CN120398944A

CN120398944A - Fluorodiethylphosphinate, flame-retardant electrolyte and lithium-ion secondary battery

Info

Publication number: CN120398944A
Application number: CN202510544354.0A
Authority: CN
Inventors: 窦伟; 胡彩华; 李孟轩; 董春旭; 杨莉梓
Original assignee: Lanzhou University
Current assignee: Lanzhou University
Priority date: 2025-04-28
Filing date: 2025-04-28
Publication date: 2025-08-01

Abstract

The present invention discloses a fluorodiethylphosphinate, a flame-retardant electrolyte, and a lithium-ion secondary battery, belonging to the field of battery technology. The present invention uses the fluorodiethylphosphinate as an additive to provide a flame-retardant electrolyte or solid electrolyte, and further uses the flame-retardant electrolyte or solid electrolyte to prepare an electrochemical energy storage device, particularly a lithium-ion secondary battery. The flame-retardant electrolyte, when oxidized, produces an electrolyte/electrode interface layer that is uniform, stable, has strong ion transport capabilities, and high mechanical strength. This layer inhibits electrolyte decomposition and irreversible phase transitions in the cathode structure, significantly improving the fast charging and safety of the lithium-ion secondary battery, or enhancing the high-voltage cycling stability and safety of the lithium-ion secondary battery.

Description

Fluorodiethyl phosphinate, flame-retardant electrolyte and lithium ion secondary battery

Technical Field

The invention belongs to the technical field of batteries, and particularly relates to fluorodiethyl phosphinate, flame-retardant electrolyte and a lithium ion secondary battery.

Background

The lithium ion battery is widely applied to portable electronic equipment with high specific capacity and excellent cycle performance, and has wider prospect in the aspects of electric and hybrid automobiles, aerospace, smart grids and the like, and the development of mobile phones, electric automobiles and the like is limited by the long-time charging process of the lithium ion battery. To solve this problem, it is important to develop a lithium ion battery having a rapid charge capability. However, side effects during rapid charging, such as lithium precipitation, solid electrolyte interface growth, mechanical degradation, and thermal production, accelerate degradation of battery performance, resulting in reduced capacity and power performance, and possibly even safety problems. Flame retardant additives can reduce the flammability of conventional electrolytes, but tend to exhibit a tradeoff between flame retardant performance and battery performance due to their high viscosity and interfacial incompatibility or anodic electrochemical instability, adversely affecting coulombic efficiency and performance.

There are many documents currently reporting the use of phosphinates as film forming additives, flame retardant additives or flame retardant solvents for electrolytes to improve the high temperature characteristics and safety performance of lithium/sodium ion secondary batteries. The prior art with publication number CN102916223a discloses a nonaqueous electrolyte containing at least one organic phosphorus compound such as phosphine oxide, phosphonate and phosphinate. In this prior art, it is mentioned that the additive phosphorus compound may be at least one organic phosphate compound selected from the group consisting of phosphine oxide, phosphonate and phosphinate, and the organic phosphate compound includes a substituent having one or more unsaturated bonds, and the substituent has a carbon atom to which phosphorus is bonded. This document considers that, in the case where a phosphorus compound is contained in an electrolyte, a coating layer derived from the phosphorus compound is formed on the surface of at least one of the positive electrode and the negative electrode during an electrode reaction, particularly at the time of initial charge or subsequent charge. The coating can improve battery characteristics such as high temperature storage characteristics and high temperature cycle characteristics. The coating derived from the phosphorus compound is a solid electrolyte interface. The prior art with publication number CN1685556a discloses an electrolyte containing phosphinate, which can prevent the electrolyte from decomposing during the process of high trickle charge or high temperature storage to cause performance degradation and gas escape, and cause deformation or rupture of the battery, thereby improving the high temperature stability of the secondary battery. Examples of which disclose that the addition of ethyl diethylphosphinate as an additive to an electrolyte results in improved high temperature storage and high temperature trickle charge performance of a lithium secondary battery, but the prior art does not relate to the fast charge capability of the battery.

In the prior art with publication number CN108017669a, a preparation method of phosphinate, in particular dibutyl phosphinate trifluoroethanol prepared in example 1, was disclosed, and its performance as an additive added to an electrolyte and applied to a battery was studied. However, the prior art also does not relate to the fast charge capability of the battery.

Although attempts have been made in the prior art to achieve flame retardant effects, improve battery performance in high temperature environments, or inhibit decomposition of the electrolyte by adding alkyl phosphinate as an additive to the electrolyte, none of these prior arts have achieved flame retardant and fast charge effects simultaneously by the addition of alkyl phosphinate, and achieving flame retardant and fast charge at the same time is an important subject to be solved in the art.

Disclosure of Invention

1. Problems to be solved

Based on this, a first object of the present invention is to provide a new fluorodialkylphosphinate, which is added to an electrolyte or a solid-state electrolyte, is applied to an electrochemical energy storage device, in particular a lithium ion secondary battery, and can achieve both flame retardant and fast charge effects, at least partially solving the problems described in the background art.

A second object of the present invention is to provide a flame retardant electrolyte or solid electrolyte containing a certain amount of a novel fluorodialkylphosphinate, which is used in electrochemical energy storage devices, particularly lithium ion secondary batteries, and can achieve both flame retardant and fast charge effects.

A third object of the present invention is to provide an electrochemical energy storage device, particularly a lithium ion secondary battery, in which an electrolyte or a solid electrolyte contains a certain amount of a novel fluorodialkylphosphinate, and which is capable of achieving both safety (i.e., flame retardant performance) and quick charge at high temperatures.

2. Technical proposal

The invention provides a new fluorodiethyl phosphinate, which is used as an additive to provide a flame-retardant electrolyte or solid electrolyte, and further adopts the flame-retardant electrolyte or solid electrolyte to prepare an electrochemical energy storage device, in particular a lithium ion secondary battery, the electrolyte/electrode interface layer generated by oxidizing the flame-retardant electrolyte has the advantages of uniformity, stability, strong ion transmission capability, high mechanical strength and the like, inhibits electrolyte decomposition and irreversible phase change of a cathode structure, and greatly improves the quick charge and safety of the lithium ion secondary battery or improves the high-voltage cycling stability and safety of the lithium ion secondary battery.

The technical scheme of the invention is as follows:

[ Compound ]

The first aspect of the present invention provides a series of compounds having the structure of formula I:

Wherein R ¹ is selected from one of pentafluorophenyl, trifluorophenyl, difluoromethyl, trifluoromethyl, difluoroethyl, trifluoroethyl, tetrafluoropropyl, pentafluoropropyl and hexafluoroisopropyl.

As a preferred embodiment of the compound of any one of the first aspect of the present invention, wherein R ¹ is selected from one of difluoromethyl, trifluoromethyl, difluoroethyl, trifluoroethyl, tetrafluoropropyl.

As a preferred preference of the compounds of any of the embodiments of the first aspect of the invention, said compounds have a structural formula selected from the group consisting of:

it is worth to say that, when the compound of formula II-IV is added into the electrolyte, the flame retardant property is improved, and meanwhile, the requirement of fast charge or high-voltage cycle stability of the lithium ion secondary battery can be met.

[ Use of Compounds as flame retardant additives ]

A second aspect of the invention provides the use of one or more of the compounds according to any of the embodiments of the first aspect of the invention as a flame retardant additive in a flame retardant electrolyte or solid state electrolyte.

[ Flame-retardant electrolyte ]

A third aspect of the invention provides a flame retardant electrolyte comprising one or more of the compounds of any of the embodiments of the first aspect.

In the flame-retardant electrolyte disclosed by the third aspect of the invention, the addition of the tetrafluoropropyl diethyl phosphinate, the trifluoroethyl diethyl phosphinate and the difluoroethyl diethyl phosphinate has the advantages that compared with the electrolyte which is not added, the flame-retardant effect is obviously improved, and the working safety of the lithium ion secondary battery at a high temperature is further improved. The flame retardant effect of diethyl phosphinic acid difluoroethyl ester and diethyl phosphinic acid trifluoroethyl ester is best when the content of the flame retardant additive in the electrolyte is between 0wt% and 5wt% (more than 0 wt%), and the flame retardant effect of diethyl phosphinic acid trifluoroethyl ester is best when the content of the flame retardant additive in the electrolyte is between 10wt% and 20 wt%. Therefore, the compound of the present invention added to the electrolyte is most preferably trifluoroethyl diethylphosphinate from the viewpoint of flame retardant effect.

As a preferred embodiment of the third aspect of the present invention, the flame-retardant electrolyte comprises:

The flame-retardant electrolyte of the third aspect of the invention is applied to lithium ion secondary batteries, and is added with 1% -3% of electrolyte of diethyl phosphinic acid tetrafluoropropyl ester, diethyl phosphinic acid trifluoroethyl ester and diethyl phosphinic acid difluoroethyl ester to prepare the lithium ion secondary batteries, compared with the lithium ion secondary batteries prepared by the electrolyte without adding the compounds, the formed cathode solid electrolyte interface film (SEI) has a good protection effect on lithium metal, and the overpotential in the circulation process is lower than that of a basic electrolyte, so that the additive fluorodiethyl phosphinate can reduce polarization in a lithium symmetrical battery, lithium ions can be better electroplated/stripped, growth of lithium dendrites is inhibited, and the cycle life of a lithium ion secondary battery is further prolonged. With the same addition amount, the cycle life is that the tetrafluoropropyl diethyl phosphinate > the trifluoroethyl diethyl phosphinate > the difluoroethyl diethyl phosphinate. Therefore, the compound of the present invention added to the electrolyte is most preferably tetrafluoropropyl diethylphosphinate from the viewpoint of cycle life.

The flame-retardant electrolyte disclosed by the third aspect of the invention is applied to a lithium ion secondary battery, and the lithium ion secondary battery prepared by the electrolyte added with the tetrafluoropropyl diethyl phosphinate, the trifluoroethyl diethyl phosphinate and the difluoroethyl diethyl phosphinate can effectively increase the capacity retention rate of the battery and improve the cycle performance of a lithium metal battery compared with the lithium ion secondary battery prepared by the electrolyte without the compounds, wherein the electrolyte is circulated for 300 circles at 0.5C or 200 circles at 1C within the voltage range of 3.0-4.3V at 25 ℃. Therefore, the compound of the present invention added to the flame-retardant electrolyte is most preferably trifluoroethyl diethylphosphinate from the viewpoint of recycling properties.

The flame-retardant electrolyte disclosed by the third aspect of the invention is applied to a lithium ion secondary battery, and compared with the lithium ion secondary battery prepared by the electrolyte without the compound, the lithium ion secondary battery prepared by the electrolyte with diethyl phosphinic acid trifluoroethyl ester added is obviously improved in capacity retention rate after 200 cycles at 0.5 ℃ within the voltage range of 3.0-4.5V at 25 ℃, and the high-voltage cycle performance of the lithium ion battery can be effectively improved. Therefore, the compound of the present invention added to the flame-retardant electrolyte is most preferably trifluoroethyl diethylphosphinate from the viewpoint of high-pressure cycle performance.

The flame-retardant electrolyte is applied to a lithium ion secondary battery, and compared with the lithium ion secondary battery prepared by the electrolyte without the compound, the lithium ion secondary battery prepared by the electrolyte with the diethyl phosphinic acid trifluoroethyl ester has improved high-voltage multiplying power performance, and test results show that when the cut-off voltage is 4.5V, the discharge specific capacity of the lithium ion secondary battery prepared by the electrolyte with the diethyl phosphinic acid trifluoroethyl ester of 1wt% is obviously higher than that of a base electrolyte at 5C and higher multiplying power, and in 5C multiplying power charge-discharge cycles, in some embodiments, the electrolyte with the diethyl phosphinic acid trifluoroethyl ester of 1wt% improves the discharge specific capacity from 101.7mAh/g to 146.8mAh/g, and the electrolyte with the diethyl phosphinic acid trifluoroethyl ester of 1wt% improves the discharge specific capacity from 36mAh/g to 68.2mAh/g at 10C ultrahigh multiplying power. Compared with the initial discharge specific capacity of 0.1C, the capacity recovery rate of the basic electrolyte is 92.6%, the capacity recovery rate of the electrolyte containing 1wt% of diethyl phosphinic acid trifluoroethyl ester is 97.3%, the discharge specific capacity and the capacity recovery rate of the diethyl phosphinic acid trifluoroethyl ester under high voltage of the lithium ion battery are effectively improved, and the rate performance of the lithium ion battery under high voltage is effectively improved. Therefore, the compound of the present invention added to the flame-retardant electrolyte is most preferably trifluoroethyl diethylphosphinate from the viewpoint of high-voltage rate performance.

Further, the flame retardant electrolyte according to the third aspect of the present invention is applied to a lithium ion secondary battery, and can achieve rapid charging at a voltage level (4.5V) higher than that in the prior art. And the data in the examples show that, for example, trifluoroethyl diethylphosphinate as an additive is added to the electrolyte at 1wt%, and the conversion (coulombic efficiency) of the lithium ion secondary battery operated at 4.5V reaches 99% or more.

The flame-retardant electrolyte disclosed by the third aspect of the invention is applied to a lithium ion secondary battery, and the lithium ion secondary battery prepared by the electrolyte added with diethyl phosphinic acid trifluoroethyl ester has improved capacity retention rate and capacity recovery rate after high-temperature storage compared with the lithium ion secondary battery prepared by the electrolyte without the compound, so that the high-temperature storage performance of the lithium ion battery can be effectively improved.

According to the invention, the flame-retardant electrolyte disclosed by the third aspect of the invention is applied to a lithium ion secondary battery, and the lithium ion secondary battery prepared by adding the electrolyte of diethyl phosphinic acid tetrafluoropropyl ester, diethyl phosphinic acid trifluoroethyl ester and diethyl phosphinic acid difluoroethyl ester can effectively improve the discharge specific capacity of the lithium ion secondary battery and improve the quick charge performance of the lithium ion secondary battery under the voltage range of 3.0-4.3V, and particularly the discharge specific capacity of the electrolyte of diethyl phosphinic acid difluoroethyl ester at 10C is far higher than that of a blank electrolyte which is not added, so that the quick charge performance of the lithium ion secondary battery is improved to the most remarkable degree, and the damage to the battery is also the least. Meanwhile, after 10C is circulated for 500 circles under the voltage range of 3.0-4.3V, the specific discharge capacity and the capacity retention rate are obviously improved by adding diethyl difluoroethyl phosphinate, and the circulation stability of the lithium ion battery under fast charge is effectively improved. Therefore, the compound of the present invention added to the flame-retardant electrolyte is most preferably difluoroethyl diethylphosphinate from the viewpoint of quick charge performance.

As a preferable example of the flame-retardant electrolyte according to any one of the embodiments of the third aspect of the present invention, the flame-retardant electrolyte further comprises:

An aprotic organic solvent, and

And (3) a lithium salt.

Preferably, the lithium salt concentration of the flame retardant electrolyte according to any one of the third aspect of the present invention is 0.5 to 2m.

As a preferred embodiment of the third aspect of the present invention, the compound selected from the group consisting of formula I, formula II, formula III, and formula IV is present in the flame-retardant electrolyte at a mass concentration of 0.5wt% to 20wt%, preferably at a mass concentration of 0.5wt% to 3 wt%.

Preferably, the compound selected from formula I, formula II, formula III, formula IV is added in an amount of the total mass of the electrolyte:

0.5wt％～18wt％;0.5wt％～15wt％;0.5wt％～12wt％;0.5wt％～10wt％;0.5wt％～8wt％;0.5wt％～5wt％;0.5wt％～4wt％;0.5wt％～3wt％;0.5wt％～2wt％;0.5wt％～1wt％;

1wt％～20wt％;1wt％～18wt％;1wt％～15wt％;1wt％～12wt％;1wt％～10wt％;1wt％～8wt％;1wt％～5wt％;1wt％～4wt％;1wt％～3wt％;1wt％～2wt％;

2wt%~20wt%;2wt%~18wt%;2wt%~15wt%;2wt%~12wt%;2wt%~10wt%;2wt%~8wt%;2wt%~5wt%;2wt%~4wt%;2wt%~3wt%;

3wt%~20wt%;3wt%~18wt%;3wt%~15wt%;3wt%~12wt%;3wt%~10wt%;3wt%~8wt%;3wt%~5wt%;3wt%~4wt%;

4wt%~20wt%;4wt%~18wt%;4wt%~15wt%;4wt%~12wt%;4wt%~10wt%;4wt%~8wt%;4wt%~5wt%;

5wt%~20wt%;5wt%~18wt%;5wt%~15wt%;5wt%~12wt%;5wt%~10wt%;5wt%~8wt%;

8wt%~20wt%;8wt%~18wt%;8wt%~15wt%;8wt%~12wt%;8wt%~10wt%;

10wt%~20wt%;10wt%~18wt%;10wt%~15wt%;10wt%~12wt%;

12wt%~20wt%;12wt%~18wt%;12wt%~15wt%;

15wt%~20wt%;15wt%~18wt%;

18wt%~20wt%。

The addition amount of the above-mentioned compound as an additive is preferably at a higher level in the above-mentioned range, for example, preferably 5 to 20wt%, more preferably 8 to 20wt%, in view of improving the flame retardant effect, but is preferably at a lower level in the above-mentioned range, for example, preferably 0.5 to 3wt%, more preferably 1 to + -0.2 wt%, most preferably 1 to + -0.1 wt%, in view of maintaining the cycle performance and the rate performance of the battery.

Preferably, in some examples, the compound selected from formula I, formula II, formula III, formula IV is added in an amount of 1.0wt%, 2.0wt%, 3.0wt%, 5.0wt% of the total mass of the electrolyte.

Preferably, in some examples, the amount of the compound selected from formula I, formula II, formula III, formula IV added is 1.0wt%, 2.0wt%, 3.0wt%, 5.0wt% of the total mass of the conventional electrolyte (total mass of the non-electrolyte) without such additives added.

As a preferable example of the flame-retardant electrolyte according to any one of the embodiments of the third aspect of the present invention, the aprotic organic solvent is present in the flame-retardant electrolyte at a mass concentration of 60% to 90%.

As a preferable example of the flame retardant electrolyte according to any one of the embodiments of the third aspect of the present invention,

The aprotic organic solvent is selected from one or more of carbonate, carboxylate, ether and sulfone;

Preferably, the carbonate-based solvent comprises one or more combinations of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, and methylpropyl carbonate;

Preferably, the carboxylic acid solvent comprises one or more of gamma-lactone, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, ethyl fluoroacetate, methyl fluoropropionate, ethyl fluoropropionate, and propyl fluoropropionate;

preferably, the ether solvent comprises one or more combinations of tetrahydrofuran, 2-methyltetrahydrofuran, 1, 3-dioxolane, 4-methyl-1, 3-dioxolane, 1, 2-dimethoxyethane, dimethoxypropane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, tetraglycine, crown ether, and cryptate;

Preferably, the sulfone-based solvent comprises one or more of sulfolane, fluorosulfolane, methyl ethyl sulfone, methyl propyl sulfone, methyl isopropyl sulfone, fluorinated methyl ethyl sulfone, fluorinated methyl propyl sulfone, and fluorinated methyl isopropyl sulfone in combination.

The lithium salt is selected from one or a combination of a plurality of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxaborate, lithium difluorooxalato borate, lithium hexafluoroarsenate, anhydrous lithium perchlorate, lithium bis (trifluoromethylsulfonyl) imide, lithium bisoxalato phosphate, lithium difluorodioxaato phosphate, lithium monooxalato difluoroborate, lithium difluorophosphate, lithium trifluoromethylsulfonate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethylsulfonyl imide, lithium bismalonate borate, lithium bis (difluoromalonate) borate, lithium malonate oxalato borate, lithium (difluoromalonate oxalato) borate and lithium tris (difluoromalonate) phosphate.

[ Flame-retardant solid electrolyte ]

In a fourth aspect the present invention provides a flame retardant solid state electrolyte comprising one or more of the compounds of any of the embodiments of the first aspect.

In the flame-retardant solid electrolyte according to the fourth aspect of the invention, the addition of the tetrafluoropropyl diethyl phosphinate, trifluoroethyl diethyl phosphinate and difluoroethyl diethyl phosphinate, which have flame-retardant properties, is advantageous for improving the flame-retardant effect compared with the solid electrolyte which is not added.

As a preferable example of the flame-retardant solid electrolyte according to any one of the embodiments of the fourth aspect of the present invention, the flame-retardant solid electrolyte includes:

Compared with a lithium ion secondary battery prepared by solid electrolyte without adding the compounds, the flame-retardant solid electrolyte is favorable for forming a positive electrolyte interface layer (CEI) film, has a good protection effect on lithium metal, has lower overpotential than a basic electrolyte in a circulating process, can reduce polarization in a lithium symmetrical battery, can better plate/strip lithium ions, inhibit growth of lithium dendrites, and further improves the cycle life of the lithium ion secondary battery. The compound of the present invention added to the flame-retardant solid electrolyte is most preferably tetrafluoropropyl diethylphosphinate from the viewpoint of cycle life.

As a preferred solid electrolyte of any one of the embodiments of the fourth aspect of the present invention, the solid electrolyte includes:

The flame-retardant solid electrolyte disclosed by the fourth aspect of the invention is applied to a lithium ion secondary battery, and is beneficial to improving the cycle performance of a lithium metal battery. The compound of the present invention added to the flame-retardant solid electrolyte is preferably trifluoroethyl diethylphosphinate from the standpoint of cycle performance.

The flame-retardant solid electrolyte disclosed by the fourth aspect of the invention is applied to a lithium ion secondary battery, and is beneficial to increasing the high-voltage cycle performance of the lithium ion battery. The compound of the present invention added to the flame-retardant solid electrolyte is preferably trifluoroethyl diethylphosphinate from the viewpoint of high-pressure cycle performance.

The flame-retardant solid electrolyte disclosed by the fourth aspect of the invention is applied to a lithium ion secondary battery, and is beneficial to improving the rate performance of the lithium ion battery under high pressure. The compound of the present invention added to the flame-retardant solid electrolyte is preferably trifluoroethyl diethylphosphinate from the viewpoint of high-voltage rate performance.

Further, the flame retardant solid electrolyte according to the fourth aspect of the present invention is applied to a lithium ion secondary battery, which is advantageous in achieving rapid charging at a voltage level (4.5V) higher than that in the prior art.

The flame-retardant solid electrolyte disclosed by the fourth aspect of the invention is applied to a lithium ion secondary battery, and is beneficial to improving the high-temperature storage performance of the lithium ion battery.

The flame-retardant solid electrolyte disclosed by the fourth aspect of the invention is applied to a lithium ion secondary battery, is beneficial to improving the discharge specific capacity of the lithium ion secondary battery and the quick charge performance of the lithium ion secondary battery, and reduces the damage to the battery. Meanwhile, the capacity retention rate can be obviously improved, and the cycling stability of the lithium ion battery under quick charge is improved. The compound of the present invention added to the flame-retardant solid electrolyte is preferably difluoroethyl diethylphosphinate from the viewpoint of fast charge performance.

As a preferred embodiment of the solid electrolyte according to any one of the fourth aspect of the present invention, the solid electrolyte further comprises:

A polymer matrix, and

Conductive lithium salts.

As a preferable example of the solid electrolyte according to any one of the fourth aspect of the present invention, the polymer matrix is selected from one or more of polyoxyethylene, polyethylene glycol, polyvinyl carbonate, polypropylene carbonate, polyacrylonitrile, polymethyl methacrylate or polyvinylidene fluoride, and/or a mixture of

The conductive lithium salt is selected from one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium tris (pentafluoroethyl) trifluorophosphate, lithium tetrafluorooxalate phosphate, lithium trioxalato phosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium bisoxalato borate, lithium difluorooxalato borate, lithium pentafluoroethyl trifluoroborate, lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethylsulfonyl) imide, lithium bis (pentafluoroethylsulfonyl) imide or lithium trifluoromethylsulfonate.

The solid electrolyte according to any one of the fourth aspect of the present invention is preferably in the form of a film having a thickness of 1 μm to 100 μm.

Electrochemical energy storage device

A fifth aspect of the invention provides an electrochemical energy storage device comprising:

A cathode;

An anode;

A diaphragm, and

According to any one of the embodiments of the third aspect of the invention, the flame-retardant electrolyte is provided.

A fifth aspect of the invention provides another electrochemical energy storage device comprising:

A cathode;

Anode, and

According to any one of the embodiments of the fourth aspect of the present invention, the flame retardant solid electrolyte.

[ Lithium ion Secondary Battery ]

A sixth aspect of the present invention provides a lithium ion secondary battery comprising:

A cathode;

An anode;

A diaphragm, and

The lithium ion secondary battery described above has excellent high-voltage cycle stability, quick charge and safety stability at least in part due to the addition of the compound of formula I to the electrolyte.

As a preferable example of the lithium ion secondary battery according to the sixth aspect of the present invention, the flame-retardant electrolyte solution contains the following compound:

As described above, the flame retardant electrolyte added with the compound of formula II is applied to a lithium ion secondary battery, and improves the cycle life of the lithium ion secondary battery.

as described above, the flame-retardant electrolyte added with the compound of formula III can be applied to a lithium ion secondary battery, so that the capacity retention rate of the battery can be effectively increased, and the cycle performance, high-voltage multiplying power performance and high-temperature storage performance of the battery can be improved.

As described above, the flame-retardant electrolyte added with the compound of formula IV is applied to the lithium ion secondary battery, so that the specific discharge capacity and the capacity retention rate are both obviously improved, and the cycle stability of the lithium ion battery under fast charge is effectively improved.

A sixth aspect of the present invention provides another lithium ion secondary battery comprising:

A cathode;

Anode, and

The flame retardant solid state electrolyte according to any one of the embodiments of the fourth aspect of the present invention.

[ Method for producing Compound ]

The seventh aspect of the invention discloses a preparation method of a compound of formula II and formula III, which comprises the following steps:

adding thionyl chloride into diethyl phosphinic acid under the protection of inert gas to generate diethyl phosphinic acid chloride;

and adding a fluoroalcohol to the diethyl phosphinic acid chloride to form diethyl phosphinic acid fluoroester.

The step of adding thionyl chloride is preferably to slowly dropwise add the thionyl chloride under the condition of stirring at room temperature, and after the dropwise adding is finished and the thionyl chloride is stable, the temperature is raised to a slightly reflux state, and the reaction duration is about 1-3 h.

The step of adding the fluoroalcohol is preferably to slowly dropwise add under the condition of stirring at room temperature, and after the dropwise adding is finished, the temperature is raised and the reflux is carried out, and the reaction duration is about 4-8 hours.

In a seventh aspect, the present invention discloses a process for the preparation of another compound of formula IV comprising the steps of:

Mixing sodium diethylphosphinate and fluoro-chlorinated alkane at low temperature, and heating in an autoclave for reaction to obtain diethyl phosphinate fluoro-ester.

The low temperature is preferably 0-10 ℃, the temperature rising range in the autoclave is preferably 100-200 ℃, and the heating reaction duration is preferably 4-8 h.

3. Advantageous effects

Compared with the prior art, the invention has the beneficial effects that:

(1) The compound of the formula I provided by the invention can be used as a flame retardant additive in conventional electrolyte or solid electrolyte, and can effectively improve the safety of a lithium ion battery;

(2) The compound shown in the formula IV provided by the invention is used as a conventional electrolyte or a solid electrolyte flame retardant additive, and not only can the specific discharge capacity and the capacity retention rate be obviously improved under normal-pressure quick charge, but also the cycling stability of the lithium ion battery under quick charge can be effectively improved, and the damage to the battery is minimum, and the specific discharge capacity and the capacity retention rate under slow charge again are hardly influenced;

(3) The compound of the formula III provided by the invention is used as a conventional electrolyte or solid electrolyte flame retardant additive, and has good circulation stability under normal pressure, and excellent high-pressure circulation stability, high-pressure multiplying power, high-pressure conversion rate and high-temperature storage performance;

(4) The compound of the formula II provided by the invention can be used as a conventional electrolyte or a solid electrolyte flame retardant additive, and can obviously improve the cycle life of a lithium ion battery;

(5) The additive provided by the invention contains P=O bond, the lone pair electron of oxygen atom can play the Lewis base role, the strong Lewis acid PF ₅ and PF ₃ O derived from LiPF ₆ are effectively removed, the corrosion and degradation of the additive to the surface of the anode material are avoided, the structural stability of the anode material is better maintained, and the cycle stability performance of the battery is further improved;

the additive provided by the invention is rich in C-F bonds, reduces the LUMO and HOMO values of the additive, is favorable for the reduction of the additive to form a stable anode Solid Electrolyte Interphase (SEI) rich in LiF, remarkably inhibits the growth of lithium dendrites, reduces electrolyte decomposition, and further leads to the improvement of the cycle stability of the battery;

the additive provided by the invention participates in the formation of a thin C-F-rich positive electrode electrolyte interface layer (CEI), and improves the stable cyclicity of the cathode under high pressure.

Drawings

FIG. 1 is a diagram showing the ¹ H NMR of the compound of formula II obtained in preparation example 1 according to the present invention;

FIG. 2 is a diagram showing the characteristics of ¹ HNMR of the compound of formula III prepared in preparation example 2 according to the present invention;

FIG. 3 is a diagram showing the ¹ H NMR of the compound of formula IV according to preparation 3 of the present invention;

FIG. 4 is a graph of self-extinguishing time measurements for electrolyte formulations with different fluorodiethyl phosphinate addition ratios;

FIG. 5 is a graph showing the cycle performance of lithium-symmetric batteries using the electrolyte formulations prepared in comparative example 1 and examples 1 to 4 as an electrolyte;

FIG. 6 is a graph showing the cycle performance of lithium-symmetric batteries using the electrolyte formulations prepared in comparative example 1 and examples 5 to 8 as an electrolyte;

FIG. 7 is a graph showing the cycle performance of lithium-symmetric batteries using the electrolyte formulations prepared in comparative example 1 and examples 9 to 12 as an electrolyte;

FIG. 8 is a graph of specific capacity performance of the electrolyte formulations prepared in comparative example 1 and examples 1,5, 9 for the discharge of NCM811 Li half-cells used as electrolyte (25 ℃ C., voltage range: 3.0-4.3V, 0.1℃ After 5 cycles of activation, 0.5C cycles of 300 cycles);

FIG. 9 is a graph of specific discharge capacity performance (25 ℃ C., voltage range: 3.0 to 4.3V, 1C cycle 200 after 5 cycles of 0.1C activation) of NCM 811I Li half-cells of the electrolyte formulations prepared in comparative example 1 and examples 1, 5,9 as the electrolyte;

FIG. 10 is a graph showing the specific discharge capacity performance of NCM811 Li half-cells (25 ℃ C., voltage range: 3.0 to 4.5V, 0.5℃ Cycle 200 after 5 cycles of 0.1C activation) using the electrolyte formulations prepared in comparative example 1 and example 5 as an electrolyte;

FIG. 11 shows the specific discharge capacity performance graphs (25 ℃ C., voltage range: 3.0 to 4.3V, 10C cycles 500 after 5 cycles of 0.1℃) of the electrolyte formulations prepared in comparative example 1 and example 9 for NCM 811I Li half cells used as electrolytes;

Fig. 12 shows the rate performance graphs of NCM811 Li half-cells (25 ℃ C., voltage range: 3.0 to 4.3v, cycled 5 cycles at 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, 5C, 10C, 0.1C) for the electrolyte formulations prepared in comparative example 1 and examples 1, 5, 9, respectively, as electrolytes;

FIG. 13 is a graph of the rate performance of NCM 811I Li half-cells (25 ℃ C., voltage range: 3.0 to 4.5V, cycled 5 cycles at 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, 5C, 10C, 0.1C) with the electrolyte formulations prepared in comparative example 1 and example 5 as electrolytes;

Fig. 14:

(a) A CEI film TEM image (50 nm) of an NCM811 Li half-cell after 200 cycles for the electrolyte formulation prepared in comparative example 1 as electrolyte;

(b) A CEI film TEM image (20 nm) of an NCM811 Li half-cell after 200 cycles for the electrolyte formulation prepared in comparative example 1 as electrolyte;

(c) A CEI film TEM image (50 nm) of the electrolyte formulation prepared for example 5 after 200 cycles of NCM811 Li half-cell cycle as electrolyte;

(d) CEI film TEM image (20 nm) after 200 cycles of the NCM811 Li half-cell for the electrolyte formulation prepared in example 5 used as electrolyte.

Detailed Description

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and the term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.

The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

As used herein, the term "about" is used to provide the flexibility and inaccuracy associated with a given term, metric or value. The degree of flexibility of a particular variable can be readily determined by one skilled in the art.

Concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a numerical range of about 1 to about 4.5 should be interpreted to include not only the explicitly recited limits of 1 to about 4.5, but also include individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges reciting only one numerical value, such as "less than about 4.5," which should be construed to include all such values and ranges. Moreover, such an interpretation should apply regardless of the breadth of the range or the characteristics being described.

The invention is further described below in connection with specific embodiments.

The preparation method comprises the following steps:

Basic electrolyte formulation (electrolyte, 1m LiPF6 EC/emc=3:7vol%), polypropylene separator from the company of the division of innovation technology in the family of dongguanaceae, lithium sheet from the company of the energy lithium industry in the Tianjin, NCM811 sheet from the company of the division of the technology of the Shenzhen hua refreshing material, diethyl phosphinic acid, sodium diethylphosphinate from the company of the lanzhou reip science, dichloromethane, thionyl chloride, tetrafluoropropanol, trifluoroethanol, sodium carbonate solution, N-Dimethylformamide (DMF), 1-difluoro-2-chloroethane from the company of the division of the biochemical technology of the shanghai aleding.

Preparation example 1

In a two-necked flask, 100g of diethyl phosphinic acid (0.82 mol,1 eq) was dissolved in 100ml of dichloromethane, and under the protection of nitrogen, 292.7g (2.46 mol,3 eq) of thionyl chloride was slowly added dropwise under stirring at room temperature, after the addition was completed, stirring was continued and the temperature was raised to slightly reflux (60 ℃) of dichloromethane, tail gas SO ₂ and HCl were absorbed with sodium carbonate solution until no tail gas was evolved (about 2 h), and then excess dichloromethane and thionyl chloride were distilled under reduced pressure to obtain diethyl phosphinic acid chloride.

200Ml of dichloromethane was added to the diethyl phosphinic acid chloride, 162.4g of tetrafluoropropanol (1.23 mol,1.5 eq) was added dropwise under nitrogen protection at room temperature under stirring, stirring was continued until the end of the dropwise addition and the temperature was raised to dichloromethane reflux (55 ℃), the tail gas was absorbed by sodium carbonate solution, after the end of the reaction for 5 hours, excess tetrafluoropropanol and dichloromethane were distilled off under reduced pressure, and after rectification and drying, tetrafluoropropyl diethyl phosphinate (formula II) was obtained, whose ¹ H NMR characterization was shown in fig. 1.

Preparation example 2

To the above diethyl phosphinic acid chloride was added 200ml of dichloromethane, and under nitrogen protection, 123.0g of trifluoroethanol (1.23 mol,1.5 eq) was added dropwise under stirring at room temperature, after the addition was completed, stirring was continued and the temperature was raised to dichloromethane reflux (55 ℃), the tail gas was absorbed with sodium carbonate solution, after the reaction was completed for 5 hours, excess trifluoroethanol and dichloromethane were distilled off under reduced pressure, and after rectification and drying, diethyl phosphinic acid trifluoroethyl ester (formula III) was obtained, whose ¹ HNMR characterization is shown in fig. 2.

Preparation example 3

400Ml of N, N-dimethylformamide (DMF, 4 times the volume of 1, 1-difluoro-2-chloroethane) and 187.2g (1.3 mol,1.3 eq) of sodium diethylphosphinate were added to a 1L autoclave, then 100.5g of 1, 1-difluoro-2-chloroethane (1 mol,1 eq) was rapidly added at 6℃and the temperature was raised and kept at 150℃for 6 hours, then the autoclave was cooled to room temperature, the solvent was distilled off under reduced pressure, and difluoroethyl diethylphosphinate (formula IV) was obtained after rectification and drying, whose ¹ HNMR characterization was shown in FIG. 3.

Preparation example 4

This preparation example is the preparation of an electrolyte formulation, the preparation process being carried out in a dry argon-filled glove box (moisture <0.1ppm, oxygen content <0.1 ppm).

The various fluorodiethyl phosphinates prepared in preparation examples 1-3 are used as flame retardant additives and added into a basic electrolyte preparation according to the weight percentage of 1, 2,3 and 5 of the electrolyte preparation respectively to obtain electrolyte preparations shown in examples 1-12 in table 1. Meanwhile, a base electrolyte formulation without additives was used as a control group (comparative example 1).

In the above-described basic electrolyte formulation, the volume ratio of Ethylene Carbonate (EC) and Ethyl Methyl Carbonate (EMC) was 3:7, and lithium hexafluorophosphate (LiPF ₆) was used as a Li ion-conducting salt at a concentration of 1M.

All electrolyte components described above were stirred and mixed in a glass vial for 24 hours to ensure complete dissolution of all solids.

TABLE 1 electrolyte formulations with different fluorodiethyl phosphinate addition ratios

Test example 1

The test example is a flame retardance test of flame-retardant electrolyte with different fluorodiethyl phosphinate addition ratios

The preparation of the electrolyte formulation used in this test example was carried out in a dry argon-filled glove box.

And adding various fluorodiethyl phosphinate prepared in preparation examples 1-3 as an additive material into a basic electrolyte preparation according to the mass concentration of the electrolyte preparation to obtain the flame-retardant electrolyte shown in table 2.

Specifically, 0.1g of the flame-retardant electrolyte is respectively sucked and dropped on a quartz cotton ball, so that the quartz cotton ball is fully soaked. Igniting cotton balls in the closed container, wherein the ignition time is unified to be 3s, recording the time from the removal of the ignition device to the extinction of the cotton balls, and calculating SET(s). The test results are shown in table 2 and fig. 4.

TABLE 2 self-extinguishing time test of flame retardant additives in different addition ratios

As can be seen from table 2 and fig. 4, the addition of fluorodiethyl phosphinate can drastically reduce the flammability of the electrolyte, the curve of diethyl phosphinate trifluoroethyl ester is uniformly reduced, and the flame retardant effect is the best among the three when the content of the additive is 10-20%. The curve of tetrafluoropropyl diethylphosphinate shows a tendency to decrease slowly and then rapidly, whereas the curve of difluoroethyl diethylphosphinate is opposite. The data and the graphs show that the flame retardant effect of diethyl phosphinic acid difluoroethyl ester and diethyl phosphinic acid trifluoroethyl ester is best when the content of the electrolyte additive is between 0 and 5 percent, and the flame retardant effect of diethyl phosphinic acid trifluoroethyl ester is best when the content of the electrolyte additive is between 10 and 20 percent.

Test example 2

This test example is a test for each performance of a lithium symmetric battery using the electrolyte formulation prepared in preparation example 4 as an electrolyte in a coin cell.

Specifically, the lithium symmetric battery adopts a CR2032 button battery, and the battery assembly process is completed in an argon glove box with H ₂O/O₂ content less than 0.1 ppm. The electrolyte was selected from the electrolyte formulation prepared in preparation example 4, the separator was selected from a polypropylene separator (Celgard 2500, thickness 25 μm, diameter 18 mm), and lithium plate diameter 16mm.

The battery assembly process comprises stacking the negative electrode shell, the negative electrode plate (lithium sheet), injecting 40 μl of electrolyte, placing the diaphragm, injecting 40 μl of electrolyte again, the positive electrode plate (lithium sheet), the gasket, the elastic sheet and the positive electrode shell in sequence. Final packaging was performed using a button cell sealer at a pressure of 0.5 MPa.

2.1 Cycle life test of lithium symmetric batteries

And (5) carrying out cycle life test on the assembled lithium symmetrical battery by adopting a blue-ray test system. The test parameters were a deposition capacity density of 0.5mAh/cm ² and a current density of 1mA/cm ². The test results are shown in Table 3.

TABLE 3 results of cycle life testing for lithium symmetric batteries containing electrolyte formulations of comparative example 1 and examples 1-12

Numbering device	Cycle life (h)
		Comparative example 1	235
Example 1	415
		Example 2	389
Example 3	373
		Example 4	215
Example 5	375
		Example 6	359
Example 7	301
		Example 8	250
Example 9	314
		Example 10	287
Example 11	286
		Example 12	146

2.2 Cycle performance test of lithium symmetric batteries

And (5) carrying out cycle performance test on the assembled lithium symmetrical battery by adopting a blue-ray test system. The test parameters were a deposition capacity density of 0.5mAh/cm ² and a current density of 1mA/cm ². The test results are shown in fig. 5-7.

The optimal adding proportion of the three additives is 1% as can be seen from the cycle test results (table 2 and fig. 5-7) of the lithium symmetric battery, and the lithium symmetric battery can be respectively and stably circulated for 415h, 375h and 314h and has low overpotential, so that the electrolyte system can effectively improve the migration rate of lithium ions and the deposition/stripping process of lithium metal has good reversibility. And when the concentration of the additive is higher, the lithium symmetrical battery has poorer cycling stability because the concentration of the additive is increased, the conductivity of the electrolyte is reduced, the impedance is increased, the polarization is increased, and the cycle life is reduced.

Test example 3

This test example was a test using comparative example 1 and examples 1, 5 9 the electrolyte formulation prepared was used as the NCM811 Li half-cell for the electrolyte.

Specifically, the NCM 811I Li half cell adopts a CR2032 button cell, and the cell assembly process is completed in an argon glove box with H ₂O/O₂ content of less than 0.1 ppm. The electrolyte was selected from the electrolyte formulations prepared in comparative example 1 and examples 1, 5, 9, and the separator was selected from the group consisting of polypropylene separator (Celgard 2500, thickness 25 μm, diameter 18 mm), NCM811 sheet diameter 12mm, lithium sheet diameter 16mm.

The battery assembly process is as follows, sequentially stacking the negative electrode shell, the negative electrode plate (lithium plate), injecting 40 μl of electrolyte, placing the diaphragm, injecting 40 μl of electrolyte again, the positive electrode plate (NCM 811 plate), the gasket, the elastic sheet and the positive electrode shell. Final packaging was performed using a button cell sealer at a pressure of 0.5 MPa.

3.1NCM811 Li half-cell cycle test

A) The NCM811 Li half cell using the electrolyte formulations prepared in comparative example 1 and examples 1, 5, 9 as an electrolyte was tested for specific discharge capacity at 0.1C for 300 cycles of 0.5C activation for 5 cycles under a voltage range of 3.0 to 4.3v at 25 ℃, and the specific discharge capacity properties thereof are shown in table 4 and fig. 8.

B) The NCM811 Li half cell using the electrolyte formulations prepared in comparative example 1 and examples 1, 5, 9 as an electrolyte was tested for specific discharge capacity at 0.1C for 200 cycles of 1C cycle after 5 cycles of activation at 0.1C under a voltage range of 3.0 to 4.3v, the specific discharge capacity properties of which are shown in table 4 and fig. 9.

Table 4 results of NCM811 Li half-cell cycle performance test containing electrolyte formulations of comparative example 1 and examples 1, 5, 9

From the results of the cycle performance test of NCM811 Li half-cells (table 4 and fig. 8, 9), it can be seen that 1% of trifluoroethyl diethylphosphinate (example 5) can effectively increase the cycle performance of lithium metal cells.

CEI film thickness measurement after 3.2NCM811 Li half-cell cycling

The thickness of the CEI film was measured by Transmission Electron Microscopy (TEM) after activating the NCM811 Li half cell using the electrolyte formulations prepared in comparative example 1 and example 5 as an electrolyte at 0.1C for 5 cycles and 0.5C for 200 cycles under 25 ℃ with a voltage ranging from 3.0 to 4.3v, and the TEM image of the measurement result is shown in fig. 14.

It can be seen from fig. 14 (a) and 14 (b) that the conventional electrolyte forms a CEI film thickness of about 18.89nm and is not uniform on the surface of NCM811 particles because the continuous deintercalation of lithium ions during the cycle causes continuous shrinkage/expansion of the NCM811 lattice volume, and the unstable CEI layer is continuously broken to cause irreversible phase transition of the layered structure, grain cracking, even particle breakage, shortening the life of the lithium battery, and from fig. 14 (c) and 14 (d), the electrolyte containing 1.0wt% trifluoroethyl diethylphosphinate forms a CEI film thickness of about 7.49nm and is continuously uniform on the surface of NCM811 particles, which can prevent corrosion of HF on the NCM811 cathode and is advantageous for the internal structure of NCM811 particles to be stable. In summary, an electrolyte containing 1.0wt% trifluoroethyl diethylphosphinate had a thinner film thickness than that of a conventional electrolyte, further resulting in an improvement in the stable cycle of the cathode under high pressure. In the presence of C-F bonds, the CEI film is more conductive, and the deposit from electrolyte decomposition is reduced, further leading to improvement of rate performance.

3.3NCM811 Li half-cell high-voltage cycle performance test

The NCM811 Li half cell using the electrolyte formulations prepared in comparative example 1 and example 5 as an electrolyte was tested for specific discharge capacity at a voltage ranging from 3.0 to 4.5v at 25 ℃ for 200 cycles of 0.5C activation at 0.1C for 5 cycles, and the specific discharge capacity performance is shown in table 5 and fig. 10.

Table 5 NCM811 Li half-cell high voltage cycle performance test results containing comparative example 1 and example 5 electrolyte formulations

From the high-voltage cycle performance test results (table 5 and fig. 10) of the NCM811 Li half battery, it is known that 1% of diethyl phosphinic acid trifluoroethyl ester (example 5) can increase the specific discharge capacity from 65.4mAh/g to 136.1mAh/g, and the capacity retention rate from 39.42% to 69.36%, so that the cycle stability of the lithium ion battery under high voltage is greatly improved, and the high-voltage cycle performance of the lithium ion battery is effectively improved.

3.4NCM811 Li half-cell quick charge performance test

The NCM811 Li half cell using the electrolyte formulations prepared in comparative example 1 and example 9 as an electrolyte was tested for specific discharge capacity at 10C cycles 500 after 5 cycles of activation at 0.1C under a voltage range of 3.0 to 4.3v at 25 ℃, and the specific discharge capacity performance is shown in fig. 11.

From the data in FIG. 11, it can be seen that 1% diethyl phosphinic acid difluoroethyl ester can increase the specific discharge capacity from 50.4mAh/g to 91.9mAh/g, and the capacity retention rate from 35.07% to 60.03%, so that the cycling stability of the lithium ion battery under fast charge is effectively improved, and the fast charge performance of the lithium metal battery is improved.

3.5NCM811 Li half-cell rate performance test

3.5.1NCM811 Li half-cell normal-pressure multiplying power performance test

The electrolyte was tested for its rate capability in a voltage range of 3.0 to 4.3v at 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, 10C, 0.1C for NCM811 Li half-cells selected from the electrolyte formulations of comparative example 1 and examples 1, 5, 9, respectively, and the test results are shown in fig. 12.

From the data in fig. 12, it can be seen that, when the cut-off voltage is 4.3V and the charge and discharge rates are different, the specific discharge capacity of the lithium metal battery can be effectively improved by 1% of diethyl phosphinate tetrafluoropropyl ester (example 1) and 1% of diethyl phosphinate difluoroethyl ester (example 9), and particularly, the electrolyte of 1% of diethyl phosphinate difluoroethyl ester (example 9) still has 106mAh/g at 10C, which is far higher than that of the blank electrolyte, and the quick charge performance of the lithium ion battery can be effectively improved.

3.5.2NCM811 Li half-cell high-voltage multiplying power performance test

The electrolyte was subjected to cycle 5 cycles of 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, 10C, and 0.1C for the NCM811||li half-cell of comparative example 1 and example 5, respectively, and the rate performance was measured, and the test results are shown in fig. 13.

As can be seen from the data in fig. 13, the 1% diethyl phosphinic acid trifluoroethyl ester (example 5) is effective in improving the specific discharge capacity and capacity recovery rate of the lithium ion battery at high voltage, and improving the rate capability of the lithium ion battery for rapid charging at high voltage, when the cut-off voltage is 4.5V and the charging and discharging are performed at different rates.

High temperature storage performance test of 3.6NCM811 Li half-cell

The electrolyte was charged at 25 ℃ to 4.5v at a constant current and constant voltage of 1C, with 0.05C off, and left to stand for 1h, for NCM811 i Li half cells selected from comparative example 1 and example 5. Then 1C constant current discharge to 2.5V, the specific discharge capacity is initial capacity C0;

the battery was charged to 4.5v at a constant current and constant voltage of 1C at 25C, and 0.05C was turned off, and then transferred to a high temperature test cabinet for storage at 60C for 28 days. Taking out the test battery after the storage is completed, standing at room temperature for 10 hours, discharging to 2.5V at a constant current of 1C, and recording the specific discharge capacity C1;

After the test battery is placed for 2 hours, the test battery is charged to 4.5V at a constant current and a constant voltage of 1C, the test battery is cut off at 0.05C, and after the test battery is placed for 1 hour, the test battery is discharged to 2.5V at a constant current of 1C, and the discharge specific capacity C2 is recorded.

The results of the high temperature storage performance test are shown in Table 6.

Capacity retention (%) =c1/c0×100%

Capacity recovery (%) =c2/c0×100%

TABLE 6 results of high temperature storage Performance test of NCM811/Li half batteries assembled in comparative example 1 and example 5

From the data in table 6, it is clear that 1% trifluoroethyl diethylphosphinate (example 5) improves both the capacity retention rate and the capacity recovery rate of the lithium ion battery after high temperature storage, and can effectively improve the high temperature storage performance of the lithium ion battery.

As can be seen from the above examples:

(1) The compound I, particularly the compound II, the compound III and the compound IV provided by the invention can be used as a flame retardant additive of conventional electrolyte, and can effectively improve the safety of a lithium ion battery.

(2) The additive provided by the invention contains P=O bond, the lone pair electron of oxygen atom can play the Lewis base role, the strong Lewis acid PF ₅ and PF ₃ O derived from LiPF ₆ are effectively removed, and the corrosion and degradation of the strong Lewis acid PF ₅ and PF ₃ O on the surface of the positive electrode material are avoided, so that the dissolution of transition metal in the positive electrode material is avoided, and the dissolution of transition metal manganese is accompanied with the loss of oxygen in the material, so that the structure of the positive electrode material is irreversibly changed, and the irreversible influence on the battery capacity is brought. The oxygen thus deposited has strong oxidizing property and reacts with the electrolyte, and manganese, which is a positive electrode material, after being eluted, can be deposited on the surface of the negative electrode by a reduction reaction, and becomes a part of the SEI film (Mn F, mnCO ₃, etc.). The deposited manganese may block migration of lithium ions in the SEI film, resulting in an increase in battery resistance. If metal ions are reduced to metal present in the SEI film, this may exacerbate the decomposition of the electrolyte since metal is a good electron conductor. Therefore, the additive provided by the invention can better maintain the structural stability of the positive electrode material, and further improve the cycle stability of the battery.

(3) The compound I, particularly the compound II, the compound III and the compound IV, provided by the invention can be used as additives to be added into electrolyte or solid electrolyte, so that the safety and stability of a lithium ion secondary battery can be effectively improved, particularly the addition of the compound IV can be used for effectively improving the quick charge performance of the lithium ion secondary battery, the conversion rate (coulomb efficiency) is more than 99% under the high voltage of 4.3V and 4.5V, and the compound III can be used for effectively improving the high-voltage cycling stability of the lithium ion secondary battery.

Finally, it should be noted that these examples are merely illustrative and not intended to limit the invention in any way, and that although the invention has been described in detail with reference to the embodiments described above, it will be understood by those skilled in the art that modifications may be made to the technical solutions described in the embodiments described above, or equivalents may be substituted for some or all of the technical features thereof, without departing from the spirit of the technical solutions of the embodiments of the invention.

Claims

1. A compound characterized by having the structure of formula I:

2. The compound of claim 1, wherein the compound has a structural formula selected from the group consisting of:

3. Use of one or more of the compounds according to claim 1 or 2 as flame retardant additive in a flame retardant electrolyte or solid electrolyte.

4. A flame retardant electrolyte comprising one or more of the compounds of claim 1 or 2.

5. The flame retardant electrolyte of claim 4, further comprising:

An aprotic organic solvent, and

And (3) a lithium salt.

6. The flame retardant electrolyte of claim 5, wherein,

The concentration of the lithium salt is 0.5-2M;

the electrolyte is a compound selected from the group consisting of formula I, formula II, formula III, and formula IV, and is present in the flame-retardant electrolyte at a mass concentration of 0.5% to 20%, preferably at a mass concentration of 0.5% to 3%;

the aprotic organic solvent is present in the flame retardant electrolyte at a mass concentration of 60% to 90%.

7. The flame retardant electrolyte of claim 6, wherein,

preferably, the sulfone-based solvent comprises one or more of sulfolane, fluoro sulfolane, methyl ethyl sulfone, methyl propyl sulfone, methyl isopropyl sulfone, fluorinated methyl ethyl sulfone, fluorinated methyl propyl sulfone and fluorinated methyl isopropyl sulfone, and/or

8. A flame retardant solid state electrolyte comprising one or more of the compounds of claim 1 or 2.

9. The flame retardant solid state electrolyte of claim 8, further comprising:

A polymer matrix, and

Conductive lithium salts.

10. The solid electrolyte of claim 9, wherein the polymer matrix is selected from the group consisting of one or more of polyethylene oxide, polyethylene glycol, polyethylene carbonate, polypropylene carbonate, polyacrylonitrile, polymethyl methacrylate, and polyvinylidene fluoride, and/or mixtures thereof

11. An electrochemical energy storage device, comprising:

A cathode;

An anode;

A diaphragm, and

The flame retardant electrolyte according to any one of claims 4 to 7.

12. A lithium ion secondary battery, comprising:

A cathode;

An anode;

A diaphragm, and

The flame retardant electrolyte according to any one of claims 4 to 7.

13. A lithium ion secondary battery comprising:

A cathode;

Anode, and

The flame retardant solid electrolyte according to any one of claims 8 to 10.