JP7177921B2 - Composition used for negative electrode, and protective film, negative electrode and device containing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a composition used in the technical field of energy storage and a protective film containing the same. In particular, the present invention relates to compositions for producing protective films for lithium metal negative electrodes, and protective films produced therewith. In addition, the present invention further relates to electrochemical devices and electronic equipment comprising said lithium metal negative electrode.

Lithium-ion batteries have advantages such as high specific energy, high operating voltage, low self-discharge rate, small volume and light weight, and are widely applied in the field of electronic equipment. However, with the rapid development of electric vehicles and portable electronic devices, the demands on battery energy density, safety and cycle performance are becoming higher and higher. Among them, volumetric energy density and mass energy density are important parameters for evaluating battery performance.

Lithium metal is the metal with the lowest relative atomic mass (6.94) and the lowest standard electrode potential (−3.045 V) among all metallic elements, and its theoretical capacity reaches 3860 mAh/g. Therefore, when lithium metal is used as the negative electrode of the battery and some positive electrode material with high energy density is also used, the energy density of the battery and the operating voltage of the battery can be greatly improved.

However, there are the following drawbacks for full-scale commercialization of batteries using lithium metal as a negative electrode material.
1) Lithium metal itself is extremely active, having a potential of −3.05 V versus a standard hydrogen electrode. Since there is no passivation film on the surface of lithium metal that has just been produced, a series of side reactions with the electrolyte system are extremely likely to occur. For example, it reacts with a trace amount of hydrogen fluoride in the electrolyte to generate lithium fluoride, or reacts with propylene carbonate, which is a common solvent used in the electrolyte, to generate C ₃ H ₆ OCO ₂ Li. As a result, lithium metal and electrolyte are depleted at the same time, and the coulombic efficiency of the cycle is much lower than that of commercial graphite anodes (99%-99.9%).
2) In lithium metal batteries, lithium may deposit on the surface of the current collector of the negative electrode during charging. Due to non-uniform current density and concentration of lithium ions in the electrolyte, the deposition rate may be too fast at some points during the deposition process, and may produce sharp dendrite structures. The presence of lithium dendrites results in significantly lower deposition densities and lower energy densities. In some lithium metal batteries, the actual deposited density of lithium metal is about 0.2 g/cm ³ , much less than its true density of 0.534 g/cm ³ . Energy density can drop by more than 100 Wh/L due to sparse deposition of lithium metal. Also, if the lithium dendrite penetrates the separator, a short circuit may occur, posing a safety hazard.
3) The thickness of the negative electrode sheet may rapidly shrink as the lithium metal negative electrode is charged and discharged. As a result, the negative electrode sheet is very likely to be peeled off from the interface with other adjacent structures, the resistance rises sharply, and in serious cases, the deformation of the entire battery may occur.

In view of the above situation, reducing the side reaction between lithium metal and electrolyte, suppressing the growth of lithium dendrites, and solving the problem of interfacial peeling and protective layer breakage during shrinkage will make the application of lithium metal anodes commercial. It is a necessary condition to make it happen.

The silicon thin film can not only protect the surface of the lithium metal, reduce the contact between the electrolyte and the lithium metal, reduce side reactions, but also have high mechanical strength and suppress the growth of lithium dendrites. can. However, silicon materials can chemically react with lithium to form Li _x Si. Since Li _x Si has high electrical conductivity, electrons can easily pass through the lithium metal and the protective film, reach the surface of the protective film, combine with Li ⁺ in the electrolyte, and finally, protect Lithium metal deposits on the surface of the film. As a result, the ability of the overcoat to mitigate side reactions and suppress lithium dendrites is reduced.

In order to solve the above problems, the present invention provides a composition for manufacturing a negative electrode protective film, comprising a silicon material and a lithium ion conductor with low electronic conductivity. In some examples, the lithium ion conductor material has an electronic conductivity of less than 1×10 ⁻⁵ S/cm.

Lithium ion conductor materials include LiF, _{Li3PO4 , Li3N} , LiPON, _{Li2O, Li4SiO4, LiAlO2, lithium titanium phosphate (Lix1Tiy1 ( PO4 ) 3 , provided that} 0<x1<2 and 0<_{y1<3), lithium aluminum titanium/germanium phosphate (Lix2Aly2 (} Ti,Ge) _z2 (PO4) ₃ , where 0<x< ₂ , 0<y<1 and 0<z<3), Li _1+x3+y3 (Al, Ga) _x3 (Ti, Ge) _2-x3 Si _y P _3-y3 O ₁₂ (where 0≦x3≦1 and 0≦ y3≦1), lithium lanthanum titanate (Li _x4 La _y4 TiO ₃ , where 0<x4<2 and 0<y4<3), lithium germanium thiophosphate (Li _x5 Ge _y5 P _z5 S _w5 , However, 0<x5<10, 0<y5<1, 0<z5<2, and 0<w5<12), _SiS2 glass (Li _x6 Si _y6 S _z6 , where 0≤x6<3, 0<y6< ₂ and 0<z6<4), _P2S5 glass ( _Lix7Py7Sz7 , _{where 0≤x7} <3, 0<y7<3 and 0<z7<7), Li 2O—Al ₂ O ₃ —SiO ₂ —P ₂ O ₅ —TiO ₂ —GeO ₂ ceramics or garnet ceramics (Li _{3 +x8} La ₃ N ₂ O ₁₂ , where 0≦x8≦5, and N is Te, Nb, or Zr).

In some embodiments, the silicon material is silicon, formula: SiM _y where y<0.05 and M is B, Al, P, Fe, Co, Ni, Zn, Ge, Ga, As, Zr , including at least one of In and Sn), or combinations thereof.

In some embodiments, the molar ratio of silicon material to lithium ion conductor material is between 1:5 and 20:1.

Further, the present invention provides a negative electrode protective film comprising a lithium metal layer, the negative electrode protective film comprising the composition according to the present invention and covering the lithium metal layer. The protective film according to the present invention further includes Li _x Si (where 1.5<x<4.0). Li _x Si has a lithium diffusion coefficient of 10 ⁻¹⁴ to 10 ⁻¹⁰ cm ² /S. In some examples, the Li _x Si has a strength greater than 10 GPa.

The protective film according to the present invention has a thickness of 0.01 μm to 5 μm.

In the present invention, the lithium metal layer includes at least one of lithium metal, lithium alloys and lithium compounds. In some examples, the lithium metal layer is a thin film layer or a powder layer. In some embodiments, the lithium metal layer and said overcoat have a molar ratio of lithium element to silicon greater than 10:1.

Furthermore, the present invention provides a negative electrode comprising the composition or protective film according to the present invention.

Furthermore, the present invention provides an electrochemical device including the negative electrode according to the present invention.

Furthermore, the present invention provides electronic equipment including the electrochemical device according to the present invention.

In the following, in order to explain the embodiments of the present invention for convenience, the drawings necessary for explaining the embodiments of the present invention and the prior art will be briefly described. Of course, the drawings described below represent only some of the embodiments of the present invention. Those skilled in the art can obtain drawings of other embodiments based on the configurations shown in these drawings to the extent that creative effort is not required.
1 is an electrode sheet (side view) comprising a protective film according to the invention; As shown in FIG. 1, a lithium metal layer 2 covers a current collector 3 and a protective film 1 according to the present invention covers the lithium metal layer 2 . 1 shows a metal powder with a protective film according to the invention; FIG. As shown in FIG. 2, the exterior of the particles of lithium metal 4 is coated with a protective coating 5 according to the invention. [0019] Figure 4 is a SEM lateral cross-section of a protective film according to the present invention deposited on lithium metal; In FIG. 3, a copper foil 6, a lithium foil 7 and a protective film 8 according to the present invention are shown in order from the top.

Embodiments according to the invention are described in detail below. Throughout the description of the present invention, the same or similar parts or parts having the same or similar functions are indicated with similar reference numerals. The embodiments described herein with respect to the drawings are descriptive and illustrative and provide a basic interpretation of the invention. It should be understood that the embodiments in accordance with the invention described herein are not intended to limit the scope of the invention.

The terms "approximately," "approximately," "substantially," and "about" as used herein are intended to describe and describe small changes. When used according to a circumstance or occasion, the term may refer to instances in which the circumstance or occurrence occur exactly as well as instances in which it occurs very closely. For example, when used in conjunction with numerical values, each of the above terms may mean a range of variation within ±10% of the numerical value, and within ±5%, within ±4%, within ±3%, It may mean within ±2%, within ±1%, within ±0.5%, within ±0.1%, or within ±0.05%. For example, if the difference between the two numerical values is within ±10% of the average value of the two (or within ±5%, within ±4%, within ±3%, within ±2%, within ±1%, within ±0. 5%, within ±0.1%, or within ±0.05%), the two numbers may be understood to be "approximately" the same.

A range format may also be used herein to express quantities, ratios, or other numerical values. It is noted that this range format is employed for convenience and brevity and is intended to include only numerical values specifically limited in that range, as well as any values subsumed within that range. Inclusion of individual numerical values or subranges should be understood flexibly and is equivalent to explicitly specifying any numerical value or subrange.

Particular embodiments and claims include "any one of", "one of", "of" connecting to a list containing multiple items. "a" or other similar term means any one of the items referred to. For example, if items A and B are listed, "one of A and B" means only A or only B. In another example, "one of A, B, and C" means only A, only B, or only C, when item A, item B, and item C are listed. Item A may comprise a single element or multiple elements, Item B may comprise a single element or multiple elements, and Item C may comprise a single element or multiple elements. .

Particular embodiments and claims include "at least one of", "at least one of", "at least one of" connecting to a list containing a plurality of items. "One" or other similar term means any combination of the items referred to. For example, if items A and B are listed, "at least one of A and B" means A only, B only, or A and B. In another example, given items A, B and C, "at least one of A, B and C" means A only, B only, C only, A and B (with C means A and C (except B), B and C (except A), or all of A, B and C. Item A may comprise a single element or multiple elements, Item B may comprise a single element or multiple elements, and Item C may comprise a single element or multiple elements. .

1. Composition A first aspect of the present invention relates to a composition comprising a silicon material and a lithium ion conductor material having low electronic conductivity. In some embodiments, the lithium ion conductor material has an electronic conductivity of less than about 1×10 ⁻⁵ S/cm, particularly an electronic conductivity of less than about 5×10 ⁻⁶ S/cm, about 1 Less than ×10 ⁻⁶ S/cm, less than approximately 5×10 ⁻⁷ S/cm, less than approximately 1×10 ⁻⁷ S/cm, less than approximately 5×10 ⁻⁸ S/cm, approximately 1×10 ⁻⁸ S/cm cm, less than about 5×10 ⁻⁹ S/cm, or less than about 1×10 ⁻⁹ S/cm. Also, the ion conductor material has a lithium ion conductivity of greater than 1×10 ⁻¹⁰ S/cm, for example, greater than approximately 1×10 ⁻⁹ S/cm, greater than approximately 1×10 ⁻⁸ S/cm, approximately greater than 1×10 ⁻⁷ S/cm, greater than about 1×10 ⁻⁶ S/cm, greater than about 1×10 ⁻⁵ S/cm, or greater than about 1×10 ⁻⁴ S/cm; It may range between any two numbers.

In embodiments of the present invention, the lithium ion conductor materials include LiF, _{Li3PO4 , Li3N} , LiPON, _Li2O , _Li4SiO4 , _LiAlO2 , lithium titanium _{phosphate ( Lix1Tiy1} ( PO ₄ ) ₃ with 0<x1<2 and 0<y1<3.), lithium aluminum titanium/germanium phosphate (Li _x2 Al _y2 (Ti, Ge) _z2 (PO ₄ ) ₃ with 0<x<2, 0<y<1, and 0<z<3.), Li _1+x3+y3 (Al, Ga) _x3 (Ti, Ge) _2-x3 Si _y P _3-y3 O ₁₂ (where 0 ≤ x3 ≤ 1 and 0 ≤ y3 ≤ 1.), lithium lanthanum titanate (Li _x4 La _y4 TiO ₃ , where 0 < x4 < 2 and 0 < y4 < 3.), lithium germanium thiophosphate salt (Li _x5 Ge _y5 P _z5 S _w5 where 0<x5<10, 0<y5<1, 0<z5<2, and 0<w5<12.), _SiS2 glass (Li _x6 Si _y6 S _z6 for 0≤x6<3, 0<y6< ₂ and 0<z6<4), _P2S5 glass (Li _{x7 Py7S} z7 for _0≤x7 <3, 0<y7< 3, and 0<z7<7.), Li ₂ O—Al ₂ O ₃ —SiO ₂ —P ₂ O ₅ —TiO ₂ —GeO ₂ ceramics, or garnet ceramics (Li _3+x8 La ₃ N ₂ O ₁₂ , provided that , 0≦x8≦5, and N is Te, Nb, or Zr.).

In some embodiments, the silicon material is silicon, formula: SiM _y where y<0.05 and M is B, Al, P, Fe, Co, Ni, Zn, Ge, Ga, As , Zr, In and Sn, for example, a combination of In and Sn, or a combination thereof. In some cases, M may include any one of B, Al, P, Fe, Co, Ni, Zn, Ge, Ga, As, Zr, In and Sn.

In compositions according to the present invention, the molar ratio of silicon material to lithium ion conductor material is from about 1:5 to about 20:1. In some embodiments, the molar ratio of silicon material to 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 It may be 15:1, or a range between any two of the above ratios.

2. Protective Film A second aspect of the present invention relates to a protective film for a negative electrode having a lithium metal layer, the protective film comprising the composition described above and covering the lithium metal layer.

In the present invention, the protective film covers the lithium metal layer, ie is interposed between the lithium metal and the electrolyte. During the cycling process, the silicon material in the composition forms a lithium silicon alloy. Therefore, the protective film according to the present invention contains Li _x Si (where 1.5<x<4.0, where x is 1.5, 2.0, 2.5, 3.0, 3 .5, 4.0, or a range between any two numbers above.

A lithium metal layer according to the present invention may comprise 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 a powder layer. When the lithium metal layer is a thin film layer, the lithium metal forms a uniform dense thin layer on the substrate, for example, coating a copper foil with the lithium metal layer. When the lithium metal layer is a powder layer, the lithium metal is applied to the substrate in powder form and the protective film described in the present invention will coat the surface of the powder particles.

The protective film according to the present invention has a thickness of about 0.01 μm to about 5 μm, for example, a thickness of about 0.05 μm, about 0.1 μm, about 0.5 μm, about 1 μm, about 2 μm, about 3 μm, It may be about 4 microns, or a range between any two numbers above.

In some embodiments, Li _x Si has a lithium diffusion coefficient of about 10 ⁻¹⁴ −10 ⁻¹⁰ cm ² /S. Preferably, Li _x Si 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. good too. In some examples, the Li _x Si may have a strength greater than about 10 GPa, such as a strength greater than about 11 GPa, greater than about 12 GPa, or greater than about 13 GPa.

In some embodiments, the lithium metal layer and protective film have a molar ratio of lithium to silicon greater than about 10:1, such as greater than about 15:1, greater than about 20:1, greater than about 25:1. greater than, or greater than about 30:1.

The protective film provided by the present invention can protect the interface of the lithium metal layer, reduce the side reaction between the lithium metal layer and the electrolyte, increase the coulombic efficiency, suppress the growth of lithium dendrites, and improve the cycle effect. can be done. Specifically, the silicon material in the protective film reacts with lithium to produce Li _x Si during the cycling process, thereby effectively improving the bonding strength between the protective film and the lithium metal layer. It is possible to avoid peeling of the protective film when the volume changes abruptly. Moreover, the Li _x Si provided by the present invention has a higher lithium diffusion coefficient (10 ⁻¹⁴ −10 ⁻¹⁰ cm ² /S) and high mechanical strength (>10 GPa), providing a channel for transferring lithium ions. can do. In addition, a low-conductivity material, that is, a lithium-ion conductor having low electronic conductivity, was introduced into the protective film according to the present invention. With such a form, the electronic conductivity of the protective film can be lowered, the deposition of lithium metal on lithium metal during the charging and discharging process can be reduced, the deposition position of lithium can be controlled, and the deposition shape of lithium can be reduced. can be improved and cycle performance can be enhanced. As described above, the protective film provided by the present invention effectively isolates the electrolytic solution, provides a channel for transferring ions, and significantly promotes the growth of lithium dendrites by combining the specified silicon material and the lithium ion conductor. It is possible to achieve the beneficial effect of being able to suppress the

3. Others Another aspect of the present invention further provides a negative electrode comprising the composition or protective film described above.
Yet another aspect of the invention relates to an electrochemical device comprising the negative electrode described above.
Another aspect of the present invention provides electronic equipment including the electrochemical device described above.

The electrochemical device according to the invention may be any device in which an electrochemical reaction occurs, specific examples being primary cells, secondary cells, fuel cells, solar cells or capacitors of any kind. In particular, the electrochemical device is a lithium secondary battery, such as a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. In some examples, the electrochemical device is a lithium ion battery.

In some embodiments, an electrochemical device according to the present invention includes a positive electrode sheet including positive electrode active material, a negative electrode sheet including negative electrode active material, and a separator.

<Positive electrode>
A positive electrode sheet included in an electrochemical device according to the present invention includes a current collector and a positive electrode active material layer disposed on the current collector. A specific type of positive electrode active material is not specifically specified, and may be selected according to need.

In some examples, the positive electrode active material includes a compound that reversibly absorbs and releases lithium ions. In some examples, the positive electrode active material may include a composite oxide, the composite oxide including lithium and at least one of cobalt, manganese, and nickel. In some more embodiments, the positive electrode active material is lithium cobaltate ₍ LiCoO2), lithium nickel manganese cobalt ternary material, lithium manganate ₍ LiMn2O4), lithium nickel manganate _{( LiNi0.5Mn 1.5} O ₄ ), lithium iron phosphate (LiFePO ₄ ).

In some embodiments, the positive electrode active material layer may have a coating layer on its surface or may be mixed with other compounds that have a coating layer.

The coating layer comprises at least one of a coating element oxide, a coating element hydrogen oxide, a coating element hydroxy oxide, a coating element oxycarbonate, or a coating element hydroxycarbonate. A coating element compound may also be included.

The compound used in the coating layer may be amorphous or crystalline.

Coating elements included in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, F, or mixtures thereof. .

Any method may be used to apply the coating layer as long as it does not adversely affect the performance of the positive electrode active material. For example, the method can be any coating method known to those skilled in the art, such as spraying or impregnation.

In some examples, the positive electrode active material layer further includes a binder and may optionally include a conductive material.

The binder can strengthen the bonding between the particles of the positive electrode active material and also strengthen the bonding between the positive electrode active material and the current collector. Binders include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyethylene fluoride, ethyleneoxy-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene. , styrene-butadiene rubber, acrylated (esterified) styrene-butadiene rubber, epoxy resin, nylon, and the like, but are not limited to these.

The positive electrode active material layer can provide electrical conductivity to the electrode by including a conductive material. Said conductive material may comprise any conductive material as long as it does not cause a chemical change. Examples of conductive materials include carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, cochin black, carbon fiber, etc.), metal-based materials (such as copper, nickel, aluminum, and silver containing metal powders and metals). fibers, etc.), conductive polymers (eg, polyphenylene derivatives), and mixtures thereof.

The current collector used in the positive electrode sheet of the secondary battery according to the present invention may be aluminum (Al), but is not limited thereto.

<Separator>
In some embodiments, electrochemical devices of the present invention have a separator between the positive and negative electrodes to prevent short circuits. The material and shape of the separator used in the electrochemical device according to the present invention are not particularly limited, and any technique disclosed in the prior art may be used. In some embodiments, the separator may include a polymer, inorganic material, or the like formed of materials that are stable to the electrolyte of the present invention.

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. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

A surface treatment layer is provided on at least one surface of the base material layer. The surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic material.

The inorganic layer contains inorganic particles and a binder. Inorganic particles include alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, hydroxide It may also include one or a combination of more than one of magnesium, calcium hydroxide and barium sulfate. Binders include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, poly It may also include one or a combination of tetrafluoroethylene and polyhexafluoropropylene.

The polymer layer includes a polymer, and the material of the polymer is polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, poly(vinylidene fluoride-hexa fluoropropylene).

Another aspect of the present invention provides electronic equipment including the electrochemical device described above.

The electrochemical device according to the present invention can be applied to electronic equipment in various fields. The electrochemical device according to the present invention is not particularly limited in its application and can be used in any application known in the prior art. In one embodiment, the electrochemical device of the present invention is a notebook computer, a pen-based computer, a mobile computer, an e-book player, a mobile phone, a mobile facsimile, a mobile copier, a mobile copier, a head-mounted stereo headphone, a video Recorders, LCD TVs, handy cleaners, portable CD players, minidiscs, transceivers, electronic notebooks, calculators, memory cards, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric assisted bicycles, bicycles, lighting equipment , toys, game machines, watches, power tools, flashes, cameras, large storage batteries for home use, and electronic equipment such as lithium-ion capacitors, but not limited thereto.

EXAMPLES Examples according to the present invention will be described below with reference to examples. It should be understood that these examples are merely illustrative of the present invention and are not intended to limit the scope of protection of the present invention.

Examples 1-13
1. 1. Manufacture of Negative Electrode Sheet 1.1 Manufacture of Negative Electrode Protective Film In Examples 1 to 11, technical solutions in which the lithium metal layer is a thin film layer are illustrated and explained. The deposition material was deposited on one side of the lithium metal layer on the lithium coated copper foil by magnetron sputtering. The molar ratio of each component in the material and the thickness of the deposited protective film are shown in Table 1 below.
In Examples 12 and 13, the technical solution in which the lithium metal layer is a powder layer is illustrated and explained. Silicon and lithium fluoride were co-deposited on lithium metal-containing carbon powder by magnetron sputtering, where the molar ratio of silicon to lithium was 2:1. In Examples 12 and 13, the deposited protective films are 0.1 μm and 0.01 μm thick, respectively.

1.2 Production of negative electrode sheet,
In Examples 1 to 11, the electrode sheets were cut into specifications with a diameter of 18 mm and subjected to the next step.
In Examples 12 and 13, the powder material having a composite negative electrode protective layer, conductive carbon black (Super P), polystyrene butadiene (SBR), and polystyrene (PS) were mixed at 80:10:5: They were mixed at a weight ratio of 5, p-xylene was added as a solvent, and stirred uniformly so as to prepare a slurry with a solid content of 0.2. The resulting slurry was uniformly applied to a copper foil as a current collector for the negative electrode, and dried at 70° C. to obtain a negative electrode sheet. Next, the electrode sheet was cut to a specification with a diameter of 18 mm and subjected to the next step.

2. Preparation of Electrolyte In a dry argon atmosphere, first, organic solvents ethylene carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) were dissolved in a mass ratio of EC:EMC:DEC = 30:50:20. Next, lithium hexafluorophosphate (LiPF ₆ ), which is a lithium salt, is added to the organic solvent, dissolved, and uniformly mixed to obtain an electrolytic solution having a lithium salt concentration of 1.15M. rice field.

3. Fabrication of Symmetrical Battery Polyethylene (PE) with a thickness of 15 μm was used as the separator, and two negative electrode sheets were each placed on either side of the separator with one side of the lithium metal layer facing the separator. Next, 75 μl of electrolyte was poured to assemble a button battery.

Contrast 1-4
For Control 1, no protective film was used, and the lithium-coated copper foil was used directly cut to 18 mm diameter specifications.
In Control 2, only silicon was deposited on one side of the lithium metal layer of the lithium-coated copper foil, ie, the protective film contained only silicon and no low electronic conductivity lithium ion conductor. The deposited thickness was 1 μm. Other than the above, the same operations as in Example 1 were performed.
In Control 3, only lithium fluoride was deposited on one side of the lithium metal layer of the lithium-coated copper foil, ie, the protective film contained only lithium fluoride and no silicon material. The deposited thickness was 1 μm. Other than the above, the same operations as in Example 1 were performed.
In contrast 4, the lithium metal layer was in the form of a powder layer, but this powder layer did not have the protective coating according to the invention. Lithium metal-containing carbon powder without any surface treatment, conductive carbon black (Super P), polystyrene butadiene (SBR), and polystyrene (PS) were mixed in a weight ratio of 80:10:5:5. , p-xylene was added as a solvent and stirred uniformly so as to prepare a slurry with a solid content of 0.2. The resulting slurry was uniformly applied to a copper foil as a current collector for the negative electrode, and dried at 70° C. to obtain a negative electrode sheet. Next, the electrode sheet was cut to a specification with a diameter of 18 mm and subjected to the next step. Other than the above, the same operations as in Example 1 were performed.

上記の表１には、ＬｉＦ及びＬｉ_３ＰＯ_４の電子伝導率が１０^－１０Ｓ／ｃｍ未満であり、Ｌｉ_３Ｎの電子伝導率が１０^－１２Ｓ／ｃｍ未満であり、Ｌｉ_７Ｌａ_３Ｚｒ_２Ｏ_１２及びＬｉ_１．３Ａｌ_０．３Ｇｅ_１．７（ＰＯ_４）_３の電子伝導率が１０^－７Ｓ／ｃｍ未満である。 <Method for measuring the number of battery cycles>
Symmetric cells were activated by discharging for 15 hours and charging for 15 hours at a current density of 0.1 mA/cm ² . It was then cycled at a current density of 0.6 mA/cm ² with a discharge and charge time of 3 hours each. The number of cycles when the cycle voltage suddenly dropped below 40 mV was taken as the number of cycles for the symmetrical battery.
Table 1: Relevant parameters and measurement results for Examples 1-13 and Controls 1-4

Table 1 above shows that the electronic conductivity of LiF and Li ₃ PO ₄ is less than 10 ⁻¹⁰ S/cm, the electronic conductivity of Li ₃ N is less than 10 ⁻¹² S/cm, and the electronic conductivity of Li ₇ La ₃ The electronic conductivity of Zr ₂ O ₁₂ and Li _1.3 Al _0.3 Ge _1.7 (PO ₄ ) ₃ is less than 10 ⁻⁷ S/cm.

Due to the different proportions of Si and LiF in Examples 1, 4 and 5, the cycle times of the symmetrical cells changed. The reason for this is mainly that when the ratio of Si is high (Example 4), the electronic conductivity of Si itself is high, so lithium tends to deposit on the negative electrode protective layer, and dendrites grow on lithium. This is thought to be because a short circuit occurred due to In addition, when the proportion of Si is low (Example 5), the bonding strength between the protective layer and lithium metal is low, resulting in a low protective effect.

"Some embodiments," "some embodiments," "one embodiment," "another example," "example," "specific example," or "one example," as used throughout the specification. Terms such as "exemplary part" mean that at least one embodiment or illustration in the invention includes the particular feature, structure, material or property described in that embodiment or illustration. Thus, for example, "in some embodiments", "in embodiments", "in one embodiment", "in other examples", "in one example" as used in many places throughout the specification. , “in a particular example” or “exemplary” do not necessarily refer to the same embodiment or illustration in accordance with the present invention. Also, any particular feature, structure, material or characteristic disclosed herein may be implemented in any suitable form in combination in one or more embodiments or illustrations.

Although illustrative embodiments have been described above, it will be appreciated by those skilled in the art that the above embodiments are not intended to limit the present invention, and without departing from the spirit, principle or scope of the present invention, Embodiments may be modified, substituted or improved.

Claims (13)

A composition for producing a protective film for a negative electrode containing a lithium metal layer ,
Silicon, and formula: SiM _y where y<0.05, M is at least one of B, Al, P, Fe, Co, Ni, Zn, Ge, Ga, As, Zr, In and Sn and at least one silicon material selected from the group consisting of silicon alloys represented by
a lithium ion conductor material having an electronic conductivity of less than 1×10 ⁻⁵ S/cm ;
A composition comprising: The composition of claim 1, wherein the molar ratio of said silicon material to said lithium ion conductor material is from 1:5 to 20:1. The lithium ion conductor material includes LiF, _{Li3PO4 , Li3N} , LiPON, Li2O, _Li4SiO4 , _LiAlO2 , _Lix1Tiy1 ( _PO4 ) _{3 (} where 0< _x1 < ₂ , and 0<y1<3), Li _x2 Al _y2 (Ti, Ge) _z2 (PO ₄ ) ₃ (where 0 < x2 < 2, 0 < y2 < 1, and 0 < z2 < 3), Li _1+x3+y3 (Al, Ga) _x3 (Ti, Ge) _2-x3 Si _y3 P _3-y3 O ₁₂ (where 0 ≤ x3 ≤ 1 and 0 ≤ y3 ≤ 1), Li _x4 La _y4 TiO ₃ (where 0<x4<2 and 0<y4<3), Li _x5 Ge _y5 P _z5 S _w5 (where 0<x5<10, 0<y5<1, 0<z5<2 and 0<w5< 12), Li _x6 Si _y6 S _z6 (where 0 ≤ x6 < 3, 0 < y6 < 2, and 0 < z6 < 4), Li _x7 P _y7 S _z7 (where 0 ≤ x7 < 3, 0 <y7<3 and 0<z7<7), Li ₂ O—Al ₂ O ₃ —SiO ₂ —P ₂ O ₅ —TiO ₂ —GeO ₂ ceramics, and Li _3+x8 La ₃ N ₂ O ₁₂ (provided that 0≦x8≦5, and N is Te, Nb, or Zr.). A protective film for a negative electrode having a lithium metal layer, comprising the composition according to any one of claims 1 to 3 ,
A protective film covering the lithium metal layer of the negative electrode. 5. The protective film of claim 4 , wherein the protective film further comprises LixSi (where 1.5< _x <4.0). The protective film according to claim 4 or 5 , having a thickness of 0.01 μm to 5 μm. The protective film according to any one of claims 4 to 6, wherein the lithium metal layer comprises at least one of lithium metal, lithium alloys and lithium compounds. The protective film according to any one of claims 4 to 7, wherein said lithium metal layer is a thin film layer or a powder layer. The protective film of any one of claims 4-8, wherein the lithium metal layer and the protective film have a molar ratio of lithium to silicon greater than 10:1. 6. The protective film according to claim 5 , wherein the Li _x Si has a lithium diffusion coefficient of 10 ⁻¹⁴ to 10 ⁻¹⁰ cm ² /S and a strength of more than 10 GPa. A negative electrode comprising the protective film according to any one of claims 4 to 10 and a lithium metal layer coated with the protective film . An electrochemical device comprising the negative electrode of claim 11 . Electronic equipment comprising an electrochemical device according to claim 12 .

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