CN112067672A - Method for testing specific capacity of pre-lithiated lithium powder and application thereof - Google Patents

Method for testing specific capacity of pre-lithiated lithium powder and application thereof Download PDF

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CN112067672A
CN112067672A CN202010951447.2A CN202010951447A CN112067672A CN 112067672 A CN112067672 A CN 112067672A CN 202010951447 A CN202010951447 A CN 202010951447A CN 112067672 A CN112067672 A CN 112067672A
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lithium powder
lithium
inert
working electrode
powder
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邱昭政
李冰
赵育松
李文龙
梁世硕
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Kunshan Bao Innovative Energy Technology Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
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    • H01—ELECTRIC ELEMENTS
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    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
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    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
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    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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Abstract

The invention discloses a method for testing the specific capacity of pre-lithiated lithium powder and application thereof, wherein the method comprises the following steps: (1) mixing inert lithium powder, a binder, a conductive agent and an organic solvent to form lithium powder slurry; (2) transferring the lithium powder slurry onto a current collector, drying and rolling to obtain a working electrode; (3) calculating according to the weight of the working electrode, the weight of the current collector and the proportion of the inert lithium powder so as to obtain the lithium powder load on the current collector; (4) assembling the working electrode and the inert metal foil into a button cell; (5) taking a working electrode as a positive electrode and an inert metal foil as a negative electrode, and adopting a charging process step so as to deposit lithium in the working electrode on the inert metal foil; (6) and calculating the effective specific capacity of the inert lithium powder according to the electric quantity obtained in the charging step and the lithium powder loading capacity. The effective specific capacity of the lithium powder measured by the method has an instructive effect on the addition amount of the lithium powder in the actual pre-lithiation process, so that the accurate addition of the inert lithium powder in the pre-lithiation negative plate is realized.

Description

Method for testing specific capacity of pre-lithiated lithium powder and application thereof
Technical Field
The invention belongs to the technical field of lithium batteries, and particularly relates to a method for testing the specific capacity of pre-lithiated lithium powder and application thereof.
Background
As the functions of electronic products in the consumer market become more and more complete, and consumers have longer and longer use of the electronic products. In the field of electric automobiles, the short endurance mileage still is a big pain point limiting the popularization of electric automobiles. These market demands require the development of batteries with high energy density. Such a trend requires the next generation of batteries to use higher capacity electrode materials. The energy density of the power battery can be obviously improved by converting the negative electrode material from graphite to a silicon-based material. However, due to the volume effect of the silicon material during the charge and discharge cycles, the industry is more inclined to use the silicon-oxygen material as the negative electrode material of the power battery. The active material of the silicon-oxygen anode material is silicon monoxide. But such materials are less conductive than graphite-based negative electrode materials. And the silicon monoxide particles are pulverized along with repeated charge and discharge cycles to separate from a conductive system, so that the silicon monoxide particles become a failure negative electrode. And the first intercalation of lithium into the silicon monoxide leads to the formation of Li2O、Li2CO3And non-reversible lithiates such as lithium silicate, reduce the utilization rate of active lithium in the battery system. A layer of SEI film formed by lithium and electrolyte is formed on the surface of the negative electrode in the process of lithium intercalation for the first time, and the consumption of active lithium is further increased. This results in a very low first efficiency of the silicon oxygen material as a lithium ion negative electrode.
In order to increase the utilization rate of electrode materials in a battery system and increase the energy density of the battery, introducing an additional lithium source into a lithium ion battery system is an effective means for supplementing the loss of active lithium. Current research has led to prelithiation of either the positive or negative electrode, where the lithium source is metallic lithium or a lithium rich compound or alloy. Of these, pre-lithiation of the negative electrode is the most studied. Prelithiation of the negative electrode using metallic lithium as the lithium source is the most directly effective prelithiation means. The pre-lithiation of lithium battery systems by using metal lithium is further divided into lithium tape pre-lithiation and lithium powder pre-lithiation. The lithium tape pre-lithiation technology is relatively mature, but the thickness control of the lithium tape is difficult, so that the pre-lithiation of a negative electrode is difficult to control, the lithium precipitation phenomenon of the lithium battery caused by excessive pre-lithiation is caused, and the safety risk is easily caused. The lithium powder pre-lithiation can be used for carrying out accurate pre-lithiation on the negative electrode by accurately controlling the adding amount of the lithium powder and improving a dispersion means, and is a subject of competitive research in the industry and academia at present.
At present, there are many methods for prelithiation by using lithium powder, which can be roughly divided into dry prelithiation and wet prelithiation. The dry pre-lithiation mainly adopts electrostatic adsorption and vibration spraying, but the phenomenon of lithium powder floating exists, and a large amount of lithium powder floating in the air not only has great potential safety hazard, but also is harmful to the health of operators. And then, a wet process is tried to disperse the lithium powder, so that the problem of the floating of the lithium powder is solved. However, with the wet pre-lithiation, in the actual operation process, the environment (temperature, humidity, atmosphere composition) and the operation time of the operation have an influence on the actual specific capacity of the lithium powder, so that in the actual application, in order to improve the first coulombic efficiency and optimize the energy density and the cycle performance of the battery, the addition of the lithium powder needs to be optimized. In the past, the addition amount of the inert lithium powder needs to be determined by depending on empirical values and combining a large amount of groping work. This reduces the operating efficiency of the prelithiation process.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. To this end, it is an object of the present invention to provide a method for testing the specific capacity of a pre-lithiated lithium powder and its use. The effective specific capacity of the lithium powder measured by the method has an instructive effect on the addition amount of the lithium powder in the actual pre-lithiation process, so that the utilization rate of the inert lithium powder in the pre-lithiation process is improved, the use amount of the inert lithium powder is reduced, the cost of the pre-lithiation process is reduced, and the requirement of the market on the reduction of the battery cost is met while the energy density of the lithium battery is improved.
In one aspect of the invention, a method of testing the specific capacity of a pre-lithiated lithium powder is presented. According to an embodiment of the invention, the method comprises:
(1) mixing inert lithium powder, a binder, a conductive agent, and an organic solvent to form a lithium powder slurry;
(2) transferring the lithium powder slurry onto a current collector, drying and rolling to obtain a working electrode;
(3) calculating according to the weight of the working electrode, the weight of the current collector and the proportion of the inert lithium powder so as to obtain the load capacity of the lithium powder on the current collector;
(4) assembling the working electrode and the inert metal foil into a button cell;
(5) depositing lithium in the working electrode on the inert metal foil by using the working electrode as a positive electrode and the inert metal foil as a negative electrode in a charging process step;
(6) and calculating the effective specific capacity of the inert lithium powder according to the electric quantity obtained in the charging step and the lithium powder loading capacity.
According to the method for testing the specific capacity of the pre-lithiated lithium powder, an electrochemical lithium deposition method is adopted for testing, the lithium powder, a conductive agent, a binder and an organic solvent are made into slurry and loaded on a current collector to make a working electrode and serve as an anode, an inert metal serves as a cathode to assemble a button cell, the charging capacity is recorded in an electrodeposition mode, and the specific capacity which can be exerted by the lithium powder is calculated according to the amount of the lithium powder loaded on the working electrode. The effective specific capacity of the lithium powder measured by the method has an instructive effect on the addition amount of the lithium powder in the actual pre-lithiation process, so that the utilization rate of the inert lithium powder in the pre-lithiation process is improved, the use amount of the inert lithium powder is reduced, the cost of the pre-lithiation process is reduced, and the requirement of the market on the reduction of the battery cost is met while the energy density of the lithium battery is improved.
In addition, the method according to the above embodiment of the present invention may also have the following additional technical features:
in some embodiments of the invention, in the step (1), the mass ratio of the inert lithium powder, the binder and the conductive agent is (20-70): 10-40): 20-50. Therefore, effective lithium in the lithium powder is completely released.
In some embodiments of the present invention, the inert lithium powder has a particle size D50 of 5 to 50 μm.
In some embodiments of the present invention, the content of Li metal in the inert lithium powder is 70 to 99 wt%.
In some embodiments of the invention, the inert lithium powder comprises an inner core comprised of lithium metal or lithium alloy and an outer shell comprised of an inert layer.
In some embodiments of the invention, the lithium alloy includes Li and at least one of Mg, Al, Si, Cu, Zn, K, Na, Co, Sn, Ca, Ti, Fe, and Ni.
In some embodiments of the invention, the inert layer comprises an inorganic or organic substance, the inorganic substance being selected from Li2CO3LiF, LiI and Li2At least one of S.
In some embodiments of the present invention, the organic matter includes a small molecule organic matter selected from at least one of hydrocarbon organic matters having a carbon number of 16 to 35, and a polymer.
In some embodiments of the invention, the binder is selected from at least one of PTFE, PVDF, NBR, PAN, PVDF-HFP copolymer, PPy, PANI, PTh, and PPTA.
In some embodiments of the present invention, the conductive agent is selected from at least one of conductive carbon black, acetylene black, conductive graphite, ketjen black, VGCF, CNT, and graphene.
In some embodiments of the invention, the organic solvent is selected from at least one of benzene, toluene, xylene, diethyl ether, acetone, EC, PC, DEC, EMC, DMC, ethanol, NMP, DMSO, DMF, trifluoroacetic acid, and chloroform.
In some embodiments of the present invention, in step (2), the lithium powder slurry is transferred onto the current collector by a coating method.
In some embodiments of the invention, in step (2), the drying is performed under conditions of vacuum of not higher than-88 kPa, temperature of 60 to 120 ℃ and time of 1 to 6 hours. Thus, the solvent in the slurry was removed by high-temperature vacuum drying.
In some embodiments of the invention, in step (2), the current collector is selected from any one of Cu, Fe, Ni, Au and Pt.
In some embodiments of the invention, in the step (3), the loading amount per unit area of the lithium powder on the current collector is 0.1-3 mg/cm2。
In some embodiments of the invention, in step (4), the inert metal foil is selected from at least one of Cu, Fe, Ni, Al, Ti, Ag, Au, and Pt.
In some embodiments of the invention, in the step (5), the discharge capacity is calibrated by adopting a low-rate charging step, and the charging rate is 0.005-0.1C, so that the polarization effect of the electrode can be reduced, the metering accuracy of the specific capacity of the lithium powder of the electrode is greatly improved, and the specific capacity actually exerted by the lithium powder can be more accurately measured.
In some embodiments of the present invention, in step (5), the cut-off voltage is 0.5-2.5V. Therefore, the specific capacity actually exerted by the lithium powder can be measured more accurately.
In some embodiments of the present invention, steps (1) to (4) are performed in a dry environment. Therefore, the specific capacity actually exerted by the lithium powder can be measured more accurately.
In some embodiments of the invention, the method further comprises: and (4) recording the ambient temperature, the humidity and the required time length of the steps (1) to (4) so as to establish a corresponding relation between the effective specific capacity of the lithium powder and the ambient temperature, the humidity, the atmosphere composition and the required time length. Therefore, the operating environment can be optimized in a targeted manner by determining the influence of environmental factors on the effective specific capacity of the lithium powder, so that the utilization rate of the inert lithium powder is further improved, the using amount of the lithium powder is reduced, the cost of the pre-lithiation process is reduced, and the requirement of the market on the reduction of the battery cost is met while the energy density of the lithium battery is further improved.
In another aspect of the invention, the invention provides an application of the method for testing the specific capacity of the pre-lithiated lithium powder in the inert lithium powder pre-lithiated negative electrode sheet. Therefore, the utilization rate of the inert lithium powder in the pre-lithiation process is improved, the using amount of the inert lithium powder is reduced, the cost of the pre-lithiation process is reduced, and the requirement of the market on reduction of the battery cost is met while the energy density of the lithium battery is improved.
In a third aspect of the invention, a prelithiated negative electrode sheet is presented. According to the embodiment of the invention, the effective specific capacity of the inert lithium powder in the pre-lithiated negative electrode sheet is 2000-3750 mAh/g, and the effective specific capacity of 2000-3750 mAh/g is obtained by adopting the method in the embodiment. Therefore, accurate addition of the inert lithium powder in the prelithiation negative plate is realized.
In a fourth aspect of the present invention, a lithium battery is provided. According to an embodiment of the present invention, the lithium battery has the pre-lithiated negative electrode sheet described in the above embodiment. Therefore, the performance of the battery subjected to the pre-lithiation treatment can be optimal, the problem of lithium precipitation of the battery caused by excessive addition of lithium powder can be avoided, and meanwhile, the cost increase caused by the pre-lithiation process can be effectively controlled.
In a fifth aspect of the present invention, an electric vehicle is provided. According to the embodiment of the invention, the electric automobile is provided with the lithium battery. Therefore, the vehicle loaded with the lithium battery has excellent cruising ability, and the using requirement of consumers is met.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
fig. 1 is a schematic flow chart of a method for testing the specific capacity of pre-lithiated lithium powder according to an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
The present invention has been completed based on the following knowledge and findings of the inventors:
the invention provides a method for testing the capacity of lithium powder, aiming at the problems that the actual capacity of the inert lithium powder is uncertain when the inert lithium powder which is a commonly used negative electrode pre-lithiation reagent is applied to the negative electrode pre-lithiation, so that the addition amount of the lithium powder can be determined only by searching and optimizing for many times, and a large amount of early work is increased. At present, lithium powder is used as a prelithiation reagent, and the addition amount of the lithium powder is determined mainly according to the lithium content and the theoretical specific capacity of inert lithium powder and an effective utilization rate. However, the amount of lithium powder added is usually determined by a series of experiments, which takes a lot of time. If the gram capacity exerted by the lithium powder can be tested under a certain condition, the addition amount of the lithium powder can be directly determined through the value, so that the investigation work for optimizing the addition amount of the lithium powder in the early stage is reduced.
In view of the above, in one aspect of the present invention, a method for testing the specific capacity of pre-lithiated lithium powder is provided. According to an embodiment of the invention, with reference to fig. 1, the method comprises:
s100: mixing inert lithium powder, a binder, a conductive agent and an organic solvent
In this step, inert lithium powder, a binder, a conductive agent, and an organic solvent are mixed to form a lithium powder slurry, which is a flowable viscous mixture. The mixing manner is not particularly limited, the inert lithium powder, the binder and the conductive agent may be mixed uniformly first and then added to the organic solvent, or the inert lithium powder, the binder or the conductive agent may be added to the organic solvent first and mixed uniformly, and then the other two raw materials are added and mixed uniformly, and the adding sequence is not particularly limited. The weight ratio of the inert lithium powder, the binder and the conductive agent is not particularly limited, and can be selected by persons in the field at will according to actual needs, and as a preferable scheme, the mass ratio of the inert lithium powder, the binder and the conductive agent is (20-70): (10-40): (20-50). Therefore, effective lithium in the lithium powder is completely released.
In the embodiment of the invention, the ratio of the lithium powder, the binder and the conductive agent is adjusted in the preparation process of the slurry, so that the lithium powder is uniformly dispersed in the slurry, and the flow property of the lithium powder slurry is optimized, so that the lithium powder slurry can be uniformly coated. Because lithium powder is very sensitive to moisture in a slurry system, the moisture of all slurry components needs to be strictly controlled in the slurry preparation process, a binder and a conductive agent need to be dried in vacuum, a solvent needs to be a new unpacked product, and if the moisture in the solvent needs to be further reduced, the solvent can be treated by using a molecular sieve.
In the embodiment of the present invention, the specific value of the particle diameter D50 of the inert lithium powder is not particularly limited, and may be arbitrarily selected by a person skilled in the art according to actual needs, and as a preferable scheme, the particle diameter D50 of the inert lithium powder is 5 to 50 μm. The specific value of the content of Li metal in the inert lithium powder is not particularly limited, and a person skilled in the art can optionally select the content according to actual needs, and as a preferable scheme, the content of Li metal in the inert lithium powder is 70-99 wt%.
Further, the inert lithium powder includes an inner core composed of lithium metal or lithium alloy and an outer shell composed of an inert layer. Specific kinds of the above lithium alloy are not particularly limited, and the lithium alloy includes Li and at least one of Mg, Al, Si, Cu, Zn, K, Na, Co, Sn, Ca, Ti, Fe, and Ni, and may select Li and one of Mg, Al, Si, Cu, Zn, K, Na, Co, Sn, Ca, Ti, Fe, and Ni, or may select Li and a plurality of Mg, Al, Si, Cu, Zn, K, Na, Co, Sn, Ca, Ti, Fe, and Ni. The inert layer is a compact layer which can isolate the inner core from the external environment, and further comprises inorganic matters or organic matters. The specific kind of the inorganic substance is not particularly limited, and as a preferable mode, the inorganic substance is selected fromFrom Li2CO3LiF, LiI and Li2At least one of S may be selected, or a plurality of S may be selected. Further, the organic matter includes a small molecule organic matter and a polymer, and a specific kind of the small molecule organic matter is not particularly limited, and as a preferable embodiment, the small molecule organic matter is at least one selected from hydrocarbon organic matters having a carbon number of 16 to 35, and one or more selected from the hydrocarbon organic matters may be selected.
In the examples of the present invention, since the lithium powder has a low density (ρ ═ 0.534 g/cm)3) The lithium powder can float upwards easily in the slurry with low viscosity to form inhomogeneous slurry, the viscosity is increased to effectively prevent the lithium powder from floating upwards, the stability of the slurry during coating is ensured, and the inconsistency of the loading amount of the coating start electrode and the coating end electrode is avoided. The binder can also uniformly disperse the lithium powder and the conductive agent and connect the lithium powder and the conductive agent into a conductive network. The binder also serves to bind the lithium powder to the surface of the negative electrode and prevent the lithium powder from falling off after drying.
In order to uniformly disperse the lithium powder in the liquid phase system to form a uniform and stable lithium powder slurry, the viscosity of the liquid phase needs to be increased to offset the problem that the lithium powder floats upwards due to low density to cause uneven distribution of the lithium powder. The use of a binder can solve the above problems, and an oily binder is used because lithium powder is sensitive to water. The proper liquid-phase system can be obtained by optimizing the type and the addition amount of the binder. After the lithium powder slurry is coated and dried, a lithium powder layer is formed on the surface of the negative electrode, and lithium powder particles can be firmly adhered to the surface of the negative electrode due to the adhesive action of the binder. The specific type of the binder is not particularly limited, and as a preferable embodiment, the binder is at least one selected from PTFE, PVDF, NBR, PAN, PVDF-HFP copolymer, PPy, PANI, PTh, and PPTA, and one or more thereof may be selected. Preferably at least one of PTFE, PVDF, NBR, PVDF-HFP copolymer, PPy, PANI and PTh, more preferably at least one of PTFE, PVDF, NBR, PVDF-HFP copolymer and PPy.
In the embodiment of the invention, the conductive agent is used for providing a conductive network, and the lithium powder loaded on the whole electrode is connected, so that all the inert lithium powder can be ensured to be electrically connected with the current collector, and the capacity of the inert lithium powder is ensured to be exerted to the maximum extent. The specific kind of the conductive agent is not particularly limited, and as a preferable mode, the conductive agent is at least one selected from the group consisting of conductive carbon black, acetylene black, conductive graphite, ketjen black, VGCF, CNT, and graphene, and one or more of them may be selected.
In the embodiment of the present invention, the organic solvent used in the preparation process of the paste is the key to provide the paste with coatable fluidity, the requirement of the organic solvent is that the selected binder can be dissolved to form a uniform glue solution, and the organic solvent has no influence on the inert lithium powder. The specific type of the organic solvent is not particularly limited, and as a preferable embodiment, the organic solvent is at least one selected from the group consisting of benzene, toluene, xylene, diethyl ether, acetone, EC, PC, DEC, EMC, DMC, ethanol, NMP, DMSO, DMF, trifluoroacetic acid and chloroform, and one or more selected therefrom may be used.
S200: transferring the lithium powder slurry onto a current collector, drying and rolling
In this step, the lithium powder slurry is transferred onto a current collector, dried and rolled, so as to obtain a working electrode. The lithium powder slurry may be coated on one surface of the working electrode current collector, or may be coated on both surfaces of the working electrode current collector. The specific manner of the above transfer is not particularly limited, and those skilled in the art can optionally select the transfer method according to actual needs, and as a preferred scheme, the lithium powder slurry is transferred onto the current collector by a coating method. Further, removing the solvent in the slurry by vacuum drying, wherein the drying condition is that the vacuum degree is lower than-88 kPa, the temperature is 60-120 ℃, the time is 1-6h, and when the vacuum oven is opened for pressure relief, inert gas is used for pressure relief, and the inert gas is selected from at least one of He, Ne and Ar. In order to fully expose the lithium-containing core in the inert lithium powder, the coated and dried pole piece needs to be properly rolled, so that the utilization rate of the lithium powder is further improved, and spherical lithium powder particles are flattened after rolling, thereby being beneficial to being in close contact with a conductive system and a current collector.
In the embodiment of the present invention, a specific kind of the current collector is not particularly limited, and as a preferable mode, the current collector is selected from any one of Cu, Fe, Ni, Au, and Pt.
S300: calculating according to the weight of the working electrode, the weight of the current collector and the proportion of the inert lithium powder
In the step, the weight of the working electrode and the weight of the current collector are respectively weighed, and the total mass of the inert lithium powder, the binder and the conductive agent loaded on the working electrode is obtained by subtracting the weight of the current collector from the weight of the working electrode. And then according to the proportion of the inert lithium powder in the inert lithium powder, the binder and the conductive agent, the lithium powder loading capacity on the current collector can be calculated. The load capacity of the lithium powder on the current collector per unit area is 0.1-3 mg/cm through calculation2. Preferably 0.2-2 mg/cm2More preferably 0.3 to 2mg/cm2. The inventors found that if the loading of the lithium powder per unit area on the current collector is more than 3mg/cm2The thickness of the lithium powder layer is too large, so that the polarization of the electrodeposition is too large during testing, and the testing precision is influenced; if the loading amount per unit area is less than 0.1mg/cm2The coating precision is required to be very high, the lithium powder coating requirement is too high, the operation is not easy, and the lithium powder is not tightly connected directly due to too low coating amount, so that the test precision is low.
S400: assembling the working electrode and the inert metal foil into a button cell
In this step, the working electrode and inert metal foil are assembled into a button cell. The assembly of the button cell has no great difference with the assembly process of the conventional button cell. The specific kind of the inert metal foil is not particularly limited, and as a preferable mode, the inert metal foil is selected from at least one of Cu, Fe, Ni, Al, Ti, Ag, Au, and Pt, and one of them may be selected, or a plurality of them may be selected to be alloyed. Preferably, a copper foil is used, and a shiny side of the copper foil may be selected as a receiving side for lithium metal deposition, and a matte side may be selected as a receiving side for lithium metal deposition.
In the embodiment of the present invention, the composition of the electrolyte in the button cell is not particularly limited, and can be prepared according to actual requirements. The electrolyte includes a lithium salt, an organic solvent, and an optional additive.
In an embodiment of the present invention, the lithium salt may be an organic lithium salt or an inorganic lithium salt, and specifically, the lithium salt may be selected from at least one of fluorine elements, boron elements, and phosphorus elements. Preferably, the lithium salt may be chosen in particular from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium tetrafluorooxalato phosphate, LiN (SO)2RF)2、LiN(SO2F)(SO2RF), bis (trifluoromethanesulfonyl) imide, lithium bis (fluorosulfonyl) imide, lithium bis (oxalato) borate, lithium difluoro (oxalato) borate; more preferably, the lithium salt is selected from LiPF6、LiN(SO2RF)2At least one of (1). Wherein the substituent RF is represented by CnF2n+1And n is an integer of 1 to 10.
In the embodiment of the present invention, the organic solvent may include a chain ester, and may also include a cyclic ester, and preferably includes a mixture of the chain ester and the cyclic ester. Wherein, the chain ester can be preferably selected from one or more of chain carbonate, chain carboxylate, chain sulfate and chain sulfite; more preferably, the chain ester may be one or more selected from dimethyl carbonate, diethyl carbonate, methylethyl carbonate, methylpropyl carbonate, methyl formate, ethyl formate, methyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, propyl butyrate, dimethyl sulfate, diethyl sulfate, dimethyl sulfite, and diethyl sulfite. The cyclic ester can be preferably selected from one or more of cyclic carbonate, cyclic sulfate, cyclic sulfite and cyclic carboxylate; more preferably, the cyclic ester can be selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, ethylene sulfite, propylene sulfite, gamma-butyrolactone and tetrahydrofuran.
Further, the type of the additive used in the electrolyte is not particularly limited, and may be a film-forming additive, or an additive capable of improving some properties of the battery, for example, an additive for improving the coulombic efficiency of the battery.
S500: charging by using the working electrode as positive electrode and the inert metal foil as negative electrode
In the step, the working electrode is used as a positive electrode, the inert metal foil is used as a negative electrode, a charging step is adopted so as to deposit lithium in the working electrode on the inert metal foil, and the capacity of the effective lithium released by the working electrode is calibrated by metering the electric quantity passing through a battery circuit in the lithium deposition process. Most of the charging curve obtained in this step is parallel to the X-axis and close to 0V, and the voltage rises rapidly at the end of the charging period. The inert metal foil described above is a negative electrode, serving as a substrate for lithium deposition.
Furthermore, the calibration of the discharge capacity is carried out by adopting a low-rate charging process step, so that the effective lithium removal capacity on the working electrode is calibrated, the lithium in the working electrode is deposited on the counter electrode, the polarization effect of the electrode can be reduced by a small charging current, the metering accuracy of the specific capacity of the lithium powder of the electrode is greatly improved, and the specific capacity actually exerted by the lithium powder can be more accurately measured. Further, the charging rate is 0.005-0.1C, preferably 0.01-0.1C, and more preferably 0.01-0.05C. The inventor finds that the charging rate is too low, the charging time is too long, for example, 200 hours is needed after the test of 0.005C, and the test time is too long; the charging with too high multiplying power can generate a larger polarization phenomenon, and the accuracy of the test can be influenced, so that the specific capacity of the tested lithium powder is lower. Furthermore, the cut-off voltage is 0.5 to 2.5V. The selection of the cut-off voltage has a certain influence on the exertion of the capacity, but the influence is not great, because when lithium metal is deposited on the counter electrode, the working electrode and the counter electrode are actually in a state of the lithium metal to the lithium metal, so-called symmetrical batteries are formed, the formed charging curve is a long straight line parallel to the X axis, when the effective lithium on the working electrode is nearly exhausted, the charging voltage of the batteries is rapidly increased, and when the voltage is more than 0.5V, the charging curve tends to be vertical to the X axis, so that the selection of the cut-off voltage has little influence on the calibration of the electrode capacity as long as the cut-off voltage is more than 0.5V.
S600: according to the electric quantity obtained in the charging step and the lithium powder loading capacity
In this step, the effective specific capacity of the inert lithium powder is calculated according to the electric quantity obtained in the charging step and the lithium powder load capacity.
Further, step S100 to step S400 are all completed in a dry environment.
Further, the method further comprises: and recording the ambient temperature, the humidity, the atmosphere composition and the required time of the steps S100-S400 so as to establish a corresponding relation between the effective specific capacity of the lithium powder and the ambient temperature, the humidity and the required time. Therefore, the operating environment can be optimized in a targeted manner by determining the influence of environmental factors on the effective specific capacity of the lithium powder, so that the utilization rate of the inert lithium powder is further improved, the using amount of the lithium powder is reduced, the cost of the pre-lithiation process is reduced, and the requirement of the market on the reduction of the battery cost is met while the energy density of the lithium battery is further improved. The inventors have found that since the inert lithium powder used is very sensitive to the ambient atmosphere, it is mainly the water and air in the ambient temperature and air that have a large effect on the lithium powder. When the ambient temperature to which the lithium powder is exposed is high, the humidity is high, and the oxygen content is high, the reaction activity of the lithium powder is high, and the lithium powder reacts with water and oxygen to generate lithium oxide or lithium hydroxide, and if the ambient contains carbon dioxide, lithium carbonate is generated, so that the lithium powder gradually loses efficacy, and the prelithiation effect of the inert lithium powder is seriously affected. And the longer the inert lithium powder is exposed to the environment, the more severe the lithium powder fails. Therefore, the time, ambient temperature, humidity, and atmosphere composition required for the above four-step operation need to be recorded.
In the embodiment of the invention, most attention needs to be paid to the operation of the lithium powder to reduce the influence of environmental factors on the effective lithium in the lithium powder and control the humidity and the atmosphere composition in the environment, and the water concentration in the glove box can reach below 0.1ppm and O can reach under an ideal state2The concentration is below 0.1 ppm. However, most of the operations for lithium powder are performed in a dry environment in order to simulate the actual production scenario. And recording the temperature, humidity, atmosphere composition and used time of the environment in each step from the operation of the lithium powder to the completion of the electricity deduction in the electricity deduction process.
According to the method for testing the specific capacity of the pre-lithiated lithium powder, an electrochemical lithium deposition method is adopted for testing, the lithium powder, a conductive agent, a binder and an organic solvent are made into slurry and loaded on a current collector to make a working electrode and serve as an anode, an inert metal serves as a cathode to assemble a button cell, the charging capacity is recorded in an electrodeposition mode, and the specific capacity which can be exerted by the lithium powder is calculated according to the amount of the lithium powder loaded on the working electrode. The effective specific capacity of the lithium powder measured by the method has an instructive effect on the addition amount of the lithium powder in the actual pre-lithiation process, so that the utilization rate of the inert lithium powder in the pre-lithiation process is improved, the use amount of the inert lithium powder is reduced, the cost of the pre-lithiation process is reduced, and the requirement of the market on the reduction of the battery cost is met while the energy density of the lithium battery is improved.
In the method for testing the specific capacity of the negative electrode pre-lithiated lithium powder, the 'unit area lithium powder loading capacity' refers to the weight of inert lithium powder in active substances loaded on a unit area current collector; "membrane capacity per unit area" refers to the capacity exerted by the working electrode plate per unit area; the unit area lithium powder load is (working electrode mass-working electrode current collector mass) x lithium powder mass percent (i.e. mass percent of inert lithium powder in the working electrode sheet); the membrane capacity per unit area is equal to the total capacity measured by the button cell/the area of the working electrode pole piece; the gram capacity of the lithium powder is the capacity of the membrane per unit area/the capacity of the lithium powder per unit area.
In another aspect of the invention, the invention provides an application of the method for testing the specific capacity of the pre-lithiated lithium powder in the inert lithium powder pre-lithiated negative electrode sheet. Therefore, the utilization rate of the inert lithium powder in the pre-lithiation process is improved, the using amount of the inert lithium powder is reduced, the cost of the pre-lithiation process is reduced, and the requirement of the market on reduction of the battery cost is met while the energy density of the lithium battery is improved.
In a third aspect of the invention, a prelithiated negative electrode sheet is presented. According to the embodiment of the invention, the effective specific capacity of the inert lithium powder in the pre-lithiated negative electrode sheet is 2000-3750 mAh/g, and the effective specific capacity of 2000-3750 mAh/g is obtained by adopting the method in the embodiment. Therefore, accurate addition of the inert lithium powder in the prelithiation negative plate is realized.
In a fourth aspect of the present invention, a lithium battery is provided. According to an embodiment of the present invention, the lithium battery has the pre-lithiated negative electrode sheet described in the above embodiment. Therefore, the performance of the battery subjected to the pre-lithiation treatment can be optimal, the problem of lithium precipitation of the battery caused by excessive addition of lithium powder can be avoided, and meanwhile, the cost increase caused by the pre-lithiation process can be effectively controlled.
In a fifth aspect of the present invention, an electric vehicle is provided. According to the embodiment of the invention, the electric automobile is provided with the lithium battery. Therefore, the vehicle loaded with the lithium battery has excellent cruising ability, and the using requirement of consumers is met.
The following embodiments of the present invention are described in detail, and it should be noted that the following embodiments are exemplary only, and are not to be construed as limiting the present invention. In addition, all reagents used in the following examples are commercially available or can be synthesized according to methods herein or known, and are readily available to those skilled in the art for reaction conditions not listed, if not explicitly stated.
Example 1
Preparation of button cell
(1) Preparation of prelithiation working electrode pole piece
2.0g of the binder PVDF was dissolved in 38.0g of NMP solution at a mass ratio of 5 wt% to prepare a dope, which took 4 hours. 6g of inert lithium powder and 2g of conductive agent acetylene black are mixed for standby, and the use time is 10 min. Slowly adding the mixture of inert lithium powder and conductive acetylene black into the glue solutionAnd mixing the lithium powder, the binder and the conductive agent uniformly to obtain lithium powder slurry, and mixing the lithium powder, the binder and the conductive agent according to a ratio of 60:20:20 to obtain the lithium powder slurry, wherein the time for use is 25 min. Then coating the surface of a current collector copper foil with the thickness of 30 mu m, wherein the coating mass of the slurry is 2mg/cm2Calculated as the lithium powder loading per unit area of 1.2mg/cm (based on the mass of the solid component not containing the solvent)2It is administered for 10 min. Drying in a vacuum oven at 100 deg.C for 2h, and ventilating with 99.9% purity Ar every 30 min. And taking out the dried pole piece, cold-pressing to obtain an initial pole piece with the lithium powder active material arranged on the surface of the current collector, and rubbing the initial pole piece into a circular pole piece with the diameter of 15mm, wherein the time is 35 min. The mass of the pole piece is weighed, and the time is 10 min. And obtaining 10 pole pieces in total, and putting the pole pieces into a glove box for later use. Except for the vacuum drying, the operation was carried out at an ambient humidity of 1%, a temperature of 28 ℃ and an air atmosphere. The whole working electrode was operated outside the glove box for 7.5 h.
(2) Preparation of counter electrode pole piece
A Cu foil 15 μm thick was rolled up into a disc 18mm in diameter.
(3) Preparation of electrolyte
Preparation of electrolyte at Water content<In a 1ppm argon atmosphere glove box, Ethylene Carbonate (EC), Propylene Carbonate (PC), and dimethyl carbonate (DMC) were mixed in a mass ratio of EC: PC: DMC of 1:1:1 to obtain a mixed organic solvent, and a fully dried lithium salt LiPF was added6Dissolving in the mixed organic solvent, and stirring to obtain electrolyte solution containing LiPF6The concentration of (2) was 1.2 mol/L.
(4) Preparation of the separator
A polyethylene porous membrane is used as a separation membrane and is expanded into a circular sheet with the diameter of 18 mm.
(5) Preparation of the Battery
The cell was assembled according to normal button cell assembly methods.
Capacity calibration of pre-lithiated lithium powder
The button cell is connected to a charging and discharging cabinet in a way that: the electrode carrying lithium powder is connected to the positive electrode terminal as a working electrode, and the inert metal sheet is connected to the negative electrode terminal as a counter electrode. And the electrode is charged at a low multiplying power by adopting a charging process step, wherein the charging multiplying power is 0.01C, and the cut-off voltage is 2.0V. The recorded charge capacity was 7.733 mAh.
Determination of specific capacity of lithium powder
And calculating the effective specific capacity of the inert lithium powder by combining the loading capacity of the lithium powder on the working electrode according to the capacity value recorded by the charging and discharging cabinet. Specific capacity (mAh/g) is charge capacity (mAh)/lithium powder loading (g).
Example 2
Preparation of button cell
(1) Preparation of prelithiation working electrode pole piece
Adhesive PVDF1.5g was dissolved in 48.5g of NMP solution at a mass ratio of 3 wt% to prepare a glue solution, which took 3 hours. 6g of inert lithium powder and 2.5g of conductive agent acetylene black are mixed for standby, and the usage time is 15 min. Slowly adding a mixture of inert lithium powder and conductive acetylene black into the glue solution, uniformly mixing to obtain lithium powder slurry, and mixing the lithium powder, the binder and the conductive agent according to a ratio of 60:15:25 to obtain the lithium powder slurry, wherein the time for use is 45 min. Then coated on the surface of a current collector copper foil with the thickness of 30 mu m, wherein the coating mass of the slurry is 1.5mg/cm2Calculated as the lithium powder loading per unit area of 0.9mg/cm (based on the mass of the solid component not containing the solvent)2It is administered for 20 min. Drying in a vacuum oven at 100 deg.C for 1.5h, and ventilating with 99.9% purity Ar every 30 min. And taking out the dried pole piece, cold-pressing to obtain an initial pole piece with the lithium powder active material arranged on the surface of the current collector, and rubbing into a circular pole piece with the diameter of 15mm, wherein the time is 30 min. The mass of the pole piece is weighed, and the time is 10 min. And obtaining 10 pole pieces in total, and putting the pole pieces into a glove box for later use. Except for the vacuum drying, the operation was carried out at an ambient humidity of 1%, a temperature of 28 ℃ and an air atmosphere. The whole working electrode was operated outside the glove box for 6.5 hours.
(2) Preparation of counter electrode pole piece
A Cu foil 15 μm thick was rolled up into a disc 18mm in diameter.
(3) Preparation of electrolyte
Preparation of electrolyte at Water content<In a 1ppm argon atmosphere glove box, Ethylene Carbonate (EC), Propylene Carbonate (PC) and dimethyl carbonate (DMC) are mixed according to the mass ratioMixing EC PC DMC 1:1:1 to obtain mixed organic solvent, and fully drying lithium salt LiPF6Dissolving in the mixed organic solvent, and stirring to obtain electrolyte solution containing LiPF6The concentration of (2) was 1.2 mol/L.
(4) Preparation of the separator
A polyethylene porous membrane is used as a separation membrane and is expanded into a circular sheet with the diameter of 18 mm.
(5) Preparation of the Battery
The cell was assembled according to normal button cell assembly methods.
Capacity calibration of pre-lithiated lithium powder
The button cell is connected to a charging and discharging cabinet in a way that: the electrode carrying lithium powder is connected to the positive electrode terminal as a working electrode, and the inert metal sheet is connected to the negative electrode terminal as a counter electrode.
And the electrode is charged at a low multiplying power by adopting a charging process step, wherein the charging multiplying power is 0.02C, and the cut-off voltage is 2.0V. The recorded charge capacity was 6.481 mAh.
Determination of specific capacity of lithium powder
And calculating the effective specific capacity of the inert lithium powder by combining the loading capacity of the lithium powder on the working electrode according to the capacity value recorded by the charging and discharging cabinet. Specific capacity (mAh/g) is charge capacity (mAh)/lithium powder loading (g).
Example 3
Preparation of button cell
(1) Preparation of prelithiation working electrode pole piece
Adhesive PVDF2.5g was dissolved in 47.5g of NMP solution at a mass ratio of 5 wt% to prepare a glue solution, which took 4 hours. 5g of inert lithium powder and 2.5g of conductive agent acetylene black are mixed for standby, and the usage time is 15 min. And slowly adding a mixture of inert lithium powder and conductive acetylene black into the glue solution, uniformly mixing to obtain lithium powder slurry, and mixing the lithium powder, the binder and the conductive agent according to a ratio of 50:25:25 to obtain the lithium powder slurry for 45 min. Then coating the surface of a current collector copper foil with the thickness of 30 mu m, wherein the coating mass of the slurry is 3mg/cm2Calculated as the lithium powder loading per unit area of 1.5mg/cm (based on the mass of the solid component not containing the solvent)2It is administered for 20 min. Drying in a vacuum oven at 100 deg.C for 2h, and ventilating with 99.9% purity Ar every 30 min. And taking out the dried pole piece, cold-pressing to obtain an initial pole piece with the lithium powder active material arranged on the surface of the current collector, and rubbing into a circular pole piece with the diameter of 15mm, wherein the time is 30 min. The mass of the pole piece is weighed, and the time is 10 min. And obtaining 10 pole pieces in total, and putting the pole pieces into a glove box for later use. Except for the vacuum drying, the operation was carried out at an ambient humidity of 1%, a temperature of 28 ℃ and an air atmosphere. The whole working electrode was used for 8.0h outside the glove box.
(2) Preparation of counter electrode pole piece
A Cu foil 15 μm thick was rolled up into a disc 18mm in diameter.
(3) Preparation of electrolyte
Preparation of electrolyte at Water content<In a 1ppm argon atmosphere glove box, Ethylene Carbonate (EC), Propylene Carbonate (PC), and dimethyl carbonate (DMC) were mixed in a mass ratio of EC: PC: DMC of 1:1:1 to obtain a mixed organic solvent, and a fully dried lithium salt LiPF was added6Dissolving in the mixed organic solvent, and stirring to obtain electrolyte solution containing LiPF6The concentration of (2) was 1.2 mol/L.
(4) Preparation of the separator
A polyethylene porous membrane is used as a separation membrane and is expanded into a circular sheet with the diameter of 18 mm.
(5) Preparation of the Battery
The cell was assembled according to normal button cell assembly methods.
Capacity calibration of pre-lithiated lithium powder
The button cell is connected to a charging and discharging cabinet in a way that: the electrode carrying lithium powder is connected to the positive electrode terminal as a working electrode, and the inert metal sheet is connected to the negative electrode terminal as a counter electrode.
And the electrode is charged at a low multiplying power by adopting a charging process step, wherein the charging multiplying power is 0.03C, and the cut-off voltage is 2.0V. The recorded charge capacity was 9.669 mAh.
Determination of specific capacity of lithium powder
And calculating the effective specific capacity of the inert lithium powder by combining the loading capacity of the lithium powder on the working electrode according to the capacity value recorded by the charging and discharging cabinet. Specific capacity (mAh/g) is charge capacity (mAh)/lithium powder loading (g).
Example 4
Preparation of button cell
(1) Preparation of prelithiation working electrode pole piece
Adhesive PVDF2.5g was dissolved in 47.5g of NMP solution at a mass ratio of 5 wt% to prepare a glue solution, which took 4 hours. 4g of inert lithium powder and 3.5g of conductive agent acetylene black are mixed for standby, and the usage time is 15 min. Slowly adding a mixture of inert lithium powder and conductive acetylene black into the glue solution, uniformly mixing to obtain lithium powder slurry, and mixing the lithium powder, the binder and the conductive agent according to a ratio of 40:25:35 to obtain the lithium powder slurry, wherein the time for use is 45 min. Then coating the surface of a current collector copper foil with the thickness of 30 mu m, wherein the coating mass of the slurry is 3mg/cm2Calculated as the lithium powder loading per unit area of 1.2mg/cm (based on the mass of the solid component not containing the solvent)2It is administered for 20 min. Drying in a vacuum oven at 100 deg.C for 2h, and ventilating with 99.9% purity Ar every 30 min. And taking out the dried pole piece, cold-pressing to obtain an initial pole piece with the lithium powder active material arranged on the surface of the current collector, and rubbing into a circular pole piece with the diameter of 15mm, wherein the time is 30 min. The mass of the pole piece is weighed, and the time is 10 min. And obtaining 10 pole pieces in total, and putting the pole pieces into a glove box for later use. Except for the vacuum drying, the operation was carried out at an ambient humidity of 1%, a temperature of 28 ℃ and an air atmosphere. The whole working electrode was used for 8.0h outside the glove box.
(2) Preparation of counter electrode pole piece
A Cu foil 15 μm thick was rolled up into a disc 18mm in diameter.
(3) Preparation of electrolyte
Preparation of electrolyte at Water content<In a 1ppm argon atmosphere glove box, Ethylene Carbonate (EC), Propylene Carbonate (PC), and dimethyl carbonate (DMC) were mixed in a mass ratio of EC: PC: DMC of 1:1:1 to obtain a mixed organic solvent, and a fully dried lithium salt LiPF was added6Dissolving in the mixed organic solvent, and stirring to obtain electrolyte solution containing LiPF6The concentration of (2) was 1.2 mol/L.
(4) Preparation of the separator
A polyethylene porous membrane is used as a separation membrane and is expanded into a circular sheet with the diameter of 18 mm.
(5) Preparation of the Battery
The cell was assembled according to normal button cell assembly methods.
Capacity calibration of pre-lithiated lithium powder
The button cell is connected to a charging and discharging cabinet in a way that: the electrode carrying lithium powder is connected to the positive electrode terminal as a working electrode, and the inert metal sheet is connected to the negative electrode terminal as a counter electrode.
And the electrode is charged at a low multiplying power by adopting a charging process step, wherein the charging multiplying power is 0.04C, and the cut-off voltage is 2.0V. The recorded charge capacity was 6.653 mAh.
Determination of specific capacity of lithium powder
And calculating the effective specific capacity of the inert lithium powder by combining the loading capacity of the lithium powder on the working electrode according to the capacity value recorded by the charging and discharging cabinet. Specific capacity (mAh/g) is charge capacity (mAh)/lithium powder loading (g).
Example 5
Preparation of button cell
(1) Preparation of prelithiation working electrode pole piece
4.0g of the binder PVDFT was dissolved in 76g of NMP solution at a mass ratio of 5 wt% to prepare a dope, which took 4 hours. 2g of inert lithium powder and 4.0g of conductive agent acetylene black are mixed for standby, and the usage time is 30 min. Slowly adding a mixture of inert lithium powder and conductive acetylene black into the glue solution, uniformly mixing to obtain lithium powder slurry, and mixing the lithium powder, the binder and the conductive agent according to a ratio of 20:40:40 to obtain the lithium powder slurry, wherein the time for use is 60 min. Then coating the surface of a current collector copper foil with the thickness of 30 mu m, wherein the coating mass of the slurry is 3mg/cm2Calculated as the amount of lithium powder supported per unit area of 0.6mg/cm (based on the mass of the solid component not containing the solvent)2It is administered for 30 min. Drying in a vacuum oven at 100 deg.C for 3.5h, and ventilating with 99.9% purity Ar every 30 min. And taking out the dried pole piece, cold-pressing to obtain an initial pole piece with the lithium powder active material arranged on the surface of the current collector, and rubbing into a circular pole piece with the diameter of 15mm, wherein the time is 30 min. The mass of the pole piece is weighed, and the time is 30 min. Obtaining 10 pole pieces in total, and putting into handAnd (5) casing for standby. Except for the vacuum drying, the operation was carried out at an ambient humidity of 1%, a temperature of 28 ℃ and an air atmosphere. The whole working electrode was used for 8.0h outside the glove box.
(2) Preparation of counter electrode pole piece
A Cu foil 15 μm thick was rolled up into a disc 18mm in diameter.
(3) Preparation of electrolyte
Preparation of electrolyte at Water content<In a 1ppm argon atmosphere glove box, Ethylene Carbonate (EC), Propylene Carbonate (PC), and dimethyl carbonate (DMC) were mixed in a mass ratio of EC: PC: DMC of 1:1:1 to obtain a mixed organic solvent, and a fully dried lithium salt LiPF was added6Dissolving in the mixed organic solvent, and stirring to obtain electrolyte solution containing LiPF6The concentration of (2) was 1.2 mol/L.
(4) Preparation of the separator
A polyethylene porous membrane is used as a separation membrane and is expanded into a circular sheet with the diameter of 18 mm.
(5) Preparation of the Battery
The cell was assembled according to normal button cell assembly methods.
Capacity calibration of pre-lithiated lithium powder
The button cell is connected to a charging and discharging cabinet in a way that: the electrode carrying lithium powder is connected to the positive electrode terminal as a working electrode, and the inert metal sheet is connected to the negative electrode terminal as a counter electrode.
And the electrode is charged at a low multiplying power by adopting a charging process step, wherein the charging multiplying power is 0.05C, and the cut-off voltage is 2.0V. The recorded charge capacity was 2.795 mAh.
Determination of specific capacity of lithium powder
And calculating the effective specific capacity of the inert lithium powder by combining the loading capacity of the lithium powder on the working electrode according to the capacity value recorded by the charging and discharging cabinet. Specific capacity (mAh/g) is charge capacity (mAh)/lithium powder loading (g).
Example 6
Preparation of button cell
(1) Preparation of prelithiation working electrode pole piece
The adhesive PVDF2.5g is added according to5 wt% of the mixture is dissolved in 47.5g of NMP solution to prepare glue solution, and the glue solution takes 1.5 h. 5g of inert lithium powder and 2.5g of conductive agent acetylene black are mixed for standby, and the usage time is 30 min. And slowly adding a mixture of inert lithium powder and conductive acetylene black into the glue solution, uniformly mixing to obtain lithium powder slurry, and mixing the lithium powder, the binder and the conductive agent according to a ratio of 50:25:25 to obtain the lithium powder slurry, wherein the time is 30 min. Then coating the surface of a current collector copper foil with the thickness of 30 mu m, wherein the coating mass of the slurry is 2mg/cm2Calculated as the lithium powder loading per unit area of 1.0mg/cm (based on the mass of the solid component not containing the solvent)2It is administered for 30 min. Drying in a vacuum oven at 100 deg.C for 1.0h, and ventilating with 99.9% purity Ar every 30 min. And taking out the dried pole piece, cold-pressing to obtain an initial pole piece with the lithium powder active material arranged on the surface of the current collector, and rubbing the initial pole piece into a circular pole piece with the diameter of 15mm, wherein the time is 15 min. The mass of the pole piece is weighed, and the time is 15 min. And obtaining 10 pole pieces in total, and putting the pole pieces into a glove box for later use. Except for the vacuum drying, the operation was carried out at an ambient humidity of 1%, a temperature of 28 ℃ and an air atmosphere. The whole working electrode was used for 4.5h outside the glove box.
(2) Preparation of counter electrode pole piece
A Cu foil 15 μm thick was rolled up into a disc 18mm in diameter.
(3) Preparation of electrolyte
Preparation of electrolyte at Water content<In a 1ppm argon atmosphere glove box, Ethylene Carbonate (EC), Propylene Carbonate (PC), and dimethyl carbonate (DMC) were mixed in a mass ratio of EC: PC: DMC of 1:1:1 to obtain a mixed organic solvent, and a fully dried lithium salt LiPF was added6Dissolving in the mixed organic solvent, and stirring to obtain electrolyte solution containing LiPF6The concentration of (2) was 1.2 mol/L.
(4) Preparation of the separator
A polyethylene porous membrane is used as a separation membrane and is expanded into a circular sheet with the diameter of 18 mm.
(5) Preparation of the Battery
The cell was assembled according to normal button cell assembly methods.
Capacity calibration of pre-lithiated lithium powder
The button cell is connected to a charging and discharging cabinet in a way that: the electrode carrying lithium powder is connected to the positive electrode terminal as a working electrode, and the inert metal sheet is connected to the negative electrode terminal as a counter electrode.
And the electrode is charged at a low multiplying power by adopting a charging process step, wherein the charging multiplying power is 0.01C, and the cut-off voltage is 2.0V. The recorded charge capacity was 8.736 mAh.
Determination of specific capacity of lithium powder
And calculating the effective specific capacity of the inert lithium powder by combining the loading capacity of the lithium powder on the working electrode according to the capacity value recorded by the charging and discharging cabinet. Specific capacity (mAh/g) is charge capacity (mAh)/lithium powder loading (g).
The glove box outside operating time, charge rate, and calculated specific capacity results for examples 1-6 are shown in table 1.
Item numbering Glove box external operation time (h) Charging multiplying power (C) Specific capacity (mAh/g)
Example 1 7.5 0.01 2766
Example 2 6.5 0.02 3091
Example 3 8.0 0.03 2767
Example 4 8.0 0.04 2380
Example 5 10.0 0.05 2000
Example 6 4.5 0.01 3750
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims (10)

1. A method for testing the specific capacity of pre-lithiated lithium powder is characterized by comprising the following steps:
(1) mixing inert lithium powder, a binder, a conductive agent, and an organic solvent to form a lithium powder slurry;
(2) transferring the lithium powder slurry onto a current collector, drying and rolling to obtain a working electrode;
(3) calculating according to the weight of the working electrode, the weight of the current collector and the proportion of the inert lithium powder so as to obtain the load capacity of the lithium powder on the current collector;
(4) assembling the working electrode and the inert metal foil into a button cell;
(5) taking the working electrode as a positive electrode and the inert metal foil as a negative electrode, and adopting a charging process step so as to deposit lithium in the working electrode on the inert metal foil;
(6) and calculating the effective specific capacity of the inert lithium powder according to the electric quantity obtained in the charging step and the lithium powder loading capacity.
2. The method according to claim 1, wherein in the step (1), the mass ratio of the inert lithium powder, the binder and the conductive agent is (20-70): (10-40): (20-50);
optionally, the particle size D50 of the inert lithium powder is 5-50 μm;
optionally, the content of Li metal in the inert lithium powder is 70-99 wt%;
optionally, the inert lithium powder comprises an inner core comprised of lithium metal or lithium alloy and an outer shell comprised of an inert layer;
optionally, the lithium alloy includes Li and at least one of Mg, Al, Si, Cu, Zn, K, Na, Co, Sn, Ca, Ti, Fe, and Ni;
optionally, the inert layer comprises inorganic or organicAn inorganic substance selected from Li2CO3LiF, LiI and Li2At least one of S;
optionally, the organic matter comprises small molecule organic matter and polymer, and the small molecule organic matter is selected from at least one of hydrocarbon organic matter with carbon number of 16 to 35;
optionally, the binder is selected from at least one of PTFE, PVDF, NBR, PAN, PVDF-HFP copolymer, PPy, PANI, PTh, and PPTA;
optionally, the conductive agent is selected from at least one of conductive carbon black, acetylene black, conductive graphite, ketjen black, VGCF, CNT, and graphene;
optionally, the organic solvent is selected from at least one of benzene, toluene, xylene, diethyl ether, acetone, EC, PC, DEC, EMC, DMC, ethanol, NMP, DMSO, DMF, trifluoroacetic acid, and chloroform.
3. The method according to claim 1, wherein in the step (2), the lithium powder slurry is transferred onto the current collector by a coating method;
optionally, in the step (2), the drying condition is that the vacuum degree is not higher than-88 kPa, the temperature is 60-120 ℃, and the time is 1-6 h;
optionally, in the step (2), the current collector is selected from any one of Cu, Fe, Ni, Au and Pt;
optionally, in the step (3), the unit area loading amount of the lithium powder on the current collector is 0.1-3 mg/cm2。
4. The method of claim 1, wherein in step (4), the inert metal foil is selected from at least one of Cu, Fe, Ni, Al, Ti, Ag, Au, and Pt.
5. The method according to claim 1, wherein in the step (5), the calibration of the discharge capacity is performed by using a low-rate charging step, wherein the charging rate is 0.005-0.1C;
optionally, the cut-off voltage is 0.5-2.5V.
6. The method of claim 1, wherein steps (1) to (4) are all performed in a dry environment;
optionally, the method further comprises:
and (4) recording the ambient temperature, the humidity, the atmosphere composition and the required time length of the steps (1) to (4) so as to establish a corresponding relation between the effective specific capacity of the lithium powder and the ambient temperature, the humidity and the required time length.
7. Use of the method of any one of claims 1 to 6 in the prelithiation of a negative electrode sheet with an inert lithium powder.
8. A pre-lithiated negative electrode sheet is characterized in that the effective specific capacity of inert lithium powder in the pre-lithiated negative electrode sheet is 2000-3750 mAh/g, and the effective specific capacity of 2000-3750 mAh/g is obtained by testing according to the method of any one of claims 1-6.
9. A lithium battery having the prelithiated negative electrode sheet of claim 8.
10. An electric vehicle characterized by having the lithium battery of claim 9.
CN202010951447.2A 2020-09-11 2020-09-11 Method for testing specific capacity of pre-lithiated lithium powder and application thereof Pending CN112067672A (en)

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