阅读说明：本技术 电解液添加剂、电解液和锂离子电池 (Electrolyte additive, electrolyte and lithium ion battery ) 是由 张丽娟 周槐 赵少怀 杨山 陈杰 李载波 于 2020-06-05 设计创作，主要内容包括：本发明属于锂离子电池技术领域,尤其涉及一种电解液添加剂,包括添加剂A和添加剂B,所述添加剂A为含硼或含磷类添加剂,所述添加剂B为具有式Ⅰ至Ⅳ所示结构式的化合物中的至少一种。另外,本发明还涉及一种电解液和一种锂离子电池。相比于现有技术,本发明的电解液添加剂/电解液在电极表面成膜性能优良,使得锂离子电池在高电压下保持良好的循环性能和高温存储性能,并且兼顾低温放电性能和倍率性能等动力学性能。(The invention belongs to the technical field of lithium ion batteries, and particularly relates to an electrolyte additive which comprises an additive A and an additive B, wherein the additive A is a boron-containing or phosphorus-containing additive, and the additive B is at least one of compounds with structural formulas shown in formulas I to IV. In addition, the invention also relates to an electrolyte and a lithium ion battery. Compared with the prior art, the electrolyte additive/electrolyte has excellent film-forming performance on the surface of an electrode, so that the lithium ion battery keeps good cycle performance and high-temperature storage performance under high voltage, and dynamic performances such as low-temperature discharge performance, rate performance and the like are considered.)

1. An electrolyte additive is characterized by comprising an additive A and an additive B, wherein the additive A is a boron-containing or phosphorus-containing additive, the additive B is at least one of compounds with structural formulas shown in formulas I to IV,

wherein R is₁～R₄、R₆～R₈、R₁₀、R₁₂And R₁₆Are respectively provided withIndependently selected from one of saturated straight-chain alkylene, saturated straight-chain alkylene containing oxygen and/or halogen elements, straight-chain alkylene containing unsaturated bonds, alkylene with saturated branched chains, alkylene containing oxygen and/or halogen elements and having saturated branched chains, alkylene containing unsaturated bonds and having saturated branched chains, wherein the number of carbon atoms in each alkylene is 1-10; r₅、R₉、R₁₁、R₁₃～R₁₅Each independently selected from any one of hydrogen atom, halogen atom, alkyl and its substitute, alkylene and its substitute, alkyne and its substitute, and alkoxy and its substitute.

2. The electrolyte additive of claim 1 wherein additive a comprises at least one of lithium difluorophosphate, lithium difluorobis-oxalate phosphate, lithium tetrafluoro-oxalate phosphate, lithium bis-oxalate borate, lithium difluorooxalate borate, lithium bis (fluoromalonate) borate, lithium tetrafluoroborate, trimethylcyclotriboroxane, trimethylcyclotriphosphaxane, trimethyl borate, trimethyl phosphate, tributyl borate, and tributyl phosphate.

3. The electrolyte additive of claim 1 wherein the additive B comprises at least one of the following compounds:

4. the electrolyte additive according to claim 1, further comprising an additive C comprising at least one of 1, 3-propane sultone, fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinyl ethylene carbonate, 1, 2-difluoroethylene carbonate, methylene methanedisulfonate, propylene sultone, vinyl sulfite, citraconic anhydride, tris (trimethyl alkane) borate, tris (trimethyl alkane) phosphate, succinonitrile, adiponitrile, ethylene glycol bis (propionitrile) ether, and hexanetricarbonitrile.

5. An electrolyte comprising a lithium salt, an organic solvent and an additive, wherein the additive is the electrolyte additive according to any one of claims 1 to 4.

6. The electrolyte according to claim 5, wherein the additive A accounts for 0.1-5.0 wt% of the total mass of the electrolyte, the additive B accounts for 0.01-10.0 wt% of the total mass of the electrolyte, and the additive C accounts for 0.1-15.0 wt% of the total mass of the electrolyte.

7. The electrolyte of claim 5, wherein the lithium salt comprises 12.5 to 17.0 wt% of lithium hexafluorophosphate based on the total mass of the electrolyte.

8. The electrolyte of claim 7, wherein the lithium salt further comprises 0.1-5.0 wt% of other lithium salts based on the total mass of the electrolyte, and the other lithium salts comprise lithium bis (trifluoromethyl) sulfinamide and/or lithium bis (fluorosulfonyl) imide.

9. The electrolyte of claim 5, wherein the organic solvent is at least one of a carbonate-based solvent, a carboxylate-based solvent, and a fluorinated organic solvent; the carbonate solvent comprises at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate and methyl propyl carbonate; the carboxylic ester solvent comprises at least one of ethyl propionate, propyl propionate, ethyl acetate, ethyl n-butyrate, propyl acetate and gamma-butyrolactone; the fluorinated organic solvent comprises at least one of fluoroethylene carbonate, propylene carbonate, 4-trifluoromethyl ethylene carbonate, methyl trifluoroethyl carbonate and bistrifluoroethyl carbonate.

10. A lithium ion battery comprises a positive electrode plate, a negative electrode plate, and a positive electrode plateThe barrier film and the electrolyte between pole piece and the negative pole piece, its characterized in that: the electrolyte is the electrolyte as defined in any one of claims 5 to 9; the positive pole piece comprises an aluminum foil current collector and a positive diaphragm, the positive diaphragm comprises a positive active substance, and the positive active substance is LiNi_{1-x-y- z}Co_xMn_yAl_zO₂Wherein: x is more than or equal to 0 and less than or equal to 0.5, y is more than or equal to 0 and less than or equal to 0.5, z is more than or equal to 0 and less than or equal to 0 and x + y + z is more than or equal to 1; the negative electrode piece comprises a copper foil current collector and a negative electrode diaphragm, the negative electrode diaphragm comprises a negative active material, and the negative active material is artificial graphite, natural graphite, lithium titanate or SiO_wA silicon-carbon composite material compounded with graphite, wherein: w is more than 1 and less than 2; the upper limit cut-off voltage of the lithium ion battery is 4.2-5.0V.

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to an electrolyte additive, an electrolyte and a lithium ion battery.

Background

With the continuous improvement of the requirements of electric equipment on the capacity of the lithium ion battery, people have higher and higher expectations for the improvement of the energy density of the lithium ion battery, and particularly various portable equipment such as smart phones, tablet computers and notebook computers have higher requirements for the lithium ion battery with small volume and long standby time. Therefore, the development of high energy density lithium ion batteries is an important research and development direction in the lithium battery industry.

In order to design a lithium ion battery with high energy density, the space utilization rate is continuously optimized, the compaction density and gram capacity of positive and negative electrode materials of the battery are improved, the high-conductivity carbon nano and a high-molecular adhesive are used for improving the content of active substances of the positive electrode and the negative electrode, and the improvement of the working voltage of the lithium ion battery is also one of important ways for increasing the energy density of the battery.

However, at a voltage of 4.4V or above, the oxidation activity of the positive electrode material is increased, the stability is reduced, and the conventional electrolyte is easily oxidized and decomposed with the positive electrode material at a high voltage, which affects the storage and cycle performance of the lithium ion battery under a high temperature condition. Especially when the operating voltage is close to or exceeds 4.5V (vs. Li/Li)⁺) In the prior art, the organic carbonate solvent in the commercial electrolyte is easily subjected to oxidative decomposition, the oxidation activity of the anode material is high under high voltage, the reaction with the electrolyte is increased, and under the condition of high temperature, the reaction between the high-voltage anode and the electrolyte is further aggravated, the electrolyte is continuously oxidized on the surface of the anode and is deposited on the surface of the anode, so that the internal resistance of the anode is continuously increased, and the poor rate capability and the poor cycle stability are caused. Meanwhile, transition metals such as nickel, cobalt, manganese and the like in the crystal lattice of the positive electrode active material are easily reduced and dissolved out, so that the structure of the positive electrode material is damaged, irreversible capacity loss is caused, and the transition metals dissolved in the electrolyteThe metal ions easily reach the surface of the negative electrode and are reduced into a metal simple substance, so that the impedance of the negative electrode is increased continuously. In addition, lattice oxygen in the anode material under high voltage is easy to participate in the charge transfer process, so that oxygen precipitation and anode structure damage can be caused, and the electrolyte is further oxidized, so that the dynamic performance, the high-temperature storage performance and the high-temperature cycle performance of the battery are continuously attenuated and failed.

Disclosure of Invention

One of the objects of the present invention is: aiming at the defects of the prior art, the electrolyte additive is provided, the film forming performance on the surface of an electrode is excellent, so that the lithium ion battery keeps good cycle performance and high-temperature storage performance under high voltage, and the low-temperature discharge performance, the rate performance and other dynamic performances are considered.

In order to achieve the purpose, the invention adopts the following technical scheme:

an electrolyte additive comprises an additive A and an additive B, wherein the additive A is a boron-containing or phosphorus-containing additive, the additive B is at least one of compounds with structural formulas shown in formulas I to IV,

wherein R is₁～R₄、R₆～R₈、R₁₀、R₁₂And R₁₆Each independently selected from one of saturated straight-chain alkylene, saturated straight-chain alkylene containing oxygen and/or halogen elements, straight-chain alkylene containing unsaturated bonds, alkylene with saturated branched chains, alkylene containing oxygen and/or halogen elements and having saturated branched chains, alkylene containing unsaturated bonds and having saturated branched chains, wherein the number of carbon atoms in each alkylene is 1-10; r₅、R₉、R₁₁、R₁₃～R₁₅Each independently selected from any one of hydrogen atom, halogen atom, alkyl and its substitute, alkylene and its substitute, alkyne and its substitute, and alkoxy and its substitute.

As an improvement of the electrolyte additive according to the present invention, the additive a includes at least one of lithium difluorophosphate, lithium difluorobis (oxalato) phosphate, lithium tetrafluorooxalato phosphate, lithium bis (oxalato) borate, lithium difluorooxalato borate, lithium bis (fluoromalonic acid) borate, lithium tetrafluoroborate, trimethylcyclotriboroxane, trimethylcyclotriphosphaxane, trimethyl borate, trimethyl phosphate, tributyl borate, and tributyl phosphate.

As an improvement of the electrolyte additive of the present invention, the additive B includes at least one of the following compounds:

as an improvement of the electrolyte additive of the present invention, the electrolyte additive further comprises an additive C, wherein the additive C comprises at least one of 1, 3-propane sultone, fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinyl ethylene carbonate, 1, 2-difluoroethylene carbonate, methylene methanedisulfonate, propylene sultone, vinyl sulfite, citraconic anhydride, tris (trimethyl alkane) borate, tris (trimethyl alkane) phosphate, succinonitrile, adiponitrile, ethylene glycol bis (propionitrile) ether, and hexanetrinitrile.

The second purpose of the invention is: there is provided an electrolyte comprising a lithium salt, an organic solvent and an additive, the additive being an electrolyte additive as described in any preceding paragraph of the specification.

As an improvement of the electrolyte, the mass of the additive A accounts for 0.1-5.0 wt% of the total mass of the electrolyte, the mass of the additive B accounts for 0.01-10.0 wt% of the total mass of the electrolyte, and the mass of the additive C accounts for 0.1-15.0 wt% of the total mass of the electrolyte.

As an improvement of the electrolyte, the lithium salt comprises 12.5-17.0 wt% of lithium hexafluorophosphate in the total mass of the electrolyte.

As an improvement of the electrolyte, the lithium salt further comprises other lithium salts accounting for 0.1-5.0 wt% of the total mass of the electrolyte, and the other lithium salts comprise lithium bis (trifluoromethyl) sulfenamide and/or lithium bis (fluorosulfonyl) imide.

As an improvement of the electrolyte, the organic solvent is at least one of a carbonate solvent, a carboxylate solvent and a fluorinated organic solvent; the carbonate solvent comprises at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate and methyl propyl carbonate; the carboxylic ester solvent comprises at least one of ethyl propionate, propyl propionate, ethyl acetate, ethyl n-butyrate, propyl acetate and gamma-butyrolactone; the fluorinated organic solvent comprises at least one of fluoroethylene carbonate, propylene carbonate, 4-trifluoromethyl ethylene carbonate, methyl trifluoroethyl carbonate and bistrifluoroethyl carbonate.

The third purpose of the invention is that: the lithium ion battery comprises a positive pole piece, a negative pole piece, an isolating membrane and electrolyte, wherein the isolating membrane and the electrolyte are arranged between the positive pole piece and the negative pole piece; the positive pole piece comprises an aluminum foil current collector and a positive diaphragm, the positive diaphragm comprises a positive active substance, and the positive active substance is LiNi_1-x-y-zCo_xMn_yAl_zO₂Wherein: x is more than or equal to 0 and less than or equal to 0.5, y is more than or equal to 0 and less than or equal to 0.5, z is more than or equal to 0 and less than or equal to 0 and x + y + z is more than or equal to 1; the negative electrode piece comprises a copper foil current collector and a negative electrode diaphragm, the negative electrode diaphragm comprises a negative active material, and the negative active material is artificial graphite, natural graphite, lithium titanate or SiO_wA silicon-carbon composite material compounded with graphite, wherein: w is more than 1 and less than 2; the upper limit cut-off voltage of the lithium ion battery is 4.2-5.0V.

Compared with the prior art, the beneficial effects of the invention include but are not limited to:

1) the additive contains an additive A (boron or phosphorus-containing additive), and can be preferentially oxidized on the surface of the positive electrode to form a thin, compact, stable and uniform CEI film, so that the charge transfer process of lattice oxygen in the positive electrode material under high voltage is effectively inhibited, the positive electrode material is protected from being further oxidized by electrolyte by inhibiting oxygen precipitation, and the high-temperature cycle performance of the high-voltage lithium ion battery is effectively improved.

2) The additive contains an additive B, and the additive B contains a nitrile group and a silicon element, wherein the nitrile group can be complexed with metal ions on the surface of an anode, so that the dissolution of metal ions such as nickel, cobalt and manganese in a high-voltage electrode is inhibited, the catalytic oxidation decomposition reaction of the metal ions on electrolyte is inhibited, the interface characteristic of the anode material and the electrolyte is improved, and the storage and cycle performance of the lithium ion battery under high temperature and high voltage is effectively improved; the silicon element can reduce the viscosity of the electrolyte, and can effectively improve the low-temperature discharge, multiplying power and other dynamic performances of the lithium ion battery compared with the traditional nitriles.

3) In the electrolyte provided by the invention, the additive A and the additive B are added into the electrolyte together, and the stability of the anode material of the lithium ion battery under high temperature and high voltage is effectively improved by chelating metal ions and lattice oxygen of the anode material respectively, and the nitrile compound can promote the boron/phosphorus-containing compound to form a CEI (ceramic electronic interface) film with small impedance and high ion conductivity, namely, the performances of high temperature cycle, high temperature storage and the like of the lithium ion battery are effectively improved under the synergistic action of the additive A and the additive B.

4) In the lithium ion battery provided by the invention, because the electrolyte additive/electrolyte provided by the invention is added, the film forming performance of the electrolyte on the surface of the electrode is excellent through the synergistic effect of different additives, so that the lithium ion battery can keep good cycle performance and high-temperature storage performance under high voltage, and can give consideration to the dynamic performances such as low-temperature discharge performance, rate performance and the like.

Drawings

FIG. 1 is a graph comparing the retention curves of the cycle capacity at 45 ℃ of the batteries manufactured in example 1 and comparative example 2 of the present invention.

Wherein curve a is example 1 and curve b is comparative example 2.

Detailed Description

The present invention will be described in further detail with reference to the following detailed description and the accompanying drawings, but the embodiments of the invention are not limited thereto.