature cycle, high temperature cycle, low temperature discharge and rate discharge performance after long-term circulation.

[0007] The object of the present invention is achieved through the following technical solutions:

[0008] A non-aqueous electrolyte additive, the non-aqueous electrolyte additive is used in combination with a fluorine-containing lithium salt, the non-aqueous electrolyte additive comprising additive A, additive B, and an auxiliary additive containing sulfur;

[0009] The additive A has the following structure:

[0010]

[0011] Wherein, R1≠R2, and said R1 and said R2 can be independently selected from any one of an alkane group, an alkene group, an aromatic hydrocarbon group, pyridine, pyrrole, thiophene, thiazole and imidazole;

[0012] The additive B has the following structure:

[0013]

[0014] The R5, R6 and R7 can be independently selected from any one of an alkane group, an alkene group, and a halogen fluorine atom substitution.

[0015] In one embodiment, the additive A has the following structure:

[0016]

[0017]

[0018] In one embodiment, the additive B has the following structure:

[0019]

[0020]

[0021] In one embodiment, the mass ratio of the additive A to the additive B is (0.02-5): (0.02-5); and / or,

[0022] The sulfur-containing auxiliary additive includes at least one of vinyl sulfate, 1.3-propylene sultone and 1.3-propane sultone.

[0023] A non-aqueous electrolyte comprises a non-aqueous organic solvent, the fluorine-containing lithium salt and the non-aqueous electrolyte additive described in any one of the above embodiments.

[0024] In one embodiment, the fluorine-containing lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate and lithium difluorophosphate.

[0025] In one embodiment, the non-aqueous organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethylformamide, diethylformamide, methylpropyl carbonate, tetrahydrofuran, propylene oxide, ethyl acetate, methyl acetate, methyl butyrate, ethyl butyrate, methyl propionate, ethyl propionate and propyl acetate.

[0026] In one embodiment, the total amount of the fluorine-containing lithium salt accounts for 7.0% to 15.0% of the total mass of the non-aqueous electrolyte.

[0027] A lithium-ion battery comprises a battery cell and the non-aqueous electrolyte described in any one of the above embodiments, wherein the positive electrode sheet, the negative electrode sheet and the separator of the battery cell are all immersed in the non-aqueous electrolyte.

[0028] In one embodiment, the active material of the positive electrode sheet is a layered oxide, and the active material of the negative electrode sheet is hard carbon; and / or,

[0029] The total content of N and P elements in the positive electrode sheet and / or the negative electrode sheet is not less than 100 ppm by mass.

[0030] Compared with the prior art, the present invention has at least the following advantages:

[0031] 1. Since the PN bond of additive A has strong Lewis base characteristics, it can effectively neutralize the acid generated by the high temperature decomposition of non-aqueous organic solvents, effectively remove the acid generated by high temperature, and generate by-product water. Additive A can fully utilize the trace water and by-product water in the non-aqueous electrolyte, so that the trace water or by-product water will ionize to produce OH in the process of multiple charge and discharge cycles of the non-aqueous electrolyte. - , so that the CO bond of the five-membered ring of additive A is bonded to OH -Under the action of HF, they break, lose electrons, and undergo polymerization reaction with HF to form a high-density, thin and tight CEI film rich in LixPOyFz and amino compounds on the surface of the positive electrode. In this way, not only can the trace water and by-product water in HF and non-aqueous electrolytes be effectively removed, but also the problem of fluorine-containing lithium salts in traditional non-aqueous electrolytes being hydrolyzed and producing corrosive HF that damages the density of the CEI film is effectively avoided, thereby improving the cycle performance of lithium-ion batteries; and the formed CEI film can inhibit the decomposition of non-aqueous electrolytes, the degradation of transition metal ions (nickel, cobalt, iron, manganese, etc.) Dissolution and protection of positive electrode materials from damage; at the same time, additive A can also reduce the viscosity of non-aqueous electrolytes and improve the kinetics of lithium ions in non-aqueous electrolytes, so additive A can improve the room temperature cycle and high temperature cycle performance of lithium-ion batteries; because the amino group in additive B can react with the S-containing compound containing S auxiliary additives to form a film, the density of the CEI film is further enhanced to better improve the protection of the positive electrode structure, and the formed CEI film has low interfacial impedance, so it can improve the rate discharge performance of lithium-ion batteries; on the other hand, the amino group in additive B can improve Li + Solvation structure, making Li + and non-aqueous organic solvents, which is beneficial for Li + It can effectively prevent Li + Oxidative decomposition; on the other hand, the silane group in additive B has strong resistance to low temperature, which can reduce the polarization of the lithium-ion battery potential in a low temperature environment and increase the migration rate of the lithium-ion battery at low temperature, thereby improving the low-temperature discharge performance of lithium ions. When additives A, additive B and S-containing auxiliary additives are used in combination, they can play a good synergistic role to ensure that the lithium-ion battery has good room temperature cycle, high temperature cycle, low temperature discharge and rate discharge performance after a long cycle.

[0032] 2. Since R1≠R2 of additive A, additive A is - Under the action of , two different substances can be generated, namely, a polymer containing LixPOyFz and an amino compound, so that the generated amino compound can not only react with the S-containing compound containing the S auxiliary additive to form a film covering the CEI film, but also further improve the density of the CEI film, effectively avoid the generated HF directly destroying the silane group in the CEI film, so as to ensure that the lithium-ion battery has better high and low temperature performance, and can also improve the Li + Solvation structure, making Li + and non-aqueous organic solvents, which is beneficial for Li + It can effectively prevent Li + Oxidative decomposition.

[0033] 3. Since the silane group in additive B can inhibit the high temperature of the non-aqueous electrolyte to a certain extent, it can effectively reduce the high-temperature decomposition rate of the non-aqueous organic solvent, thereby effectively inhibiting the growth rate of the LixPOyFz-rich CEI film, and effectively avoiding the LixPOyFz-rich CEI film from growing too fast and causing the LixPOyFz-rich CEI film to be too thick, thereby affecting the deintercalation of lithium ions, thereby better ensuring that the lithium-ion battery has good high-temperature cycling, room-temperature cycling, low-temperature discharge performance and rate discharge performance after long-term cycling. Specific embodiments

[0034] In order to facilitate understanding of the present invention, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0035] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly attached to the other element or there may be an intermediate element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only embodiments.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0037] In order to better understand the technical solutions and beneficial effects of the present disclosure, the present disclosure is further described in detail below with reference to specific embodiments:

[0038] A non-aqueous electrolyte additive according to an embodiment of the present invention is used in combination with a fluorine-containing lithium salt, and the non-aqueous electrolyte additive includes additive A, additive B, and an auxiliary additive containing sulfur;

[0039] The additive A has the following structure:

[0040]

[0041] Wherein, R1≠R2, and said R1 and said R2 can be independently selected from any one of an alkane group, an alkene group, an aromatic hydrocarbon group, pyridine, pyrrole, thiophene, thiazole and imidazole;

[0042] The additive B has the following structure:

[0043]

[0044] The R5, R6 and R7 can be independently selected from any one of an alkane group, an alkene group, and a halogen fluorine atom substitution.

[0045] It should be noted that there are currently some practices that remove trace water from the electrolyte by adding additives to the electrolyte. For example, Chinese patent number CN 111628220 A discloses an electrolyte additive and specifically discloses that the electrolyte additive is a succinimidyl carbonate compound. Although the additive can effectively remove trace water from the electrolyte and inhibit the decomposition of lithium salts, thereby improving its high-temperature storage performance, it cannot adapt well to low-temperature storage performance and cannot effectively remove the byproduct HF of the hydrolysis of fluorine-containing lithium salts. When the generated HF accumulates to a certain extent, it will destroy the CEI membrane, causing the non-aqueous organic solvent in the non-aqueous electrolyte to easily enter the positive electrode material and damage its structure, thereby causing the cycle performance of the lithium-ion battery to still not break through the long and high capacity retention rate. In addition, since the non-aqueous organic solvent of the non-aqueous electrolyte is easily decomposed and acidified during repeated charge and discharge at high temperature, the lithium-ion battery is prone to bloating, resulting in its high-temperature cycle performance still not having a good breakthrough.

[0046] In order to find a non-aqueous electrolyte additive that has high-temperature performance, room-temperature performance, low-temperature performance, and rate performance at the same time, so as to achieve a breakthrough in high-temperature cycle performance for a long time. Therefore, in the present disclosure, additive A, additive B, and S-containing auxiliary additive are compounded and used. Since the PN bond of additive A has strong Lewis base characteristics, it can effectively neutralize the acid decomposed by the non-aqueous organic solvent at high temperature, effectively remove the acid generated at high temperature, and generate by-product water. Additive A can fully utilize the trace water and by-product water in the non-aqueous electrolyte, so that additive A can react with HF to form a high-density, thin, and tight LixPOyFz-rich CEI film and amino-containing compound on the positive electrode surface. The amino-containing compound can react with the S-containing compound of the S-containing auxiliary additive to form a film covering the CEI film, further improving the density of the CEI film. The silane group of additive B can effectively inhibit the growth rate of the CEI film to avoid the phenomenon of excessive growth of the CEI film, and the amino group of additive B can improve Li + Solvation structure, making Li + and non-aqueous organic solvents, which is beneficial for Li + It can effectively prevent Li +Oxidative decomposition, when the three are used together, can play a very good synergistic role, which can remove trace water in the non-aqueous electrolyte of lithium-ion batteries, HF, acid and by-product water in the circulation process, so as to ensure that the lithium-ion battery has good room temperature cycle, high temperature cycle, low temperature discharge and rate discharge performance after long-term circulation.

[0047] It is understood that in the present disclosure, since trace water or by-product water in the non-aqueous electrolyte will ionize to produce OH after multiple charge and discharge cycles, - , so that the CO bond of the five-membered ring of additive A is bonded to OH - Under the action of HF, the additive breaks, loses electrons, and undergoes a polymerization reaction with HF to form a high-density, thin and tight LixPOyFz-rich CEI film and amino-containing compounds on the surface of the positive electrode. In this way, it not only effectively removes HF, trace water and by-product water in the non-aqueous electrolyte, but also effectively avoids the problem that the fluorine-containing lithium salts in the traditional non-aqueous electrolyte will hydrolyze and produce corrosive HF to damage the density of the CEI film, thereby improving the cycle performance of the lithium-ion battery; and the formed CEI film can inhibit the decomposition of the non-aqueous electrolyte, the dissolution of transition metal ions (nickel, cobalt, iron, manganese, etc.), and protect the positive electrode material from damage; at the same time, additive A can also reduce the viscosity of the non-aqueous electrolyte and improve the kinetic properties of lithium ions in the non-aqueous electrolyte. Therefore, additive A can improve the room temperature cycle and high temperature cycle performance of the lithium-ion battery.

[0048] Furthermore, since the amino group in additive B can react with the S-containing compound of the S-containing auxiliary additive to form a film, the density of the CEI film is further enhanced to better protect the positive electrode structure, and the formed CEI film has low interfacial impedance, so it can improve the rate discharge performance of lithium-ion batteries; on the other hand, the amino group in additive B can improve the Li + Solvation structure, making Li + and non-aqueous organic solvents, which is beneficial for Li + It can effectively prevent Li + Oxidative decomposition; on the other hand, the silane group in additive B has strong resistance to low temperature, which can reduce the polarization of the lithium-ion battery potential under low temperature environment, increase the migration rate of the lithium-ion battery at low temperature, and thus improve the low-temperature discharge performance of lithium ions. When additives A, additives B and S-containing auxiliary additives are used in combination, they can play a good synergistic role, which can remove trace water in the non-aqueous electrolyte of the lithium-ion battery, HF, acid and by-product water in the cycle process, so as to ensure that the lithium-ion battery has good room temperature cycle, high temperature cycle, low temperature discharge and rate discharge performance after long-term cycling.

[0049] It should also be noted that, since R1≠R2 of additive A, additive A- Under the action of , two different substances can be generated, namely, polymers containing LixPOyFz and amino compounds. The generated amino compounds can not only react with the S-containing compounds containing S auxiliary additives to form a film covering the CEI film, but also further improve the density of the CEI film, effectively avoiding the generated HF directly destroying the silane groups in the CEI film, so as to ensure that the lithium-ion battery has better high and low temperature performance, and can also improve Li + Solvation structure, making Li + and non-aqueous organic solvents, which is beneficial for Li + It can effectively prevent Li + Oxidative decomposition.

[0050] Furthermore, the silane group in Additive B can inhibit the high temperature of the non-aqueous electrolyte to a certain extent, thereby effectively reducing the high-temperature decomposition rate of the non-aqueous organic solvent, thereby effectively inhibiting the growth rate of the LixPOyFz-rich CEI film, effectively preventing the LixPOyFz-rich CEI film from growing too fast, resulting in the LixPOyFz-rich CEI film being too thick, thereby affecting the deintercalation of lithium ions, thereby better ensuring that the lithium-ion battery simultaneously has good high-temperature cycling, room-temperature cycling, low-temperature discharge performance, and rate discharge performance. In other words, Additive B can effectively inhibit the growth rate of the LixPOyFz-rich CEI film, thereby avoiding the phenomenon of excessive growth of the LixPOyFz-rich CEI film.

[0051] Furthermore, the amino compound generated by the additive A reacts with the S-containing compound of the S-containing auxiliary additive to form a film covering the CEI membrane, thereby achieving good protection for the silane groups in the CEI membrane and effectively preventing the silane groups in the CEI membrane from being directly exposed to the non-aqueous electrolyte, which would cause HF to directly destroy the structure of the silane groups and affect the low-temperature resistance of the silane groups.

[0052] In one embodiment, the additive A has the following structure:

[0053]

[0054]

[0055] In one embodiment, the additive B has the following structure:

[0056]

[0057]

[0058]

[0059] In one embodiment, the mass ratio of the additive A to the additive B is (0.02-5): (0.02-5), so as to ensure that the usage ratio of the additive A and the additive B is appropriate, thereby ensuring that the additive A and the additive B can play a better synergistic effect. Those skilled in the art can select an appropriate ratio according to actual conditions, which can be 1:0.02, 1:0.05, 1:0.5, 1:1, 1:2, 1:5, 0.02:1, 0.05:1, 0.5:1, 2:1, 5:1, therefore, it is not specifically limited in this disclosure.

[0060] In one embodiment, the S-containing auxiliary additive includes at least one of vinyl sulfate, 1.3-propylene sultone, and 1.3-propane sultone, to ensure that the S-containing auxiliary additive can provide a S-containing compound, thereby ensuring that it can react with the amino-containing compound generated by additive A to form a film covering the CEI membrane, thereby better ensuring the density of the CEI membrane.

[0061] The present disclosure further provides a non-aqueous electrolyte solution, comprising a non-aqueous organic solvent, the fluorine-containing lithium salt, and the non-aqueous electrolyte solution additive described in any one of the above embodiments.

[0062] It is understandable that fluorinated lithium salts are commonly used in electrolytes because they have suitable solubility and high ionic conductivity in non-aqueous solvents; they can form a stable passivation film on the surface of the aluminum foil current collector; and they can work in conjunction with non-aqueous organic solvents, such as carbonate solvents (DEC, DMC), to form a stable SEI film on the surface of the negative electrode, thereby providing excellent protection for the negative electrode's active material (graphite). Therefore, fluorinated lithium salts are commonly used in electrolytes. However, since fluorinated lithium salts are accompanied by corrosive HF during hydrolysis, the generated HF can easily damage the density of the CEI film, affecting the cycling performance of lithium-ion batteries.

[0063] Therefore, in order to remove HF in the non-aqueous electrolyte, the present invention uses a compound of additive A, additive B and S-containing auxiliary additives. When the lithium-ion battery is charged and discharged for multiple cycles, the trace water or by-product water in the non-aqueous electrolyte will ionize to produce OH. - , so that the CO bond of the five-membered ring of additive A is bonded to OH -Under the action of HF, it breaks and undergoes polymerization reaction with HF to form a high-density, thin and tight CEI film rich in LixPOyFz and amino compounds on the surface of the positive electrode. In this way, it not only effectively removes trace water and by-product water in HF and non-aqueous electrolytes, but also effectively avoids the problem that fluorine-containing lithium salts in traditional non-aqueous electrolytes will hydrolyze and produce corrosive HF to damage the density of the CEI film. At the same time, additive A can also reduce the viscosity of the non-aqueous electrolyte and improve the kinetic properties of lithium ions in the non-aqueous electrolyte. Therefore, additive A can improve the room temperature cycle and high temperature cycle performance of lithium-ion batteries. At the same time, since R1≠R2 of additive A, additive A is - Under the action of B, two different substances can be generated, namely, polymers containing LixPOyFz and amino compounds. The amino compounds will react with the S-containing compounds containing S auxiliary additives to form a film covering the CEI film, further improving the density of the CEI film. The silane group of additive B can effectively inhibit the growth rate of the CEI film to avoid the phenomenon of excessive growth of the CEI film, and the amino group of additive B can improve the Li + Solvation structure, making Li + and non-aqueous organic solvents, which is beneficial for Li + It can effectively prevent Li + Oxidative decomposition; when the three are used together, they can play a very good synergistic role, which can remove trace water in the non-aqueous electrolyte of lithium-ion batteries, HF, acid and by-product water in the circulation process, so as to ensure that the lithium-ion battery has good room temperature cycle, high temperature cycle, low temperature discharge and rate discharge performance after long-term circulation.

[0064] In one embodiment, the fluorine-containing lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, and lithium difluorophosphate. It is understood that lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, and lithium difluorophosphate all have suitable solubility and high ionic conductivity, ensuring that they can form a stable passivation film on the surface of the aluminum foil current collector. Simultaneously, they can cooperate with the non-aqueous organic solvent to form a stable SEI film on the surface of the negative electrode, thereby achieving better protection for the active materials of the positive and negative electrodes.

[0065] In one embodiment, the non-aqueous organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethylformamide, diethylformamide, methylpropyl carbonate, tetrahydrofuran, propylene oxide, ethyl acetate, methyl acetate, methyl butyrate, ethyl butyrate, methyl propionate, ethyl propionate and propyl acetate.

[0066] In a preferred embodiment, the non-aqueous organic solvent is a mixture of propylene carbonate (PC), diethyl carbonate (DMC), and ethyl methyl carbonate (DEC) in a mass ratio of 1:1:1.

[0067] In one embodiment, the total amount of the fluorine-containing lithium salt accounts for 7.0% to 15.0% of the total mass of the non-aqueous electrolyte.

[0068] The present disclosure also provides a lithium-ion battery, comprising a battery cell and the non-aqueous electrolyte described in any of the above embodiments, wherein the positive electrode sheet, the negative electrode sheet and the separator of the battery cell are all immersed in the non-aqueous electrolyte.

[0069] It can be understood that since the positive electrode sheet, the negative electrode sheet and the separator of the lithium-ion battery are all immersed in the non-aqueous electrolyte disclosed in the present invention, the additive A, the additive B and the S-containing auxiliary additive of the non-aqueous electrolyte can remove trace water, HF, acid and by-product water generated in the non-aqueous electrolyte of the lithium-ion battery when used in combination, thereby ensuring that the lithium-ion battery has good normal temperature cycling, high temperature cycling, low temperature discharge and rate discharge performance after long-term cycling.

[0070] In one embodiment, the active material of the positive electrode sheet is a layered oxide, and the active material of the negative electrode sheet is hard carbon. It is understood that because the layered oxide has higher specific capacity and electrical conductivity, especially when used in conjunction with hard carbon, the structurally stable hard carbon can effectively ensure the charge and discharge cycle life and safety performance of the lithium-ion battery. This ensures that the lithium-ion battery maintains excellent high-temperature cycling, room-temperature cycling, low-temperature discharge performance, and rate discharge performance after long-term cycling. Furthermore, it can significantly improve the energy density and high potential of the lithium-ion battery. This is particularly suitable for lithium-ion batteries prepared with non-aqueous electrolytes in applications with potentials above 2.0V at high, low, and room temperatures, thereby better meeting market developments.

[0071] It should be noted that in the actual application of lithium-ion batteries, layered oxides have high specific capacity, high voltage platform and good cycle stability, while lithium-ion batteries made from fluorine-containing lithium salts have good overall performance and safety. In addition, lithium hexafluorophosphate has better solubility and conductivity than lithium tetrafluoroborate, lithium difluorooxalatoborate and lithium difluorophosphate. Therefore, layered oxides and lithium hexafluorophosphate are currently the preferred materials for most manufacturers to prepare high-performance lithium-ion batteries. However, since lithium hexafluorophosphate easily absorbs water and hydrolyzes to produce corrosive HF, the water content requirements during the preparation of lithium hexafluorophosphate are quite strict. However, most traditional lithium hexafluorophosphates cannot remove trace water 100%, resulting in the presence of a small amount of trace water (usually <100 ppm) in the prepared non-aqueous electrolyte. As mentioned in the background art, after a long period of lithium-ion battery cycling, the fluorine-containing lithium salt in the non-aqueous electrolyte hydrolyzes to produce corrosive HF, which easily damages the structure of the layered oxide, leading to structural instability of the layered oxide. For this reason, some scholars have proposed to find a new type of lithium salt to replace the traditional fluorine-containing lithium salt, but no good breakthrough has been made so far.

[0072] In order to find a better new non-aqueous electrolyte to better adapt to the development of high-performance lithium-ion batteries, the present disclosure optimizes both the positive and negative electrode materials and the non-aqueous electrolyte. In a preferred embodiment, the layered oxide is Li[Ni 0.33 Fe 0.33 Cu 0.33 ]O2, hard carbon is Beiterry BSHC-300 hard carbon. It can be understood that due to Li[Ni 0.33 Fe 0.33 Cu 0.33 ]O2 material has a more stable layered structure than general layered oxides (lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, etc.), which can prevent HF corrosion in non-aqueous electrolytes and avoid the dissolution of transition metal ions, which is beneficial to improving the long cycle performance of lithium-ion batteries; and the volume of BYD BSHC-300 hard carbon becomes smaller after lithium insertion, which reduces the thickness expansion change rate of lithium-ion batteries and has abundant lithium storage space, thereby improving the energy density of lithium-ion batteries; therefore, when Li[Ni 0.33 Fe 0.33 Cu 0.33 ] When O2 and BYD BSHC-300 hard carbon are used in combination with the non-aqueous electrolyte disclosed herein, the high-temperature cycle, room-temperature cycle, low-temperature discharge performance and rate discharge performance of the lithium-ion battery can be improved, while the thickness expansion change rate of the lithium-ion battery can be reduced and the energy density of the lithium-ion battery can be improved.

[0073] It should also be noted that although the volume deformation of BYD BSHC-300 hard carbon after lithium insertion can reduce the thickness expansion change rate of lithium-ion batteries, the volume deformation will affect the deintercalation rate of lithium ions. 0.33 Fe 0.33 Cu 0.33 ]O2 has a stable structure during the charge and discharge process, which is beneficial to Li + Rapid deintercalation, and the non-aqueous organic solvents of propylene carbonate (PC), diethyl carbonate (DMC), and ethyl methyl carbonate (DEC) in the non-aqueous electrolyte can ensure that the non-aqueous electrolyte has a higher dielectric constant, which is beneficial to Li + In the transmission of non-aqueous organic solvent, under the action of additive B, Li + and non-aqueous organic solvents, which is beneficial for Li + The lithium ion is transported from the non-aqueous organic solvent layer into the electrolyte, which better balances the problem of slow lithium ion deintercalation rate due to the small volume deformation after the hard carbon is embedded in lithium. In addition, the S-containing auxiliary additive (auxiliary additive PS) in the non-aqueous electrolyte can be used in combination with additives A and B to improve the performance of the layered oxide Li[Ni 0.33 Fe 0.33 Cu 0.33 ]O2 and BYD BSHC-300 hard carbon can both play a positive protection role, effectively removing trace water in the non-aqueous electrolyte of lithium-ion batteries, HF, acid and by-product water generated during the circulation process, so as to ensure that lithium-ion batteries have good room temperature cycling, high temperature cycling, low temperature discharge, rate discharge performance and higher energy density after a long cycle process, so as to better adapt to the development trend of the market.

[0074] In one embodiment, the total content of N and P elements in the positive electrode sheet and the negative electrode sheet is not less than 100 ppm by mass.

[0075] Compared with the prior art, the present invention has at least the following advantages:

[0076] 1. Since the PN bond of additive A has strong Lewis base characteristics, it can effectively neutralize the acid generated by the high temperature decomposition of non-aqueous organic solvents, effectively remove the acid generated by high temperature, and generate by-product water. Additive A can fully utilize the trace water and by-product water in the non-aqueous electrolyte, so that the trace water or by-product water will ionize to produce OH in the process of multiple charge and discharge cycles of the non-aqueous electrolyte. - , so that the CO bond of the five-membered ring of additive A is bonded to OH -Under the action of HF, they break, lose electrons, and undergo polymerization reaction with HF to form a high-density, thin and tight CEI film rich in LixPOyFz and amino compounds on the surface of the positive electrode. In this way, not only can the trace water and by-product water in HF and non-aqueous electrolytes be effectively removed, but also the problem of fluorine-containing lithium salts in traditional non-aqueous electrolytes being hydrolyzed and producing corrosive HF that damages the density of the CEI film is effectively avoided, thereby improving the cycle performance of lithium-ion batteries; and the formed CEI film can inhibit the decomposition of non-aqueous electrolytes, the degradation of transition metal ions (nickel, cobalt, iron, manganese, etc.) Dissolution and protection of positive electrode materials from damage; at the same time, additive A can also reduce the viscosity of non-aqueous electrolytes and improve the kinetics of lithium ions in non-aqueous electrolytes, so additive A can improve the room temperature cycle and high temperature cycle performance of lithium-ion batteries; because the amino group in additive B can react with the S-containing compound containing S auxiliary additives to form a film, the density of the CEI film is further enhanced to better improve the protection of the positive electrode structure, and the formed CEI film has low interfacial impedance, so it can improve the rate discharge performance of lithium-ion batteries; on the other hand, the amino group in additive B can improve Li + Solvation structure, making Li + and non-aqueous organic solvents, which is beneficial for Li + It can effectively prevent Li + Oxidative decomposition; on the other hand, the silane group in additive B has strong resistance to low temperature, which can reduce the polarization of the lithium-ion battery potential under low temperature environment and increase the migration rate of the lithium-ion battery at low temperature, thereby improving the low-temperature discharge performance of lithium ions. When additives A, additives B and S-containing auxiliary additives are used in combination, they can play a good synergistic role, that is, they can remove trace water in the non-aqueous electrolyte of the lithium-ion battery, HF, acid and by-product water generated during the cycle, so as to ensure that the lithium-ion battery has good room temperature cycle, high temperature cycle, low temperature discharge and rate discharge performance after long-term cycling.

[0077] 2. Since R1≠R2 of additive A, additive A is - Under the action of , two different substances can be generated, namely, polymers containing LixPOyFz and amino compounds. The generated amino compounds can not only react with the S-containing compounds containing S auxiliary additives to form a film covering the CEI film, but also further improve the density of the CEI film, effectively avoid the generated HF directly destroying the silane group in the CEI film, so as to ensure that the lithium-ion battery has better high and low temperature performance, and can also improve the Li+ solvation structure, so that Li + and non-aqueous organic solvents, which is beneficial for Li + It can effectively prevent Li + Oxidative decomposition.

[0078] 3. Since the silane group in additive B can inhibit the high temperature of the non-aqueous electrolyte to a certain extent, it can effectively reduce the high-temperature decomposition rate of the non-aqueous organic solvent, thereby effectively inhibiting the growth rate of the LixPOyFz-rich CEI film, and effectively avoiding the LixPOyFz-rich CEI film from growing too fast and causing the LixPOyFz-rich CEI film to be too thick, thereby affecting the deintercalation of lithium ions, thereby better ensuring that the lithium-ion battery has good high-temperature cycling, room-temperature cycling, low-temperature discharge performance and rate discharge performance after long-term cycling.

[0079] The following examples illustrate some specific embodiments, where percentages are expressed by weight. It should be noted that the following examples do not exhaust all possible situations, and that the materials used in the following examples, unless otherwise specified, can be obtained from commercial sources.

[0080] Comparative Examples 1 to 11 and Examples 1 to 23

[0081] Preparation of the non-aqueous electrolyte: Propylene carbonate (PC), diethyl carbonate (DMC), and ethyl methyl carbonate (DEC) were mixed in a 1:1:1 mass ratio to serve as the non-aqueous organic solvent. Additives were added to the non-aqueous organic solvent at the mass percentages shown in the formula in Table 1. After mixing thoroughly, 12% by mass of lithium hexafluorophosphate (LiPF6) was added. Additives A1, B2, and 1.3% propane sultone (PS) were all provided by Aladdin.

[0082] Production of positive electrode: Using Li[Ni 0.33 Fe 0.33 Cu 0.33 The positive electrode sheet is made of 92% O2 layered oxide as the positive electrode active material, 4% PVDF as the binder, and 4% SP as the conductive agent. The negative electrode sheet is made of 94% BYD BSHC-300 hard carbon as the negative electrode active material, 3% SP as the conductive agent, 2% SBR1346 as the binder, and 1% MAC500 as the thickener.

[0083] A battery cell was prepared using the positive and negative electrode sheets and dried in an oven at 80°C to 85°C for 48 hours before being moved into a glove box for later use. The lithium-ion battery electrolytes prepared in Examples 1 to 23 and Comparative Examples 1 to 11 were injected into the dried battery cell. The cells were then packaged, activated, formed, aged, repackaged, and then capacity-divided to produce lithium-ion batteries.

[0084] Examples 1-23 and Comparative Examples 1-11 use the same method, the difference being the different ratios of additive A, additive B, and S-containing auxiliary additive in the non-aqueous electrolyte. Specific differences can be found in Table 1.

[0085] The prepared lithium-ion battery was then tested for high temperature, room temperature, low temperature performance and rate performance:

[0086] 1. 45℃ cycle test

[0087] In a 45±2°C constant temperature chamber, charge the lithium-ion batteries at a constant current and constant voltage of 0.5C to 4.5V, then discharge them at a cutoff current of 0.05C, then at a constant current of 0.2C to 3.0V. Repeat these charge and discharge cycles multiple times. Calculate the capacity retention of the batteries after 600 cycles, with 5 batteries per group.

[0088] Capacity retention (%) = discharge capacity corresponding to the number of cycles (mAh) / discharge capacity at the 600th cycle (mAh) * 100%

[0089] 2. 25℃ cycle test

[0090] In a 25±2°C constant temperature chamber, charge the lithium-ion batteries at a constant current and constant voltage of 0.5C to 4.5V, then discharge them at a cutoff current of 0.05C, then discharge them at 0.2C to 3.0V. Repeat these charge and discharge cycles multiple times. Calculate the capacity retention of the batteries after 800 cycles, with 5 batteries per group.

[0091] Capacity retention (%) = discharge capacity corresponding to the number of cycles (mAh) / discharge capacity at the 800th cycle (mAh) * 100%

[0092] 3. -20℃ discharge test

[0093] In a constant temperature box at 25±2℃, the lithium-ion battery was charged at a constant current and constant voltage of 0.5C to 4.5V, with a cut-off current of 0.05C, and allowed to stand for 10min; discharged at 0.2C to 3.0V at 25℃, and the discharge capacity was recorded; charged at a constant current and constant voltage of 2C to 4.5V at 25℃, with a cut-off current of 0.05C, and allowed to stand at -20℃ for 3h, and then discharged at 0.2C to 3.0V, and the discharge capacity at a low temperature of -20℃ was recorded.

[0094] The formula of low-temperature discharge capacity ratio = -20°C discharge capacity / initial discharge capacity × 100%.

[0095] 4. 2C rate discharge test

[0096] In a constant temperature box at 25±2℃, the lithium-ion battery was charged at 0.5C constant current and constant voltage to 4.5V, with a cutoff current of 0.05C, and allowed to stand for 30min. It was then discharged at 0.2C to 3.0V, allowed to stand for 10min, and the 0.2C discharge capacity was recorded. The lithium-ion battery was charged at 0.5C constant current and constant voltage to 4.5V, with a cutoff current of 0.05C, and allowed to stand for 30min. It was then discharged at 2C to 3.0V, and the 2C discharge capacity was recorded.

[0097] Rate discharge capacity ratio = 2C discharge capacity / 0.2C discharge capacity * 100%.

[0098] Table 1

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105] The data of Comparative Examples 1 and 2 in Table 1 show that the addition of additive A alone can improve the room temperature and high temperature cycle performance, but will deteriorate the low temperature discharge and rate discharge performance. This may be because the interface film formed by additive A has a large impedance.

[0106] From the data of Comparative Examples 1 and 3 in Table 1, it can be seen that the addition of Additive B alone can improve the low-temperature discharge and rate discharge performance, but will deteriorate the room-temperature cycle and high-temperature cycle performance.

[0107] It can be seen from the data of Comparative Examples 1 to 3 in Table 1 that the addition of additive A alone can only improve the room temperature cycle and high temperature cycle performance of the lithium ion battery alone, and the addition of additive B alone can only improve the low temperature discharge and rate discharge performance of the lithium ion battery alone, and it is impossible to improve the room temperature cycle, high temperature cycle performance, low temperature discharge and rate discharge performance of the lithium ion battery at the same time.

[0108] The data from Comparative Examples 2 to 5 in Table 1 show that when the amount of Additive A alone in Comparative Example 4 exceeds 8%, the room-temperature cycling performance of the lithium-ion battery deteriorates. When the amount of Additive B alone in Comparative Example 5 exceeds 8%, the low-temperature discharge performance of the lithium-ion battery deteriorates. This is primarily due to the fact that excessive addition of either Additive A or Additive B increases the viscosity of the non-aqueous electrolyte, reducing its fluidity and increasing the impedance of the CEI interface film. Therefore, it is appropriate to control the amount of Additive A and Additive B added within the range of 0.02% to 8%.

[0109] It can be seen from Comparative Examples 10 to 11 and Examples 1 to 22 in Table 1 that only when Additive A and Additive B are added at the same time can the two play a synergistic role and significantly improve the comprehensive performance of the lithium-ion battery, that is, simultaneously have good room temperature cycle performance, high temperature cycle performance, low temperature discharge and rate discharge performance.

[0110] From the data of Examples 1 to 6 in Table 1, it can be seen that as the content of Additive B increases, the high-temperature cycle and room-temperature cycle performance of the lithium-ion battery will be improved, but the low-temperature discharge and rate discharge performance of the lithium-ion battery will be deteriorated.

[0111] The data of Examples 7 to 9 in Table 1 show that as the content of additive A increases, the low-temperature discharge and rate discharge performance of the lithium-ion battery will be significantly improved, but the room-temperature cycle and high-temperature cycle performance of the lithium-ion battery will be deteriorated.

[0112] From the data of Comparative Examples 6 to 9 and Examples 1 to 12 in Table 1, it can be seen that when the mass ratio of Additive A to Additive B is within the range of (0.02 to 5): (0.02 to 5), the two can exert a good synergistic effect. Among them, Example 3, which adds 1% Additive A and 0.5% Additive B, has the best overall performance.

[0113] From the data of Examples 3, 7-9, and 12-14 in Table 1, it can be seen that when the amount of Additive A relative to the amount of dimethyl carbonate is a / c, when a / c is less than 0.033, the high-temperature cycle performance of Examples 7-9 is inferior to that of the lithium-ion batteries of Examples 12-14. This is because when the amount of dimethyl carbonate is low, the effect of Additive A on forming a stable CEI film with denseness is not obvious. When a / c is greater than 0.1, the room-temperature cycle performance of Example 11 is inferior to that of the lithium-ion batteries of Examples 12-14. This is because when the amount of dimethyl carbonate is excessive, the viscosity of the non-aqueous electrolyte increases, which increases the impedance of the non-aqueous electrolyte interface film and deteriorates the dynamics. Therefore, when the amount of Additive A and the amount of dimethyl carbonate meet 0.033≤a / c≤0.1, to ensure that Additive A forms a stable and dense CEI film and also reduce the viscosity of the non-aqueous electrolyte, Example 3 has the best overall performance.

[0114] Assuming the amount of Additive B relative to the amount of LiPF6 is b / d, the data from Examples 1-3 and Examples 15-19 show that when b / d is less than 0.031, the rate discharge performance of Examples 1-2 is inferior to that of Examples 15-19. Combined with the data from Examples 3-6 and Examples 15-19, it can be seen that when b / d is greater than 0.0625, the low-temperature discharge performance of Examples 4-6 is inferior to that of Examples 15-19. This is because when LiPF6 is excessive, the effect of Additive B in protecting LiPF6 from decomposition is not significant. Therefore, when the amount of Additive B and the amount of LiPF6 satisfy 0.031≤b / d≤0.0625, Example 3 exhibits superior overall performance.

[0115] In summary, when the mass ratio of additive A to additive B is within the range of (0.02-5): (0.02-5), and the amount of additive A and dimethyl carbonate satisfies 0.033≤a / c≤0.1, and the amount of additive B and lithium hexafluorophosphate satisfies 0.031≤b / d≤0.0625, additive A and additive B can better play a synergistic role, that is, significantly enhance the room temperature cycle, high temperature cycle performance, low temperature discharge and rate discharge performance of the lithium ion battery. Among them, the comprehensive performance of Example 3 is better.

[0116] From the data of Examples 20-22, it can be seen that the combination of other structural formulas of Additive A and other structural formulas of Additive B also has a good combined effect on improving high-temperature cycling, room-temperature cycling, low-temperature discharge and rate discharge performance.

[0117] From the data of Example 3 and Example 23, it can be seen that under the action of the auxiliary additive PS containing S, the synergistic effect of additives A and B is more obvious, and the overall performance of the lithium-ion battery is more significantly improved. Among them, the comprehensive performance of Example 23 is the best.

[0118] The above-described embodiments merely represent several embodiments of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A non-aqueous electrolyte additive, characterized in that The non-aqueous electrolyte additive is used in combination with a fluorine-containing lithium salt, and the non-aqueous electrolyte additive includes additive A, additive B, and an auxiliary additive containing S; The additive A has the following structure: Formula I Wherein, R1≠R2, and said R1 and said R2 are independently selected from any one of an alkane group, an alkene group, an aromatic hydrocarbon group, pyridine, pyrrole, thiophene, thiazole and imidazole; The additive B has the following structure: Formula II The R5, R6 and R7 are independently selected from any one of an alkane group, an alkene group and a halogen fluorine atom; The sulfur-containing auxiliary additive includes at least one of vinyl sulfate, 1.3-propylene sultone and 1.3-propane sultone; The mass percentage (wt%) of the additive A and the additive B added is 0.02% to 5%.

2. The non-aqueous electrolyte additive according to claim 1, characterized in that The additive A formula I structure has the following structural formula: A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15 A16 A17.

3. The non-aqueous electrolyte additive according to claim 1, characterized in that The additive B formula II structure has the following structural formula: B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12 B13 B14 B15 B16 B17 B18.

4. A non-aqueous electrolyte, characterized in that The invention comprises a non-aqueous organic solvent, the fluorine-containing lithium salt and the non-aqueous electrolyte additive according to any one of claims 1 to 3.

5. The non-aqueous electrolyte according to claim 4, characterized in that The fluorine-containing lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate and lithium difluorophosphate.

6. The non-aqueous electrolyte according to claim 4, characterized in that The non-aqueous organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethylformamide, diethylformamide, methylpropyl carbonate, tetrahydrofuran, propylene oxide, ethyl acetate, methyl acetate, methyl butyrate, ethyl butyrate, methyl propionate, ethyl propionate and propyl acetate.

7. The non-aqueous electrolyte according to claim 4, characterized in that The total amount of the fluorine-containing lithium salt accounts for 7.0% to 15.0% of the total mass of the non-aqueous electrolyte.

8. A lithium ion battery, characterized in that: The invention comprises a battery cell and the non-aqueous electrolyte according to any one of claims 4 to 7, wherein the positive electrode sheet, the negative electrode sheet and the separator of the battery cell are all immersed in the non-aqueous electrolyte.

9. The lithium-ion battery according to claim 8, characterized in that The active material of the positive electrode sheet is a layered oxide, and the active material of the negative electrode sheet is hard carbon; and / or, The total content of N and P elements in the positive electrode sheet and / or the negative electrode sheet is not less than 100 ppm by mass.

Images