An electrolyte and a lithium-ion battery

Abstract

This invention provides an electrolyte comprising: an organic solvent; an electrolyte salt, wherein the electrolyte salt does not contain lithium ions; and additives. The problem solved by this invention is the high dependence on lithium salts in existing lithium-ion battery electrolytes, where the electrolyte salt is exclusively lithium salt. The electrolyte provided in this invention reduces the dependence of lithium-ion battery electrolytes on lithium salts, achieving the technical effect of completing lithium-ion battery charge-discharge operations without the need for lithium salts.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to an electrolyte and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are lightweight and have high energy storage capacity, making them suitable as mobile energy storage devices and power batteries. They are widely used in small electronic devices, electric vehicles, drones, and electric ships.

[0003] Lithium-ion battery electrolytes generally consist of organic solvents, lithium salts, and additives. Lithium hexafluorophosphate (LiPF6) is a commonly used lithium salt in lithium-ion battery electrolytes. However, in recent years, the price of LiPF6 has risen, leading to a gradual increase in the manufacturing cost of lithium-ion batteries.

[0004] Lithium-ion batteries achieve charging and discharging through the transport of lithium ions between the positive and negative electrodes. In principle, the electrolyte in a lithium-ion battery acts as an intermediate carrier for lithium ion transport and does not consume lithium ions during charging and discharging. While other salts can replace lithium salts, the performance of these alternative lithium salts in lithium-ion batteries is not as good as that of lithium hexafluorophosphate (LiPF6), and therefore they cannot completely replace LiPF6. Current lithium-ion battery electrolytes are highly dependent on lithium ions and require large quantities of lithium salts; there is currently no electrolyte salt that can completely replace LiPF6. Summary of the Invention

[0005] The problem solved by this invention is that the electrolyte salt in existing lithium-ion batteries is all lithium salt, which is a high degree of dependence on lithium salt. The electrolyte provided in this invention can reduce the dependence of lithium-ion battery electrolyte on lithium salt, and achieve the technical effect of lithium-ion battery transport and charging and discharging without the need for lithium salt.

[0006] To address the above problems, this invention provides an electrolyte comprising: an organic solvent; an electrolyte salt, wherein the electrolyte salt does not contain lithium ions; and an additive; wherein the cation of the electrolyte salt is one of imidazole, pyrrole, pyridinyl, or piperidinyl; and the anion of the electrolyte salt is tetrafluoroborate (BF4). - PF6 hexafluorophosphate - TFSI bis(trifluoromethanesulfonyl)imide - , difluorosulfonamide FSI - One of them.

[0007] Compared with existing technologies, the technical effects achieved by this solution are as follows: The electrolyte is the liquid used in lithium-ion batteries for lithium-ion exchange between the positive and negative electrodes. Typical electrolytes include organic solvents, electrolyte salts, and additives. Organic solvents are used to reduce the viscosity of the ionic liquid and increase the transport efficiency of lithium ions between the positive and negative electrodes. While lithium salts are generally used in lithium-ion batteries, this solution selects a lithium-ion-free salt. The additives are commonly used in lithium-ion batteries. Furthermore, selecting salts other than lithium salts as electrolyte salts helps existing lithium-ion batteries reduce their dependence on lithium. This solution, by selecting salts other than lithium salts to improve the working efficiency of lithium-ion batteries, can achieve the effect of saving lithium elements and reducing the manufacturing cost of lithium-ion batteries.

[0008] In one embodiment of the present invention, the structural formula of the imidazole group is:

[0009]

[0010] The structural formula of pyrrole is:

[0011]

[0012] The structural formula of pyridyl is:

[0013]

[0014] The structural formula of piperidinyl is:

[0015]

[0016] Tetrafluoroborate (BF4) - The structural formula is:

[0017]

[0018] hexafluorophosphate PF6 - The structural formula is:

[0019]

[0020] The structural formula of bis(trifluoromethanesulfonyl)imide TFSI is:

[0021]

[0022] The structural formula of bis(fluorosulfonyl)imide FSI is:

[0023]

[0024] R is one of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, and octyl.

[0025] Compared with existing technologies, the technical effects achieved by this technical solution are as follows: The above structural formula is a schematic diagram of the specific structure of the anions and cations of the electrolyte salt in the electrolyte of the lithium-ion battery in this case. The above electrolyte salt can effectively replace the lithium salt in the lithium-ion battery without reducing the transport efficiency of lithium ions in the electrolyte.

[0026] In one embodiment of the present invention, the electrolyte salt is one of imidazolyl hexafluorophosphate and imidazolyl bis(trifluoromethanesulfonyl)imide salt;

[0027] The structural formula of imidazole hexafluorophosphate is as follows:

[0028]

[0029] The structural formula of imidazole bis(trifluoromethanesulfonyl)imide salt is:

[0030]

[0031] R1 and R2 are each independently selected from one of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, and octyl.

[0032] Compared with existing technologies, the technical advantages achieved by this solution are as follows: This solution specifically selects two salts, imidazolyl hexafluorophosphate and imidazolyl bis(trifluoromethanesulfonyl)imide, as electrolyte salts in lithium-ion batteries. These two salts have relatively simple structures, are readily available, and outperform other salts in the electrolyte.

[0033] In one embodiment of the present invention, the imidazolyl hexafluorophosphate is 1-butyl-3-methylimidazolyl hexafluorophosphate;

[0034] The structural formula of 1-butyl-3-methylimidazolium hexafluorophosphate is:

[0035]

[0036] The imidazole bis(trifluoromethanesulfonyl)imide salt is 1-ethyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt;

[0037] The structural formula of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is:

[0038]

[0039] Compared with existing technologies, the technical effects achieved by adopting this technical solution are as follows: the selected electrolyte salts are 1-butyl-3-methylimidazolium hexafluorophosphate or 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and these two salts perform better than other salts in lithium-ion batteries.

[0040] In one embodiment of the present invention, the mass ratio of electrolyte salt in the electrolyte is 1%-10%.

[0041] Compared with existing technologies, the technical effects achieved by adopting this technical solution are as follows: the mass ratio of electrolyte salt in the electrolyte is 1%-10%, which is the optimal mass ratio. The content of electrolyte salt should not be too high, and should not exceed 50%.

[0042] In one embodiment of the invention, the mass of the additive is 0-50% of the mass of the electrolyte salt.

[0043] Compared with existing technologies, the technical effects achieved by this solution are as follows: the mass of the additive cannot exceed half the mass of the electrolyte salt. The additive is a functional additive that plays an auxiliary role in lithium-ion batteries. Its functions include: helping to form the solid electrolyte interphase (SEI) film, increasing ionic conductivity, flame retardancy, improving low-temperature or high-temperature performance, and improving the cycle stability of lithium-ion batteries. The additive includes, but is not limited to, additives containing the above functions. The mass of the additive in the lithium-ion battery electrolyte shall not exceed half the total mass of imidazole-based hexafluorophosphate and imidazole-based bis(trifluoromethanesulfonyl)imide salt.

[0044] In one embodiment of the present invention, the organic solvent is two or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, vinylene carbonate, methyl ethyl carbonate, methyl propyl carbonate, dipropyl carbonate, acid anhydride, sulfolane, dimethyl sulfoxide, dimethyl sulfite, fluorine-containing cyclic organic esters, sulfur-containing cyclic organic esters, cyclic organic esters containing unsaturated bonds, linear organic esters, and ethers.

[0045] Compared with existing technologies, the technical effects achieved by this technical solution are as follows: the organic solvent is preferably selected from two of the following: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), vinylene carbonate (VC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), and dipropyl carbonate (DPC). Preferred examples include an EC / DMC volume ratio of 3:7 and a PC / EMC volume ratio of 1:1.

[0046] In one embodiment of the present invention, the lithium-ion battery includes: an electrolyte as described in any of the above embodiments; a positive electrode, comprising a positive electrode current collector and a positive electrode material coated on the positive electrode current collector, the positive electrode material comprising a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent; and a negative electrode, comprising a negative electrode current collector and a negative electrode material coated on the negative electrode current collector, the negative electrode material comprising a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent.

[0047] In one embodiment of the present invention, the positive electrode adhesive is a mixture of a hydrophobic adhesive and a hydrophilic adhesive, wherein the mass ratio of the hydrophobic adhesive to the hydrophilic adhesive is 0.3:1 to 1:1.

[0048] Compared with existing technologies, the technical advantages achieved by this solution are as follows: there are no particular limitations on the positive electrode binder; all known positive electrode binders suitable for lithium-ion batteries can be used. Preferably, the positive electrode binder is a mixture of a hydrophobic binder and a hydrophilic binder. The ratio of the hydrophobic to the hydrophilic binder is not particularly limited and can be determined according to actual needs; for example, the mass ratio of the hydrophilic to the hydrophobic binder can be 0.3:1 to 1:1.

[0049] In one embodiment of the present invention, the mass of the positive electrode binder is 1%-5% of the mass of the positive electrode active material; the mass of the negative electrode binder is 2-5% of the mass of the negative electrode active material.

[0050] Compared with existing technologies, the technical effects achieved by this technical solution are as follows: the content of the positive electrode binder is 0.01-8% of the mass ratio of the positive electrode active material, preferably 1-5% by mass. Generally, the content of the negative electrode binder is 0.5-8% of the mass ratio of the negative electrode active material, preferably 2-5% by mass. Detailed Implementation

[0051] This invention provides an electrolyte comprising: an organic solvent; an electrolyte salt, wherein the electrolyte salt does not contain lithium ions; and additives.

[0052] The cation of the electrolyte salt is one of imidazole, pyrrole, pyridinyl, or piperidinyl; the anion of the electrolyte salt is tetrafluoroborate (BF4). - PF6 hexafluorophosphate - TFSI bis(trifluoromethanesulfonyl)imide - , difluorosulfonamide FSI - One of them.

[0053] In this embodiment, the electrolyte is the liquid used in lithium-ion batteries for lithium-ion exchange between the positive and negative electrodes. Typical electrolytes include organic solvents, electrolyte salts, and additives. The organic solvent is used to reduce the viscosity of the ionic liquid and increase the transport efficiency of lithium ions between the positive and negative electrodes. In lithium-ion batteries, lithium salts are generally used as electrolyte salts, but in this embodiment, a lithium-ion-free salt is selected. The additives are commonly used in lithium-ion batteries.

[0054] Furthermore, selecting salts other than lithium as electrolyte salts can help existing lithium-ion batteries break free from their dependence on lithium. This approach aims to improve the working efficiency of lithium-ion batteries by selecting salts other than lithium, thereby saving lithium and reducing the manufacturing cost of lithium-ion batteries.

[0055] Furthermore, this scheme provides other electrolyte salts to replace lithium salts, mainly including: the cation of the electrolyte salt is one of imidazole, pyrrole, pyridinyl, or piperidinyl; the anion of the electrolyte salt is tetrafluoroborate (BF4). - PF6 hexafluorophosphate - TFSI bis(trifluoromethanesulfonyl)imide - , difluorosulfonamide FSI - One of them.

[0056] The structural formula of the imidazole group is:

[0057]

[0058] The structural formula of pyrrole is:

[0059]

[0060] The structural formula of pyridyl is:

[0061]

[0062] The structural formula of piperidinyl is:

[0063]

[0064] Tetrafluoroborate (BF4) - The structural formula is:

[0065]

[0066] hexafluorophosphate PF6 - The structural formula is:

[0067]

[0068] The structural formula of bis(trifluoromethanesulfonyl)imide TFSI is:

[0069]

[0070] The structural formula of bis(fluorosulfonyl)imide FSI is:

[0071]

[0072] R is one of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, and octyl.

[0073] In this embodiment, the above structural formula is a schematic diagram of the specific structures of the anions and cations of the electrolyte salt in the electrolyte of the lithium-ion battery in this case. The above electrolyte salt can effectively replace the lithium salt in the lithium-ion battery and will not reduce the transport efficiency of lithium ions in the electrolyte.

[0074] The electrolyte salt is one of imidazolyl hexafluorophosphate and imidazolyl bis(trifluoromethanesulfonyl)imide salt;

[0075] The structural formula of imidazole hexafluorophosphate is as follows:

[0076]

[0077] The structural formula of imidazole bis(trifluoromethanesulfonyl)imide salt is:

[0078]

[0079] R1 and R2 are each independently selected from one of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, and octyl.

[0080] In this embodiment, imidazole-based hexafluorophosphate and imidazole-based bis(trifluoromethanesulfonyl)imide salt are specifically selected as electrolyte salts for use in lithium-ion batteries. These two salts have relatively simple structures, are readily available, and are superior to other salts in the electrolyte.

[0081] Imidazolyl hexafluorophosphate is 1-butyl-3-methylimidazolyl hexafluorophosphate;

[0082] The structural formula of 1-butyl-3-methylimidazolium hexafluorophosphate is:

[0083]

[0084] The imidazole bis(trifluoromethanesulfonyl)imide salt is 1-ethyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt;

[0085] The structural formula of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is:

[0086]

[0087] In this embodiment, the selected electrolyte salt is 1-butyl-3-methylimidazolium hexafluorophosphate or 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt. These two salts are more effective than other salts in lithium-ion batteries.

[0088] The mass ratio of electrolyte salts in the electrolyte is 1%-10%.

[0089] In this embodiment, the electrolyte salt content is 1%-10% by mass, which is the most preferred mass ratio. The electrolyte salt content should not be too high and should not exceed 50%.

[0090] Specifically, the total content of imidazole hexafluorophosphate and imidazole bis(trifluoromethanesulfonyl)imide salt is 0.1%-50% by mass, preferably 3-6% by mass. If 5% by mass of 1-butyl-3-methylimidazole hexafluorophosphate is added to the electrolyte of a lithium-ion battery, the total mass ratio of organic solvents and additives is 95%.

[0091] In the electrolyte, the mass of the additive is 0-50% of the mass of the electrolyte salt.

[0092] In this embodiment, the mass of the additive cannot exceed half the mass of the electrolyte salt. The additive is a functional additive that plays an auxiliary role in the lithium-ion battery. Its functions include: helping to form the solid electrolyte interphase (SEI) film, increasing ionic conductivity, flame retardancy, improving low-temperature or high-temperature performance, and improving the cycle stability of the lithium-ion battery. The additive includes, but is not limited to, additives containing the above-mentioned functions. The mass of the additive in the lithium-ion battery electrolyte does not exceed half the total mass of imidazole hexafluorophosphate and imidazole bis(trifluoromethanesulfonyl)imide salt.

[0093] The organic solvent is two or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, vinylene carbonate, methyl ethyl carbonate, methyl propyl carbonate, dipropyl carbonate, acid anhydride, sulfolane, dimethyl sulfoxide, dimethyl sulfite, fluorine-containing cyclic organic esters, sulfur-containing cyclic organic esters, cyclic organic esters containing unsaturated bonds, linear organic esters, and ethers.

[0094] In this embodiment, the organic solvent is preferably two selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), vinylene carbonate (VC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), and dipropyl carbonate (DPC). Preferred examples include an EC / DMC volume ratio of 3:7 and a PC / EMC volume ratio of 1:1.

[0095] This invention provides a lithium-ion battery, which includes:

[0096] The electrolyte as described in any of the above embodiments;

[0097] The positive electrode includes a positive current collector and a positive electrode material. The positive electrode material is coated on the positive current collector and includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0098] The negative electrode includes a negative current collector and a negative electrode material. The negative electrode material is coated on the negative current collector and includes a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent.

[0099] In this embodiment, the positive electrode of a lithium-ion battery typically includes a positive current collector and a positive electrode material coated or filled on the current collector. The current collector can be any type of current collector known to those skilled in the art, such as aluminum foil, copper foil, nickel-plated steel strip, etc. In this invention, aluminum foil is selected as the positive current collector. The positive electrode material can be any type of positive electrode material known to those skilled in the art, typically including a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent. The positive electrode active material can be selected from conventional positive electrode active materials used in lithium-ion batteries.

[0100] The content of the positive electrode conductive agent is as follows: based on the positive electrode material, the content of the positive electrode conductive agent is generally 0-15% by mass, preferably 0-10% by mass. The positive electrode conductive agent can be selected from one or more of conductive carbon black, acetylene black, nickel powder, copper powder and conductive graphite.

[0101] The negative electrode includes a negative electrode current collector and a negative electrode material coated or filled on the negative electrode current collector. The negative electrode current collector is well-known to those skilled in the art and can be selected from one or more of aluminum foil, copper foil, nickel-plated steel strip, and perforated steel strip; preferably, the negative electrode current collector is copper foil. The negative electrode material includes a negative electrode active material and a negative electrode binder, and optionally includes a negative electrode conductive agent. The negative electrode active material can be selected from one or more of conventional negative electrode active materials for lithium-ion batteries, such as natural graphite, artificial graphite, petroleum coke, organic pyrolysis carbon, mesophase carbon microspheres, carbon fiber, tin alloy, and silicon alloy.

[0102] The adhesive can be selected from one or more of the commonly used adhesives for lithium-ion batteries, such as polyvinyl alcohol, polytetrafluoroethylene, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0103] The positive electrode adhesive is a mixture of hydrophobic and hydrophilic adhesives, with a mass ratio of 0.3:1 to 1:1.

[0104] In this embodiment, there are no particular limitations on the positive electrode adhesive; any positive electrode adhesive known in the art that can be used in lithium-ion batteries can be employed. Preferably, the positive electrode adhesive is a mixture of a hydrophobic adhesive and a hydrophilic adhesive. The ratio of the hydrophobic adhesive to the hydrophilic adhesive is not particularly limited and can be determined according to actual needs; for example, the mass ratio of the hydrophilic adhesive to the hydrophobic adhesive can be 0.3:1 to 1:1.

[0105] The positive electrode binder can be used in aqueous solution or emulsion form, or in solid form, preferably in aqueous solution or emulsion form. In this case, there are no particular limitations on the concentration of the hydrophilic binder solution and the concentration of the hydrophobic binder emulsion; these concentrations can be flexibly adjusted according to the viscosity and operability requirements of the positive and negative electrode slurries to be prepared for coating. For example, the concentration of the hydrophilic binder solution can be 0.5-4% by mass, and the concentration of the hydrophobic binder emulsion can be 10-80% by mass. The hydrophobic binder can be polytetrafluoroethylene, styrene-butadiene rubber, or mixtures thereof. The hydrophilic binder can be hydroxypropyl methylcellulose, sodium carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, or mixtures thereof.

[0106] The mass of the positive electrode binder is 1%-5% of the mass of the positive electrode active material;

[0107] The mass of the negative electrode binder is 2-5% of the mass of the negative electrode active material.

[0108] In this embodiment, the content of the positive electrode binder is 0.01-8% of the positive electrode active material by mass, preferably 1-5% by mass. Generally, the content of the negative electrode binder is 0.5-8% of the negative electrode active material by mass, preferably 2-5% by mass.

[0109] The organic solvents used in this invention to prepare the positive and negative electrode slurries can be selected from conventional solvents, including but not limited to one or more of N-methylpyrrolidone (NMP), dimethylformamide (DMF), diethylformamide (DEF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), water, and alcohols. The amount of solvent used is sufficient to coat the slurry onto the current collector. Generally, the amount of solvent is such that the concentration of the positive electrode active material in the slurry is 40-90% by mass, preferably 50-85% by mass.

[0110] The separator layer, possessing both electrical insulation and liquid retention properties, is positioned between the positive and negative electrodes and is sealed together with the positive and negative electrodes and the electrolyte within the battery casing. The separator layer can be any type of separator layer commonly used in the art, such as a composite membrane formed by welding or bonding various brands of modified polyethylene felt, modified polypropylene felt, ultrafine glass fiber felt, vinylon felt, or nylon felt to a wettable polyolefin microporous membrane, sourced commercially available to those skilled in the art.

[0111] Similar to existing technologies, the preparation method of the positive electrode involves coating a slurry containing a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent onto a positive electrode current collector, followed by drying, rolling, and slicing to obtain the positive electrode. Drying is typically carried out at 50-100°C, preferably at 60-80°C.

[0112] The preparation method of the negative electrode and the preparation method of the positive electrode both involve coating a slurry containing a negative electrode active material, a negative electrode binder and a selectively contained negative electrode conductive agent onto a negative electrode current collector, followed by drying, rolling, and slicing to obtain the negative electrode.

[0113] Example 1:

[0114] Organic solvent: EC + DMC. The organic solvent is obtained by mixing EC and DMC in a volume ratio of 3:7. The above steps are carried out in a glove box containing argon.

[0115] The salt used in this embodiment is 1-ethyl-3-methylimidazolium hexafluorophosphate, with the following structural formula:

[0116]

[0117] The salts mentioned above are liquid at room temperature, i.e., ionic liquids. The ionic liquids are vacuum dried at 80°C for 4 hours in a vacuum drying oven.

[0118] The salts mentioned above were added to the organic solvent in a ratio relative to the mass of the electrolyte, and the mixture was stirred until homogeneous to obtain the desired electrolyte. The above steps were carried out in a glove box containing argon gas. The content of each component of the resulting electrolyte is shown in Table 1.

[0119] No additives were used in any of the examples or comparative examples.

[0120] Positive electrode material: Active material LiFePO4, conductive carbon black, and polyvinylidene fluoride are dissolved in N-methylpyrrolidone at a weight ratio of 8:1:1 to form a battery slurry with a solid content of 25wt%. After stirring for 4-6 hours, the slurry is coated on both sides of an aluminum foil with a thickness of 16μm and dried at 60℃±5℃ for 4-8 hours. Then, after calendering and vacuum drying, a material layer with a thickness of 230μm±10μm is formed to obtain the positive electrode material.

[0121] Negative electrode material: Graphite, conductive carbon black, and carboxymethyl cellulose are dissolved in deionized water at a weight ratio of 9:0.5:0.5 to obtain a negative electrode slurry. The slurry is stirred for 4-6 hours and then coated on both sides of a copper foil with a thickness of 12μm. The foil is then dried at 60℃±5℃ for 4-8 hours. After calendering and vacuum drying, a material layer with a thickness of 320μm±10μm is formed, thus obtaining the negative electrode material.

[0122] Assembly of the pouch battery: The above-mentioned positive and negative electrode sheets are wound with a 20-micron-thick polypropylene separator into a rectangular lithium-ion battery pack, which is then placed into a pouch battery and sealed. Subsequently, the electrolyte prepared above is injected into the pouch battery, and the pack is sealed. The above lithium-ion battery assembly process is carried out in a glove box. The battery prepared according to Example 1 is designated as C1.

[0123] Example 2:

[0124] Organic solvent: EC + DMC. The organic solvent is obtained by mixing EC and DMC in a volume ratio of 3:7. The above steps are carried out in a glove box containing argon.

[0125] The salt used in this embodiment is 1-butyl-3-methylimidazolium hexafluorophosphate, with the following structural formula:

[0126]

[0127] The salts mentioned above are liquid at room temperature, i.e., ionic liquids. The ionic liquids are vacuum dried at 80°C for 4 hours in a vacuum drying oven.

[0128] The salts mentioned above were added to the organic solvent in a ratio relative to the mass of the electrolyte, and the mixture was stirred until homogeneous to obtain the desired electrolyte. The above steps were carried out in a glove box containing argon gas. The content of each component of the resulting electrolyte is shown in Table 1.

[0129] No additives were used in any of the examples or comparative examples.

[0130] Positive electrode material: Active material LiFePO4, conductive carbon black, and polyvinylidene fluoride are dissolved in N-methylpyrrolidone at a weight ratio of 8:1:1 to form a battery slurry with a solid content of 25wt%. After stirring for 4-6 hours, the slurry is coated on both sides of an aluminum foil with a thickness of 16μm and dried at 60℃±5℃ for 4-8 hours. Then, after calendering and vacuum drying, a material layer with a thickness of 230μm±10μm is formed to obtain the positive electrode material.

[0131] Negative electrode material: Graphite, conductive carbon black, and carboxymethyl cellulose are dissolved in deionized water at a weight ratio of 9:0.5:0.5 to obtain a negative electrode slurry. The slurry is stirred for 4-6 hours and then coated on both sides of a copper foil with a thickness of 12μm. The foil is then dried at 60℃±5℃ for 4-8 hours. After calendering and vacuum drying, a material layer with a thickness of 320μm±10μm is formed, thus obtaining the negative electrode material.

[0132] Assembly of the pouch battery: The above-mentioned positive and negative electrode sheets and a 20-micron-thick polypropylene separator are wound into a rectangular lithium-ion battery pack, which is then placed into a pouch battery and sealed. Subsequently, the electrolyte prepared earlier is injected into the pouch battery, and the pack is sealed. The above lithium-ion battery assembly process is carried out in a glove box. The battery prepared according to Example 2 is designated as C2.

[0133] Example 3:

[0134] Organic solvent: EC + DMC. The organic solvent is obtained by mixing EC and DMC in a volume ratio of 3:7. The above steps are carried out in a glove box containing argon.

[0135] The salt used in this embodiment is 1-butyl-3-methylimidazolium hexafluorophosphate, with the following structural formula:

[0136]

[0137] The salts mentioned above are liquid at room temperature, i.e., ionic liquids. The ionic liquids are vacuum dried at 80°C for 4 hours in a vacuum drying oven.

[0138] The salt, in proportion to the mass ratio of the electrolyte, was added to the organic solvent and stirred until homogeneous to obtain the desired electrolyte. The above steps were performed in a glove box containing argon gas. The composition of the resulting electrolyte is shown in Table 1. In this embodiment, it contains 50 wt% 1-butyl-3-methylimidazolium hexafluorophosphate.

[0139] No additives were used in any of the examples or comparative examples.

[0140] Positive electrode material: Active material LiFePO4, conductive carbon black, and polyvinylidene fluoride are dissolved in N-methylpyrrolidone at a weight ratio of 8:1:1 to form a battery slurry with a solid content of 25wt%. After stirring for 4-6 hours, the slurry is coated on both sides of an aluminum foil with a thickness of 16μm and dried at 60℃±5℃ for 4-8 hours. Then, after calendering and vacuum drying, a material layer with a thickness of 230μm±10μm is formed to obtain the positive electrode material.

[0141] Negative electrode material: Graphite, conductive carbon black, and carboxymethyl cellulose are dissolved in deionized water at a weight ratio of 9:0.5:0.5 to obtain a negative electrode slurry. The slurry is stirred for 4-6 hours and then coated on both sides of a copper foil with a thickness of 12μm. The foil is then dried at 60℃±5℃ for 4-8 hours. After calendering and vacuum drying, a material layer with a thickness of 320μm±10μm is formed, thus obtaining the negative electrode material.

[0142] Assembly of the pouch cell: The positive and negative electrode sheets described above are wound together with a 20-micron-thick polypropylene separator to form a rectangular lithium-ion battery pack, which is then placed into a pouch cell and sealed. The electrolyte prepared earlier is then injected into the pouch cell, and the pack is sealed. The lithium-ion battery assembly process described above is carried out in a glove box. The battery prepared according to Example 3 is designated C3.

[0143] Example 4:

[0144] Organic solvent: EC + DMC. The organic solvent is obtained by mixing EC and DMC in a volume ratio of 3:7. The above steps are carried out in a glove box containing argon.

[0145] The salt used in this embodiment is 1-hexyl-3-methylimidazolium hexafluorophosphate, with the following structural formula:

[0146]

[0147] The salts mentioned above are liquid at room temperature, i.e., ionic liquids. The ionic liquids are vacuum dried at 80°C for 4 hours in a vacuum drying oven.

[0148] The salts mentioned above were added to the organic solvent in a ratio relative to the mass of the electrolyte, and the mixture was stirred until homogeneous to obtain the desired electrolyte. The above steps were carried out in a glove box containing argon gas. The content of each component of the resulting electrolyte is shown in Table 1.

[0149] No additives were used in any of the examples or comparative examples.

[0150] Positive electrode material: Active material LiFePO4, conductive carbon black, and polyvinylidene fluoride are dissolved in N-methylpyrrolidone at a weight ratio of 8:1:1 to form a battery slurry with a solid content of 25wt%. After stirring for 4-6 hours, the slurry is coated on both sides of an aluminum foil with a thickness of 16μm and dried at 60℃±5℃ for 4-8 hours. Then, after calendering and vacuum drying, a material layer with a thickness of 230μm±10μm is formed to obtain the positive electrode material.

[0151] Negative electrode material: Graphite, conductive carbon black, and carboxymethyl cellulose are dissolved in deionized water at a weight ratio of 9:0.5:0.5 to obtain a negative electrode slurry. The slurry is stirred for 4-6 hours and then coated on both sides of a copper foil with a thickness of 12μm. The foil is then dried at 60℃±5℃ for 4-8 hours. After calendering and vacuum drying, a material layer with a thickness of 320μm±10μm is formed, thus obtaining the negative electrode material.

[0152] Assembly of the pouch battery: The above-mentioned positive and negative electrode sheets and a 20-micron-thick polypropylene separator are wound into a rectangular lithium-ion battery pack, which is then placed into a pouch battery and sealed. Subsequently, the electrolyte prepared earlier is injected into the pouch battery, and the pack is sealed. The above lithium-ion battery assembly process is carried out in a glove box. The battery prepared according to Example 4 is designated as C4.

[0153] Example 5:

[0154] Organic solvent: EC + DMC. The organic solvent is obtained by mixing EC and DMC in a volume ratio of 3:7. The above steps are carried out in a glove box containing argon.

[0155] The salt used in this embodiment is 1-octyl-3-methylimidazolium hexafluorophosphate, with the following structural formula:

[0156]

[0157] The salts mentioned above are liquid at room temperature, i.e., ionic liquids. The ionic liquids are vacuum dried at 80°C for 4 hours in a vacuum drying oven.

[0158] The salts mentioned above were added to the organic solvent in a ratio relative to the mass of the electrolyte, and the mixture was stirred until homogeneous to obtain the desired electrolyte. The above steps were carried out in a glove box containing argon gas. The content of each component of the resulting electrolyte is shown in Table 1.

[0159] No additives were used in any of the examples or comparative examples.

[0160] Positive electrode material: Active material LiFePO4, conductive carbon black, and polyvinylidene fluoride are dissolved in N-methylpyrrolidone at a weight ratio of 8:1:1 to form a battery slurry with a solid content of 25wt%. After stirring for 4-6 hours, the slurry is coated on both sides of an aluminum foil with a thickness of 16μm and dried at 60℃±5℃ for 4-8 hours. Then, after calendering and vacuum drying, a material layer with a thickness of 230μm±10μm is formed to obtain the positive electrode material.

[0161] Negative electrode material: Graphite, conductive carbon black, and carboxymethyl cellulose are dissolved in deionized water at a weight ratio of 9:0.5:0.5 to obtain a negative electrode slurry. The slurry is stirred for 4-6 hours and then coated on both sides of a copper foil with a thickness of 12μm. The foil is then dried at 60℃±5℃ for 4-8 hours. After calendering and vacuum drying, a material layer with a thickness of 320μm±10μm is formed, thus obtaining the negative electrode material.

[0162] Assembly of the pouch battery: The above-mentioned positive and negative electrode sheets and a 20-micron-thick polypropylene separator are wound into a rectangular lithium-ion battery pack, which is then placed into a pouch battery and sealed. Subsequently, the electrolyte prepared earlier is injected into the pouch battery, and the pack is sealed. The above lithium-ion battery assembly process is carried out in a glove box. The battery prepared according to Example 5 is designated as C5.

[0163] Example 6:

[0164] Organic solvent: EC + DMC. The organic solvent is obtained by mixing EC and DMC in a volume ratio of 3:7. The above steps are carried out in a glove box containing argon.

[0165] The salt used in this embodiment is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, with the following structural formula:

[0166]

[0167] 1-Ethyl-3-methylimidazolium hexafluorophosphate is a solid salt at room temperature and needs to be dried in an oven at 60°C for 4 hours.

[0168] The salts mentioned above were added to the organic solvent in a ratio relative to the mass of the electrolyte, and the mixture was stirred until homogeneous to obtain the desired electrolyte. The above steps were carried out in a glove box containing argon gas. The content of each component of the resulting electrolyte is shown in Table 1.

[0169] No additives were used in any of the examples or comparative examples.

[0170] Positive electrode material: Active material LiFePO4, conductive carbon black, and polyvinylidene fluoride are dissolved in N-methylpyrrolidone at a weight ratio of 8:1:1 to form a battery slurry with a solid content of 25wt%. After stirring for 4-6 hours, the slurry is coated on both sides of an aluminum foil with a thickness of 16μm and dried at 60℃±5℃ for 4-8 hours. Then, after calendering and vacuum drying, a material layer with a thickness of 230μm±10μm is formed to obtain the positive electrode material.

[0171] Negative electrode material: Graphite, conductive carbon black, and carboxymethyl cellulose are dissolved in deionized water at a weight ratio of 9:0.5:0.5 to obtain a negative electrode slurry. The slurry is stirred for 4-6 hours and then coated on both sides of a copper foil with a thickness of 12μm. The foil is then dried at 60℃±5℃ for 4-8 hours. After calendering and vacuum drying, a material layer with a thickness of 320μm±10μm is formed, thus obtaining the negative electrode material.

[0172] Assembly of the pouch battery: The above-mentioned positive and negative electrode sheets and a 20-micron-thick polypropylene separator are wound into a rectangular lithium-ion battery pack, which is then placed into a pouch battery and sealed. Subsequently, the electrolyte prepared earlier is injected into the pouch battery, and the pack is sealed. The above lithium-ion battery assembly process is carried out in a glove box. The battery prepared according to Example 6 is designated as C6.

[0173] Comparative Example 1:

[0174] Organic solvent: EC + DMC. The organic solvent is obtained by mixing EC and DMC in a volume ratio of 3:7. The above steps are carried out in a glove box containing argon.

[0175] The salt used in this embodiment is lithium hexafluorophosphate with a concentration of 1 mol / L.

[0176] The salts mentioned above were added to the organic solvent in a ratio relative to the mass of the electrolyte, and the mixture was stirred until homogeneous to obtain the desired electrolyte. The above steps were carried out in a glove box containing argon gas. The content of each component of the resulting electrolyte is shown in Table 1.

[0177] No additives were used in any of the examples or comparative examples.

[0178] Positive electrode material: Active material LiFePO4, conductive carbon black, and polyvinylidene fluoride are dissolved in N-methylpyrrolidone at a weight ratio of 8:1:1 to form a battery slurry with a solid content of 25wt%. After stirring for 4-6 hours, the slurry is coated on both sides of an aluminum foil with a thickness of 16μm and dried at 60℃±5℃ for 4-8 hours. Then, after calendering and vacuum drying, a material layer with a thickness of 230μm±10μm is formed to obtain the positive electrode material.

[0179] Negative electrode material: Graphite, conductive carbon black, and carboxymethyl cellulose are dissolved in deionized water at a weight ratio of 9:0.5:0.5 to obtain a negative electrode slurry. The slurry is stirred for 4-6 hours and then coated on both sides of a copper foil with a thickness of 12μm. The foil is then dried at 60℃±5℃ for 4-8 hours. After calendering and vacuum drying, a material layer with a thickness of 320μm±10μm is formed, thus obtaining the negative electrode material.

[0180] Assembly of the pouch battery: The positive and negative electrode sheets described above are wound together with a 20-micron-thick polypropylene separator to form a rectangular lithium-ion battery pack, which is then placed into a pouch battery and sealed. The electrolyte prepared earlier is then injected into the pouch battery, and the pack is sealed. The above lithium-ion battery assembly process is carried out in a glove box. The battery prepared according to Comparative Example 1 is designated as C7.

[0181] Table 1

[0182]

[0183]

[0184] Performance testing:

[0185] Pouch cell formation treatment: The batteries C1-C7 prepared according to the above embodiments underwent formation treatment before all tests began. This involved activating the batteries with a high current, allowing them to stand for at least 6 hours after installation, then charging them to 3.8V with a 228mA current and discharging them to 2.0V with a 228mA current. Pouch cell formation has no special requirements regarding ambient temperature; however, high-temperature formation can be performed if conditions permit.

[0186] The lithium-ion battery electrolytes and lithium-ion batteries prepared in Examples 1 to 6 and Comparative Example 1 were tested as follows:

[0187] Conductivity test: The conductivity of the electrolytes prepared in Examples 1 to 6 and Comparative Example 1 was tested at 25°C using a conductivity meter. The test results are shown in Table 1.

[0188] Cyclic performance testing: Batteries C1-C7 were installed in the Blue Battery testing system and subjected to 200 cycles in a 25°C constant temperature chamber with a current of 57mA, an upper voltage of 3.8V, and a lower voltage of 2.3V. The discharge specific capacity of the battery in the first cycle and the capacity retention rate at 100 and 200 cycles (i.e., the ratio of the capacity at the 100th and 200th cycles to the capacity at the 1st cycle) were recorded.

[0189] The test results are shown in Table 2:

[0190] Table 2

[0191]

[0192]

[0193] The data in Table 1 show that the electrolytes prepared according to Examples 1 to 6 of the present invention have lower conductivity than the conventional LiPF6 electrolyte compared to Comparative Example 1, but are within an acceptable range, greater than 2.0 mS / cm. The lithium salt-free solvent can be used as an electrolyte for lithium-ion batteries.

[0194] As can be seen from the data in Table 2, the batteries C1-C6 prepared according to Examples 1 to 6 of the present invention have a slightly higher 100-cycle capacity retention rate than the battery prepared according to Comparative Example 1 C7, and a significantly higher 200-cycle capacity retention rate than the conventional lithium-ion battery electrolyte using LiPF6.

[0195] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A lithium-ion battery, characterized by, The lithium ion battery comprises: an electrolyte solution, the electrolyte solution not containing lithium ions, the electrolyte solution comprising an organic solvent and an electrolyte salt, a cation of the electrolyte salt being one of an imidazole group, a pyrrole group, a pyridine group, and a piperidine group; an anion of the electrolyte salt being one of a tetrafluoroborate ion, a hexafluorophosphate ion, a bistrifluoromethanesulfonylimide ion, and a bisfluorosulfonylimide ion; a positive electrode, the positive electrode comprising a positive electrode current collector and a positive electrode material, the positive electrode material being coated on the positive electrode current collector, the positive electrode material comprising a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent; a negative electrode, the negative electrode comprising a negative electrode current collector and a negative electrode material, the negative electrode material being coated on the negative electrode current collector, the negative electrode material comprising a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent.

2. The lithium ion battery according to claim 1, wherein a structure formula of the imidazole group is: a structure formula of the pyrrole group is: a structure formula of the pyridine group is: a structure formula of the piperidine group is: a structure formula of the tetrafluoroborate ion is: a structure formula of the hexafluorophosphate ion is: a structure formula of the bistrifluoromethanesulfonylimide ion is: a structure formula of the bisfluorosulfonylimide ion is: R is one of a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, and an octyl group. the electrolyte salt is one of an imidazole hexafluorophosphate salt and an imidazole bistrifluoromethanesulfonylimide salt; 3. The lithium-ion battery of claim 1, wherein, a structure formula of the imidazole hexafluorophosphate salt is: a structure formula of the imidazole bistrifluoromethanesulfonylimide salt is: R1 and R2 are independently selected from one of a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, and an octyl group.

4. The lithium ion battery according to claim 3, wherein the imidazole hexafluorophosphate salt is a 1-butyl-3-methyl imidazole hexafluorophosphate salt; a structure formula of the 1-butyl-3-methyl imidazole hexafluorophosphate salt is: the imidazole bistrifluoromethanesulfonylimide salt is a 1-ethyl-3-methyl imidazole bistrifluoromethylsulfonylimide salt; a structure formula of the 1-ethyl-3-methyl imidazole bistrifluoromethylsulfonylimide salt is: a mass ratio of the electrolyte salt in the electrolyte solution is 1% to 10%. the organic solvent is two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, vinylene carbonate, methyl ethyl carbonate, methyl propyl carbonate, dipropyl carbonate, an anhydride, a cyclic sulfone, dimethyl sulfoxide, dimethyl sulfite, a fluorine-containing cyclic organic ester, a sulfur-containing cyclic organic ester, an unsaturated bond-containing cyclic organic ester, a linear organic ester, and an ether. 。 5. The lithium-ion battery of any one of claims 1-4, wherein, the positive electrode binder is a mixture of a hydrophobic binder and a hydrophilic binder, a mass ratio of the hydrophobic binder to the hydrophilic binder being 0.3:1 to 1:

1.

6. The lithium-ion battery of any one of claims 1-4, wherein, 8. The lithium ion battery according to claim 1, wherein a mass of the positive electrode binder is 1% to 5% of a mass of the positive electrode active material; and a mass of the negative electrode binder is 2% to 5% of a mass of the negative electrode active material.

7. The lithium-ion battery of claim 1, wherein, ​ ​ ​ ​

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