CN114023965B - Solid lithium battery - Google Patents
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- CN114023965B CN114023965B CN202111263312.8A CN202111263312A CN114023965B CN 114023965 B CN114023965 B CN 114023965B CN 202111263312 A CN202111263312 A CN 202111263312A CN 114023965 B CN114023965 B CN 114023965B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0565—Polymeric materials, e.g. gel-type or solid-type
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention relates to the technical field of solid-state lithium batteriesThe solid-state lithium battery comprises a positive electrode, a negative electrode and a polymer solid-state electrolyte positioned between the positive electrode and the negative electrode, wherein the polymer solid-state electrolyte comprises a polymer, the positive electrode comprises a positive electrode material layer, the positive electrode material layer comprises a positive electrode active material and a compound shown in a structural formula 1, and the structural formula 1 is
Description
Technical Field
The invention relates to the technical field of lithium batteries, in particular to a solid-state lithium battery.
Background
With the development of new energy industry, the rechargeable lithium battery market puts higher requirements on performance indexes such as battery energy density, cycle life, safety performance and the like. The solid-state lithium battery uses the polymer solid electrolyte without leakage risk, so that the safety performance of the battery is greatly improved, and the use of a high-capacity electrode material is possible, therefore, the solid-state lithium battery has the potential of high energy density and high safety performance.
At present, increasing the operating voltage of the battery is an effective means for increasing the energy density of the battery. However, the electrochemical stability of the polymer solid electrolyte under high voltage is not good, and the problems of rapid cycle capacity decay and low capacity retention rate are easily caused, mainly because: in the process of charging and discharging of the solid-state lithium battery, the processes of oxygen evolution of the anode active substance, generation of active free radicals and the like under high voltage can cause the breakage of macromolecular chains in the polymer solid-state electrolyte, the performance of the polymer solid-state electrolyte and the attenuation of the interface performance of the electrolyte and the anode are caused, along with the increase of the number of charging and discharging cycles, the attenuation degree of the performance of the polymer solid-state electrolyte is continuously increased, and the cycle performance is reduced. Therefore, how to improve the matching of the positive electrode and the polymer solid electrolyte under high voltage becomes a key issue for improving the service life of the battery.
Aiming at the problem of poor cycling stability of the solid-state lithium battery under higher voltage, the prior art mainly inhibits the side reaction of the anode to the polymer solid-state electrolyte by coating the surface of the anode active substance, and improves the cycling stability of the solid-state lithium battery.
Disclosure of Invention
Aiming at the problem of poor cycle stability of the solid-state lithium battery under high voltage, the invention provides the anode for the solid-state lithium battery, the cycle performance of the battery is improved by doping the unsaturated phosphate compound with a specific structure into the anode material layer, and the specific technical scheme is as follows:
a solid lithium battery includes a positive electrode, a negative electrode, and a polymer solid electrolyte interposed between the positive electrode and the negative electrode, the polymer solid electrolyte including a polymer, the positive electrode including a positive electrode material layer including a positive electrode active material and a compound represented by formula 1,
structural formula 1
Wherein R is 1 、R 2 、R 3 Each independently selected from a hydrogen atom, a substituted or unsubstituted C 1 -C 12 Saturated aliphatic hydrocarbon group of (1), substituted or unsubstituted C 2 -C 12 Unsaturated aliphatic hydrocarbon group, and R 1 、R 2 、R 3 In which at least one is substituted or unsubstituted C 2 -C 12 An unsaturated aliphatic hydrocarbon group;
the solid-state lithium battery meets the following conditions:
5≤uL/wd≤500；
wherein u is the mass percentage of the polymer in the total mass of the polymer solid electrolyte, and the unit is;
w is the mass percentage of the compound shown in the structural formula 1 in the mass of the positive active material, and the unit is;
l is the thickness of the anode material layer and the unit is mum;
d is the thickness of the polymer solid electrolyte in μm.
The solid-state lithium battery is characterized in that the positive electrode material layer contains a compound shown in a structural formula 1, the unsaturated phosphate compound with a specific structure is uniformly attached to the surface of the positive electrode active material in situ, the positive electrode active material is inhibited from generating oxygen evolution reaction or generating active free radicals to a certain extent under high voltage, and the probability of chain breakage of a polymer macromolecular chain of the polymer solid-state electrolyte due to the attack of the positive electrode precipitated material is reduced, so that the electrochemical stability of the polymer solid-state electrolyte is improved, and the cycle stability of the solid-state lithium battery is improved. Through extensive research, the inventor finds that the thickness of the positive electrode material layer is increased, the damage probability of the positive electrode to the polymer is increased, and the content of the compound shown in the structural formula 1 needs to be correspondingly increased; in a polymer solid electrolyte, a polymer is a main source of electrolyte decomposition, the content of the polymer is increased, and the content of the compound represented by the structural formula 1 is also required to be increased; the increase in the thickness of the polymer solid electrolyte decreases the probability of deterioration of the polymer by the positive electrode, and accordingly, the content of the compound represented by formula 1 decreases. Therefore, the inventor researches and summarizes a relation that uL/wd is more than or equal to 5 and less than or equal to 500, and reasonably quantifies parameters such as mass percentage u of the polymer in the total mass of the polymer solid electrolyte, thickness d of the polymer solid electrolyte, mass percentage w of the compound shown in the structural formula 1 in the mass of the positive electrode active material, thickness L of the positive electrode material layer and the like, so as to obtain the solid lithium battery with high energy density and stable cycle performance.
As a preferable embodiment of the solid-state lithium battery, the charge cut-off voltage of the solid-state lithium battery is more than or equal to 4.2V.
It should be noted that the positive active material is more prone to oxygen evolution and active radical generation at high voltage, and side reaction occurs with the polymer solid electrolyte, which results in deterioration of cycle performance of the solid lithium battery. The protection effect of the compound on the polymer solid electrolyte is particularly obvious under the condition that the charge cut-off voltage is more than or equal to 4.2V.
In a preferred embodiment, the solid-state lithium battery satisfies the following conditions:
10≤uL/wd≤300；
in a more preferred embodiment, the solid-state lithium battery satisfies the following conditions:
15≤uL/wd≤200。
when the content of the compound represented by formula 1 in the solid lithium battery, the thickness of the positive electrode material layer, the content of the polymer in the polymer solid electrolyte, and the thickness of the polymer solid electrolyte are in the above-described relationship ranges, the cycle performance of the battery can be further improved.
As a preferred embodiment of the solid-state lithium battery of the present invention, R 1 、R 2 、R 3 Each independently selected from a hydrogen atom, a substituted or unsubstituted C 1 -C 5 Saturated aliphatic hydrocarbon group of (1), substituted or unsubstituted C 2 -C 5 Unsaturated aliphatic hydrocarbon group, and R 1 、R 2 、R 3 In which at least one is substituted or unsubstituted C 2 -C 5 Unsaturated aliphatic hydrocarbon radical, R 1 、R 2 Or R 3 When substituted, the substituents are selected from halogens.
As a preferred embodiment of the solid lithium battery of the present invention, in the structural formula 1, unsubstituted C 1 -C 5 The saturated aliphatic hydrocarbon group is selected from one of methyl, ethyl, propyl, isopropyl and butyl; substituted C 1 -C 5 The saturated aliphatic hydrocarbon group of (a) is selected from the group consisting of a monofluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a 2-fluoroethyl group, a 2, 2-difluoroethyl group, a 2, 2-trifluoroethyl group, a 3, 3-difluoropropyl group, a 3, 3-trifluoropropyl groupOne of hexafluoroisopropyl; unsubstituted C 2 -C 5 The unsaturated alkyl is selected from one of vinyl, allyl, 3-butenyl, isobutenyl, 4-pentenyl, ethynyl, propargyl, 3-butynyl and 1-methyl-2-propynyl; substituted C 2 -C 5 The unsaturated hydrocarbon group of (a) is one selected from the group consisting of 2, 2-difluoroethenyl group, 3-fluoro-propenyl group, 1-difluoro-propenyl group, 4-fluoro-3-butenyl group, 4-difluoro-3-butenyl group, 2-methyl-3, 3-difluoro-2-propenyl group, 5-difluoro-4-pentenyl group, 2-fluoroethynyl group, 3-fluoro-2-propynyl group, 4-fluoro-3-butynyl group, and 1-methyl-3-fluoro-2-propynyl group.
As a preferable embodiment of the solid lithium battery of the present invention, the compound represented by structural formula 1 is at least one selected from the group consisting of compounds represented by structural formulae 1-1, 1-2, or 1-3,
structural formula 1-1
Structural formula 1-2
Structural formulae 1 to 3
Wherein R is 4 、R 5 、R 6 Each independently selected from a hydrogen atom, a substituted or unsubstituted C 1 -C 11 Saturated aliphatic hydrocarbon group, substituted or unsubstituted C 2 -C 11 Unsaturated aliphatic hydrocarbon group of (2), and R 4 、R 5 、R 6 In which at least one is substituted or unsubstituted C 2 -C 11 Unsaturated aliphatic hydrocarbon group of (1).
As a preferred embodiment of the solid lithium battery of the present invention, the compound represented by structural formula 1 is at least one selected from the group consisting of compounds 1 to 6,
compound 1:
compound 2:
compound 3:
compound 4:
compound 5:
compound 6:
the above-mentioned compounds may be used alone or in combination of two or more.
As a preferred embodiment of the solid-state lithium battery of the present invention, the positive electrode active material is selected from at least one of compounds represented by the following general formula:
LiL x M y N z O 2 l, M and N are respectively and independently selected from at least one element of Ni, co, mn, V, fe and Al, and x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, x + y + z =1;
LiL x M y N z O 4 l, M and N are respectively and independently selected from at least one element of Ni, co, mn, V, fe and Al, x is more than or equal to 0 and less than or equal to 2, y is more than or equal to 0 and less than or equal to 2, z is more than or equal to 0 and less than or equal to 2, and x +, y +, z =2.
Preferably, the positive electrode active material is selected from at least one of compounds represented by the following general formula:
LiL x M y O 2 wherein, L and M are selected from at least one element of Ni, co and Mn, and x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, x + y=1;
LiL x M y O 4 wherein, L and M are selected from at least one element of Ni, co and Mn, and x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, x + y=2.
More preferably, the positive electrode active material is at least one selected from the group consisting of compounds represented by the following general formulae:
LiNi x Co y Mn z O 2 x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, x + y + z =1;
LiNi x Co y Al z O 2 x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, x + y + z =1;
LiNi x Co y Mn z O 4 x is more than or equal to 0 and less than or equal to 2, y is more than or equal to 0 and less than or equal to 2, z is more than or equal to 0 and less than or equal to 2, x + y + z =2;
LiNi x Co y Al z O 4 x is more than or equal to 0 and less than or equal to 2, y is more than or equal to 0 and less than or equal to 2, z is more than or equal to 0 and less than or equal to 2, and x + y + z =2.
More preferably, the positive electrode active material is selected from LiMnO 2 、LiNiO 2 、LiCoO 2 、LiNi 0.5 Mn 0.5 O 2 、LiNi 0.5 Co 0.2 Mn 0.3 O 2 、LiNi 0.6 Co 0.2 Mn 0.2 O 2 、LiNi 0.8 Co 0.1 Mn 0.1 O 2 、LiMn 2 O 4 、LiNi 2 O 4 、LiCo 2 O 4 、LiNi 0.5 Mn 1.5 O 4 、LiNiMnO 4 At least one of (1).
As a preferred embodiment of the solid-state lithium battery, the mass percentage w of the compound shown in the structural formula 1 in the mass of the positive active material is 1-10%, the content of the compound shown in the structural formula 1 is less than 1%, and the polymer solid electrolyte is decomposed to cause low cycle life; the content of the compound shown in the structural formula 1 is higher than 10%, the battery resistance is high, and the battery capacity is low.
As a preferred embodiment of the solid lithium battery of the present invention, the polymer solid electrolyte has a thickness d of 10 to 200. Mu.m. The thinner the electrolyte thickness is, the greater the probability that the polymer component in the solid electrolyte is decomposed by attack, and the poorer the battery cycle stability is; the electrolyte thickness is too big, increases battery internal ion transmission path, increases battery impedance and polarization, reduces battery capacity.
As a preferable embodiment of the solid lithium battery of the present invention, the polymer accounts for 50 to 90 mass% of the total mass of the polymer solid electrolyte. In a solid electrolyte, the polymer content is too low, and the blocking capability of the electrolyte on the positive electrode and the negative electrode is weak, so that the cycling stability of a lithium negative electrode is not facilitated; the polymer content is too high, the electrolyte resistance is large, and the capacity of the battery is low.
As a preferred embodiment of the solid lithium battery of the present invention, the thickness L of the positive electrode material layer is 50 to 200 μm. The increase of the thickness of the positive electrode is beneficial to increasing the energy density of the battery, but the probability of the polymer component in the solid electrolyte being attacked and decomposed is increased, and the cycling stability of the battery is deteriorated. Therefore, the thickness of the positive electrode has a reasonable range, the practical energy density application requirement of the battery is met, and the cycle stability is considered.
As a more preferable embodiment of the solid lithium battery of the present invention, the mass percentage w of the compound represented by the structural formula 1 to the mass of the positive active material is 1 to 8%;
the thickness d of the polymer solid electrolyte ranges from 20 to 100 μm;
the mass percent u of the polymer in the total mass of the polymer solid electrolyte is 60-80%;
the thickness L of the positive electrode material layer is 60-150 mu m.
The analysis is only based on the influence of each parameter on the battery when the parameter exists independently, but in the practical battery application process, the four parameters are correlated and inseparable. The relation provided by the invention relates the four factors and affects the capacity and the cycling stability of the battery together, so that the content of the compound shown in the structural formula 1, the thickness of the anode material layer, the content of the polymer in the polymer solid electrolyte and the thickness of the polymer solid electrolyte are adjusted to enable uL/wd to be more than or equal to 5 and less than or equal to 500, and the cycling performance of the solid lithium battery can be effectively improved on the premise of ensuring that the secondary battery has higher initial specific capacity. If the uL/wd value is too high or too low, the dynamic deterioration of the battery will occur, so that the cycling performance of the battery at high voltage is significantly reduced.
As a preferred embodiment of the solid lithium battery according to the present invention, the compound represented by formula 1 is formed on the surface of the positive electrode material layer, or the compound represented by formula 1 is mixed in the inside of the positive electrode material layer.
When the compound represented by the structural formula 1 is formed on the surface of the positive electrode material layer, the preparation method thereof may be as follows:
specifically, a positive electrode active substance, a positive electrode conductive agent and a positive electrode binder are dispersed in an organic solvent to prepare a positive electrode slurry, the positive electrode slurry is coated and dried to form a positive electrode material layer, then the compound shown in the structural formula 1 is dispersed in the organic solvent, the obtained compound solution shown in the structural formula 1 is sprayed on the surface of the positive electrode material layer, and the solvent is dried and removed to obtain the positive electrode material layer containing the compound shown in the structural formula 1.
When the compound represented by the structural formula 1 is blended in the inside of the positive electrode material layer, the preparation thereof may be made in the following manner:
1. the positive electrode slurry for preparing the positive electrode material layer contains a compound shown in a structural formula 1, specifically, the compound shown in the structural formula 1, a positive electrode active substance, a positive electrode conductive agent and a positive electrode binder are dispersed in an organic solvent to prepare positive electrode slurry, and the positive electrode slurry is coated and dried to form the positive electrode material layer;
2. after preparing the positive electrode material layer, soaking the positive electrode material layer in a solution of a compound shown in a structural formula 1 to enable the compound shown in the structural formula 1 to permeate into the positive electrode material layer, and drying to remove the solvent to obtain the positive electrode material layer containing the compound shown in the structural formula 1.
As a preferred embodiment of the solid lithium battery of the present invention, the compound represented by the structural formula 1 is blended inside the positive electrode material layer. More preferably, the compound represented by formula 1 is added to the slurry for preparing the positive electrode material layer.
The compound shown in structural formula 1 is additionally added into the mixed positive electrode slurry of the solid-state lithium battery provided by the invention, and the unsaturated phosphate compound with a specific structure is attached to the surface of a positive electrode active material in situ, so that a positive electrode with unsaturated phosphate uniformly dispersed in a bulk phase can be prepared, and the solid-state lithium battery is simple in process and low in operation difficulty. In addition, compared with the existing modification technology of the cathode material such as inorganic doping and inorganic coating, the preparation method of the cathode does not need to pretreat the cathode active substance, and avoids the influence of the pretreatment process on the structure of the cathode active substance.
As a preferred embodiment of the solid lithium battery according to the present invention, the polymer is selected from at least one of linear or branched polyethylene oxide (PEO), polyethylene carbonate (PEC), polypropylene carbonate (PPC), polymethyl methacrylate (PMMA), polylactic acid (PLA), polycaprolactone (PCL), polycaprolactam (PA), polysiloxane, polyvinylidene fluoride (PVDF), a copolymer of styrene and ethylene oxide (PS-PEO), and a copolymer of ethylene oxide and caprolactam (PEO-PA).
As a preferred embodiment of the solid-state lithium battery of the present invention, the negative electrode includes a simple substance or an alloy of one or two or more elements of lithium, carbon, silicon, and tin.
As a preferred embodiment of the solid lithium battery of the present invention, the positive electrode material layer further includes a binder and a conductive agent. The binder, the conductive agent, and the like used herein are not particularly limited, and known binders and conductive agents can be used. For example, the binder is selected from at least one of a polyvinyl alcohol binder, a polyurethane binder, a polyacrylate binder, a butyl rubber binder, an epoxy resin binder, a vinyl acetate resin binder, a chlorinated rubber binder, a polyvinylidene fluoride binder, and a polytetrafluoroethylene binder; more preferably, the binder is a polyvinylidene fluoride binder. The conductive agent is selected from at least one of conductive carbon black, superconducting carbon black, conductive graphite, acetylene black and carbon nanotubes; preferably, the conductive agent is selected from at least one of conductive carbon black, conductive graphite and acetylene black; more preferably, the conductive agent is conductive carbon black and/or acetylene black; most preferably, the conductive agent is conductive carbon black.
In the field of lithium secondary batteries using an electrolyte, the liquid electrolyte is free to flow, and the electrolyte carries substances dissolved therein to diffuse to various parts inside the battery, including a positive electrode and a negative electrode. In the solid lithium battery, the polymer solid electrolyte is not flowable, and the additive used in the polymer solid electrolyte cannot effectively act on the positive electrode or the negative electrode, and has little influence on the electrochemical process of the positive electrode bulk phase.
Therefore, the solid-state lithium battery provided by the invention has the following beneficial effects:
the compound shown in the structural formula 1 is doped into the positive electrode of the solid-state lithium battery, the unsaturated phosphate with the specific structure can be adsorbed on the surface of a positive active material in situ, the processes of oxygen evolution and generation of active free radicals of the positive active material under high voltage are inhibited, and the probability of chain breakage caused by the attack of the end group of a polymer macromolecular chain in the polymer solid-state electrolyte is reduced, so that the electrochemical stability of the polymer solid-state electrolyte is improved, and the cycle stability of the solid-state lithium battery is improved; meanwhile, by adjusting the relationship among the compound content shown in the structural formula 1, the thickness of the anode material layer, the content of the polymer in the polymer solid electrolyte and the thickness of the polymer solid electrolyte, the cycle performance of the solid electrolyte can be effectively improved on the premise that the secondary battery has higher initial specific capacity.
Detailed Description
In view of the problems that the production process of the existing coating method for modifying the positive active material is complex and the structure of the positive active material can be damaged, the application is researched, creatively designs and invents a simple and effective method for modifying the positive active material, namely, a compound shown in a structural formula 1 is added into a conventional positive material layer, an unsaturated phosphate compound with a specific structure can be attached to the surface of the positive active material in situ, the processes of oxygen evolution and active free radical generation of the positive active material are inhibited, the macromolecular chain of the polymer solid electrolyte is protected from being broken by the attack of oxygen or active free radicals, and meanwhile, the cycle performance of the solid electrolyte can be effectively improved on the premise of ensuring that a secondary battery has higher initial specific capacity by regulating the relationship among the content of the compound shown in the structural formula 1, the thickness of the positive material layer, the content of a polymer in the polymer solid electrolyte and the thickness of the polymer solid electrolyte.
The technical solutions of the present invention will be described clearly and completely with reference to specific embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The phosphate ester compounds used in the examples and comparative examples of the present invention are shown in table 1, in which compounds 1 to 6 are unsaturated phosphate ester compounds and compounds 7 to 9 are saturated phosphate ester compounds.
TABLE 1 phosphoric acid ester-based compounds used in examples and comparative examples
LiNi was used as a positive electrode active material 0.5 Mn 0.5 O 2 、LiNi 0.5 Co 0.2 Mn 0.3 O 2 、LiNi 0.6 Co 0.2 Mn 0.2 O 2 、LiNi 0.8 Co 0.1 Mn 0.1 O 2 Or LiNi 0.5 Mn 1.5 O 4 One of (1);
the polymer solid electrolyte adopts one of PEO/LiTFSI, PCL/LiFSI or PEC/LiFSI;
furthermore, polyvinylidene fluoride (PVDF) is used as a binder of the positive electrode; the conductive agent adopts conductive carbon black; the positive current collector adopts a carbon-coated aluminum foil; NMP is adopted as the solvent of the anode slurry; the negative electrode adopts lithium metal or lithium-tin alloy.
Example 1
The positive electrode of this example was formed of a positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O 2 The solid lithium battery comprises a compound 1, a binder Polyoxyethylene (PEO) and a conductive agent conductive carbon black, wherein the components are mixed with a solvent to form positive electrode slurry, the positive electrode slurry is coated on the surface of a positive electrode current collector and dried to prepare a positive electrode comprising the positive electrode material, and then the positive electrode material is assembled into the solid lithium battery. The method comprises the following specific steps:
preparation of the positive electrode: liNi as positive electrode active material 0.6 Co 0.2 Mn 0.2 O 2 And mixing the compound 1, a binder Polyoxyethylene (PEO) and conductive carbon black, uniformly dispersing the mixture in N-methylpyrrolidone (NMP) to obtain anode slurry, coating the anode slurry on a carbon-coated aluminum foil, and drying in vacuum to obtain the anode.
Preparing a solid lithium battery: the positive electrode, the polymer solid electrolyte PEO/LiTFSI and the negative electrode lithium metal prepared in the embodiment are assembled into a solid lithium battery.
Performance testing
1. Testing the initial specific capacity: and (3) charging the assembled solid lithium battery to 4.2V at 60 ℃ by using a current constant current of 0.2C, then discharging to 3.0V by using a current constant current of 0.2C, and measuring the initial discharge specific capacity of the battery. The specific capacity of the battery is the battery capacity exerted by the unit positive electrode active material, namely the battery capacity is divided by the mass of the positive electrode active material in the battery.
2. And (3) testing the cycle performance: and (3) at 60 ℃, the assembled solid lithium battery is subjected to constant current charging to 4.2V at 0.2C, then is subjected to constant current discharging to 3.0V at 0.2C, and is cycled 200 times, and the 1 st discharge capacity and the last 1 discharge capacity are recorded.
The capacity retention for the high temperature cycle was calculated as follows:
capacity retention = discharge capacity of the last 1 time/discharge capacity of the 1 st time × 100%.
Examples 2 to 18
Examples 2-18 illustrate a solid state lithium battery of the present disclosure, including most of the operational steps of example 1, except that:
the mass percentage u of the polymer in the total mass of the polymer solid electrolyte, the thickness d of the polymer solid electrolyte, the mass percentage w of the compound shown in the structural formula 1 in the mass of the positive electrode active material and the thickness L of the positive electrode material layer have different values, and the specific information is shown in Table 2.
Comparative examples 1 to 4
Comparative examples 1 to 4 are comparative illustrations of the solid-state lithium battery disclosed in the present invention, which includes most of the operational steps of example 1, except that:
the mass percentage u of the polymer in the total mass of the polymer solid electrolyte, the thickness d of the polymer solid electrolyte, the mass percentage w of the compound shown in the structural formula 1 in the mass of the positive electrode active material and the thickness L of the positive electrode material layer have different values, and the specific information is shown in Table 2.
The results of the battery performance tests of examples 1 to 18 and comparative examples 1 to 4 are shown in table 2.
Table 2 information on and results of testing of batteries of examples 1 to 18 and comparative examples 1 to 4
From the test results of examples 1 to 18 and comparative example 1, it can be seen that a solid lithium battery having high energy density and stable cycle performance can be obtained when the relationship among the content of the compound represented by formula 1, the polymer content, the thickness of the positive electrode material layer, and the thickness of the polymer solid electrolyte is controlled by adding the compound represented by formula 1 to the positive electrode material layer and when it satisfies 5. Ltoreq. UL/wd.ltoreq.500. The capacity retention rate of the solid-state lithium battery prepared in example 1 and comparative example 1 is 200 times of cycling, the capacity retention rate of the solid-state lithium battery prepared in example 1 is 95% after 200 times of cycling, and the capacity retention rate of the solid-state lithium battery prepared in comparative example 1 is only 70%. The unsaturated phosphate compounds are uniformly attached to the surface of the positive active material in situ, so that the positive active material is inhibited from generating oxygen evolution reaction or generating active free radicals under high voltage, the probability of chain breakage of polymer macromolecular chains of the polymer solid electrolyte due to the attack of the positive precipitated material is reduced, the electrochemical stability of the polymer solid electrolyte is improved, and the cycle stability of the solid lithium battery is improved.
The single parameters u, L, w and d of comparative examples 2 to 4 are all in the preferred range, but the uL/wd value is not in the preferred range, and the effect is not good. Comparative example 2 compared with example 2, the initial capacity of comparative example 2 is only 110mAh/g, and under the combination of thin positive electrode, thick electrolyte and low polymer content, the higher content of the phosphate ester additive shown in the structural formula 1 causes the initial specific capacity of the battery to be too low, which is not beneficial to the exertion of the battery capacity. Comparative example 4 compared with example 14, the cycle capacity retention of comparative example 4 was only 73%, and in the combination of thick positive electrode, thin electrolyte, and high polymer content, insufficient phosphate additive of formula 1 resulted in poor cycle stability. Therefore, the better effect can be achieved only if the values of the single parameters u, L, w, d and uL/wd simultaneously satisfy the preferred ranges.
Examples 8 to 11 compare the parameter combinations under the condition of the same cathode thickness: in comparative examples 8 to 9, when the polymer content was the same, the electrolyte thickness decreased and accordingly the probability of chain scission increased, and by increasing the phosphate additive content in the positive electrode, the cycle capacity retention rate could be improved; comparing example 9 with example 11, the electrolyte thickness was small, and a suitable increase in the phosphate ester content, although it resulted in a decrease in the initial specific capacity, significantly improved the cycle stability.
Examples 19 to 23
Examples 19 to 23 are for explaining a solid lithium battery disclosed in the present invention, and include most of the operational steps of example 1, except that:
the compound shown in formula 1 is added to the positive active material layer, and see table 3. The test results are shown in Table 3.
Comparative examples 5 to 7
Comparative examples 5 to 7 are comparative illustrations of the solid-state lithium battery disclosed in the present invention, which includes most of the operating steps of example 1, except that:
the phosphate structure in the positive active material layer is different, see table 3. The results are shown in Table 3.
TABLE 3 Battery information and test results for examples 1, 19-23 and comparative examples 1, 5-7
As can be seen from examples 1, 19 to 23 and comparative example 1, the cycle capacity retention rate of the battery was improved to some extent by the compounds 1 to 6. Therefore, the unsaturated phosphate compound can be attached to the surface of the positive active material in situ, so that the positive active material is inhibited from generating oxygen evolution reaction or generating active free radicals at high voltage to a certain extent, the probability of chain breakage of a polymer macromolecular chain of the polymer solid electrolyte due to the attack of the positive precipitated material is reduced, the electrochemical stability of the polymer solid electrolyte is improved, and the cycle stability of the solid lithium battery is improved.
As can be seen from example 1 and comparative example 5, the chemical structures of compound 1 and compound 7 differ only in that compound 1 contains one unsaturated bond, while compound 7 does not contain an unsaturated bond. The battery cycle performance of the solid-state lithium battery prepared in the embodiment 1 is obviously superior to that of the comparative example 5, so that the unsaturated property of the unsaturated phosphate compound is presumed to be a key for playing the battery protection role, and the carbon-carbon double bond or carbon-carbon triple bond with higher bond energy can obviously improve the reaction activity of the phosphate compound and promote the in-situ adsorption effect of the phosphate compound and the surface of the positive active material, thereby protecting the polymer solid electrolyte and improving the battery cycle performance. Similarly, the same conclusion can be drawn for comparative example 20 and comparative example 6, and for example 21 and comparative example 7. Further, it is clear from comparison between example 1 and example 19 that the capacity retention ratio of the phosphate containing a carbon-carbon triple bond having a higher degree of unsaturation is more remarkably improved. As can be seen from comparison of examples 1 and 22 and comparative example 5, when an unsaturated bond and a fluorine-substituted structure coexist in the phosphate structure, the overall performance of the battery is better, and the initial capacity and the cycle stability are better.
Examples 24 to 29
Examples 24-29 are provided to illustrate a solid state lithium battery disclosed in the present invention, including most of the operational steps of example 1, except that:
the positive electrode active materials or charge cut-off voltages shown in examples 24 to 29 in Table 4 were added differently. The results are shown in Table 4.
Comparative examples 8 to 10, which are illustrative of the solid state lithium battery disclosed in the present invention, include most of the operational steps of example 1, except that:
the positive electrode did not contain the compound represented by structural formula 1, i.e., w =0, and the positive electrode active materials shown in comparative examples 8 to 10 in table 4 were added or the charge cut-off voltages were different. The results are shown in Table 4.
TABLE 4 Positive electrode slurry Components in examples 1, 24 to 29 and comparative examples 1, 8 to 10 and test results
As can be seen from table 4, the solid lithium batteries prepared in examples 1 and 24 to 29, comparative example 1, and comparative examples 8 to 10 all had good battery cycle performance, and thus it was found that the in-situ adsorption of the unsaturated phosphate compound of the present invention was suitable for various positive active materials. Particularly, under the condition that the higher charge cut-off voltage is more than or equal to 4.2V, the compound shown in the structural formula 1 with a specific structure is added into the positive electrode, so that the improvement on the cycle performance of the battery is more obvious, probably because the active substance of the positive electrode is easier to generate oxygen and active free radicals under high voltage and generates side reaction with the polymer solid electrolyte, so that the cycle performance of the solid lithium battery is deteriorated, and the compound shown in the structural formula 1 is added into the positive electrode, so that the cycle performance of the solid lithium battery can be obviously improved.
Examples 30 to 32
Examples 30 to 32 are for explaining a solid lithium battery disclosed in the present invention, and include most of the operation steps in example 1, except that:
the polymer solid electrolytes shown in examples 30 to 32 in table 5 were added. The results are shown in Table 5.
TABLE 5 Battery information and test results for example 1, examples 30-32
The solid lithium batteries prepared in examples 1 and 30 to 32 still have high capacity retention after 200 cycles, and the polymer solid electrolyte commonly used in the art can be used for preparing the solid lithium battery of the present invention. Through the experiments of the inventor, the polymer in the solid-state electrolysis of the polymer of the invention can be selected from one or more of linear or branched polyethylene oxide (PEO), polyethylene carbonate (PEC), polypropylene carbonate (PPC), polymethyl methacrylate (PMMA), polylactic acid (PLA), polycaprolactone (PCL), polycaprolactam (PA), polysiloxane, polyvinylidene fluoride (PVDF), styrene and ethylene oxide copolymer (PS-PEO), and copolymer of ethylene oxide and caprolactam (PEO-PA).
The present invention has been further described with reference to specific embodiments, but it should be understood that the detailed description should not be construed as limiting the spirit and scope of the present invention, and various modifications made to the above-described embodiments by those of ordinary skill in the art after reading this specification are within the scope of the present invention.
Claims (10)
1. A solid-state lithium battery comprising a positive electrode, a negative electrode, and a polymer solid electrolyte disposed between the positive electrode and the negative electrode, the polymer solid electrolyte comprising a polymer, the positive electrode comprising a positive electrode material layer, wherein the positive electrode material layer comprises a positive electrode active material and a compound represented by structural formula 1:
structural formula 1
Wherein R is 1 、R 2 、R 3 Each independently selected from hydrogen atom, substituted or unsubstituted C 1 -C 12 Saturated aliphatic hydrocarbon group of (1), substituted or unsubstituted C 2 -C 12 Unsaturated aliphatic hydrocarbon group, and R 1 、R 2 、R 3 In which at least one is substituted or unsubstituted C 2 -C 12 An unsaturated aliphatic hydrocarbon group;
the solid-state lithium battery satisfies the following conditions:
5≤uL/wd≤500；
wherein u is the mass percentage of the polymer in the total mass of the polymer solid electrolyte, and the unit is;
w is the mass percentage of the compound shown in the structural formula 1 in the mass of the positive active material, and the unit is;
l is the thickness of the anode material layer and the unit is mum;
d is the thickness of the polymer solid electrolyte in μm.
2. The lithium solid state battery of claim 1, wherein the charge cutoff voltage of the lithium solid state battery is greater than or equal to 4.2V.
3. The lithium solid state battery according to claim 1, characterized in that it satisfies the following condition:
10≤uL/wd≤300。
4. the lithium solid state battery according to claim 1, wherein in the structural formula 1, R is 1 、R 2 、R 3 Each independently selected from hydrogen atom, substituted or unsubstituted C 1 -C 5 Saturated aliphatic hydrocarbon group of (1), substituted or unsubstituted C 2 -C 5 Unsaturated aliphatic hydrocarbon group, and R 1 、R 2 、R 3 In which at least one is substituted or unsubstituted C 2 -C 5 Unsaturated aliphatic hydrocarbon radical, R 1 、R 2 Or R 3 When substituted, the substituents are selected from halogens.
5. The lithium solid state battery according to claim 1, wherein the compound represented by formula 1 is at least one selected from the group consisting of compounds represented by formula 1-1, formula 1-2, and formula 1-3,
structural formula 1-1
Structural formula 1-2
Structural formulae 1 to 3
Wherein R is 4 、R 5 、R 6 Each independently selected from a hydrogen atom, a substituted or unsubstituted C 1 -C 11 Saturated aliphatic hydrocarbon group of (1), substituted or unsubstituted C 2 -C 11 Unsaturated aliphatic hydrocarbon group of (A), and R 4 、R 5 、R 6 In which at least one is substituted or unsubstituted C 2 -C 11 Unsaturated aliphatic hydrocarbon group of (2).
6. The lithium solid state battery according to claim 1, wherein the compound represented by structural formula 1 is at least one compound selected from the group consisting of compounds 1 to 6:
compound 1:
compound 2:
compound 3:
compound 4:
compound 5:
compound 6:
7. the solid lithium battery according to claim 1, wherein the positive electrode active material is at least one selected from the group consisting of compounds represented by the following general formulae:
LiL x M y N z O 2 l, M and N are respectively and independently selected from at least one element of Ni, co, mn, V, fe and Al, and x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, x + y + z =1;
LiL x M y N z O 4 l, M and N are respectively and independently selected from at least one element of Ni, co, mn, V, fe and Al, x is more than or equal to 0 and less than or equal to 2, y is more than or equal to 0 and less than or equal to 2, z is more than or equal to 0 and less than or equal to 2, and x + y + z =2.
8. The solid state lithium battery of claim 1, wherein the polymer is selected from at least one of linear or branched polyethylene oxide, polyethylene carbonate, polypropylene carbonate, polymethyl methacrylate, polylactic acid, polycaprolactone, polycaprolactam, polysiloxane, polyvinylidene fluoride, copolymers of ethylene oxide and styrene, and copolymers of ethylene oxide and caprolactam.
9. The solid lithium battery as claimed in any one of claims 1 to 8, wherein the compound represented by the structural formula 1 accounts for 1 to 10% by mass of the positive electrode active material;
the thickness d of the polymer solid electrolyte ranges from 10 to 200 μm;
the mass percent u of the polymer in the total mass of the polymer solid electrolyte is 50-90%;
the thickness L of the positive electrode material layer is 50-200 mu m.
10. The solid lithium battery according to claim 1, wherein the compound represented by formula 1 is formed on a surface of the positive electrode material layer, or the compound represented by formula 1 is mixed in an interior of the positive electrode material layer.
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| CN114883519A (en) * | 2022-03-17 | 2022-08-09 | 深圳新宙邦科技股份有限公司 | Positive plate and lithium ion battery |
| CN114843512A (en) * | 2022-03-22 | 2022-08-02 | 深圳新宙邦科技股份有限公司 | Positive plate and lithium ion battery |
| CN114864922B (en) * | 2022-04-29 | 2024-02-09 | 深圳新宙邦科技股份有限公司 | Lithium ion battery |
| CN115000401A (en) * | 2022-05-27 | 2022-09-02 | 珠海冠宇电池股份有限公司 | Positive electrode active material, positive plate comprising same and battery |
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| KR101748037B1 (en) * | 2015-10-07 | 2017-06-15 | 주식회사 엘지화학 | Cathode active material having high electrochemical properties and lithium secondary battery comprising the same |
| JP6384467B2 (en) * | 2015-12-18 | 2018-09-05 | トヨタ自動車株式会社 | Lithium solid state battery |
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