CN115036465A - Lithium metal negative electrode, preparation method thereof and lithium secondary battery - Google Patents
Lithium metal negative electrode, preparation method thereof and lithium secondary battery Download PDFInfo
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Abstract
The invention belongs to the technical field of negative electrode structures, and particularly relates to a lithium metal negative electrode, a preparation method thereof and a lithium secondary battery. The lithium metal cathode comprises a metal lithium body and a composite protective layer, wherein the composite protective layer is arranged on at least one surface of the metal lithium body, and the material of the composite protective layer comprises lithium fluoride and a lithium-philic metal simple substance. Lithium fluoride can prevent electrons from passing into the electrolyte to alleviate the problem of lithium dendrite growth in the electrolyte; the lithium-philic metal simple substance has the characteristic of dissolving Li, and can be dissolved into the lithium-philic metal simple substance to form an alloy solid solution when lithium ions are deposited on the surface of the lithium metal cathode, so that the problem of dendritic crystal nucleation caused by over-fast local deposition of the lithium ions is avoided, the formation of lithium dendritic crystals is avoided, and the cycle life of the battery is prolonged.
Description
Technical Field
The invention belongs to the technical field of negative electrode structures, and particularly relates to a lithium metal negative electrode and a preparation method thereof, and a lithium secondary battery.
Background
The theoretical specific capacity of the lithium metal negative electrode is 3860mAh/g, which is 10 times higher than that of a graphite negative electrode (372 mAh/g). However, the battery using the lithium metal negative electrode has poor cycle performance, and short-circuiting occurs in several tens of weeks, mainly because deposition and peeling of lithium ions on the negative electrode side are not uniform, lithium dendrites easily nucleate and grow fast, and the positive and negative electrodes are short-circuited by piercing the separator. The widely adopted scheme at present is to add a protective layer on the surface of a lithium metal negative electrode, and the main method comprises the following steps: 1) hot pressing; 2) a preliminary electrochemical reaction method; 3) an in situ generation method. The hot pressing method is to stack the protective layer on the surface of the lithium metal and heat and press the protective layer to combine the lithium metal and the lithium metal, and has the problems that the additional protective layer is thicker and the internal resistance of the battery is increased; the electrochemical reaction method is to carry out electrochemical reaction in a mould in advance, prepare a film, then superpose the film on the surface of the lithium metal cathode, and pressurize the film and the lithium metal cathode to combine the film and the lithium metal cathode, and has the problems that the electrochemical reaction carried out in the mould in advance greatly reduces the production efficiency and cannot be compatible with the existing electrode preparation process; the in-situ generation method is to add an additive into the electrolyte and generate a protective layer in situ in the first charge-discharge process, and has the problems that the additive has certain influence on the performance of the electrolyte, the reaction occurs in the battery core, and side reaction products have negative influence on the performance of the battery.
Therefore, how to add a protective layer on the surface of the lithium metal negative electrode and to be compatible with the existing electrode preparation process is one of the major research points of the current battery negative electrode.
Disclosure of Invention
The invention aims to provide a lithium metal negative electrode, a preparation method thereof and a lithium secondary battery, and aims to solve the technical problems that the conventional lithium metal negative electrode has lithium dendrite growth and the preparation method of a protective layer is difficult to be compatible with the conventional electrode preparation process.
In order to achieve the above object, according to one aspect of the present invention, there is provided a lithium metal negative electrode including a metallic lithium body and a composite protective layer disposed on at least one surface of the metallic lithium body; the composite protective layer is made of lithium fluoride and lithium-philic metal simple substance.
According to the lithium metal cathode provided by the invention, the composite protective layer is arranged on the metal lithium body, and the composite protective layer is of a composite structure formed by a lithium-philic metal simple substance and lithium fluoride. Lithium fluoride can prevent electrons from passing into the electrolyte to alleviate the problem of lithium dendrite growth in the electrolyte; the lithium-philic metal simple substance has the characteristic of dissolving Li, and can be dissolved into the lithium-philic metal simple substance to form an alloy solid solution when lithium ions are deposited on the surface of the lithium metal cathode, so that the problem of dendritic crystal nucleation caused by the over-fast local deposition of the lithium ions is avoided, the formation of lithium dendritic crystals is further avoided, and the cycle life of the battery is prolonged.
As a preferred technical scheme of the lithium metal cathode, the lithium-philic metal simple substance is a zinc simple substance and/or a silver simple substance.
As a preferable technical scheme of the lithium metal cathode, the molar ratio of the lithium-philic metal simple substance to the lithium fluoride is (2-3): 5.
As a preferable technical scheme of the lithium metal negative electrode, the thickness of the composite protective layer is 10-30 μm.
As a preferable technical scheme of the lithium metal negative electrode, the thickness of the lithium metal body is 20-40 μm.
In another aspect of the present invention, a method for preparing a lithium metal negative electrode is provided, which includes the steps of:
providing a metal lithium matrix and a metal fluoride solution, wherein metal ions in the metal fluoride solution are lithium-philic metal ions;
and coating the metal fluoride solution on the surface of a metal lithium matrix in an inert environment for replacement reaction, and drying to obtain the lithium metal cathode.
According to the preparation method of the lithium metal cathode provided by the invention, the metal fluoride solution is coated on the surface of a metal lithium matrix for replacement reaction to generate a lithium fluoride material, and lithium-philic metal ions in the metal fluoride solution are reduced into a lithium-philic metal simple substance under the action of strong reducing lithium metal, namely, a composite protective layer structure of the lithium-philic metal simple substance-lithium fluoride material is generated on the surface of the metal lithium matrix through reaction, and the composite protective layer is thinner. The lithium fluoride material has the characteristics of conducting lithium ions and insulating electrons, so that the composite protective layer containing the lithium fluoride material can prevent the electrons from being transmitted into the electrolyte, and the problem of growth of lithium dendrites in the electrolyte is solved. In addition, the lithium-philic metal simple substance has the characteristic of dissolving Li, and can be dissolved into the lithium-philic metal simple substance to form an alloy solid solution when lithium ions are deposited on the surface of the lithium metal negative electrode, so that the problem of dendritic crystal nucleation caused by over-fast local deposition of the lithium ions is avoided, and further the formation of lithium dendritic crystals is avoided. The preparation method provided by the invention can be compatible with the existing battery cell preparation process, and is beneficial to realizing large-scale production.
As a preferable embodiment of the method for preparing a lithium metal negative electrode according to the present invention, the method for preparing a metal fluoride solution comprises: and mixing the metal fluoride, the electrolyte lithium salt and the organic solvent to obtain a metal fluoride solution.
As a further preferable embodiment of the method for producing a lithium metal negative electrode of the present invention, the electrolyte lithium salt is at least one selected from the group consisting of lithium hexafluorophosphate, lithium perchlorate, lithium hexafluoroarsenate and lithium tetrafluoroborate.
In a more preferable embodiment of the method for producing a lithium metal negative electrode according to the present invention, the organic solvent is at least one selected from the group consisting of dimethyl sulfoxide, tetrahydrofuran, ethylene carbonate, diethyl carbonate, and dimethyl carbonate.
As a preferable embodiment of the method for manufacturing a lithium metal negative electrode according to the present invention, the metal fluoride solution is at least one selected from a silver fluoride solution and a zinc fluoride solution.
As a preferable technical scheme of the preparation method of the lithium metal cathode, the concentration of the metal fluoride solution is 1mmol/L-10 mmol/L.
As a preferable technical scheme of the preparation method of the lithium metal cathode, in the step of coating the metal fluoride solution on the surface of the metal lithium matrix for reaction, the reaction time is 5-15 min, and the reaction temperature is 60-100 ℃.
In a final aspect of the present invention, a lithium secondary battery is provided, which includes a positive electrode, a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode, wherein the negative electrode is the lithium metal negative electrode provided in the present invention, or the lithium metal negative electrode prepared by the method for preparing the lithium metal negative electrode provided in the present invention.
The lithium secondary battery provided by the invention comprises the lithium metal negative electrode provided by the invention, and the lithium metal negative electrode can inhibit dendritic crystal nucleation and relieve the growth of lithium dendritic crystals in an electrolyte, so that the lithium secondary battery provided by the invention has longer cycle life, and has good application prospect and market value.
Drawings
Fig. 1 is a schematic structural diagram of a lithium metal negative electrode according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a lithium ion deposition process of a lithium metal negative electrode provided in an embodiment of the present invention;
FIG. 3 is a schematic diagram of a lithium ion deposition process for a conventional lithium metal negative electrode;
FIG. 4 is a schematic view showing a process for preparing a lithium metal negative electrode and a lithium secondary battery according to an embodiment of the present invention;
FIG. 5 is a sectional electron micrograph of a lithium metal negative electrode obtained in example 1 of the present invention;
FIG. 6 is a graph comparing AC impedance spectra before and after cycling of a lithium metal negative electrode obtained in example 3 of the present invention with a conventional lithium metal negative electrode obtained in comparative example 1;
FIG. 7 is a graph showing the comparison of the cycle characteristics of batteries fabricated using a lithium metal negative electrode obtained in example 3 according to the present invention and a conventional lithium metal negative electrode obtained in comparative example 1;
the reference numbers in fig. 1-3 are as follows:
10-a bulk of metallic lithium; 20-a composite protective layer; 22-lithium-philic metal simple substance; 24-lithium fluoride; 26-alloy solid solution.
Detailed Description
In order to make the objects, technical solutions and technical effects of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described, and the embodiments described below are a part of the embodiments of the present invention, but not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art without any inventive step in connection with the embodiments of the present invention shall fall within the scope of protection of the present invention. Those whose specific conditions are not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer; the reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
In the description of the present invention, the term "and/or" describes an association relationship of associated objects, which means that there may be three relationships, for example, a and/or B, which may mean: a is present alone, A and B are present simultaneously, and B is present alone. Wherein A and B can be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship.
In the description of the present invention, "at least one" means one or more, "a plurality" means two or more. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of the singular or plural items. For example, "at least one (a), b, or c", or "at least one (a), b, and c", may each represent: a. b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, wherein a, b, and c can be single or multiple respectively.
It should be understood that the weight of the related components mentioned in the embodiments of the present invention may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, it is within the scope of the disclosure that the content of the related components is scaled up or down according to the embodiments of the present invention. Specifically, the weight described in the embodiments of the present invention may be a unit of mass known in the chemical field such as μ g, mg, g, kg, etc.
In addition, unless the context clearly uses otherwise, an expression of a word in the singular is to be understood as including the plural of the word. The terms "comprises" or "comprising" are intended to specify the presence of stated features, quantities, steps, operations, elements, portions, or combinations thereof, but are not intended to preclude the presence or possible addition of one or more other features, quantities, steps, operations, elements, portions, or combinations thereof.
Fig. 1 shows a structure of a lithium metal negative electrode provided in an embodiment of the present invention. With reference to fig. 1, an embodiment of the present invention provides a lithium metal negative electrode including a lithium metal body 10 and a composite protective layer 20, the composite protective layer 20 being disposed on at least one surface of the lithium metal body 10; the material forming the composite protective layer 20 includes a lithium-philic metal simple substance 22 and lithium fluoride 24.
According to the lithium metal negative electrode provided by the embodiment of the invention, the composite protective layer 20 is arranged on the metal lithium body 10, and the composite protective layer 20 is a composite structure formed by a lithium-philic metal simple substance 22-lithium fluoride 24. The lithium fluoride 24 can prevent electrons from passing through an interface layer of the electrode and the electrolyte, so that the deposition of lithium ions in the electrolyte is avoided, and the problem of the growth of lithium dendrites in the electrolyte is solved; the lithium-philic metal simple substance 22 has the characteristic of dissolving Li, and can be dissolved into the lithium-philic metal simple substance 22 to form an alloy solid solution when lithium ions are deposited on the surface of the lithium metal negative electrode, so that the problem of dendritic crystal nucleation caused by the too fast local deposition of the lithium ions is avoided, the formation of lithium dendritic crystals is further avoided, and the cycle life of the battery is prolonged.
The following will describe the lithium ion deposition process of the lithium metal negative electrode provided in the embodiment of the present invention and the conventional lithium metal negative electrode in comparison with fig. 2 and 3. As can be seen from fig. 2, by disposing the composite protective layer 20 on the lithium metal body 10, the composite protective layer 20 includes lithium fluoride 24 and a lithium-philic metal simple substance. In the charging and discharging process, when lithium ions transmitted from the positive electrode to the negative electrode pass through the composite protective layer 20, because the lithium-philic metal simple substance in the composite protective layer 20 has the characteristic of dissolving the lithium simple substance, when the lithium simple substance is locally deposited, the lithium-philic metal simple substance and the lithium-philic metal simple substance form an alloy solid solution 26, so that excessive lithium simple substance deposition is avoided, and lithium dendrite nucleation is inhibited. As can be seen from fig. 3, the conventional lithium metal negative electrode only has the metal lithium body 10, and because there is no protection of the composite protective layer, once there is deposition of lithium simple substance during the charging and discharging process, the subsequent lithium ions are limited to be deposited at the formed nucleation sites, which causes growth of lithium dendrite and causes a safety problem of the battery.
In the lithium metal negative electrode provided in the embodiment of the present invention, the composite protective layer 20 may be disposed on a single surface of the lithium metal body 10 facing the electrolyte direction, or may be disposed on both surfaces of the lithium metal body 10, or even the entire lithium metal body 10 is coated to form a coating layer. In practical applications, the composite protective layer 20 may be disposed on one side, the composite protective layer 20 may be disposed on both sides, or the composite protective layer 20 may be disposed in a full-coating manner according to the specific structure of the battery and the position relationship between the lithium metal negative electrode and the electrolyte.
In some embodiments, the lithium-philic metal is elemental zinc and/or elemental silver. The simple substance of zinc and the simple substance of silver have higher Li solubility to the metal lithium, which is more beneficial to forming alloy solid solution. Correspondingly, the simple substance of zinc and Li form a Zn-Li alloy solid solution, and the simple substance of silver and Li form an Ag-Li alloy solid solution.
In some embodiments, the molar ratio of the lithium philic metal elemental to lithium fluoride is (2-3): 5. If the proportion of the lithium-philic metal simple substance is too low, the ion conductivity of the obtained lithium metal cathode is not enough, which is not beneficial to improving the performance of the lithium metal cathode; if the proportion of the lithium-philic metal simple substance is too high, the strength of the obtained lithium metal negative electrode is poor, and the cycle stability of the lithium metal negative electrode is influenced.
In some embodiments, the thickness of the composite protective layer is set to be in the range of 10 μm to 30 μm, and in this range, the composite protective layer can both protect and avoid adversely affecting the capacity. If the composite protective layer is too thin, the inhibition effect on lithium dendrites is small; if the composite protective layer is too thick, the problem of high resistance of the obtained lithium metal negative electrode is easily caused. In particular, typical, but not limiting, composite protective layers are 10 μm, 15 μm, 20 μm, 25 μm, 30 μm thick.
In some embodiments, the thickness of the lithium metal body is set to 20 μm to 30 μm. If the lithium metal body is too thick, the energy density of the obtained lithium metal cathode is reduced, which is not beneficial to improving the performance of the battery; if the bulk of the lithium metal is too thin, the cost increases and even the problem of non-producibility arises. In particular, typical, but not limiting, bulk thicknesses of metallic lithium are 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm.
The lithium metal negative electrode provided by the embodiment of the invention can be prepared by the following preparation method.
Correspondingly, the embodiment of the invention provides a preparation method of a lithium metal negative electrode, which comprises the following steps:
s1, providing a metal lithium matrix and a metal fluoride solution, wherein metal ions in the metal salt solution are lithium-philic metal ions;
and S2, coating the metal fluoride solution on the surface of the metal lithium matrix in an inert environment for displacement reaction, and drying to obtain the lithium metal negative electrode.
In the preparation method of the lithium metal cathode provided by the embodiment of the invention, the metal fluoride solution is coated on the surface of the metal lithium matrix for a displacement reaction to generate the lithium fluoride material, and simultaneously, under the action of the strong reducing lithium metal, lithium-philic metal ions in the metal fluoride solution are reduced into a lithium-philic metal simple substance, namely, a composite protective layer structure of the lithium-philic metal simple substance-lithium fluoride material is generated on the surface of the metal lithium matrix by a reaction. The lithium fluoride material has the characteristics of conducting lithium ions and insulating electrons, so that the composite protective layer containing the lithium fluoride material can prevent the electrons from being transmitted into the electrolyte, and the problem of growth of lithium dendrites in the electrolyte is solved. In addition, the lithium-philic metal simple substance has the characteristic of dissolving Li, and when lithium ions are deposited on the surface of the lithium metal negative electrode, the lithium-philic metal simple substance can be dissolved into the lithium-philic metal simple substance to form an alloy solid solution, so that the problem of dendritic crystal nucleation caused by the local deposition of the lithium ions is avoided, and further the formation of lithium dendritic crystals is avoided.
Specifically, in S1, the lithium metal matrix serves as both a supplier of the lithium metal in the lithium metal negative electrode provided in the embodiment of the present invention and a reaction material for generating lithium fluoride and a lithium-philic metal simple substance in the composite protective layer. In some embodiments, the lithium metal matrix may be selected from a lithium ribbon or a lithium sheet commonly used in the art, and the thickness thereof may be selected from 5 μm to 50 μm.
In some embodiments, lithium is an active metal, and oxides and pollutants are more present on the surface of the metal lithium matrix, so that the surface pretreatment of the metal lithium matrix is beneficial to the reaction of the metal lithium matrix and a metal salt solution, and the generation of impurities is avoided to influence the performance of the obtained lithium metal negative electrode. In some embodiments, a method of surface pre-treating a lithium metal substrate comprises: and (3) soaking the metal lithium matrix in a tetrahydrofuran solution for 10 min.
In some embodiments, the method of preparing the metal fluoride solution comprises: and mixing the metal fluoride, the electrolyte lithium salt and the organic solvent to obtain a metal fluoride solution. The preparation method can promote the metal fluoride to be dispersed in the organic solvent more uniformly by adding the electrolyte lithium salt, and is favorable for ensuring that the obtained metal fluoride solution has good uniformity. The metal fluoride solution with good uniformity is coated on the surface of the metal lithium substrate, so that the lithium-philic metal simple substance in the obtained composite protective layer is more uniformly distributed, and nucleation and growth of lithium dendrite are further inhibited. In some embodiments, the metal fluoride is silver fluoride and/or zinc fluoride, and accordingly, the obtained metal fluoride solution is a silver fluoride solution and/or a zinc fluoride solution; the electrolyte lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium hexafluoroarsenate and lithium tetrafluoroborate; the organic solvent is at least one selected from dimethyl sulfoxide, tetrahydrofuran, ethylene carbonate, diethyl carbonate and dimethyl carbonate, and the electrolyte lithium salt and the organic solvent are selected to be favorable for improving the dispersibility of the metal fluoride.
In S2, the metal fluoride solution is coated on the surface of the lithium metal substrate, and the lithium metal on the surface of the lithium metal substrate and the metal fluoride solution undergo a displacement reaction to generate lithium fluoride and a lithium-philic metal simple substance, which then serve as a composite protective layer. Accordingly, the lithium metal substrate that has not reacted with the metal fluoride solution serves as the lithium metal body. Since lithium is an active metal, the reaction should be carried out in an inert environment. During coating, according to actual needs, the metal fluoride solution can be coated on the surface of one side of the metal lithium matrix, also can be coated on the surfaces of two sides of the metal lithium matrix, and even the whole outer surface of the metal lithium matrix is coated with the metal fluoride solution, so that a composite protective layer is formed at the corresponding position.
According to the embodiment of the invention, the metal fluoride solution is coated on the surface of the metal lithium substrate, so that the thickness of the obtained composite protective layer is relatively thin. In some embodiments, the thickness of the resulting composite protective layer is from 10 μm to 30 μm.
In some embodiments, the metal fluoride solution is a silver fluoride solution and/or a zinc fluoride solution. Silver ions in the silver fluoride solution and zinc ions in the zinc fluoride solution are lithium-philic metal cations, and when the silver fluoride solution and/or the zinc fluoride solution are coated on the surface of a metal lithium substrate, lithium-philic metal simple substance silver and/or zinc can be generated under the reduction of metal lithium; meanwhile, the negative fluorine in the metal fluoride solution reacts with the lithium metal to generate lithium fluoride. Specifically, when a zinc fluoride solution is coated on the surface of a metal lithium substrate, a zinc simple substance and lithium fluoride are generated; when the silver fluoride solution is coated on the surface of the metal lithium substrate, a silver simple substance and lithium fluoride are generated.
In some embodiments, the molar concentration of the metal fluoride solution is controlled to be 1mmol/L-10mmol/L, and the obtained composite protective layer formed by the lithium fluoride and the lithium-philic metal simple substance has a proper thickness, so that the interface between the lithium metal cathode and the electrolyte is stabilized, and the interface impedance is prevented from increasing in the circulation process. If the molar concentration of the metal fluoride solution is too high, the obtained composite protective layer is too thick, so that the volume of the lithium metal negative electrode is too large, the assembly of the battery is not facilitated, and the capacity of the battery is also influenced; if the molar concentration of the metal fluoride solution is too low, the time of the displacement reaction is too long, and the reaction effect is poor. Specifically, the metal fluoride solution typically, but not by way of limitation, has a molar concentration of 1mmol/L, 2mmol/L, 3mmol/L, 4mmol/L, 5mmol/L, 6mmol/L, 7mmol/L, 8mmol/L, 9mmol/L, 10 mmol/L.
In some embodiments, the step of coating the metal fluoride solution on the surface of the lithium metal substrate for reaction is performed for 5min to 15min, preferably 10min, and the reaction temperature is 60 ℃ to 100 ℃, preferably 80 ℃. By optimizing the temperature and time of the reaction, the thickness of the obtained composite protective layer is moderate, and the problems of high resistance caused by over-thick composite protective layer and insufficient inhibition of lithium dendrite due to over-thin composite protective layer are avoided.
In the method for preparing the lithium metal negative electrode provided in the embodiment of the present invention, the thickness of the prepared lithium metal body is 5 μm to 50 μm, and the advantages of setting the thickness range are as described above, and are not described herein again for the sake of brevity.
Taking the preparation of a lithium secondary solid-state battery as an example, fig. 4 shows a flow chart of the preparation of a lithium metal negative electrode and a secondary battery, and it can be seen from the flow chart that the lithium metal negative electrode is obtained by sequentially performing a cleaning pretreatment, a substitution reaction with a metal fluoride solution, and a drying treatment on a metal lithium substrate (such as a lithium ribbon) in the example of the present invention. The step of assembling the lithium metal cathode into the lithium secondary solid-state battery can be compatible with the existing battery core preparation process, and is beneficial to realizing large-scale production.
The embodiment of the invention also provides a lithium secondary battery, which comprises a positive electrode, a negative electrode and an electrolyte arranged between the positive electrode and the negative electrode, wherein the negative electrode is the lithium metal negative electrode provided by the embodiment of the invention or the lithium metal negative electrode prepared by the preparation method of the lithium metal negative electrode provided by the embodiment of the invention.
The lithium secondary battery provided by the embodiment of the invention comprises the lithium metal negative electrode provided by the invention, and the lithium metal negative electrode can inhibit dendritic nucleation and relieve the growth of lithium dendrites in an electrolyte, so that the lithium secondary battery provided by the embodiment of the invention has longer cycle life, and has good application prospect and market value.
In some embodiments, when the lithium secondary battery is a solid-state battery, the lithium metal negative electrode provided by the embodiments of the present invention can prevent the formation and growth of lithium dendrites, so that the lithium metal negative electrode and the solid-state electrolyte are always in close contact, and an interface is stabilized, thereby improving the overall performance of the solid-state battery.
In order to make the above implementation details and operations of the present invention clearly understood by those skilled in the art, and to make the progress of the lithium metal negative electrode, the preparation method thereof, and the lithium secondary battery of the embodiments of the present invention obviously manifest, the above technical solutions are exemplified by a plurality of examples below.
Example 1
The embodiment provides a preparation method of a lithium metal negative electrode, which comprises the following steps:
under the protection of argon, firstly, soaking a lithium sheet with the thickness of 50 microns in tetrahydrofuran solution for 10min, and removing surface pollutants to obtain the lithium sheet with a smooth surface. Dissolving 1.27mg AgF in 10mL dimethyl sulfoxide (DMSO) solvent, stirring for 2h on a magnetic stirring table at the rotating speed of 500r/min to prepare 1mmol/L AgF/LiPF 6 DMSO solution. Take 20. mu.L of AgF/LiPF with pipette 6 /DMAnd uniformly dripping the SO solution on the surface of the lithium sheet, and drying the lithium sheet on a heating table at the temperature of 80 ℃ for 10min to obtain the lithium metal cathode, wherein the lithium metal cathode consists of a lithium metal body and a composite protective layer, and the composite protective layer is made of lithium fluoride and silver simple substance. The cross-sectional electron micrograph of the lithium metal negative electrode obtained in this example is shown in fig. 5. As can be seen from FIG. 5, the thickness of the composite protective layer of the lithium metal negative electrode was about 10 μm, and the thickness of the lithium metal bulk was 40 μm.
Example 2
The embodiment provides a preparation method of a lithium metal negative electrode, which comprises the following steps:
under the protection of argon, firstly, soaking a lithium sheet with the thickness of 50 microns in tetrahydrofuran solution for 10min, and removing surface pollutants to obtain the lithium sheet with a smooth surface. 2.54mg AgF is dissolved in 10mL dimethyl sulfoxide (DMSO) solvent, and is stirred for 2 hours on a magnetic stirring table at the rotating speed of 500r/min to prepare 2mmol/L AgF/LiPF 6 DMSO solution. 20 μ L of AgF/LiPF was taken with pipette 6 And (3) uniformly dripping a DMSO solution on the surface of the lithium sheet, and drying the lithium sheet on a heating table at the temperature of 80 ℃ for 10min to obtain the lithium metal cathode. The lithium metal cathode consists of a metal lithium body and a composite protective layer, wherein the composite protective layer is made of lithium fluoride and silver simple substance. The thickness of the composite protective layer of the lithium metal negative electrode is about 20 μm, and the thickness of the lithium metal body is 30 μm.
Example 3
The embodiment provides a preparation method of a lithium metal negative electrode, which comprises the following steps:
under the protection of argon, firstly, soaking a lithium sheet with the thickness of 50 microns in tetrahydrofuran solution for 10min, and removing surface pollutants to obtain the lithium sheet with a smooth surface. 5.08mg AgF is dissolved in 10mL dimethyl sulfoxide (DMSO) solvent, and is stirred for 2 hours on a magnetic stirring table at the rotating speed of 500r/min to prepare 4mmol/L AgF/LiPF 6 A DMSO solution. Take 20. mu.L of AgF/LiPF with pipette 6 And (3) uniformly dripping a DMSO solution on the surface of the lithium sheet, and drying the lithium sheet on a heating table at the temperature of 80 ℃ for 10min to obtain the lithium metal cathode. The lithium metal cathode consists of a metal lithium body and a composite protective layer, wherein the composite protective layer is made of lithium fluoride and silver simple substances. TheThe thickness of the composite protective layer of the lithium metal negative electrode was about 25 μm, and the thickness of the lithium metal bulk was 25 μm.
Example 4
The embodiment provides a preparation method of a lithium metal negative electrode, which comprises the following steps:
under the protection of argon, firstly, soaking a lithium sheet with the thickness of 50 microns in tetrahydrofuran solution for 10min, and removing surface pollutants to obtain the lithium sheet with a smooth surface. Dissolving 12.70mg AgF in 10mL dimethyl sulfoxide (DMSO) solvent, stirring for 2h on a magnetic stirring table at the rotating speed of 500r/min to prepare 10mmol/L AgF/LiPF 6 DMSO solution. Take 20. mu.L of AgF/LiPF with pipette 6 And (3) uniformly dripping a DMSO solution on the surface of the lithium sheet, and drying the lithium sheet on a heating table at the temperature of 80 ℃ for 10min to obtain the lithium metal cathode. The lithium metal cathode consists of a metal lithium body and a composite protective layer, wherein the composite protective layer is made of lithium fluoride and silver simple substance. The thickness of the composite protective layer of the lithium metal negative electrode is about 30 μm, and the thickness of the lithium metal body is 20 μm.
Comparative example 1
The comparative example provides a method for preparing a lithium metal negative electrode, comprising the steps of:
and under the argon protection atmosphere, soaking the lithium belt with the thickness of 20 microns in Tetrahydrofuran (THF) solution for 10min, and removing surface pollutants to obtain the lithium belt with a smooth surface.
Comparative example 2
The comparative example provides a method for preparing a lithium metal negative electrode, comprising the steps of:
one side surface of a lithium sheet having a thickness of 20 μm was buffed and polished in an argon atmosphere, and 1.0mg of zinc phosphate tetrahydrate was calcined at 200 ℃ for 2 hours in an argon atmosphere to conduct dehydration treatment. And then coating anhydrous zinc phosphate obtained through dehydration treatment on the polished side surface of the lithium sheet in an argon atmosphere at 25 ℃, rolling for 10min to form a lithium-zinc alloy layer (the thickness of the lithium-zinc alloy layer is 10 mu m), and obtaining a metal lithium sheet, namely the lithium metal negative electrode.
Experimental example 1
Examples 1-4 and comparative examples 1-2 lithium metal anodes were obtained prior to cyclingThe interface impedance after the test was performed. The test method is as follows: cutting the lithium metal cathode to a diameter of 10mm, and manufacturing a symmetrical battery by adopting a button battery manufacturing method, wherein the electrolyte is 1M LiPF 6 and/EC + EMC. The test was carried out using the Biologic VMP electrochemical workstation, with a test frequency range of 0.1Hz-1 MHz, and the test results are shown in Table 1.
TABLE 1 interfacial resistance of lithium metal negative electrodes obtained in examples 1 to 4 and comparative examples 1 to 2
As can be seen from the results of table 1, the lithium metal negative electrode prepared by the preparation method of the embodiment of the present invention can significantly suppress the increase in interface resistance after cycling. Meanwhile, as the concentration of the metal fluoride solution increases, the ohmic resistance of the obtained electrode also increases, which is mainly caused by the fact that the thickness of the composite protective layer formed by the high-concentration metal fluoride solution becomes larger. The increase of the thickness of the composite protective layer is beneficial to stabilizing the interface of the lithium metal negative electrode and the electrolyte and preventing the increase of the interface impedance in the circulation process.
Experimental example 2
The ac impedance spectra of the lithium metal negative electrodes obtained in example 3 and comparative example 1 were compared, and the test methods were as follows: cutting the lithium metal cathode to a diameter of 10mm, and manufacturing a symmetrical battery by adopting a button battery manufacturing method, wherein the electrolyte is 1M LiPF 6 and/EC + EMC. The results are shown in FIG. 6 for the Biologic VMP electrochemical workstation, testing frequency range 0.1Hz-1 MHz.
As can be seen from fig. 6, the ohmic internal resistance of the lithium metal negative electrode obtained in example 3 was 29 Ω, which was slightly higher than that of the lithium metal negative electrode without the composite protective layer (21 Ω) obtained in comparative example 1 due to the presence of the composite protective layer, indicating that the ionic conductivity of the composite protective layer was higher and the influence on the ohmic internal resistance of the battery was not great. The interfacial resistance of the lithium metal negative electrode without the composite protective layer obtained in comparative example 1 significantly increased as the number of battery cycles increased, mainly due to the formation of lithium dendrites breaking the close contact of the lithium metal negative electrode with the electrolyte interface, resulting in an increase in contact resistance. The interface impedance of the lithium metal negative electrode with the composite protective layer obtained in the embodiment 3 is always kept at about 80 Ω after circulation without obvious increase, which indicates that the composite protective layer of the lithium metal negative electrode obtained in the embodiment of the present invention has an effect of stabilizing the interface between the lithium metal negative electrode and the electrolyte, and the mechanism of the composite protective layer is that the composite protective layer can promote uniform deposition of lithium ions and inhibit formation of lithium dendrites, so that the lithium metal negative electrode can always keep close contact with the electrolyte, and the interface impedance can be kept unchanged.
Experimental example 3
The cycle performance of the lithium metal negative electrodes obtained in example 3 and comparative example 1 were compared, and a symmetric battery having a lithium metal negative electrode and an LLZO electrolyte composition and a test current density of 1.5mAh/cm was used -2 . The results are shown in FIG. 7.
As can be seen from fig. 7, the battery sample prepared from the lithium metal negative electrode obtained in comparative example 1 suffered lithium dendrite penetration of LLZO electrolyte after 23 hours of cycling, resulting in short circuiting. However, the battery sample prepared from the lithium metal negative electrode obtained in example 3 has no short circuit after 30 hours of circulation, which proves that the lithium metal negative electrode obtained in the embodiment of the invention has better lithium dendrite inhibiting effect.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A lithium metal anode comprising a metallic lithium body and a composite protective layer disposed on at least one surface of the metallic lithium body; the composite protective layer is made of lithium fluoride and a lithium-philic metal simple substance.
2. The lithium metal anode of claim 1, wherein the lithium-philic metal element is an element of zinc and/or an element of silver.
3. The lithium metal anode of claim 1, wherein the molar ratio of the lithium philic elemental metal to the lithium fluoride is (2-3): 5.
4. The lithium metal anode of any of claims 1 to 3, wherein the composite protective layer has a thickness of 10 μm to 30 μm; and/or
The thickness of the metallic lithium body is 20-40 μm.
5. A preparation method of a lithium metal negative electrode is characterized by comprising the following steps:
providing a metal lithium matrix and a metal fluoride solution, wherein metal ions in the metal fluoride solution are lithium-philic metal ions;
and coating the metal fluoride solution on the surface of the metal lithium matrix in an inert environment for replacement reaction, and drying to obtain the lithium metal negative electrode.
6. The method of making a lithium metal anode of claim 5, wherein the method of making the metal fluoride solution comprises: and mixing the metal fluoride, the electrolyte lithium salt and the organic solvent to obtain a metal fluoride solution.
7. The method of manufacturing a lithium metal negative electrode according to claim 6, wherein the electrolyte lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium hexafluoroarsenate, lithium tetrafluoroborate; and/or
The organic solvent is at least one selected from dimethyl sulfoxide, tetrahydrofuran, ethylene carbonate, diethyl carbonate and dimethyl carbonate.
8. The method for manufacturing a lithium metal anode according to any one of claims 5 to 7, wherein the metal fluoride solution is at least one selected from a silver fluoride solution and a zinc fluoride solution; and/or
The concentration of the metal fluoride solution is 1mmol/L-10 mmol/L.
9. The method for preparing a lithium metal negative electrode according to any one of claims 5 to 7, wherein the step of applying the metal fluoride solution to the surface of the lithium metal substrate to perform a reaction is performed for a time ranging from 5min to 15min at a temperature ranging from 60 ℃ to 100 ℃.
10. A lithium secondary battery comprising a positive electrode and a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode, wherein the negative electrode is the lithium metal negative electrode according to any one of claims 1 to 4, or the lithium metal negative electrode produced by the method for producing the lithium metal negative electrode according to any one of claims 5 to 9.
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| CN106257714A (en) * | 2015-12-21 | 2016-12-28 | 上海卡耐新能源有限公司 | A kind of new system lithium ion battery and preparation method thereof |
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| CN112335077A (en) * | 2019-03-08 | 2021-02-05 | 株式会社Lg化学 | Negative electrode for lithium secondary battery, method for producing same, and lithium secondary battery comprising same |
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