Secondary batteries and electrical equipment

Abstract

The present invention discloses a secondary battery and an electrical device. The secondary battery comprises a lithium metal layer, a solid electrolyte layer, and a negative electrode interface modification layer disposed between the lithium metal layer and the solid electrolyte layer. The negative electrode interface modification layer comprises lithium fluoride, a metal lithium alloy, PEG, a lithium salt, and a carbon material. The negative electrode interface modification layer comprises a carbon skeleton structure that can conduct both lithium ions and electrons. The metal lithium alloy promotes the transport of lithium ions in the interface modification layer. The lithium fluoride has excellent ion conductivity, inhibits the growth of lithium dendrites, protects the metal lithium negative electrode, and improves the cycle stability of the metal lithium negative electrode.

Description

Technical Field

[0001] The present invention relates to the field of secondary batteries, and in particular to secondary batteries and electrical equipment. Background Art

[0002] The metallic lithium anode has a low chemical potential (-3.04 V vs. SHE) and a high theoretical capacity (3860 mAh g -1 ) and other advantages, and has long been considered the most ideal lithium battery anode material. However, the high activity of metallic lithium and the formation of lithium dendrites during battery cycling have seriously hindered the commercialization of metallic lithium anodes.

[0003] Solid-state batteries are considered the most effective way to overcome lithium dendrites. They use high-mechanical-strength solid electrolytes to inhibit the penetration of lithium dendrites. However, most solid-state electrolytes are unstable with metallic lithium. During static and cycling, an interfacial layer forms, consuming metallic lithium. Furthermore, the high impedance of the interfacial layer reduces battery performance and can lead to battery failure.

[0004] In previous studies, the interface modification layer was often used to modify the lithium metal negative electrode to inhibit the growth of lithium dendrites. For example, patent CN110915049A used a highly elastic polymer anode protection layer to modify the lithium metal negative electrode. However, the interface modification layer of this method has poor ionic conductivity, and the ionic conductivity of the modification layer is basically around 10 -4 S / cm, which prevents effective lithium ion conduction at the interface of the modified layer. Patent CN108736056A coats a coating composed of metal fluoride / carbon material / binder on the surface of a current collector made of copper foil, nickel foil, stainless steel foil, or other metal substrates that do not alloy with lithium metal. After the current collector is electrochemically reduced by lithium ions, a self-supporting structure with a lithium fluoride framework is formed. However, this method is cumbersome to operate (it requires deposition and disassembly of the initial battery and then reassembly), and cannot be used to produce large-capacity solid-state batteries. Summary of the Invention

[0005] The present invention addresses the problems of poor chemical stability at the interface between a solid electrolyte and a metallic lithium negative electrode, high interfacial impedance, and the susceptibility to lithium dendrite growth. The invention provides a secondary battery comprising a lithium metal layer, a solid electrolyte layer, and a negative electrode interface modification layer disposed between the lithium metal layer and the solid electrolyte layer. The negative electrode interface modification layer reduces direct contact between the solid electrolyte and metallic lithium, significantly improving the interfacial stability of the negative electrode, facilitating uniform deposition of lithium ions, and inhibiting the growth of lithium dendrites, thereby increasing battery utilization and cycle life.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned negative electrode interface modification layer.

[0007] Another object of the present invention is to provide an electric device comprising the secondary battery.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] On the one hand, the present invention provides a secondary battery comprising a lithium metal layer, a solid electrolyte layer, and a negative electrode interface modification layer arranged between the lithium metal layer and the solid electrolyte layer, wherein the negative electrode interface modification layer comprises lithium fluoride, a metal lithium alloy, PEG (polyethylene glycol), a lithium salt and a carbon material.

[0010] In the negative electrode interface modification layer, the weight of lithium fluoride accounts for 0.1% to 2% of the total weight of the entire interface modification layer.

[0011] The metal lithium alloy includes one or more of AgLi, SnLi, AlLi, TiLi, ZnLi, and ZrLi;

[0012] The metal lithium alloy accounts for 0.5% to 10% of the total weight of the entire interface modification layer.

[0013] The carbon material is selected from one or more of conductive carbon black, graphene, and vapor-grown carbon fiber;

[0014] Based on the total weight of the negative electrode interface modification layer, the content of the carbon material is 70 wt% to 95 wt%, preferably 80% to 93%.

[0015] The weight of the PEG accounts for 0.1 wt% to 5 wt% of the total weight of the interface modification layer, preferably 1% to 3%.

[0016] The PEG is one or more PEGs with a weight average molecular weight of 200 to 10,000, and specifically can be PEG with a weight average molecular weight of 1,000.

[0017] Based on the total weight of the negative electrode interface modification layer, the content of the lithium salt is 0.1% to 2%, preferably 0.5% to 1%;

[0018] The lithium salts include lithium perchlorate (abbreviated as LiClO4), lithium hexafluorophosphate (abbreviated as LiPF6), lithium tetrafluoroborate (abbreviated as LiBF4), lithium hexafluoroarsenide (abbreviated as LiAsF6), lithium trifluoromethanesulfonate (abbreviated as LiCF3SO3), lithium bis(trifluoromethanesulfonylimide) (abbreviated as LiN(CF3SO2)2), lithium bis(oxalato)borate (abbreviated as LiBOB), lithium difluorooxalatoborate (abbreviated as LiBF 2C2O4), lithium difluorooxalatoborate (abbreviated as LiBF2C2O4), lithium nitrate (abbreviated as LiNO3), lithium fluoroalkyl phosphate (abbreviated as LiPF3(CF2CF3)3), lithium bisperfluoroethylsulfonyl imide (abbreviated as LiBETI), lithium bis(trifluoromethanesulfonyl) imide (abbreviated as LiTFSI), lithium bis(fluorosulfonyl) imide (abbreviated as LiFSI), and one or more of ionic liquid-based lithium salts.

[0019] The negative electrode interface modification layer further includes a binder, and the content of the binder is the balance based on the total weight of the negative electrode interface modification layer.

[0020] The thickness of the negative electrode interface modification layer may be 1 to 50 μm, preferably 5 to 15 μm.

[0021] The interface modification layer is dense and has no obvious voids.

[0022] Specifically, the porosity of the interface modification layer is less than or equal to 5%, preferably lower than 3%, and more preferably lower than 1%.

[0023] The carbon material in the negative electrode interface modification layer serves as a skeleton structure and can conduct both lithium ions and electrons; the metallic lithium alloy promotes the transmission of lithium ions in the interface modification layer; lithium fluoride has good ion conductivity, inhibits the growth of lithium dendrites, protects the metallic lithium negative electrode, and improves the cycle stability of the metallic lithium negative electrode; PEG and lithium salt are common polymer electrolyte components, which can improve the ion conductivity of the modification layer, and at the same time, the polymer PEG can reduce the amount of binder used and reduce the polarization voltage.

[0024] The negative electrode interface modification layer is located between the solid electrolyte and the lithium metal negative electrode and is applied on the solid electrolyte, which can significantly improve the interface stability of the lithium metal negative electrode side, inhibit the growth of lithium dendrites, and increase the cycle life of the battery.

[0025] In the secondary battery, the solid electrolyte layer has a thickness of 1000 μm to 5000 μm.

[0026] The present invention also provides a method for preparing the negative electrode interface modification layer.

[0027] The method for preparing the negative electrode interface modification layer provided by the present invention comprises the following steps:

[0028] Mixing metal fluoride, carbon material, PEG, lithium salt, binder and solvent to obtain composite buffer layer slurry;

[0029] The metal fluoride in the composite buffer layer slurry is converted into a metal lithium alloy and lithium fluoride through an in-situ electrochemical reaction to obtain the negative electrode interface modification layer.

[0030] The metal fluoride comprises one or more of AgF, SnF, AlF3, TiF4, ZnF2, and ZrF4;

[0031] The weight of lithium fluoride in the obtained negative electrode interface modification layer accounts for 0.1% to 2% of the total weight of the entire interface modification layer. If the content of metal fluoride used is too high, the reduction process will consume too much metal lithium, affecting the initial effect; if too little, it will not work;

[0032] The proportion of carbon material is 70wt% to 95wt%, preferably 80wt% to 93wt%. Too much carbon content will affect the conductivity of the interface layer, and too little carbon content will not play a supporting role.

[0033] The PEG content is about 0.1 wt% to 5 wt%, preferably 1 wt% to 3 wt%. Too much PEG will reduce the ionic conductivity of the interface modification layer, and a lower PEG content will result in too many voids in the interface modification layer.

[0034] The lithium salt accounts for 0.1wt% to 2wt%, preferably 0.5wt% to 1wt%, to ensure the conduction of lithium ions;

[0035] The content of the binder is the balance.

[0036] The carbon material is selected from one or more of SP, graphene, and VGCF;

[0037] The binder can be one or more of CMC, PVA, PAA, SBR, PEO, and PVDF;

[0038] The solvent may be one or more of NMP, acetone, THF, water, and DMF;

[0039] The PEG is one or more PEGs with a weight average molecular weight of 200 to 10,000;

[0040] The lithium salts include lithium perchlorate (abbreviated as LiClO4), lithium hexafluorophosphate (abbreviated as LiPF6), lithium tetrafluoroborate (abbreviated as LiBF4), lithium hexafluoroarsenide (abbreviated as LiAsF6), lithium trifluoromethanesulfonate (abbreviated as LiCF3SO3), lithium bistrifluoromethanesulfonyl imide (abbreviated as LiN(CF3SO2)2), lithium bis(oxalato)borate (abbreviated as LiBOB), lithium difluorooxalatoborate (abbreviated as LiBF2 C2O4), lithium difluorooxalatoborate (abbreviated as LiBF2C2O4), lithium nitrate (abbreviated as LiNO3), lithium fluoroalkyl phosphate (abbreviated as LiPF3(CF2CF3)3), lithium bisperfluoroethylsulfonyl imide (abbreviated as LiBETI), lithium bis(trifluoromethanesulfonyl) imide (abbreviated as LiTFSI), lithium bis(fluorosulfonyl) imide (abbreviated as LiFSI), and one or more of ionic liquid-based lithium salts.

[0041] The invention also provides an electrical device.

[0042] The electric device includes the secondary battery.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The carbon material in the negative electrode interface modification layer used in the present invention can conduct both lithium ions and electrons; the lithium metal alloy promotes the transmission of lithium ions in the interface modification layer; lithium fluoride has good ion conductivity, inhibits the growth of lithium dendrites, protects the metal lithium negative electrode, and improves the cycle stability of the metal lithium negative electrode; PEG and lithium salt can improve the ion conductivity of the modification layer, and the polymer PEG can reduce the amount of binder used and reduce the polarization voltage. DETAILED DESCRIPTION

[0045] The present invention will be further described in detail below in conjunction with specific embodiments. The examples provided are only for illustrating the present invention and are not intended to limit the scope of the present invention. The examples provided below can serve as a guide for further improvements by those skilled in the art and are not intended to limit the present invention in any way.

[0046] Unless otherwise specified, the experimental methods in the following examples are conventional methods and were performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials and reagents used in the following examples, unless otherwise specified, were all commercially available.

[0047] The present invention provides a secondary battery comprising a lithium metal layer, a solid electrolyte layer, and a negative electrode interface modification layer arranged between the lithium metal layer and the solid electrolyte layer, wherein the negative electrode interface modification layer comprises lithium fluoride, a metal lithium alloy, PEG, a lithium salt and a carbon material.

[0048] In the negative electrode interface modification layer, the weight of lithium fluoride accounts for 0.1% to 2% of the total weight of the entire interface modification layer, preferably 0.6% to 1.9%;

[0049] The metal lithium alloy includes one or more of AgLi, SnLi, AlLi, TiLi, ZnLi, and ZrLi;

[0050] The metal lithium alloy accounts for 0.5% to 10% of the total weight of the entire interface modification layer.

[0051] The carbon material is selected from one or more of conductive carbon black, graphene, and vapor-grown carbon fiber;

[0052] Based on the total weight of the negative electrode interface modification layer, the content of the carbon material is 70 wt% to 95 wt%, preferably 80% to 93%.

[0053] The weight of the PEG accounts for 0.1 wt% to 5 wt% of the total weight of the interface modification layer, preferably 1% to 3%.

[0054] The PEG is one or more PEGs with a weight average molecular weight of 200 to 10,000, and specifically can be PEG with a weight average molecular weight of 2,000.

[0055] Based on the total weight of the negative electrode interface modification layer, the content of the lithium salt is 0.1% to 2%, preferably 0.5% to 1%;

[0056] The thickness of the negative electrode interface modification layer may be 1 to 50 μm, preferably 5 to 15 μm.

[0057] When the negative electrode interface layer is too thin, the interface resistance is low, but the stability of the interface layer is poor, and the metal lithium dendrites will pierce the interface modification layer quickly, causing the battery to short circuit and fail; when the interface layer is too thick, the interface resistance increases, but the interface layer has good stability and the battery cycle life is long; when the thickness of the negative electrode interface modification layer is preferably 5 to 15 μm, the battery internal resistance and cycle life reach a better balance.

[0058] The interface modification layer is dense and has no obvious voids.

[0059] Specifically, the porosity of the interface modification layer is less than or equal to 5%, preferably less than 3%, and more preferably less than 1%;

[0060] The greater the porosity of the interface layer, the worse the ion conductivity of the interface layer, the higher the interface resistance, the lower the cycle life, and the easier it is for lithium dendrites to pierce the interface modification layer and the electrolyte layer, causing battery short circuit failure.

[0061] In the secondary battery, the solid electrolyte layer has a thickness of 1000 μm to 5000 μm.

[0062] Increasing the thickness of the electrolyte layer will lead to an increase in the polarization voltage and increase the cycle life of the symmetric battery.

[0063] The present invention also provides a method for preparing the above-mentioned negative electrode interface modification layer, which comprises the following steps:

[0064] S1. Mixing metal fluoride, carbon material, PEG, lithium salt, adhesive and solvent to obtain a composite buffer layer slurry;

[0065] S2. Converting the metal fluoride in the composite buffer layer slurry into a metal lithium alloy and lithium fluoride through an in-situ electrochemical reaction to obtain the negative electrode interface modification layer.

[0066] In this embodiment, the metal fluoride is selected from one or more of AgF, SnF, AlF3, TiF4, ZnF2, and ZrF4;

[0067] The carbon material is selected from one or more of SP, graphene, and VGCF;

[0068] The binder is selected from one or more of CMC, PVA, PAA, SBR, PEO, and PVDF;

[0069] In one embodiment, step S1 includes the following steps:

[0070] S11, mixing the metal fluoride, the carbon material, the PEG, the lithium salt, the binder, and the solvent in proportion, and stirring and dispersing the mixture to obtain a composite buffer layer slurry;

[0071] S12, coating the composite buffer layer slurry on one side of a sacrificial substrate, and drying the composite buffer layer to obtain the composite buffer layer, wherein the composite buffer layer is supported on the sacrificial substrate.

[0072] Step S2 includes the following steps:

[0073] S21, covering one side of the composite buffer layer with a solid electrolyte, and pressing the composite buffer layer and the solid electrolyte together through a pressing process;

[0074] S22, removing the sacrificial substrate;

[0075] S23, assembling a negative electrode, a positive electrode, and the composite buffer layer covered with a solid electrolyte into a solid-state battery; the negative electrode includes a lithium metal negative electrode;

[0076] S24, performing activation treatment on the solid-state battery, whereby the metal fluoride in the composite buffer layer is converted into a metal lithium alloy and lithium fluoride after activation to form the negative electrode interface modification layer.

[0077] In this embodiment, the metal lithium alloy includes one or more of silver-lithium alloy, tin-lithium alloy, titanium-lithium alloy, zinc-lithium alloy and zirconium-lithium alloy.

[0078] The activation treatment includes high-temperature activation, the temperature of the high-temperature activation is 60-150° C., and the time is 2-12 hours.

[0079] This method does not need to consider the influence of solvents on the electrolyte layer and the metal lithium negative electrode during the preparation of the interface modification layer. For example, polar solvents such as acetonitrile cannot be used to directly prepare the modification layer on the surface of the sulfide electrolyte. Solvents such as water and ethanol react with metal lithium and cannot prepare the modification layer on the surface of metal lithium. Therefore, this method broadens the range of solvent selection.

[0080] In the secondary battery, the interface modification layer can significantly improve the interface stability of the lithium metal negative electrode side of the secondary battery, inhibit the growth of lithium dendrites, and increase the cycle life of the battery.

[0081] Example 1

[0082] This embodiment provides a method for preparing a secondary battery, comprising the following steps:

[0083] (1) AgF (3 wt%), carbon material (SP, 90 wt%), PEG1000 (3 wt%), LiTFSI (1 wt%), PVDF (3 wt%) and NMP were mixed and stirred to obtain a composite buffer layer slurry;

[0084] (2) After a doctor blade coating process, the buffer layer slurry was applied to a sacrificial substrate (Al, 8 μm) with a thickness of 60 μm and dried to obtain a pole piece loaded with a composite buffer layer;

[0085] (3) 100 mg of LGPS powder (particle size 5 μm) was pressed at a pressure of 360 MPa for 1 min to obtain an electrolyte sheet. At this time, the electrolyte layer had a porosity of 5% and a layer thickness of 1000 μm. The electrode sheet was cut into a suitable size and covered with a solid electrolyte sheet on the electrode sheet of the load buffer layer. The electrode sheet and the solid electrolyte layer were pressed tightly together under a pressure of 200 MPa for 1 min.

[0086] (4) mechanically peeling the sacrificial substrate from the solid electrolyte layer so that the composite buffer layer is applied to the solid electrolyte side;

[0087] (5) Assembling a solid-state symmetrical battery: Li metal is applied to both sides of the solid electrolyte modified with a buffer layer;

[0088] (6) The obtained solid-state battery was placed at 100°C for 6 hours for high-temperature activation. After activation, AgF reacted with metallic lithium to form LiF and silver-lithium alloy, thereby obtaining an interface modification layer. The obtained interface modification layer had a LiF content of 0.6124%, a silver-lithium alloy content of 2.5465%, a carbon material content of 89.8525%, a PEG1000 content of 2.9951%, a lithium salt content of 0.9984%, and a binder balance. The porosity of the interface modification layer was less than 1%, and the modification layer thickness was 5 μm.

[0089] Example 2

[0090] This embodiment differs from Example 1 in that SnF is used instead of AgF. The resulting interface modification layer has a LiF content of 0.9906%, a tin-lithium alloy content of 2.2665%, a carbon material content of 89.7615%, a PEG1000 content of 2.9920%, a lithium salt content of 0.9973%, and a binder content as the remainder. The interface modification layer has a porosity of less than 1% and a thickness of 5 μm.

[0091] Example 3

[0092] This embodiment differs from Example 1 in that ZnF is used instead of AgF. The resulting interface modification layer has a LiF content of 1.4995%, a zinc-lithium alloy content of 1.8897%, a carbon material content of 89.6389%, a PEG1000 content of 2.9880%, a lithium salt content of 0.9960%, and a binder content as the remainder. The interface modification layer has a porosity of less than 1% and a thickness of 5 μm.

[0093] Example 4

[0094] This embodiment differs from Example 1 in that ZrF is used instead of AgF. The resulting interface modification layer comprises 1.8522% LiF, 1.6284% zirconium-lithium alloy, 89.5540% carbon material, 2.9851% PEG1000, 0.9950% lithium salt, and the remainder is binder. The porosity of the interface modification layer is less than 1%, and the modification layer thickness is 5 μm.

[0095] Example 5

[0096] The difference between this embodiment and Example 1 is that the content of AgF is adjusted to 0.49wt%, the content of LiF in the obtained interface modification layer is 0.1%, the content of silver-lithium alloy is 0.42%, the content of carbon material is 92.48607%, the content of PEG1000 is 2.99920%, the content of lithium salt is 0.9997%, the binder is the remainder, the porosity of the interface modification layer is less than 1%, and the thickness of the modification layer is 5μm.

[0097] Example 6

[0098] The difference between this embodiment and Example 1 is that the content of AgF is adjusted to 9.83%, and in the obtained interface modification layer, the content of LiF is 2%, the content of silver-lithium alloy is 8.32%, the content of carbon material is 82.72114%, the content of PEG1000 is 2.98403%, the content of lithium salt is 0.9947%, the binder is the remainder, and the porosity of the interface modification layer is less than 1%; the thickness of the modification layer is 5 μm.

[0099] Example 7

[0100] The difference between this embodiment and Example 1 is that the content of AgF is adjusted to 14.79%, and in the obtained interface modification layer, the content of LiF is 3.00%, the content of silver-lithium alloy is 12.47%, the content of carbon material is 76.58953%, the content of PEG1000 is 2.97611%, the content of lithium salt is 0.9920%, the binder is the remainder, and the porosity of the interface modification layer is less than 1%; the thickness of the modification layer is 5 μm.

[0101] Example 8

[0102] The difference between this embodiment and Example 1 is that the content of AgF is adjusted to 0.24%, and in the obtained interface modification layer, the content of LiF is 0.05%, the content of silver-lithium alloy is 0.21%, the content of carbon material is 94.74277%, the content of PEG1000 is 2.99960%, the content of lithium salt is 0.9999%, the binder is the remainder, and the porosity of the interface modification layer is less than 1%; the thickness of the modification layer is 5 μm.

[0103] Example 9

[0104] The difference between this embodiment and Example 1 is that the PEG content is adjusted to 0.1002%, and the obtained interface modification layer has a LiF content of 0.61%, a silver-lithium alloy content of 2.55%, a carbon material content of 92.74761%, a PEG1000 content of 0.1%, a lithium salt content of 0.9984%, a binder balance, and a porosity of the interface modification layer of less than 1%; the modification layer thickness is 5 μm.

[0105] Example 10

[0106] The difference between this embodiment and Example 1 is that the PEG content is adjusted to 1.0016%, and the obtained interface modification layer has a LiF content of 0.61%, a silver-lithium alloy content of 2.55%, a carbon material content of 91.84761%, a PEG1000 content of 1%, a lithium salt content of 0.9984%, a binder balance, and a porosity of the interface modification layer of less than 1%; the modification layer thickness is 5 μm.

[0107] Example 11

[0108] The difference between this embodiment and Example 1 is that the PEG content is adjusted to 5.0082%, and the obtained interface modification layer has a LiF content of 0.61%, a silver-lithium alloy content of 2.55%, a carbon material content of 87.84761%, a PEG1000 content of 5%, a lithium salt content of 0.9984%, a binder balance, and a porosity of the interface modification layer of less than 1%; the modification layer thickness is 5 μm.

[0109] Example 12

[0110] The difference between this embodiment and Example 1 is that the PEG content is adjusted to 0.0501%, the LiF content in the obtained interface modification layer is 0.61%, the silver-lithium alloy content is 2.55%, the carbon material content is 92.79761%, the PEG content is adjusted to 0.05%, the lithium salt content is 0.9984%, the binder balance, the porosity of the interface modification layer is less than 1%, and the modification layer thickness is 5 μm.

[0111] Example 13

[0112] The difference between this embodiment and Example 1 is that the PEG content is adjusted to 10.0164%, the LiF content in the obtained interface modification layer is 0.61%, the silver-lithium alloy content is 2.55%, the carbon material content is 82.84761%, the PEG content is adjusted to 10%, the lithium salt content is 0.9984%, the binder balance, the porosity of the interface modification layer is less than 1%, and the modification layer thickness is 5 μm.

[0113] Example 14

[0114] The difference between this embodiment and Example 1 is that the lithium salt content is adjusted to 0.1002%, and the obtained interface modification layer has a LiF content of 0.61%, a silver-lithium alloy content of 2.55%, a carbon material content of 90.75088%, a PEG1000 content of 2.99509%, a lithium salt content of 0.1%, a binder balance, and a porosity of the interface modification layer of less than 1%; the modification layer thickness is 5 μm.

[0115] Example 15

[0116] The difference between this embodiment and Example 1 is that the lithium salt content is adjusted to 0.5008%, and the obtained interface modification layer has a LiF content of 0.61%, a silver-lithium alloy content of 2.55%, a carbon material content of 90.35088%, a PEG1000 content of 2.99509%, a lithium salt content of 0.5%, a binder balance, and a porosity of the interface modification layer of less than 1%; the modification layer thickness is 5 μm.

[0117] Example 16

[0118] The difference between this embodiment and embodiment 1 is that the lithium salt content is adjusted to 2.0033%, and the obtained interface modification layer has a LiF content of 0.61%, a silver-lithium alloy content of 2.55%, a carbon material content of 88.85088%, a PEG1000 content of 2.99509%, a lithium salt content of 2%, a binder balance, and a porosity of the interface modification layer of less than 1%; the modification layer thickness is 5 μm.

[0119] Example 17

[0120] The difference between this embodiment and embodiment 1 is that the lithium salt content is adjusted to 0.0501%, and the obtained interface modification layer has a LiF content of 0.61%, a silver-lithium alloy content of 2.55%, a carbon material content of 90.80088%, a PEG1000 content of 2.99509%, a lithium salt content of 0.05%, a binder balance, and a porosity of the interface modification layer of less than 1%; the modification layer thickness is 5 μm.

[0121] Example 18

[0122] The difference between this embodiment and Example 1 is that the lithium salt content is adjusted to 10.0164%, and the obtained interface modification layer has a LiF content of 0.61%, a silver-lithium alloy content of 2.55%, a carbon material content of 80.85088%, a PEG1000 content of 2.99509%, a lithium salt content of 10%, a binder balance, and a porosity of the interface modification layer of less than 1%; the modification layer thickness is 5 μm.

[0123] Example 19

[0124] The difference between this embodiment and embodiment 1 is that the amount of electrolyte powder used is 80 mg, and the thickness of the electrolyte layer is adjusted to 800 microns.

[0125] Example 20

[0126] The difference between this embodiment and embodiment 1 is that the amount of electrolyte powder used is 300 mg, and the thickness of the electrolyte layer is adjusted to 3000 microns.

[0127] Example 21

[0128] The difference between this embodiment and embodiment 1 is that the amount of electrolyte powder used is 500 mg, and the thickness of the electrolyte layer is adjusted to 5000 microns.

[0129] Example 22

[0130] The difference between this embodiment and embodiment 1 is that the amount of electrolyte powder used is 1000 mg, and the thickness of the electrolyte layer is adjusted to 10,000 microns.

[0131] Example 23

[0132] The difference between this embodiment and embodiment 1 is that the coating thickness of the negative electrode interface layer slurry is 120 microns, and the thickness of the negative electrode interface modification layer is adjusted to 10 microns.

[0133] Example 24

[0134] The difference between this embodiment and embodiment 1 is that the coating thickness of the negative electrode interface layer slurry is 180 microns, and the thickness of the negative electrode interface modification layer is adjusted to 15 microns.

[0135] Example 25

[0136] The difference between this embodiment and embodiment 1 is that the coating thickness of the negative electrode interface layer slurry is 300 microns, and the thickness of the negative electrode interface modification layer is adjusted to 25 microns.

[0137] Example 26

[0138] The difference between this embodiment and embodiment 1 is that the coating thickness of the negative electrode interface layer slurry is 600 microns, and the thickness of the negative electrode interface layer is adjusted to 50 microns.

[0139] Example 27

[0140] The difference between this embodiment and embodiment 1 is that the coating thickness of the negative electrode interface layer slurry is 12 microns, and the thickness of the negative electrode interface layer is adjusted to 1 micron.

[0141] Example 28

[0142] The difference between this embodiment and embodiment 1 is that the cold pressing pressure is changed to 150 MPa, so that the porosity of the negative electrode interface modification layer is 2%.

[0143] Example 29

[0144] The difference between this embodiment and embodiment 1 is that the cold pressing pressure is changed to 100 MPa, so that the porosity of the negative electrode interface modification layer is 5%.

[0145] Comparative Example 1

[0146] This comparative example does not contain a negative electrode interface modification layer, and is otherwise the same as Example 1.

[0147] Comparative Example 2

[0148] This comparative example does not contain a carbon material, and only adds a metal fluoride. All other conditions are the same as in Example 1. The resulting interface modification layer has a carbon material content of 0, a LiF content of 18.0317%, a silver-lithium alloy content of 74.9797%, a PEG1000 content of 2.99509%, a lithium salt content of 0.9984%, and a binder balance. The porosity of the interface modification layer is less than 1%, and the modification layer thickness is 5 μm.

[0149] Performance Testing

[0150] In Examples 1 to 29 and Comparative Examples 1 to 2, after the electrolyte layer with the modified layer was pressed, the sacrificial substrate was removed, metallic lithium was added on both sides to assemble a symmetrical battery, and then performance testing was performed.

[0151] Symmetrical battery performance test method is as follows: At room temperature, 10mA blue electric charge and discharge test equipment is used to perform symmetrical battery performance test, and the charge and discharge current density is 0.1mA / cm 2 , the charge and discharge capacity is 0.1mAh / cm 2 The polarization voltage and lithium stability cycle time test results are shown in Table 1.

[0152] Table 1

[0153]

[0154]

[0155] It can be seen from the embodiments and comparative examples in Table 1 that the negative electrode interface modification layer of the present invention is arranged between the metallic lithium negative electrode and the solid electrolyte, which can reduce the polarization voltage and prolong the lithium stability cycle time, thereby improving the interface chemical stability between the solid electrolyte and the metallic lithium negative electrode, reducing lithium dendrites and reducing the interface impedance.

[0156] Comparison with Examples 1 to 4 shows that the present invention has no special requirements on the type of metal in the metal fluoride, and any metal that can form an alloy with metallic lithium can be used in the present invention.

[0157] By comparing Example 1 with Examples 5 to 8, it can be seen that the content of lithium fluoride in the negative electrode interface modification layer is controlled within the range of 0.1% to 2% by adjusting the content of metal fluoride. If the metal fluoride content is too high, the ionic conductivity of the interface modification layer before formation will be greatly reduced, resulting in a too high polarization voltage in the early stage of formation and a high metal cost. If the metal fluoride content is too low, sufficient LiF cannot be formed, and the content of the formed metal lithium alloy is also low, resulting in poor stability.

[0158] Comparing Example 1 with Examples 9 to 13, it can be seen that too high or too low a PEG content in the interface modification layer will result in a large internal resistance, a high polarization voltage, and a short symmetrical battery life. In addition, too low a PEG content will also result in a low strength of the interface modification layer.

[0159] By comparing Example 1 with Examples 14 to 18, it can be seen that too little lithium salt content will lead to poor ion conductivity of the interface modification layer, high internal resistance of the interface modification layer, high polarization voltage, and short symmetrical battery life; too high lithium salt content will also lead to increased polarization voltage and shortened symmetrical battery life.

[0160] Comparing Example 1 with Examples 19 to 22, it can be seen that increasing the thickness of the electrolyte layer will lead to an increase in the polarization voltage and increase the cycle life of the symmetrical battery.

[0161] By comparing Example 1 with Examples 23 to 27, it can be seen that as the thickness of the interface modification layer increases, the interface resistance increases, but the interface layer has good stability and the battery cycle life is long. When the thickness of the interface modification layer is preferably 5 to 15 μm, the battery performance is relatively balanced.

[0162] Comparing Example 1 with Examples 28 to 29, it can be seen that increasing the porosity of the interface layer will increase the polarization voltage of the symmetrical battery and reduce the cycle life of the symmetrical battery.

[0163] By comparing Example 1 with Comparative Example 1, it can be seen that the negative electrode interface modification layer of the present invention can reduce the voltage of the symmetrical battery and improve the cycle life of the symmetrical battery.

[0164] Comparison of Example 1 and Comparative Example 2 shows that the absence of carbon material will increase the internal resistance of the symmetrical battery and reduce the cycle life of the symmetrical battery.

[0165] The present invention has been described in detail above. For those skilled in the art, without departing from the purpose and scope of the present invention, and without the need to carry out unnecessary experimental conditions, the present invention can be implemented in a wide range under equivalent parameters, concentrations and conditions. Although the present invention provides specific embodiments, it should be understood that further improvements can be made to the present invention. In short, according to the principles of the present invention, this application is intended to include any changes, uses or improvements to the present invention, including changes that depart from the disclosed scope in this application and are made using conventional techniques known in the art.

Claims

1. A secondary battery, characterized in that The invention comprises a lithium metal layer, a solid electrolyte layer, and a negative electrode interface modification layer provided between the lithium metal layer and the solid electrolyte layer, wherein the negative electrode interface modification layer comprises lithium fluoride, a metal lithium alloy, PEG, a lithium salt and a carbon material; In the negative electrode interface modification layer, the weight of lithium fluoride accounts for 0.1% to 2% of the total weight of the negative electrode interface modification layer; The metal lithium alloy accounts for 0.5% to 10% of the total weight of the negative electrode interface modification layer; The lithium salt includes one or more of lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenide, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium nitrate, lithium fluoroalkyl phosphate, lithium bis(perfluoroethylsulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and ionic liquid-based lithium salts; The weight of the PEG accounts for 0.1wt% to 5wt% of the total weight of the negative electrode interface modification layer; Based on the total weight of the negative electrode interface modification layer, the content of the lithium salt is 0.1% to 2%.

2. The secondary battery according to claim 1, wherein The metal lithium alloy includes one or more of AgLi, SnLi, AlLi, TiLi, ZnLi, and ZrLi.

3. The secondary battery according to claim 1, wherein The carbon material is selected from one or more of conductive carbon black, graphene, and vapor-grown carbon fiber; Based on the total weight of the negative electrode interface modification layer, the content of the carbon material is 70 wt % to 95 wt %.

4. The secondary battery according to claim 3, wherein Based on the total weight of the negative electrode interface modification layer, the content of the carbon material is 80% to 93%.

5. The secondary battery according to claim 1, wherein The weight of the PEG accounts for 1% to 3% of the total weight of the negative electrode interface modification layer; based on the total weight of the negative electrode interface modification layer, the content of the lithium salt is 0.5% to 1%.

6. The secondary battery according to claim 1, wherein The thickness of the negative electrode interface modification layer is 1 to 50 μm; The porosity of the negative electrode interface modification layer is less than or equal to 5%.

7. The secondary battery according to claim 6, characterized in that The thickness of the negative electrode interface modification layer is 5-15 μm; the porosity of the negative electrode interface modification layer is less than 3%.

8. The secondary battery according to claim 7, wherein: The porosity of the negative electrode interface modification layer is less than 1%.

9. The secondary battery according to claim 1, wherein The negative electrode interface modification layer is prepared by the following method: Mixing metal fluoride, carbon material, PEG, lithium salt, binder and solvent to obtain composite buffer layer slurry; The metal fluoride in the composite buffer layer slurry is converted into a metal lithium alloy and lithium fluoride through an in-situ electrochemical reaction to obtain the negative electrode interface modification layer.

10. The secondary battery according to claim 1, wherein: The thickness of the solid electrolyte layer is 1000 μm to 5000 μm.

11. Electrical equipment, characterized in that: The electrical device comprises the secondary battery according to any one of claims 1 to 10.

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