EP3948991A1

EP3948991A1 - Composition for anode, and protective film, anode, and device comprising same

Info

Publication number: EP3948991A1
Application number: EP20894239.1A
Authority: EP
Inventors: Maohua Chen; Daguang Li; Yuansen Xie
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2019-11-28
Filing date: 2020-06-29
Publication date: 2022-02-09
Also published as: JP7177921B2; JP2022515951A; CN110911685A; EP3948991A4; CN110911685B; WO2021103523A1

Abstract

A composition for an anode, and a protective film, an anode and a device comprising the same are disclosed. The composition comprises a silicon material and a lithium ion conductor material having low electronic conductivity, wherein the electronic conductivity of the lithium ion conductor material is less than 1E-5 S/cm.

Description

[Title established by the ISA under Rule 37.2] COMPOSITION FOR ANODE, AND PROTECTIVE FILM, ANODE, AND DEVICE COMPRISING SAME

1. Field of the Invention

The present application relates to a composition used in the technical field of energy storage technologies, and a protective film comprising the composition. Particularly, the present application relates to a composition for preparing a protective film for a lithium metal anode and a protective film prepared therefrom. Further, the present application also relates to an electrochemical device and an electronic device comprising the lithium metal anode.

2. Description of the Related Art

Lithium-ion batteries have advantages, such as large specific energy, high working voltage, low self-discharge rate, small volume, and light weight, and are widely used in applications of consumer electronics. However, with the rapid development of electric vehicles and mobile electronic devices, there is higher and higher demand for energy density, safety, and cycle performance of batteries and the like. Among others, volume energy density and mass energy density are important parameters for measuring battery performance.
Lithium is a metal with the smallest relative atomic mass (6.94) and the lowest standard electrode potential (-3.045 V) among all metal elements, and has a theoretical gram capacity up to 3860 mAh/g. Therefore, using lithium metal as an anode in a battery in combination with certain cathode materials of high energy density can greatly increase the energy density and working voltage of batteries.
However, the practical commercialization of batteries with lithium metal as the anode material still faces the following problems:
1) The lithium metal itself is extremely active, and has a potential of -3.05 V relative to a standard hydrogen electrode. Freshly produced lithium metal has no passivation layer on the surface, and is prone to a series of side reactions with the electrolyte system, for example, reaction with a trace amount of hydrogen fluoride in the electrolyte forming lithium fluoride, or reaction with propylene carbonate, which is a common solvent in the electrolyte, generating C ₃H ₆OCO ₂Li, which causes the lithium metal and electrolyte to be consumed at the same time, and a coulombic efficiency during the cycles much lower than a commercial graphite anode (99%-99.9%) .
2) During the charging process of lithium metal batteries, lithium will be deposited on the surface of the anode current collector. Due to the non-uniformity of the current density and the lithium ion concentration in the electrolyte, the deposition rate is too fast at some sites during the deposition process, causing the formation of sharp dendritic structures. The presence of lithium dendrites will lead to a significant reduction in deposition density, which reduces energy density. In some lithium metal batteries, the actual deposition density of the lithium metal is about 0.2 g/cm ³, which is far less than the true density of lithium metal of 0.534 g/cm ³. Energy density will decrease by more than 100 Wh/L due to the loose deposition of the lithium metal. In addition, lithium dendrites may also pierce the separator, causing a short circuit and thus safety issues.
3) As the lithium metal anode is charged and discharged, the thickness of the anode will expand and contract drastically. This will easily incur peeling at the interface between the anode and other adjacent structures, resulting in a sharp increase in impedance, and in severe cases, even deformation of the whole battery.
Based on the above discussion, reducing side reactions of the lithium metal with the electrolyte, suppressing the growth of lithium dendrites, and solving the problems of interface peeling and fragmentation of the protective layer caused during the expansion-contraction process are essential conditions to be met for the commercialization of a lithium metal anode.
Silicon film can protect the surface of the lithium metal, and reduce contact between the electrolyte and lithium metal to reduce side reactions; and has high mechanical strength and can inhibit the growth of lithium dendrites. However, silicon materials chemically react with lithium to form Li _xSi. Li _xSi has high electronic conductivity, causing electrons to easily pass through the lithium metal and protective film to reach the surface of the protective film and to bind to Li ⁺ in the electrolyte. Ultimately, this causes lithium metal deposits to form on the surface of the protective film, leading to a lowered performance of the protective film in reducing side reactions and inhibiting lithium dendrites.
SUMMARY OF THE INVENTION
In order to solve the above technical problems, the present application provides a composition comprising a silicon material and a lithium ion conductor with low electronic conductivity. The composition can be used to prepare a protective film for an anode. In some embodiments, the electronic conductivity of the lithium ion conductor material is less than 1E-5 S/cm.
The lithium ion conductor material comprises at least one of LiF, Li ₃PO ₄, Li ₃N, LiPON, Li ₂O, Li ₄SiO ₄, LiAlO ₂, and lithium titanium phosphate (Li _x1Ti _y1 (PO ₄) ₃, wherein 0<x1<2 and 0<y1<3) , lithium aluminum titanium/germanium phosphate (Li _x2Al _y2 (Ti, Ge) _z2 (PO ₄) ₃, wherein 0<x2<2, 0<y2<1, and 0<z2<3) , Li _1+x3+y3 (Al, Ga) _x3 (Ti, Ge) _2-x3Si _y3P _3-y3O ₁₂ (wherein 0≤x3≤1 and 0≤y3≤1) , lithium lanthanum titanate (Li _x4La _y4TiO ₃, wherein 0<x4<2 and 0<y4<3) , lithium germanium thiophosphate (Li _x5Ge _y5P _z5S _w5, wherein 0<x5<10, 0<y5<1, 0<z5<2, and 0<w5<12) , SiS ₂ glass (Li _x6Si _y6S _z6, wherein 0≤x6<3, 0<y6<2, and 0<z6<4) , P ₂S ₅ glass (Li _x7P _y7S _z7, wherein 0≤x7<3, 0<y7<3, and 0<z7<7) , Li ₂O-Al ₂O ₃-SiO ₂-P ₂O ₅-TiO ₂-GeO ₂ ceramics, or Garnet ceramics (Li _3+x8La ₃N ₂O ₁₂, wherein 0≤x8≤5, and N is Te, Nb, or Zr) .
In some embodiments, the silicon material includes silicon, a silicon alloy SiM _y, or a combination thereof, wherein y<0.05, and M includes at least one of B, Al, P, Fe, Co, Ni, Zn, Ge, Ga, As, Zr, In or Sn.
In some embodiments, the molar ratio of the silicon material to the lithium ion conductor material is 1: 5 to 20: 1.
The present application also provides a protective film for an anode, which comprises the composition described herein. The anode comprises a lithium metal layer, and the protective film described herein is coated on the lithium metal layer of the anode. The protective film of the present application further comprises Li _xSi, wherein 1.5<x<4.0. Li _xSi has a lithium diffusion coefficient of 10 ^-14 to10 ^-10 cm ²/S. In some embodiments, Li _xSi has a strength greater than 10 GPa.
The protective film according to the present application has a thickness of 0.01 to 5 microns.
In the present application, the lithium metal layer includes at least one of lithium metal, a lithium alloy, or a lithium compound. In some embodiments, the lithium metal layer is a thin film layer or a powder layer. In some embodiments, the molar ratio of lithium element to silicon element in the lithium metal layer and the protective film is greater than 10: 1.
The present application also provides an anode comprising the composition or the protective film as described herein.
The present application provides an electrochemical device comprising the anode as described herein.
The present application provides an electronic device comprising the electrochemical device as described herein.

Brief description of the drawings

The following will briefly illustrate the accompanying drawings, which are necessary to describe the embodiments of the present application or the prior art, so as to facilitate depicting the embodiments of the present application. Obviously, the accompanying drawings described below show only some embodiments of the present application. For those skilled in the art, the drawings of other embodiments can still be obtained according to the structures illustrated in the drawings without any creative effort.
Fig. 1 shows a side view of the anode comprising the protective film according to the present application. As shown in Fig. 1, a lithium metal layer 2 is coated on the current collector 3, and the protective film 1 of the present application is coated on the lithium metal layer 2.
Fig. 2 shows a metal powder having a protective film according to the present application. As shown in Fig. 2, the particles of the lithium metal 4 are coated externally with a protective film 5 according to the present application.
Fig. 3 shows an SEM image at the cross section of the protective film according to the present application deposited on lithium metal. The layers in the figure are copper foil 6, lithium foil 7 and protective film 8 according to the present application in order from top to bottom.

Detailed Description

Embodiments of the present application will be described in detail below. Throughout the specification, the same or similar components and components having the same or similar functions are denoted by similar reference numerals. The embodiments described herein with respect to the drawings are illustrative and graphical, and are used for providing a basic understanding of the present application. The embodiments of the present application should not be interpreted as limitations to the present application.
As used in the present application, terms "approximately" , "substantially" , "essentially" , and "about" are used for describing and explaining a small variation. When being used in combination with an event or circumstance, the terms may refer to an example wherein the event or circumstance occurs precisely, and an example wherein the event or circumstance occurs approximately. For example, when being used in combination with a value, the terms may refer to a variation range of less than or equal to ±10%of the value, for example, less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, if the difference between two numerical values is less than or equal to ±10%of the average of the values (e.g., less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%) , the two values may be considered "substantially" the same.
In addition, sometimes, a quantity, a ratio, and another value are presented in a range format in the present application. It should be appreciated that such range formats are for convenience and conciseness, and should be flexibly understood as including not only values explicitly specified to range constraints, but also all individual values or sub-ranges within the ranges, like explicitly specifying each value and each sub-range.
In the detailed description and the claims, a list of items connected by the term "one of" or similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B and C" means only A; only B; or only C. The item A may include a single component or multiple components. The item B may include a single component or multiple components. The item C may include a single component or multiple components.
In the detailed description and the claims, a list of items connected by the term "at least one of" or similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B and C are listed, then the phrase "at least one of A, B and C" means only A; only B; only C; A and B (excluding C) ; A and C (excluding B) ; B and C (excluding A) ; or all of A, B and C. The item A may include a single component or multiple components. The item B may include a single component or multiple components. The item C may include a single component or multiple components.
I. Composition
A first aspect of the present application relates to a composition comprising a silicon material and a lithium ion conductor material having low electronic conductivity. In some embodiments, the electronic conductivity of the lithium ion conductor material is less than about 1E-5 S/cm. In particular, the electronic conductivity is less than about 5E-6 S/cm, less than about 1E-6 S/cm, less than about 5E-7 S/cm, less than about 1E-7 S/cm, less than about 5E-8 S/cm, less than about 1E-8 S/cm, less than about 5E-9 S/cm, or less than about 1E-9 S/cm. The electronic conductivity of the lithium ion conductor material needs to be greater than 1E-10 S/cm, for example, greater than about 1E-9 S/cm, greater than about 1E-8 S/cm, greater than about 1E-7 S/cm, greater than about 1E-6 S/cm, greater than about 1E-5 S/cm, greater than about 1E-4 S/cm, or any range therebetween.
In embodiments of the present application, the lithium ion conductor material comprises at least one of LiF, Li ₃PO ₄, Li ₃N, LiPON, Li ₂O, Li ₄SiO ₄, LiAlO ₂, lithium titanium phosphate (Li _x1Ti _y1 (PO ₄) ₃, wherein 0<x1<2 and 0<y1<3) , lithium aluminum titanium/germanium phosphate (Li _x2Al _y2 (Ti, Ge) _z2 (PO ₄) ₃, wherein 0<x2<2, 0<y2<1, and 0<z2<3) , Li _1+x3+y3 (Al, Ga) _x3 (Ti, Ge) _2-x3Si _y3P _3-y3O ₁₂ (wherein 0≤x3≤1 and 0≤y3≤1) , lithium lanthanum titanate (Li _x4La _y4TiO ₃, wherein 0<x4<2 and 0<y4<3) , lithium germanium thiophosphate (Li _x5Ge _y5P _z5S _w5, wherein 0<x5<10, 0<y5<1, 0<z5<2, and 0<w5<12) , SiS ₂ glass (Li _x6Si _y6S _z6, wherein 0≤x6<3, 0<y6<2, and 0<z6<4) , P ₂S ₅ glass (Li _x7P _y7S _z7, wherein 0≤x7<3, 0<y7<3, and 0<z7<7) , Li ₂O-Al ₂O ₃-SiO ₂-P ₂O ₅-TiO ₂-GeO ₂ ceramics, or Garnet ceramics (Li _3+x8La ₃N ₂O ₁₂, wherein 0≤x8≤5, and N is Te, Nb, or Zr) .
In some embodiments, the silicon material includes silicon, a silicon alloy SiM _y, or a combination thereof, wherein y<0.05, and M includes at least one of B, Al, P, Fe, Co, Ni, Zn, Ge, Ga, As, Zr, In or Sn, for example, a combination of In and Sn. In some instances, M includes any of B, Al, P, Fe, Co, Ni, Zn, Ge, Ga, As, Zr, In, or Sn.
In the composition of the present application, the molar ratio of the silicon material to the lithium ion conductor material is about 1: 5 to about 20: 1. In some embodiments, the molar ratio of the silicon material to the lithium ion conductor material is about 1: 4, about 1: 3, about 1: 2, about 1: 1, about 1.5: 1, about 2: 1, about 2.5: 1, about 3: 1, about 4: 1, about 5: 1, about 6: 1, about 7: 1, about 8: 1, about 9: 1, about 10: 1, about 15: 1, or a range between any two of the above ratios.
II. Protective film
The second aspect of the present application relates to a protective film for an anode, which comprises the composition described above, and the protective film is coated on the lithium metal layer of the anode.
In this application, the protective film is coated on the lithium metal layer, that is, between the lithium metal and the electrolyte. During a cycle, the silicon material in the composition can form a lithium-silicon alloy. Therefore, the protective film of the present application also includes Li _xSi, wherein 1.5<x<4.0, for example, x is 1.5, 2.0, 2.5, 3.0, 3.5, 4.0 or any range therebetween.
The lithium metal layer involved in the present application may include at least one of lithium metal, a lithium alloy, or a lithium compound. In some embodiments, the lithium metal layer may be in the form of a thin film layer or in the form of a powder layer. When the lithium metal layer is a thin film layer, lithium metal forms a uniform and dense thin layer on the substrate, for example, a lithium metal layer coated on a copper foil. When the lithium metal layer is a powder layer, the lithium metal in the form of a powder is coated on a substrate; and the protective film according to the present application is coated on the surface of the powder particles.
The thickness of the protective film according to the present application is about 0.01 to about 5 microns, for example, the thickness is about 0.05, about 0.1, about 0.5, about 1, about 2, about 3, or about 4 microns, or any range therebetween.
In some embodiments, Li _xSi has a lithium diffusion coefficient of about 10 ^-14 to 10 ^- ¹⁰cm ²/S. Preferably, Li _xSi has a lithium diffusion coefficient of about 10 ^-13 cm ²/S, about 10 ^-12 cm ²/S, about 10 ^-11 cm ²/, or about 10 ^-10 cm ²/S. In some embodiments, Li _xSi has a strength of greater than about 10 GPa, for example, the strength of Li _xSi is greater than about 11 GPa, greater than about 12 GPa or greater than about 13 GPa.
In some embodiments, the molar ratio of the lithium element to the silicon element in the lithium metal layer and the protective film is greater than about 10: 1, for example, greater than about 15: 1, greater than about 20: 1, greater than about 25: 1, or greater than about 30: 1.
The protective film provided in the present application can protect the interface of the lithium metal layer, reduce side reactions of the lithium metal layer with the electrolyte, improve coulombic efficiency, inhibit the growth of lithium dendrites, and improve cycle performance. Specifically, the silicon material in the protective film reacts with lithium to generate Li _xSi during the cycle, so that the bonding strength between the protective film and the lithium metal layer is effectively improved, and the protective film is prevented from peeling off during a dramatic volume change. Moreover, the Li _xSi provided in the present application has a high lithium diffusion coefficient (10 ^-14 to 10 ^-10 cm ²/S) and high mechanical strength (>10 GPa) , and can provide a lithium ion transport channel. In addition, a material with poor conductivity, that is, a lithium ion conductor with low electronic conductivity, is also introduced into the protective film of the present application. In this way, the electronic conductivity of the protective film can be reduced, thereby reducing the deposition of lithium on the lithium metal during the charge and discharge process, controlling the position of lithium deposition, improving the morphology of lithium deposition, and improving the cycling performance. To sum up, the protective film provided in the present application achieves the following beneficial technical effects through the combination of a specific silicon material and lithium ion conductor: the protective film can effectively isolate the electrolyte, provide an ion transmission channel, and meanwhile significantly suppress the growth of lithium dendrites.
III. Others
Another aspect of the present application also provides an anode comprising the composition or the protective film as described herein.
Another aspect of the present application also provides an electrochemical device comprising the anode as described herein.
Another aspect of the present application provides an electronic device comprising the electrochemical device as described herein.
The electrochemical device of the present application includes any device in which an electrochemical reaction takes place, and specific examples include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery. In some embodiments, the electrochemical device is a lithium ion battery.
In some embodiments, the electrochemical device according to the present application includes a cathode, an anode, and a separator, wherein the cathode comprises a cathode active material, and the anode comprises an anode active material.
Cathode
In the electrochemical device according to the present application, the cathode includes a current collector and a cathode active material layer provided on the current collector. The specific types of the cathode active material are not particularly limited, and may be selected as desired.
In some embodiments, the cathode active material comprises a compound that reversibly intercalates and deintercalates lithium ions. In some embodiments, the cathode active material comprises a composite oxide that contains lithium and at least one element selected from cobalt, manganese, or nickel. In some embodiments, the cathode active material comprises at least one of lithium cobalt oxide (LiCoO ₂) , a lithium nickel manganese cobalt ternary material, lithium manganese oxide (LiMn ₂O ₄) , lithium nickel manganese oxide (LiNi _0.5Mn _1.5O ₄) , and lithium iron phosphate (LiFePO ₄) .
In some embodiments, the cathode active material layer can have a coating on its surface or can be mixed with another compound having a coating.
The coating may include at least one coating element compound selected from an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, or a hydroxycarbonate of a coating element.
The compound used for the coating may be amorphous or crystalline.
The coating element contained in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, F or a mixture thereof.
The coating can be applied by any method as long as the method does not adversely affect the performance of the cathode active material. For example, the method may include any coating method known to those skilled in the art, such as spraying, dipping, and others.
In some embodiments, the cathode active material layer further comprises a binder, and optionally a conductive material.
The binder increases the binding of the cathode active material particles to each other and the binding of the cathode active material to the current collector. Non-limiting examples of the binder include, but are not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, poly (1, 1-vinylidene fluoride) , polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resins, Nylon and the like.
The cathode active material layer includes a conductive material to impart conductivity to the electrode. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the conductive material include a carbon-based material (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc. ) , a metal-based material (e.g., a metal powder, a metal fiber, etc., including for example copper, nickel, aluminum, silver, and the like) , a conductive polymer (for example, polyphenylene derivatives) and a mixture thereof.
The current collector used for the cathode of the secondary battery according to the present application may be aluminum (Al) , but is not limited thereto.
Separator
In some embodiments, the electrochemical device of the present application is provided with a separator between the cathode and the anode to prevent a short circuit. The material and shape of the separator used in the electrochemical device of the present application are not particularly limited, and may be any of those disclosed in prior art. In some embodiments, the separator includes a polymer or an inorganic substance or the like formed of a material which is stable against the electrolyte according to the present application.
For example, the separator may include a substrate layer and a surface treatment layer.
The substrate layer is a non-woven fabric, film, or composite film having a porous structure, and the material of the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Particularly, a porous polypropylene film, a porous polyethylene film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, and a porous polypropylene-polyethylene-polypropylene composite film may be used.
At least one surface of the substrate layer is provided with a surface treatment layer, which may be a polymer layer or an inorganic layer, or a layer formed with a mixture of a polymer and an inorganic material.
The inorganic layer comprises inorganic particles and a binder. The inorganic particles include one of alumina, silica, magnesia, titania, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate, or a combination of more than one thereof. The binder includes one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a polyamide, polyacrylonitrile, a polyacrylic ester, polyacrylic acid, a polyacrylic salt, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene, or a combination of more than one thereof.
The polymer layer contains a polymer, and the material of the polymer includes at least one of a polyamide, polyacrylonitrile, a polyacrylic ester, polyacrylic acid, a polyacrylic salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene) .
In another aspect, the present application also provides an electronic device comprising the electrochemical according to the present application.
The electrochemical device according to the present application is suitable for use in electronic devices in various fields. The use of the electrochemical device of the present application is not particularly limited and can be used for any purpose known in the art. In an embodiment, the electrochemical device according to the present application is applicable to, without limitation, notebook computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, minidisc players, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power sources, motors, vehicles, motorcycles, scooters, bicycles, lighting apparatus, toys, game consoles, clocks, electric tools, flash lights, cameras, large batteries for household use, and lithium ion capacitors.
Examples
The implementations of the present application are exemplified below with reference to embodiments. It should be understood that these embodiments are only used to illustrate the present application and are not intended to limit the protection scope of the present application.
Examples 1-13
1. Preparation of anode
1.1 Preparation of protective film for anode:
Examples 1-11 exemplify technical solutions wherein the lithium metal layer is a thin film layer. The deposition material was deposited on the side of the lithium metal layer of a lithium-coated copper foil by magnetron sputtering. The molar ratio of each component in the material and the thickness of the protective film obtained by the deposition are listed in Table 1 below.
Examples 12 and 13 exemplify technical solutions wherein the lithium metal layer is a powder layer. By magnetron sputtering, silicon and lithium fluoride were simultaneously deposited on a lithium metal containing carbon powder, wherein the molar ratio of silicon to lithium was 2: 1, and the thickness of the protective film deposited in Examples 12 and 13 was 0.1 and 0.01 μm, respectively.
1.2 Preparation of anode
Examples 1-11: The anode was cut to have a diameter of 18mm for use.
Examples 12 and 13: A powder material containing a composite anode protective layer was mixed with conductive carbon black (Super P) , polystyrene butadiene (SBR) , and polystyrene (PS) at a weight ratio of 80: 10: 5: 5, and p-xylene was added as a solvent, to prepare a slurry with a solid content of 0.2, which was then stirred evenly. The slurry was uniformly coated on a copper foil as an anode current collector, and dried at 70℃ to obtain an anode. The anode was then cut to have a diameter of 18mm for use.
2 Preparation of electrolyte
Under a dry argon atmosphere, the organic solvents of ethylene carbonate (EC) , ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed at a weight ratio of EC:EMC: DEC = 30: 50: 20, and then lithium hexafluorophosphate (LiPF ₆) was added to the mixture, dissolved and mixed fully, to obtain an electrolyte with lithium salt at a concentration of 1.15M.
3. Preparation of symmetrical batteries
A polyethylene (PE) film with a thickness of 15 μm was used as the separator, and two anodes were respectively placed at each side of the separator, with the lithium metal side of the anode facing the separator. Then 75 μl of electrolyte was injected, and a button cell was assembled.
Comparative Examples 1-4
In Comparative Example 1, no protective film was used, and the lithium-coated copper foil was directly cut to have a diameter of 18 mm for use.
In Comparative Example 2, only silicon was deposited on the lithium metal layer side of the lithium-coated copper foil, that is, the protective film contained only silicon without a lithium ion conductor having low electronic conductivity. The deposition thickness was 1 micron. The other steps were the same as in Example 1.
In Comparative Example 3, only lithium fluoride was deposited on the lithium metal layer side of the lithium-coated copper foil, that is, the protective film contained only lithium fluoride without a silicon material. The deposition thickness was 1 micron. The other steps were the same as in Example 1.
In Comparative Example 4, the lithium metal layer was in the form of a powder layer, but the powder layer did not have the protective film according to the present application. A lithium metal-containing carbon powder without any surface treatment was mixed with conductive carbon black (Super P) , polystyrene butadiene (SBR) , and polystyrene (PS) at a weight ratio of 80: 10: 5: 5, and p-xylene was added as a solvent, to prepare a slurry with a solid content of 0.2, which was then stirred evenly. The slurry was uniformly coated on a copper foil as an anode current collector, and dried at 70℃ to obtain an anode. The anode was then cut to have a diameter of 18mm for use. The other steps were the same as in Example 1.
Method for testing cycle numbers of batteries
The symmetrical battery was activated by discharging and charging for 15 hrs at a current density of 0.1 mA/cm ². Then the battery was cyclically discharged and charged at a current density of 0.6 mA/cm ², wherein both the charge and discharge time was set as 3 hrs. When the voltage during the cycle dropped sharply to a value of lower than 40 mV, the corresponding number of cycles was recorded as the cycle numbers of the symmetrical battery.
Table 1. Related parameters and test results of Examples 1-13 and Comparative Examples 1-4
In Table 1 as above, the electronic conductivity of LiF and Li ₃PO ₄ is less than 10 ^-10 S/cm; the electronic conductivity of Li ₃N is less than 10 ^-12 S/cm; and the electronic conductivity of Li ₇La ₃Zr ₂O ₁₂ and Li _1.3Al _0.3Ge _1.7 (PO ₄) ₃ is less than 10 ^-7 S/cm.
The ratios of Si to LiF in Examples 1, 4, and 5 are different, resulting in a change in the cycle numbers of the symmetrical batteries. This is because when the proportion of Si is high (Example 4) , due to the high electronic conductivity of Si itself, lithium tends to deposit on the anode protection layer, and lithium dendrites grow, causing a short circuit. When the proportion of Si is low (Example 5) , the bonding strength between the protective layer and lithium metal is reduced, and the protective effect is also reduced.
Throughout the specification, references to “embodiment” , “part of the embodiments” , “one embodiment” , “another example” , “example” , “specific example” or “part of the examples” mean that at least one embodiment or example of the present application includes specific features, structures, materials or characteristics described in the embodiment or example. Thus, the descriptions appearing throughout the specification, such as "in some embodiments, " "in an embodiment, " "in one embodiment, " "in another example, " "in an example, " "in a particular example" or "for example, " are not necessarily the same embodiment or example in the application. Furthermore, the specific features, structures, materials or characteristics in the descriptions can be combined in any suitable manner in one or more embodiments or examples.
Although the illustrative embodiments have been shown and described, it should be understood by those skilled in the art that the above embodiments cannot be interpreted as limitations to the present application, and the embodiments can be changed, substituted and modified without departing from the spirit, principle and scope of the present application.

Claims

A composition for preparing a protective film for an anode, comprising:

a silicon material; and

a lithium ion conductor material having low electronic conductivity.
The composition according to claim 1, wherein the electronic conductivity of the lithium ion conductor material is less than 1E-5 S/cm.
The composition according to claim 1, wherein the silicon material comprises silicon, a silicon alloy SiM _y, or a combination thereof, wherein y<0.05, and M includes at least one of B, Al, P, Fe, Co, Ni, Zn, Ge, Ga, As, Zr, In or Sn.
The composition according to claim 1, wherein a molar ratio of the silicon material to the lithium ion conductor material is 1: 5 to 20: 1.
The composition according to claim 1, wherein the lithium ion conductor material comprises at least one of

LiF; Li ₃PO ₄; Li ₃N; LiPON; Li ₂O; Li ₄SiO ₄; LiAlO ₂; Li _x1Ti _y1 (PO ₄) ₃, wherein 0<x1<2 and 0<y1<3; Li _x2Al _y2 (Ti, Ge) _z2 (PO ₄) ₃, wherein 0<x2<2, 0<y2<1, and 0<z2<3; Li _1+x3+y3 (Al, Ga) _x3 (Ti, Ge) _2-x3Si _y3P _3-y3O ₁₂, wherein 0≤x3≤1 and 0≤y3≤1; Li _x4La _y4TiO ₃, wherein 0<x4<2 and 0<y4<3; Li _x5Ge _y5P _z5S _w5, wherein 0<x5<10, 0<y5<1, 0<z5<2, and 0<w5<12; Li _x6Si _y6S _z6, wherein 0≤x6<3, 0<y6<2, and 0<z6<4; Li _x7P _y7S _z7, wherein 0≤x7<3, 0<y7<3, and 0<z7<7; Li ₂O-Al ₂O ₃-SiO ₂-P ₂O ₅-TiO ₂-GeO ₂ ceramics; or Li _3+x8La ₃N ₂O ₁₂, wherein 0≤x8≤5, and N is Te, Nb, or Zr.
A protective film for an anode, comprising a composition according to any one of claims 1 to 5, wherein the anode comprises a lithium metal layer, and the protective film is coated on the lithium metal layer of the anode.
The protective film according to claim 6, further comprising Li _xSi, wherein 1.5<x<4.0.
The protective film according to claim 6, which has a thickness of 0.01 to 5 microns.
The protective film according to claim 6, wherein the lithium metal layer comprises at least one of lithium metal, a lithium alloy, or a lithium compound.
The protective film according to claim 6, wherein the lithium metal layer is a thin film layer or a powder layer.
The protective film according to claim 6, wherein a molar ratio of the lithium element to the silicon element in the lithium metal layer and the protective film is greater than 10: 1.
The protective film according to claim 7, wherein the Li _xSi has a lithium diffusion coefficient of 10 ^-14 to 10 ^-10 cm ²/S, and the Li _xSi has a strength of greater than 10 GPa.
An anode, comprising the composition according to any one of claims 1 to 5 or the protective film according to any one of claims 6 to 12.
An electrochemical device, comprising the anode according to claim 13.
An electronic device, comprising the electrochemical device according to claim 14.