CN111454183B - Lithium negative electrode pretreatment protective agent, lithium negative electrode pretreatment protection method and lithium negative electrode with protective layer - Google Patents
Lithium negative electrode pretreatment protective agent, lithium negative electrode pretreatment protection method and lithium negative electrode with protective layer Download PDFInfo
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Abstract
The embodiment of the invention provides a lithium negative electrode pretreatment protective agent which comprises a compound containing a sulfonyl fluoride structure shown in a formula (1),
wherein R is an n-valent alkyl group, a substituted alkyl group or an alkoxy group, and n is an integer of 1-3; the sulfur atom in the sulfonyl fluoride structure is bonded to a carbon atom in the hydrocarbyl group, the substituted hydrocarbyl group, or to an oxygen atom in the hydrocarbyloxy group. The pretreatment protective agent is adopted to pretreat the lithium cathode, and a protective layer rich in lithium fluoride and sulfur-containing compounds can be formed on the surface of the lithium cathode in situ, so that the lithium cathode can be effectively stabilized, side reactions are reduced, the generation of lithium dendrites is relieved, and the coulombic efficiency and the safety of the lithium battery are improved. The embodiment of the invention also provides a lithium negative electrode pretreatment protection method and a lithium negative electrode with the protection layer.
Description
Technical Field
The embodiment of the invention relates to the technical field of lithium secondary batteries, in particular to a lithium negative electrode pretreatment protective agent, a lithium negative electrode pretreatment protection method and a lithium negative electrode with a protective layer.
Background
With the change of science and technology, consumers have higher and higher requirements on the energy density of mobile terminal equipment, and the energy density of lithium ion batteries based on traditional graphite cathodes approaches to ceilings. The energy density of the lithium battery can be greatly improved by adopting the metal lithium cathode, and the user experience is remarkably improved. However, the lithium metal negative electrode has the characteristics of high chemical activity (causing low coulombic efficiency), lithium dendrite growth (causing side reactions and potential safety hazards), large volume expansion (continuous fracture and reconstruction of SEI film) and the like, and the commercialization process of the high-energy density lithium metal battery is hindered.
Aiming at the problems of the lithium metal negative electrode, the currently adopted main strategies have the following four aspects: 1) the lithium deposition is adjusted through electrolyte engineering, the deposition/dissolution coulombic efficiency of the metal lithium is improved by optimizing the electrolyte composition and/or adding additives, although the strategy is strong in operability and remarkable in effect and is one of effective ways for improving the stable circulation of the lithium cathode, the appropriate electrolyte formula and additives are the difficulties of current research and need to be continuously iterated and optimized for a long time; 2) the solid electrolyte inhibits the spread of dendritic crystals, and the growth of lithium dendritic crystals can be inhibited or slowed down to a certain extent by adopting the solid electrolyte, but the problem of the lithium dendritic crystals cannot be fundamentally solved, and the serious interface problem can be caused by the contact of the solid and the solid; 3) the customized main body limits the volume change, the lithium dendrite and the volume change can be relieved to a great extent by adopting the customized main body (such as a 3D current collector or a 3D nano framework), but the customized main body does not have a lithium source, or the specific capacity is reduced after the lithium metal is compounded, so that the performance of the high energy density characteristic of the customized main body can be directly influenced; 4) the lithium cathode is stabilized through interface engineering, a stable interface is constructed on the surface of the lithium cathode through a physical or chemical mode, uniform lithium ion current is achieved, the coulombic efficiency is improved, and the growth of lithium dendrites is relieved.
Disclosure of Invention
In view of this, embodiments of the present invention provide a lithium negative electrode pretreatment protective agent, which is used to pretreat a lithium negative electrode, and a protective layer rich in lithium fluoride and a sulfur-containing compound can be formed in situ on the surface of the lithium negative electrode, so that the lithium negative electrode can be effectively stabilized, side reactions can be reduced, the generation of lithium dendrites can be alleviated, and the coulombic efficiency and safety of a lithium battery can be improved, so as to solve the problems of the conventional lithium negative electrode that the side reactions are easy to occur and the lithium dendrites grow to a certain extent.
Specifically, according to a first aspect of the embodiments of the present invention, there is provided a lithium anode pretreatment protecting agent including a compound having a sulfonyl fluoride structure as shown in formula (1),
wherein R is an n-valent alkyl group, a substituted alkyl group or an alkoxy group, and n is an integer of 1 to 3; the sulfur atom in the sulfonyl fluoride structure is bonded to a carbon atom in the hydrocarbyl group, the substituted hydrocarbyl group, or to an oxygen atom in the hydrocarbyloxy group.
In an embodiment of the present invention, R is a hydrocarbon group, a substituted hydrocarbon group, or a hydrocarbon oxy group having 1 to 20 carbon atoms.
In an embodiment of the present invention, R is selected from any one of alkyl, alkylene, haloalkyl, haloalkylene, alkoxy, alkyleneoxy, haloalkoxy, haloalkyleneoxy, alkenyl, alkenylene, haloalkenyl, haloalkenylene, alkenyloxy, haloalkenyloxy, haloalkenylene oxy, aryl, arylene, haloaryl, haloarylene, aryloxy, haloaryloxy, and haloaryloxyl.
In an embodiment of the present invention, the halogen in the haloalkyl group, the haloalkylene group, the haloalkoxy group, the haloalkenylene oxy group, the haloaryl group, the haloarylene group, the haloaryloxy group, and the haloaryloxide group includes fluorine, chlorine, bromine, and iodine, and the halogen is a perhalogenated or partially halogenated group.
In an embodiment of the invention, the lithium negative electrode pretreatment protective agent further comprises an organic solvent, and the organic solvent comprises one or more of tetrahydrofuran, dimethyl ether, dimethyl sulfide, 1, 3-dioxolane, 1, 4-dioxane, 1, 2-dimethoxyethane, diglyme, bis-trifluoroethyl ether, hexafluoroisopropyl methyl ether, hexafluoroisopropyl ethyl ether, perfluorobutyl methyl ether, perfluorobutyl ethyl ether, tetrafluoroethyl tetrafluoropropyl ether and tetrafluoroethyl octafluoropentyl ether.
In an embodiment of the present invention, in the lithium negative electrode pretreatment protective agent, a mass ratio of the compound having a sulfonyl fluoride structure is 50% or more.
The lithium negative electrode pretreatment protective agent provided by the first aspect of the embodiment of the invention comprises a compound containing a sulfonyl fluoride structure, the pretreatment protective agent is adopted to pretreat a lithium negative electrode, the compound containing the sulfonyl fluoride structure can chemically react with the lithium negative electrode, so that a protective layer rich in lithium fluoride and sulfur-containing compounds is formed on the surface of the lithium negative electrode in situ, the protective layer can effectively reduce side reactions caused by direct contact of the lithium negative electrode and electrolyte and inhibit growth of lithium dendrites, and further the cycle efficiency and the safety of a lithium secondary battery are remarkably improved.
In a second aspect, an embodiment of the present invention further provides a lithium negative electrode pretreatment protection method, including the following steps:
the lithium negative electrode pretreatment protective agent provided by the first aspect of the embodiment of the invention is coated on the surface of a lithium negative electrode, the lithium negative electrode pretreatment protective agent and the lithium negative electrode undergo a chemical reaction, a protective layer is formed in situ on the surface of the lithium negative electrode, and the lithium negative electrode with the protective layer is obtained, wherein the protective layer comprises lithium fluoride and a sulfur-containing compound, and the sulfur-containing compound comprises Li 2 S、Li 2 SO 3 、Li 2 SO 4 And LiSO 3 And R' is one or more of monovalent hydrocarbon group, substituted hydrocarbon group or hydrocarbonoxy group.
In an embodiment of the invention, the lithium negative electrode pretreatment protective method further comprises, before coating, performing drying dehydration treatment on the lithium negative electrode pretreatment protective agent so that the water content of the lithium negative electrode pretreatment protective agent is less than 50 ppm.
In the embodiment of the invention, the coating mode comprises at least one of brushing, rolling, spraying, blade coating, dipping and spin coating, and the coating time is 1min-24 h.
In the embodiment of the invention, the temperature range of the chemical reaction is-10 ℃ to 50 ℃.
In an embodiment of the present invention, the thickness of the protective layer is 1nm to 5 μm.
In an embodiment of the present invention, the lithium negative electrode includes at least one of metallic lithium, a lithium silicon alloy, a lithium aluminum alloy, a lithium tin alloy, and a lithium indium alloy.
The lithium negative electrode pretreatment protection method provided by the second aspect of the embodiment of the invention is simple to operate, efficient and environment-friendly.
Third aspect of the inventionThe embodiment of the invention also provides a lithium negative electrode with a protective layer, which comprises the lithium negative electrode and the protective layer formed on one side or two sides of the lithium negative electrode, wherein the protective layer comprises lithium fluoride and a sulfur-containing compound, and the sulfur-containing compound comprises Li 2 S、Li 2 SO 3 、Li 2 SO 4 And LiSO 3 And R' is one or more of monovalent hydrocarbon group, substituted hydrocarbon group or hydrocarbonoxy group.
In an embodiment of the present invention, R' is a monovalent hydrocarbon group, substituted hydrocarbon group or hydrocarbonoxy group having 1 to 20 carbon atoms.
In an embodiment of the present invention, the thickness of the protective layer is 1nm to 5 μm.
In an embodiment of the present invention, the lithium negative electrode includes at least one of metallic lithium, a lithium silicon alloy, a lithium aluminum alloy, a lithium tin alloy, and a lithium indium alloy.
According to the lithium negative electrode with the protective layer provided by the third aspect of the embodiment of the invention, the protective layer can effectively reduce side reactions caused by direct contact between the lithium negative electrode and the electrolyte, and the cycle efficiency of the lithium secondary battery is improved; the protective layer can also inhibit the growth of lithium dendrites and improve the safety of the lithium secondary battery.
In addition, the embodiment of the invention also provides a lithium secondary battery, which comprises a positive pole piece, a negative pole piece, a diaphragm and electrolyte, wherein the negative pole piece comprises the lithium negative pole with the protective layer in the third aspect of the embodiment of the invention. The lithium secondary battery has high cycle performance and high safety.
Drawings
Fig. 1 and 2 are schematic structural views of a lithium negative electrode having a protective layer according to an embodiment of the present invention;
FIG. 3 is a graph of coulombic efficiency during 100 cycles for the copper/lithium batteries of example 2 of the present invention and comparative example 1;
FIG. 4 is a Scanning Electron Microscope (SEM) photograph of a lithium metal anode with a protective layer of example 2 of the present invention after cycling for 100 weeks;
FIG. 5 is a Scanning Electron Microscope (SEM) photograph of the unprotected lithium metal anode of comparative example 1 after cycling for 100 weeks;
fig. 6 is a graph showing the cycle curves of lithium/lithium batteries in example 2 of the present invention and comparative example 3.
Detailed Description
The embodiments of the present invention will be described below with reference to the drawings.
With the continuous development of high energy density devices, the cycle life and safety problems of high energy density liquid metal lithium secondary batteries are receiving more and more attention. The core components of the lithium metal secondary battery are mainly a positive electrode, a lithium metal negative electrode, an electrolyte and a diaphragm. During charging, lithium ions are extracted from crystal lattices of the anode material and deposited into a metal lithium cathode after passing through the electrolyte; during discharging, lithium ions are extracted from the metallic lithium negative electrode and inserted into the crystal lattice of the positive electrode material after passing through the electrolyte. During charge and discharge cycles, interfacial protection film instability leads to exposure of freshly deposited metallic lithium to direct contact with the electrolyte, causing severe side reactions and inducing lithium dendrite formation, thereby reducing coulombic efficiency and causing safety issues. In order to solve the above problems, embodiments of the present invention provide a lithium negative electrode pretreatment protective agent that can effectively stabilize a lithium negative electrode interface.
Specifically, the embodiment of the invention provides a lithium negative electrode pretreatment protective agent, which comprises a compound containing a sulfonyl fluoride structure as shown in a formula (1),
wherein R is an n-valent alkyl group, a substituted alkyl group or an alkoxy group, and n is an integer of 1-3; the sulfur atom in the sulfonyl fluoride structure is bonded to a carbon atom in the hydrocarbyl group, the substituted hydrocarbyl group, or to an oxygen atom in the hydrocarbyloxy group.
The lithium negative electrode pretreatment protective agent provided by the embodiment of the invention comprises a compound containing a sulfonyl fluoride structure, wherein the compound containing the sulfonyl fluoride structure can chemically react with a lithium negative electrode when being in contact with the lithium negative electrode, so that a protective layer rich in lithium fluoride and sulfur-containing compounds is formed on the surface of the lithium negative electrode in situ, and the protective layer can be used as a protective layerThe barrier layer isolates the direct contact of the electrolyte and the lithium cathode, so that the side reaction is reduced, and the coulomb efficiency of the lithium cathode is improved; on the other hand, the protective layer contains lithium fluoride having a high lithium ion diffusion rate and a sulfur compound having a high lithium ion conductivity (mainly Li) 2 S、Li 2 SO 3 、Li 2 SO 4 And LiSO 3 R', and the like) can homogenize the lithium ion flow, effectively stabilize the deposition/dissolution of the lithium ions of the lithium cathode and inhibit the growth of lithium dendrites, thereby improving the coulombic efficiency and safety of the lithium battery.
In an embodiment of the present invention, R may specifically be a hydrocarbyl, substituted hydrocarbyl or hydrocarbyloxy group having a valence of 1, 2 or 3, and accordingly n in formula (1) is 1, 2 or 3. The hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group, and may be a straight-chain hydrocarbon group, a branched-chain hydrocarbon group, a cyclic hydrocarbon group or an aromatic hydrocarbon group. Likewise, the substituted hydrocarbyl, hydrocarbyloxy groups may be saturated or unsaturated, straight-chain, branched, cyclic or aromatic.
In an embodiment of the present invention, R is a hydrocarbon group, a substituted hydrocarbon group, or a hydrocarbon oxy group having 1 to 20 carbon atoms. Further, the number of carbon atoms is 1 to 10.
In a specific embodiment of the present invention, R is selected from any one of alkyl, alkylene, haloalkyl, haloalkylene, alkoxy, alkyleneoxy, haloalkoxy, haloalkyleneoxy, alkenyl, alkenylene, haloalkenyl, haloalkenylene, alkenyloxy, haloalkenyloxy, haloalkenylene oxy, aryl, arylene, haloaryl, haloarylene, aryloxy, haloaryloxy, and haloaryloxyl. The alkyl group, the alkylene group, the halogenated alkyl group, the halogenated alkylene group, the alkoxy group, the alkyleneoxy group, the halogenated alkoxy group, and the halogenated alkyleneoxy group have 1 to 20 carbon atoms, and further have 1 to 8 carbon atoms; the number of carbon atoms of the alkenyl group, alkenylene group, haloalkenylene group, alkenyloxy group, haloalkenyloxy group, and haloalkenylene oxy group is 2 to 20, and further, the number of carbon atoms is 2 to 8; the aryl group, the arylene group, the haloaryl group, the haloarylene group, the aryloxy group, the aryloxylene group, the haloaryloxy group, and the haloaryloxylene group have 6 to 20 carbon atoms, and further have 6 to 10 carbon atoms.
In an embodiment of the present invention, the halogen in the haloalkyl group, the haloalkylene group, the haloalkoxy group, the haloalkenylene oxy group, the haloaryl group, the haloarylene group, the haloaryloxy group, and the haloaryloxide group includes fluorine, chlorine, bromine, and iodine, and the halogen is a perhalogenated or partially halogenated group.
In a particular embodiment of the invention, R includes, but is not limited to, n-propyl (-CH) 2 CH 2 CH 3 ) Fluoro-n-propyl (-CH) 2 CF 2 CF 3 ) Perfluoro-n-butyl (-CF) 2 CF 2 CF 2 CF 3 ) Ethylene (-CH) 2 CH 2 -), fluoromethylene (-CF) 2 -) and phenylene.
In a specific embodiment of the present invention, the molecular structural formula of the compound containing a sulfonyl fluoride structure may be represented by formulas (a-F):
in an embodiment of the present invention, the lithium negative electrode pretreatment protective agent further includes an organic solvent, which is an anhydrous organic solvent, and does not react or reacts very weakly in contact with the lithium negative electrode, and specifically includes, but is not limited to, one or more of tetrahydrofuran, dimethyl ether, dimethyl sulfide, 1, 3-dioxolane, 1, 4-dioxan, 1, 2-dimethoxyethane, diglyme, bis-trifluoroethyl ether, hexafluoroisopropyl methyl ether, hexafluoroisopropyl ethyl ether, perfluorobutyl methyl ether, perfluorobutyl ethyl ether, tetrafluoroethyl tetrafluoropropyl ether, and tetrafluoroethyl octafluoropentyl ether.
In the embodiment of the present invention, the pretreatment protective agent for a lithium negative electrode may be composed of only the compound having a sulfonyl fluoride structure, may be composed of a combination of the compound having a sulfonyl fluoride structure and an organic solvent, and may further contain other components as needed. For the compound containing the sulfonyl fluoride structure in the liquid form, adding an organic solvent to adjust the concentration of the compound containing the sulfonyl fluoride structure; for a compound containing a sulfonyl fluoride structure in a solid form, adding an organic solvent to dissolve and then coating on the surface of a lithium anode can shorten the reaction time. In the lithium negative electrode pretreatment protective agent, the mass ratio of the compound containing the sulfonyl fluoride structure is greater than or equal to 50%, the specific mass ratio can be 50-100%, and the further mass ratio is 70-95%.
The pretreatment protective agent for the lithium cathode provided by the embodiment of the invention comprises a compound containing a sulfonyl fluoride structure, the pretreatment protective agent is adopted to pretreat the lithium cathode, the compound containing the sulfonyl fluoride structure can chemically react with the lithium cathode, so that a protective layer rich in lithium fluoride and sulfur-containing compounds is formed on the surface of the lithium cathode in situ, the protective layer can effectively reduce side reactions caused by the contact of the lithium cathode and electrolyte and inhibit the growth of lithium dendrites, and the cycle efficiency and the safety of a lithium secondary battery are obviously improved.
Correspondingly, the embodiment of the invention also provides a lithium negative electrode pretreatment protection method, which comprises the following steps:
the lithium negative electrode pretreatment protective agent provided by the embodiment of the invention is coated on the surface of a lithium negative electrode, the lithium negative electrode pretreatment protective agent and the lithium negative electrode are subjected to chemical reaction, a protective layer is formed in situ on the surface of the lithium negative electrode, and the lithium negative electrode with the protective layer is obtained, wherein the protective layer comprises lithium fluoride and a sulfur-containing compound, and the sulfur-containing compound comprises Li 2 S、Li 2 SO 3 、Li 2 SO 4 And LiSO 3 And R' is one or more of monovalent hydrocarbon group, substituted hydrocarbon group or hydrocarbonoxy group.
In an embodiment of the present invention, R' is a monovalent hydrocarbon group, substituted hydrocarbon group or hydrocarbonoxy group having 1 to 20 carbon atoms, and further has 1 to 10 carbon atoms. The R' is determined by the R group in the compound containing the sulfonyl fluoride structure, and is derived from the R group. The number of carbon atoms of R' may be the same as that of the R group, or may be smaller than that of the R group, and the R group is decomposed to obtain the compound. The hydrocarbon group may be a saturated hydrocarbon group, an unsaturated hydrocarbon group, a straight-chain hydrocarbon group, a branched-chain hydrocarbon group, a cyclic hydrocarbon group or an aromatic hydrocarbon group. Likewise, the substituted hydrocarbyl, hydrocarbyloxy groups may be saturated or unsaturated, straight-chain, branched, cyclic or aromatic.
In a specific embodiment of the present invention, R' is selected from any one of alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, alkenylene, haloalkenyl, alkenyloxy, haloalkenyloxy, aryl, haloaryl, aryloxy, and haloaryloxy. The number of carbon atoms of the alkyl group, the halogenated alkyl group, the alkoxy group and the halogenated alkoxy group is 1 to 20, further, the number of carbon atoms is 1 to 8 and 1 to 3; the carbon atom number of the alkenyl, the halogenated alkenyl, the alkenyloxy and the halogenated alkenyloxy is 2-20, and further, the carbon atom number is 2-8 and 3-5; the aryl group, the halogenated aryl group, the aryloxy group and the halogenated aryloxy group have 6 to 20 carbon atoms, and further have 6 to 10 and 6 to 8 carbon atoms.
In an embodiment of the present invention, the halogen in the haloalkyl, haloalkoxy, haloalkenyl, haloalkenyloxy, haloaryl or haloaryloxy group includes fluorine, chlorine, bromine or iodine, and the halogen is a perhalogenated or partially halogenated group.
In a particular embodiment of the invention, R' includes, but is not limited to, n-propyl (-CH) 2 CH 2 CH 3 ) Fluoro-n-propyl (-CH) 2 CF 2 CF 3 ) Perfluoro-n-butyl (-CF) 2 CF 2 CF 2 CF 3 ) Ethyl (-CH) 2 CH 3 ) Methyl (-CH) 3 ) Trifluoromethyl (-CF) 3 ) And a phenyl group.
In embodiments of the invention, the protective layer may also include other substances (e.g., decomposition products of the R group).
In an embodiment of the invention, the lithium negative electrode pretreatment protective method further comprises, before coating, performing drying dehydration treatment on the lithium negative electrode pretreatment protective agent so that the water content of the lithium negative electrode pretreatment protective agent is less than 50 ppm. The drying and water removal method includes but is not limited to the methods of molecular sieve, distillation, rectification, vacuum drying under reduced pressure and the like.
In the embodiment of the invention, the coating mode comprises at least one of brushing, rolling, spraying, blade coating, dipping and spin coating, and the coating time is 1min-24 h. The specific time for coating can be specifically set according to the thickness of the preset protective layer, the mass ratio of the sulfonyl fluoride structure-containing compound in the pretreatment protective agent, the specific coating process mode and other factors. Further, the coating time can be 10min-12h, 30min-4 h. In the embodiment of the present invention, the coating operation may be, but is not limited to, performed in a drying room or under a protective atmosphere. In the embodiment of the invention, the temperature range of the chemical reaction is-10 ℃ to 50 ℃. Further, the temperature range of the chemical reaction is 10-30 ℃.
In an embodiment of the present invention, the thickness of the protective layer may be 1nm to 5 μm, further, the thickness of the protective layer may be 10nm to 1 μm, and further, the thickness of the protective layer may be 100nm to 800 nm. The appropriate thickness of the protective layer can maintain long-term stable circulation, and can not cause larger interface impedance to block lithium ion transmission.
In an embodiment of the present invention, the lithium negative electrode includes a lithium metal or lithium alloy negative electrode, and specifically may include at least one of lithium metal, a lithium silicon alloy, a lithium aluminum alloy, a lithium tin alloy, and a lithium indium alloy.
In the embodiment of the invention, when the pretreatment protective agent for the lithium negative electrode is in contact with the lithium negative electrode, a compound containing a sulfonyl fluoride structure in the pretreatment protective agent and the lithium negative electrode can generate a chemical reaction to generate lithium fluoride and a sulfur-containing compound, so that a protective layer is formed in situ on the surface of the lithium negative electrode. The chemical reaction can take place at a lower temperature, so the process is simple and easy to operate. The specific kind of the sulfur-containing compound depends on the kind of the compound having a sulfonyl fluoride structure.
The pretreatment protection method for the lithium cathode provided by the embodiment of the invention is simple to operate, high-efficiency and environment-friendly.
The embodiment of the invention also provides a lithium negative electrode with a protective layer, as shown in fig. 1, the lithium negative electrode with the protective layer comprises a lithium negative electrode 10 and protective layers 11 formed on two side surfaces of the lithium negative electrode 10, and the protective layers 11 comprise lithium fluoride and a sulfur compound The sulfur-containing compound comprises Li 2 S、Li 2 SO 3 、Li 2 SO 4 And LiSO 3 And R' is one or more of monovalent hydrocarbon group, substituted hydrocarbon group or hydrocarbonoxy group.
In an embodiment of the present invention, R' is a monovalent hydrocarbon group, substituted hydrocarbon group or hydrocarbonoxy group having 1 to 20 carbon atoms.
In the embodiment of the present invention, as shown in fig. 2, the protective layer 11 may be provided only on one surface of the lithium negative electrode 10.
In the embodiment of the present invention, the thickness of the protective layer 11 may be 1nm to 5 μm, further, the thickness of the protective layer may be 10nm to 1 μm, and further, the thickness of the protective layer may be 100nm to 800 nm.
In the embodiment of the present invention, other specific features of the protection layer 11 can be referred to the description of the protection method for lithium negative electrode pretreatment in the above-mentioned embodiment of the present invention.
In the embodiment of the present invention, the lithium negative electrode 10 includes a metal lithium or lithium alloy negative electrode, and specifically may include at least one of metal lithium, a lithium silicon alloy, a lithium aluminum alloy, a lithium tin alloy, and a lithium indium alloy.
In addition, the embodiment of the invention also provides a lithium secondary battery, which comprises a positive pole piece, a negative pole piece, a diaphragm and electrolyte, wherein the negative pole piece comprises the lithium negative pole with the protective layer provided by the embodiment of the invention. Specifically, the negative electrode sheet may be directly served by a lithium negative electrode having a protective layer, or may be a lithium negative electrode including a current collector and a protective layer disposed on the current collector. The current collector may be a conventional negative current collector such as copper foil, carbon-coated copper foil, or the like. The lithium secondary battery provided by the embodiment of the invention has high cycle performance and high safety due to the adoption of the lithium negative electrode with the protective layer provided by the embodiment of the invention.
The following examples are intended to illustrate the invention in more detail.
Example 1
A lithium negative electrode pretreatment protection method comprises the following steps:
s10, rectifying 1kg of propyl sulfonyl fluoride (A) through a rectifying column for 12h in a drying room, drying and removing water to obtain dried propyl sulfonyl fluoride, and stirring and mixing the dried propyl sulfonyl fluoride and perfluorobutyl methyl ether according to the mass ratio of 70:30 to form uniform mixed liquid serving as the lithium negative electrode pretreatment protective agent in the embodiment 1;
s20, in a glove box filled with argon, coating the lithium negative electrode pretreatment protective agent in the embodiment 1 on the surface of an unprotected metal lithium negative electrode in a brush coating mode, wherein the brush coating time is 20min, propyl sulfonyl fluoride and metal lithium are subjected to chemical reaction, and a protective layer with the thickness of 50nm is formed on the surface of the metal lithium negative electrode in situ to obtain the lithium negative electrode with the protective layer, wherein the protective layer comprises lithium fluoride and a sulfur-containing compound, and the sulfur-containing compound comprises Li 2 S、Li 2 SO 3 、Li 2 SO 4 、LiSO 3 CH 3 And LiSO 3 CH 2 CH 2 CH 3 One or more of (a).
Example 2
A lithium negative electrode pretreatment protection method comprises the following steps:
s10, in an argon-filled glove box, 100g of perfluorobutanesulfonyl fluoride (C) liquid was added
Standing the molecular sieve for 10h, drying and removing water, and filtering to obtain dried perfluorobutanesulfonyl fluoride liquid serving as the lithium negative electrode pretreatment protective agent in the embodiment 2;
S20, soaking the unprotected lithium metal negative electrode in the lithium negative electrode pretreatment protective agent in the embodiment 2 in a glove box filled with argon for 10min, and carrying out chemical reaction on perfluorobutanesulfonyl fluoride and lithium metal to form a protective layer with the thickness of 20nm on the surface of the lithium metal negative electrode in situ to obtain the lithium negative electrode with the protective layer, wherein the protective layer comprises lithium fluoride and a sulfur-containing compound, and the sulfur-containing compound comprises Li 2 S、Li 2 SO 3 、Li 2 SO 4 、LiSO 3 CF 3 And LiSO 3 CF 2 CF 2 CF 2 CF 3 One or more ofAnd (4) seed selection.
Example 3
A lithium negative electrode pretreatment protection method comprises the following steps:
s10, in an argon-filled glove box, 100g of a p-benzenesulfonyl fluoride (F) liquid was added
Standing the molecular sieve for 10 hours, drying and removing water, filtering to obtain dry p-benzenesulfonyl fluoride liquid, and stirring and mixing the dry p-benzenesulfonyl fluoride and 1, 2-dimethoxyethane according to the mass ratio of 80:20 to form uniform mixed liquid serving as the lithium negative electrode pretreatment protective agent in the embodiment 3;
s20, in a glove box filled with argon, coating the lithium negative electrode pretreatment protective agent in the embodiment 3 on the surface of an unprotected lithium-aluminum alloy negative electrode in a spin coating mode, wherein the spin coating time is 30min, chemical reaction is carried out on benzenesulfonyl fluoride and lithium, a protective layer with the thickness of 30nm is formed on the surface of the lithium-aluminum alloy negative electrode in situ, and the lithium negative electrode with the protective layer is obtained, wherein the protective layer comprises lithium fluoride and a sulfur-containing compound, and the sulfur-containing compound comprises Li 2 S、Li 2 SO 3 、Li 2 SO 4 And LiSO 3 C 6 H 5 One or more of (a).
In order to strongly support the beneficial effects brought by the technical scheme provided by the embodiment of the invention, the following tests are provided:
and (3) testing the performance of the copper/lithium battery: the lithium negative electrode with the protective layer, the copper sheet positive electrode and the diaphragm prepared in the embodiments 1 to 3 of the invention are assembled into a button cell, and 100 mu L1.0mol/L LiPF is dripped 6 Electrolyte (EC, DEC, VC weight ratio 47:47:6), the unprotected lithium metal negative electrode of example 2 of the invention and the unprotected lithium aluminum alloy negative electrode of example 3 of the invention were assembled into button cells as comparative examples 1 and 2, respectively, in the same manner, and then the charging and discharging current was 0.5mA/cm 2 The capacity is 1.0mAh/cm 2 The system (2) was subjected to charge and discharge tests, and the test results are shown in Table 1.
TABLE 1 results of performance tests on different lithium negative batteries
Meanwhile, fig. 3 shows coulombic efficiency profiles during 100 cycles of the cu/li batteries of example 2 of the present invention and comparative example 1. From the test results in table 1 and fig. 3, it can be known that the first coulombic efficiency and the 100-week average coulombic efficiency of the copper/lithium battery in the examples 1 to 3 of the present invention are both higher than those of the copper/lithium battery in the comparative examples 1 to 2, which indicates that the cycle performance of the battery can be significantly improved by the protective lithium negative electrode pretreated by the protective agent pretreated in the examples of the present invention. The protective lithium cathode is pretreated by the protective agent containing the compound with the sulfonyl fluoride structure, a stable protective layer is formed on the surface of the lithium cathode, the protective layer is a composite protective film, and the specific components of the protective layer comprise lithium fluoride and a sulfur-containing compound (mainly Li) 2 S、Li 2 SO 3 、Li 2 SO 4 And LiSO 3 R', etc.). On one hand, the composite protective film can serve as a barrier layer to isolate the direct contact of the electrolyte and the lithium cathode, so that side reactions are reduced, and the coulomb efficiency of the lithium cathode is improved; on the other hand, lithium fluoride having a high lithium ion diffusion rate and a sulfur-containing compound having a high lithium ion conductivity (mainly Li) are used as the composite protective film 2 S、Li 2 SO 3 、Li 2 SO 4 And LiSO 3 R', and the like) can homogenize the lithium ion flow, effectively stabilize the deposition/dissolution of the lithium ions of the lithium cathode and inhibit the growth of lithium dendrites, thereby improving the coulombic efficiency and safety of the lithium battery. The unprotected lithium cathodes in comparative examples 1 and 2 have high reactivity due to no pretreatment protection, and are in direct contact with the electrolyte, so that severe side reactions occur, the coulombic efficiency of the lithium cathodes is reduced, and the battery cycling stability is poor.
In addition, as can be seen from fig. 4 and fig. 5, after the lithium metal negative electrode with the protective layer in example 2 of the present invention is cycled for 100 weeks, the surface of the lithium metal negative electrode is smooth and flat, and there is no obvious corrosion and dendrite generation, which is mainly because after the lithium metal negative electrode is pretreated by perfluorobutyl sulfonyl fluoride, a composite protective film rich in lithium fluoride and sulfur-containing compounds is formed in situ on the surface of the lithium metal negative electrode, so that the side reaction between the lithium metal negative electrode and the electrolyte is effectively reduced, and the lithium dendrite generation is alleviated. After the unprotected lithium metal negative electrode in the comparative example 1 is cycled for 100 weeks, the surface of the lithium metal negative electrode is rough and has cracks, and serious corrosion occurs, which is mainly caused by serious side reactions due to the direct contact of the unprotected lithium metal negative electrode and the electrolyte.
Lithium/lithium battery performance test: the lithium negative electrode with the protective layer prepared in the embodiment 2 of the invention and a diaphragm are assembled into a button symmetrical battery, the diaphragm is clamped between the two lithium negative electrodes with the protective layers, and 100 mu L1.0mol/L LiPF is dripped 6 Electrolyte (EC, DEC, VC weight ratio 47:47:6), unprotected lithium metal negative electrode of example 2 of the present invention was used as comparative example 3 in the same manner, and then the charging and discharging current was 1.0mA/cm 2 The capacity is 1.0mAh/cm 2 The charge and discharge tests were conducted, and fig. 6 is a lithium/lithium battery cycle graph of example 2 and comparative example 3.
As can be seen from the test results in fig. 6, the lithium/lithium battery in example 2 of the present invention has a small polarization and can stably cycle for a long time (>300 hours), while the lithium/lithium battery in comparative example 3 has a large polarization and cannot stably cycle for a long time (<130 hours), which is mainly because after the metal lithium anode is pretreated with the perfluorobutanesulfonyl fluoride, a composite protective film rich in lithium fluoride and a sulfur-containing compound is formed in situ on the surface of the metal lithium anode, so that the side reaction between the metal lithium anode and the electrolyte is effectively reduced, and the flow of lithium ions can be homogenized, thereby facilitating the improvement of the cycle performance of the lithium/lithium battery. In contrast, the unprotected lithium metal negative electrode in comparative example 3 directly contacts with the electrolyte, and serious side reactions occur, and lithium dendrites are easily formed, resulting in poor cycle performance of the lithium/lithium battery.
Claims (16)
1. The application of the compound containing the sulfonyl fluoride structure shown in the formula (1) in the preparation of the lithium negative electrode pretreatment protective agent,
wherein R is an n-valent alkyl or substituted alkyl, and n is an integer of 1 to 3; the sulfur atom in the sulfonyl fluoride structure is connected with the carbon atom in the alkyl or substituted alkyl, and in the lithium negative electrode pretreatment protective agent, the mass ratio of the compound containing the sulfonyl fluoride structure is greater than or equal to 50%.
2. The use of claim 1, wherein R is a hydrocarbyl or substituted hydrocarbyl group having 1 to 20 carbon atoms.
3. The use of claim 1 or 2, wherein R is selected from any one of alkyl, alkylene, haloalkyl, haloalkylene, alkenyl, alkenylene, haloalkenyl, haloalkenylene, aryl, arylene, haloaryl, and haloarylene.
4. The use according to claim 3, wherein the halogen of the haloalkyl, haloalkylene, haloalkenyl, haloalkenylene, haloaryl or haloarylene is selected from the group consisting of fluorine, chlorine, bromine and iodine, and the halogen is perhalogenated or partially halogenated.
5. The use of claim 1, wherein the lithium negative electrode pretreatment protectant further comprises an organic solvent selected from one or more of tetrahydrofuran, dimethyl ether, dimethyl sulfide, 1, 3-dioxolane, 1, 4-dioxan, 1, 2-dimethoxyethane, diglyme, bis-trifluoroethyl ether, hexafluoroisopropyl methyl ether, hexafluoroisopropyl ethyl ether, perfluorobutyl methyl ether, perfluorobutyl ethyl ether, tetrafluoroethyl tetrafluoropropyl ether, tetrafluoroethyl octafluoropentyl ether.
6. A lithium negative electrode pretreatment protection method is characterized by comprising the following steps:
coating a lithium negative electrode pretreatment protective agent on the surface of a lithium negative electrode, wherein the lithium negative electrode pretreatment protective agent comprises a compound containing a sulfonyl fluoride structure shown in a formula (1),
wherein R is an n-valent alkyl or substituted alkyl, and n is an integer of 1 to 3; the sulfur atom in the sulfonyl fluoride structure is connected with the carbon atom in the alkyl and the substituted alkyl; in the lithium negative electrode pretreatment protective agent, the mass ratio of the compound containing the sulfonyl fluoride structure is more than or equal to 50%;
the lithium negative electrode pretreatment protective agent and the lithium negative electrode generate a chemical reaction, a protective layer is formed on the surface of the lithium negative electrode in situ, and the lithium negative electrode with the protective layer is obtained, wherein the protective layer comprises lithium fluoride and a sulfur-containing compound, and the sulfur-containing compound is Li 2 S、Li 2 SO 3 、Li 2 SO 4 And LiSO 3 And R' is one or more of monovalent hydrocarbon group or substituted hydrocarbon group.
7. The lithium negative electrode pretreatment protection method according to claim 6, further comprising, prior to the coating, subjecting the lithium negative electrode pretreatment protection agent to a drying and water removal treatment so that the water content of the lithium negative electrode pretreatment protection agent is less than 50 ppm.
8. The lithium negative electrode pretreatment protection method according to claim 6, wherein the coating manner is at least one selected from brushing, rolling, spraying, blade coating, dip coating and spin coating, and the coating time is 1min-24 h.
9. The lithium negative electrode pretreatment protection method of claim 6, wherein the temperature range of the chemical reaction is-10 ℃ to 50 ℃.
10. The lithium negative electrode pretreatment protection method of claim 6, wherein the protective layer has a thickness of 1nm to 5 μm.
11. The lithium negative electrode pre-treatment protection method of claim 6, wherein the lithium negative electrode is selected from at least one of a metallic lithium negative electrode, a lithium silicon alloy negative electrode, a lithium aluminum alloy negative electrode, a lithium tin alloy negative electrode, and a lithium indium alloy negative electrode.
12. A lithium negative electrode having a protective layer, comprising a lithium negative electrode and a protective layer formed on one or both surfaces of the lithium negative electrode, the protective layer being obtained by the method according to any one of claims 6 to 11.
13. The lithium negative electrode having a protective layer according to claim 12, wherein R' is a monovalent hydrocarbon group or a substituted hydrocarbon group having 1 to 20 carbon atoms.
14. The lithium anode having a protective layer according to claim 12, wherein the protective layer has a thickness of 1nm to 5 μm.
15. The lithium negative electrode having a protective layer according to claim 12, wherein the lithium negative electrode is at least one selected from the group consisting of a metallic lithium negative electrode, a lithium silicon alloy negative electrode, a lithium aluminum alloy negative electrode, a lithium tin alloy negative electrode, and a lithium indium alloy negative electrode.
16. The lithium secondary battery is characterized by comprising a positive pole piece, a negative pole piece, a diaphragm and an electrolyte, wherein the negative pole piece is the lithium negative pole with the protective layer according to any one of claims 12 to 15.
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| 高稳定性锂氧气电池负极和电解液的研究;黄志梅;《中国博士学位论文全文数据库 过程科技I辑》;20190515(第5期);B015-45页 * |
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