阅读说明：本技术 一种高功率电解液及含有该电解液的锂离子电池 (High-power electrolyte and lithium ion battery containing same ) 是由 廖波 李素丽 王海 徐延铭 李俊义 于 2020-06-11 设计创作，主要内容包括：本发明属于锂离子电池技术领域,具体涉及一种高功率电解液及含有该电解液的锂离子电池。本发明采用功率性能较好的磷酸铁锂正极材料,同时使用了高锂离子迁移率的溶剂、添加剂组合和锂盐,提高电解液性能的功率性能。本发明的电解液添加剂能够在正负极表面性能强度较高的保护膜进而提高了电池的高温性能。同时使用了分解温度较高的锂盐,进而提高了锂离子电池的安全性能。(The invention belongs to the technical field of lithium ion batteries, and particularly relates to a high-power electrolyte and a lithium ion battery containing the same. The lithium iron phosphate anode material with good power performance is adopted, and the solvent with high lithium ion mobility, the additive combination and the lithium salt are used, so that the power performance of the electrolyte is improved. The electrolyte additive can be used for protecting the surface of the anode and the cathode with higher performance strength, so that the high-temperature performance of the battery is improved. And meanwhile, the lithium salt with higher decomposition temperature is used, so that the safety performance of the lithium ion battery is improved.)

1. An electrolyte comprising a conductive lithium salt, an additive, and a solvent; wherein the additive comprises lithium difluorophosphate, ethylene sulfate, vinylene carbonate and lithium borophosphate oxalate; the solvent comprises ethyl 3-methoxypropionate.

2. The electrolyte of claim 1, wherein the solvent further comprises at least one of a cyclic carbonate, a linear carbonate, and a linear carboxylate.

3. The electrolyte of claim 2, wherein the cyclic carbonate is selected from at least one of ethylene carbonate and propylene carbonate;

the linear carbonate is at least one selected from dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate;

the linear carboxylic acid ester is at least one selected from ethyl propionate, propyl propionate and propyl acetate.

4. The electrolyte of any one of claims 1-3, wherein the ethyl 3-methoxypropionate is added in an amount of 10% to 50% by weight of the total electrolyte.

5. The electrolyte of any one of claims 1 to 4, wherein the lithium boron phosphorus oxalate is selected from at least one compound represented by the following structural formula:

wherein R is₁-R₈Identical or different, independently of one another, from H, F, halogen-substituted C_1-6Alkyl (e.g. CF)₃-)。

6. The electrolyte as claimed in any one of claims 1 to 5, wherein the addition amount of the lithium boron phosphorus oxalate accounts for 0.1 to 4 percent of the total mass of the electrolyte; and/or the addition amount of the vinyl sulfate accounts for 0.1-5% of the total mass of the electrolyte; and/or the addition amount of the lithium difluorophosphate accounts for 0.1-2% of the total mass of the electrolyte; and/or the addition amount of the vinylene carbonate accounts for 0.1-3% of the total mass of the electrolyte.

7. The electrolyte of any one of claims 1-6, wherein the conductive lithium salt is selected from lithium bis-fluorosulfonylimide and lithium hexafluorophosphate;

the addition amount of the conductive lithium salt accounts for 14-20% of the total mass of the electrolyte.

8. A lithium ion battery comprising the electrolyte of any of claims 1-7.

9. The lithium ion battery of claim 8, wherein the lithium ion battery further comprises a positive electrode, a negative electrode, a separator;

the positive electrode comprises a positive electrode active substance layer and a positive electrode current collector, the positive electrode active substance layer is arranged on the surface of one side or two sides of the positive electrode current collector, the positive electrode active substance layer comprises a positive electrode active substance, a conductive agent and a binder, and the positive electrode active substance is lithium iron phosphate; the median particle size of the lithium iron phosphate is 0.2-5 mu m; the specific surface area of the lithium iron phosphate is 4-22m²/g。

10. The lithium ion battery of claim 8 or 9, wherein the lithium ion battery has at least one of the following properties:

(1) the lithium ion battery is a high-power lithium ion battery, and the power density of the lithium ion battery is more than or equal to 5000W/kg;

(2) the capacity retention rate of the lithium ion battery after being stored for 90 days at 60 ℃ is more than or equal to 85 percent;

(3) the capacity recovery rate of the lithium ion battery after being stored for 90 days at 60 ℃ is more than or equal to 89%;

(4) the thickness change rate of the lithium ion battery after being stored for 90 days at 60 ℃ is less than or equal to 6 percent;

(5) the capacity retention rate of the lithium ion battery after circulation for 500 weeks at 55 ℃ is more than or equal to 86 percent;

(6) the voltage of the lithium ion battery after discharging for 2s at the rate of 10C is more than or equal to 2.4V.

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a high-power electrolyte and a lithium ion battery containing the same.

Background

In recent years, the automobile industry in China is rapidly developed, and the quantity of automobiles in China is continuously improved. In the face of increasingly serious energy and environmental crisis, a plurality of laws and regulations for energy conservation and emission reduction of automobiles are provided in China. The 48V hybrid power system for the automobile can realize the functions of sliding start-stop, kinetic energy recovery, auxiliary acceleration and the like, and the oil saving rate is 14-17%.

However, compared with a pure electric lithium ion battery, starting and stopping the lithium ion battery provides higher requirements for high and low temperature performance, power performance, index of cycle life and consideration of all performances. The design of the anode and the electrolyte which are used as main components of the lithium ion battery is a main factor for hindering the performance of starting and stopping the high-power lithium ion battery. Therefore, the combination of the electrolyte and the anode material which can meet the requirements of high-power discharge and high-temperature performance needs to be developed, which has important significance for the application development of starting and stopping high-power batteries.

Disclosure of Invention

The invention provides a high-power electrolyte with high and low temperature performance, and a high-power lithium ion battery using the electrolyte, aiming at solving the problems that the current lithium ion battery has low power density and is difficult to give consideration to high and low temperature performance, and the like.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

an electrolyte comprising a conductive lithium salt, an additive, and a solvent; wherein the additive comprises lithium difluorophosphate, ethylene sulfate, vinylene carbonate and lithium borophosphate oxalate; the solvent comprises ethyl 3-methoxypropionate.

According to the present invention, the solvent further includes at least one of a cyclic carbonate, a linear carbonate and a linear carboxylate.

Wherein the cyclic carbonate is selected from at least one of ethylene carbonate and propylene carbonate.

Wherein the linear carbonate is at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

Wherein the linear carboxylic acid ester is at least one selected from ethyl propionate, propyl propionate and propyl acetate.

According to the invention, the viscosity of the ethyl 3-methoxypropionate is higher than that of the cyclic carbonate, the linear carbonate and the linear carboxylate, but the number of polar functional groups in the molecular structure is larger, and when the ethyl 3-methoxypropionate is used as an electrolyte solvent, the ethyl 3-methoxypropionate can form a solvation structure with the following structural formula with lithium ions in the electrolyte, and the solvation structure can jump-move the lithium ions in the electrolyte, so that the migration rate of the lithium ions in the electrolyte can be rapidly increased, the purpose of rapidly moving the lithium ions between a positive electrode and a negative electrode of the electrolyte is realized, and the power density of the lithium ion battery is increased. The mechanism of action of the solvated structure is as follows:

according to the invention, the adding amount of the ethyl 3-methoxypropionate accounts for 10-50% of the total mass of the electrolyte, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% and 50%.

According to the invention, the boron phosphorus lithium oxalate is selected from at least one of the compounds shown in the following structural formula:

wherein R is₁-R₈Identical or different, independently of one another, from H, F, halogen-substituted C_1-6Alkyl (e.g. CF)₃-)。

Illustratively, the boron phosphorus lithium oxalate is selected from at least one of the compounds shown in the following structural formula:

according to the invention, the addition amount of the boron phosphorus lithium oxalate accounts for 0.1-4%, such as 0.1-2%, such as 0.1-1%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4% of the total mass of the electrolyte.

According to the invention, the addition amount of the vinyl sulfate accounts for 0.1-5% of the total mass of the electrolyte, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.4%, 4.5%, 4.8%, 5%.

According to the invention, the addition amount of the lithium difluorophosphate accounts for 0.1-2% of the total mass of the electrolyte, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8% and 2%.

According to the invention, the vinylene carbonate is added in an amount of 0.1-3% of the total mass of the electrolyte, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%.

The additive is added with the ethylene sulfate, the lithium difluorophosphate, the vinylene carbonate and the boron phosphorus lithium oxalate at the same time, and the four synergistic effects can form a new high-conductivity ion protective film with low impedance on the surfaces of a positive electrode and a negative electrode, because the formed components are mostly inorganic lithium salt compounds which can rapidly transfer lithium ions in electrolyte to an electrode active material through the replacement of the lithium ions in the compounds, thereby improving the power density of the lithium ion battery. In addition, the obtained novel low-impedance high-conductivity ion protective film is very complete, can completely prevent the direct contact between the electrolyte and the electrode active material, prevents the side reaction of the electrolyte component and the electrode active material, reduces the consumption of the electrolyte component in the use of the lithium ion battery, and further improves the cycle performance of the lithium ion battery.

According to the invention, the conductive lithium salt is selected from lithium bis-fluorosulfonylimide and lithium hexafluorophosphate.

According to the invention, the addition amount of the conductive lithium salt accounts for 14-20% of the total mass of the electrolyte, such as 14%, 15%, 16%, 17%, 18%, 19% and 20%.

According to the invention, the addition amount of the lithium bis (fluorosulfonate) imide accounts for 4-17% of the total mass of the electrolyte, such as 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%.

According to the invention, the high-temperature performance and the safety performance of the electrolyte can be obviously improved by using the lithium bis (fluorosulfonate) imide, and because the anion of the lithium bis (fluorosulfonate) imide has a larger radius and the acting force between the lithium bis (fluorosulfonate) imide and the cation lithium ion is small, the migration speed of the lithium ion can be improved, and the safety of the lithium ion is further improved. In addition, the decomposition temperature of lithium bis (fluorosulfonate) imide>200 ℃ far higher than LiPF₆The problem of decomposition of (2) can also improve the safety of lithium ions.

According to the invention, the addition amount of the lithium hexafluorophosphate accounts for 3-16% of the total mass of the electrolyte, such as 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%.

The invention also provides a lithium ion battery which comprises the electrolyte.

According to the invention, the lithium ion battery also comprises a positive electrode, a negative electrode and a diaphragm.

According to the invention, the positive electrode comprises a positive electrode active material layer and a positive electrode current collector, the positive electrode active material layer is arranged on one side or two side surfaces of the positive electrode current collector, the positive electrode active material layer comprises a positive electrode active material, a conductive agent and a binder, and the positive electrode active material is lithium iron phosphate.

According to the invention, the chemical formula of the lithium iron phosphate is represented as LiFePO₄。

According to the present invention, the material of the positive electrode current collector may be at least one of an aluminum foil and a nickel foil.

According to the present invention, the conductive agent may be at least one selected from carbon black, acetylene black, graphene, ketjen black, carbon fiber, and carbon nanotube.

According to the present invention, the binder may be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide containing polymers, polyvinylpyrrolidone, polyurethane.

According to the invention, the positive active material layer comprises the following components in percentage by mass:

80-99.8 wt% of positive active material, 0.1-10 wt% of binder and 0.1-10 wt% of conductive agent.

Preferably, the positive electrode active material layer comprises the following components in percentage by mass:

84-99 wt% of negative electrode active material, 0.5-8 wt% of binder and 0.5-8 wt% of conductive agent.

Still preferably, the mass percentage of each component in the positive electrode active material layer is:

90-99 wt% of positive electrode active substance, 0.5-5 wt% of binder and 0.5-5 wt% of conductive agent.

According to the invention, the lithium iron phosphate has a median particle size of 0.2 to 5 μm, such as 0.4 to 2 μm, such as 0.5 to 1.5 μm.

According to the invention, the specific surface area of the lithium iron phosphate is 4-22m²In g, e.g. 5-20m²In g, e.g. 6-15m²/g。

The anode of the invention uses lithium iron phosphate as the anode active material, which can improve the energy density of the lithium ion battery, and the invention also further providesThe specific surface area and the median diameter of the lithium iron phosphate are limited, and the lithium iron phosphate adopting the median diameter and the specific surface area can reduce the migration distance of lithium ions in the positive active material, so that the lithium ions in the lithium iron phosphate can be rapidly de-intercalated, and the lithium iron phosphate has better power density. The major bottlenecks of high power discharge lithium ion batteries are the transport of lithium ions and the insertion of lithium ions into the positive electrode. The lithium iron phosphate with the specified surface area and median particle size has better power performance, but the high-temperature performance is poorer, and the high-temperature performance can be remarkably improved by combining the electrolyte provided by the invention, because the additives can form a protective layer with more inorganic components on the surface of the anode, the forming mechanism is that the solvation capability of lithium ions in the ethyl 3-methoxypropionate is strong, and the ethyl 3-methoxypropionate solvation cluster containing more lithium ions can be formed. The electrolyte of the invention can form Li during first charging⁺[ (3-Methoxypropionic acid ethyl ester)_a(Difluorophosphate)_b(vinyl sulfate)_c(vinylene carbonate)_d(boron phosphorus oxalate)_e]^-The solvated cluster of (a) can form a protective film on the surface of the positive electrode material better than that of vinyl sulfate, lithium difluorophosphate, vinylene carbonate, lithium borophosphooxalate and the like which are used alone, because the oxidation potential of the cluster is lower than that of the cluster. In addition, in the absence of ethyl 3-methoxypropionate, organic sulfur-containing compounds, boron-containing compounds, and the like, which are decomposed to form vinyl sulfate, vinylene carbonate, lithium borophosphate oxalate, and the like and have poor thermal stability, are liable to crack due to poor stability, and unlike this, the inorganic layer formed by oxidation of the cluster oxidation contains Li as a main component₂CO₃、Li₂SO₄、LiBO₃、Li₃PO₄And LiF, these inorganic components have a high decomposition temperature and are not easily dissolved by the electrolyte. Therefore, the inorganic protective layers have high strength, can be stable and not broken under a high-temperature condition, can better protect the positive electrode and prevent the electrolyte from being oxidized by the positive electrode, and therefore, the inorganic protective layers have better high-temperature and safety performance.

According to the present invention, the anode includes an anode active material layer provided on one or both side surfaces of an anode current collector, and the anode active material layer includes an anode active material, a conductive agent, a dispersant, and a binder.

According to the present invention, the negative electrode active material is at least one of graphite, a silicon-containing compound, and silicon.

According to the present invention, the material of the negative electrode current collector may be at least one of copper foil, nickel foam, and copper foam.

According to the present invention, the conductive agent may be at least one selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, graphene, and carbon nanotube.

According to the present invention, the binder may be selected from at least one of sodium carboxymethylcellulose (CMC), Styrene Butadiene Rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyvinyl alcohol, sodium polyacrylate.

According to the invention, the mass percentage of each component in the negative electrode active material layer is as follows:

70-99.7 wt% of negative electrode active material, 0.1-10 wt% of binder, 0.1-10 wt% of dispersant and 0.1-10 wt% of conductive agent.

Preferably, the negative electrode active material layer comprises the following components in percentage by mass:

76-98.5 wt% of negative electrode active material, 0.5-8 wt% of binder, 0.5-8 wt% of dispersant and 0.5-8 wt% of conductive agent.

Still preferably, the negative electrode active material layer contains the following components in percentage by mass:

85-98.5 wt% of negative electrode active material, 0.5-5 wt% of binder, 0.5-5 wt% of dispersant and 0.5-5 wt% of conductive agent.

According to the invention, the binder is selected from at least one of high molecular polymers such as polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), Polyethyleneimine (PEI), Polyaniline (PAN), polyacrylic acid (PAA), sodium alginate, Styrene Butadiene Rubber (SBR), sodium carboxymethylcellulose (CMC-Na), phenolic resin or epoxy resin.

According to the present invention, the dispersant is selected from at least one of Polypropylene (PVA), cetylammonium bromide, sodium dodecylbenzenesulfonate, a silane coupling agent, ethanol, N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), etc., and more preferably at least one of cetylammonium bromide, sodium dodecylbenzenesulfonate, a silane coupling agent, and ethanol.

According to the invention, the conductive agent is selected from at least one of the conductive agents commonly used in industry, such as Carbon Nanotubes (CNTs), carbon fibers (VGCF), conductive graphite (KS-6, SFG-6), mesocarbon microbeads (MCMB), graphene, Ketjen black, Super P, acetylene black, conductive carbon black or hard carbon.

According to the present invention, the separator may be a separator material commonly used in current lithium ion batteries, such as one of a coated or uncoated polypropylene separator (PP), polyethylene separator (PE), and polyvinylidene fluoride separator.

According to the invention, the lithium ion battery is a high-power lithium ion battery, and the power density of the lithium ion battery is more than or equal to 5000W/kg, such as 5000-.

According to the invention, the capacity retention rate of the lithium ion battery after being stored for 90 days at 60 ℃ is more than or equal to 85%.

According to the invention, the capacity recovery rate of the lithium ion battery after 90 days of storage at 60 ℃ is more than or equal to 89%.

According to the invention, the thickness change rate of the lithium ion battery after being stored for 90 days at 60 ℃ is less than or equal to 6%.

According to the invention, the capacity retention rate of the lithium ion battery after 500 weeks of circulation at 55 ℃ is more than or equal to 86%.

According to the invention, the voltage of the lithium ion battery after discharging for 2s at the rate of 10C is more than or equal to 2.4V.

Has the advantages that:

1. the lithium iron phosphate anode material with good power performance is adopted, and the solvent with high lithium ion mobility, the additive combination and the lithium salt are used, so that the power performance of the electrolyte is improved.

2. The electrolyte additive can be used for protecting the surface of the anode and the cathode with higher performance strength, so that the high-temperature performance of the battery is improved. And meanwhile, the lithium salt with higher decomposition temperature is used, so that the safety performance of the lithium ion battery is improved.

Detailed Description

The present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.

The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.