Self-supported lithium-free negative electrode sheet, preparation method therefor and lithium battery

Abstract

A self-supported lithium-free negative electrode sheet, a preparation method therefor and a lithium battery. The self-supported lithium-free negative electrode sheet comprises a current collector, a porous skeleton structure arranged on at least one side of the current collector and, distributed on the porous skeleton structure, a lithium storage material and a nucleating material; the porous skeleton structure comprises carbon materials and a binder disposed between the carbon materials; the lithium storage material comprises any one of Si, SiO, CoSe or CO3O4 or a combination of at least two thereof; the nucleating material comprises any one of Ag, ZnO, MgO or Mo2N or a combination of at least two thereof; the synergy between the nucleating material and the lithium storage material can reduce a nucleation barrier in the porous skeleton structure and promote lithium deposition in a framework of the porous skeleton structure.

Description

Self-supporting lithium-free negative electrode sheet, preparation method thereof and lithium battery TECHNICAL FIELD

[0001] The present application relates to the technical field of battery electrode materials, for example, a self-supporting lithium-free negative electrode sheet, a preparation method thereof and a lithium battery. BACKGROUND

[0002] At present, lithium ion batteries are important industrial products for electric vehicles and energy storage systems. In the past decade, the energy and power density of lithium ion batteries has greatly improved, and the price of batteries has also greatly decreased. However, the thermal instability of lithium ion batteries has attracted great attention in the safety problems of electric vehicles and energy storage power grids. Studies have shown that the risk of thermal failure is mainly attributed to flammable organic electrolytes, and the use of solid inorganic electrolytes to replace flammable liquid electrolytes can fundamentally prevent the occurrence of thermal runaway hazards. When solid-state batteries are combined with high-nickel layered positive electrode materials and high-energy negative electrode materials such as silicon (4200 mA / g) or lithium metal (3800 mA / g), solid-state batteries can exhibit a specific energy of more than 500 Wh / kg.

[0003] However, there are some problems to be solved in the practical application of solid-state batteries, especially the problems of negative electrode expansion and lithium ion large-rate deposition of solid-state batteries. When lithium metal is used as the negative electrode, since lithium metal is very active, it will continuously react with the solid electrolyte, and during the charging and discharging process, the uneven plating and deposition of lithium lead to a large volume change of the lithium negative electrode (volume change > 320%), which causes the electrolyte to have poor contact with the lithium metal, thereby leading to the failure of the lithium metal solid-state battery. This is because the nucleation sites of lithium metal and silicon negative electrode are less, which easily leads to uneven deposition of lithium ions and then pierces the solid-state electrolyte.

[0004] When a silicon negative electrode is used to assemble a solid-state battery, its sharp volume expansion (Li 4.4 Si about 360%) during the charging and discharging process will generate a huge stress, which leads to electrode crushing, cracking and causes the deterioration of the structural integrity of the electrode. This is because the silicon negative electrode has poorer conductivity, which leads to uneven deposition of metal lithium, and the volume expansion problem of the solid-state battery can cause considerable safety problems.

[0005] In the related art, for the application of high-energy solid-state battery negative electrodes, the following four problems need to be solved: first, the problem of large volume change of the negative electrode during the charging and discharging process of the solid-state battery; second, the problem of uneven deposition of lithium ions caused by the fewer nucleation sites of the negative electrode of the solid-state battery; third, the problem of unstable structure of the negative electrode structure during the charging and discharging process; and fourth, the problem of poor compatibility with the existing lithium battery process production.

[0006] Therefore, how to realize low volume expansion rate of high-energy solid-state battery negative electrode, uniform deposition of metal lithium, maintain long cycle stability of the battery, and achieve the goal of being compatible with the current lithium battery process production has become a problem to be solved. SUMMARY

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0008] The present application provides a self-supporting lithium-free negative electrode sheet, a preparation method thereof and a lithium battery. The self-supporting lithium-free negative electrode sheet can realize self-supporting, has good electrical conductivity and structural stability, can realize uniform deposition of metal lithium, and provides necessary space for storage of metal lithium through its porous framework structure, greatly alleviates the volume expansion of the battery, and improves the long cycle stability of the lithium ion battery.

[0009] In a first aspect, the present application provides a self-supporting lithium-free negative electrode sheet, which comprises a current collector, a porous framework structure arranged on at least one side of the current collector, and a lithium storage material and a nucleation material distributed on the porous framework structure.

[0010] The porous framework structure comprises a carbon material and a binder lapped between the carbon materials.

[0011] The lithium storage material comprises any one or a combination of at least two of Si, SiO, CoSe or Co3O4, typical but non-limiting combinations include a combination of Si and SiO, a combination of CoSe and Co3O4, a combination of Si and CoSe, a combination of Si, SiO and CoSe, or a combination of CoSe and Co3O4, etc.

[0012] The nucleation material comprises any one or a combination of at least two of Ag, ZnO, MgO or Mo2N, typical but non-limiting combinations include a combination of Ag and ZnO, a combination of MgO and Mo2N, a combination of Ag and MgO, a combination of ZnO and Mo2N, a combination of Ag, ZnO and MgO, or a combination of Ag, ZnO, MgO or Mo2N, etc.

[0013] The porous framework structure in the self-supporting lithium-free negative electrode sheet provided by the application provides necessary space for lithium storage, solves the problem of high volume shrinkage and expansion of the battery negative electrode during charging and discharging, and also provides a high-speed transmission channel for electrons, reduces ion concentration polarization, and is beneficial to lithium ion deposition. The nucleation material and the lithium storage material in the porous framework structure can cooperatively reduce the nucleation barrier, induce rapid and uniform deposition of lithium from the bottom of the current collector to the electrolyte during charging and discharging, promote lithium deposition in the framework of the porous framework structure, avoid problems such as easy expansion of the volume caused by lithium deposition outside the framework, and avoid the problem of uneven lithium ion deposition. The use of the binder can improve the stability of the self-supporting lithium-free negative electrode sheet and avoid the problems of structure collapse and poor negative electrode adhesion.

[0014] The following is an optional technical solution of the application, but is not a limitation on the technical solutions provided by the application. Through the following optional technical solutions, the technical purposes and beneficial effects of the application can be better achieved and implemented.

[0015] In one embodiment, the mass ratio of the lithium storage material to the carbon material is 1:(5-10), for example, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10, but is not limited to the listed values, and other unlisted values within the value range are also applicable.

[0016] In the application, the mass ratio of the lithium storage material to the carbon material is 1:(5-10). The lithium storage material is lithiumophilic and can effectively guide the deposition of lithium. The carbon material is not lithiumophilic, and lithium ions are not easily uniformly deposited after obtaining electrons and being not compatible with the carbon material. Therefore, the lithium storage material needs to be dispersed and dotted in the porous framework structure composed of the carbon material to induce lithium deposition. When the mass ratio of the lithium storage material to the carbon material is within a suitable range, a strong conductive framework, an expanded reaction surface, and adjusted Li + flux can be provided to provide necessary space for lithium storage.

[0017] In one embodiment, the mass of the nucleation material accounts for 1-8wt% of the total mass of the lithium storage material and the carbon material, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%, but is not limited to the listed values, and other unlisted values within the value range are also applicable.

[0018] In the application, the mass of the nucleation material accounts for 1-8wt% of the total mass of the lithium storage material and the carbon material. When the mass ratio of the nucleation material is controlled within a suitable range, the nucleation barrier of lithium deposition can be reduced, and uniform deposition under high rate conditions can be ensured.

[0019] In one embodiment, the mass of the binder is 2-8 wt% of the total mass of the lithium storage material and the carbon material, for example 2%, 3%, 4%, 5%, 6%, 7%, or 8%, but not limited to the listed values, and other values not listed in the range are also applicable.

[0020] In the present application, the mass of the binder is 2-8 wt% of the total mass of the lithium storage material and the carbon material. Controlling the mass ratio of the binder in the appropriate value range can improve the stability of the skeleton structure without affecting the conductivity of the skeleton structure, the lithium deposition rate, and the rate performance.

[0021] In one embodiment, the median particle size of the lithium storage material is 60 nm-10 μm, for example 60 nm, 100 nm, 300 nm, 500 nm, 700 nm, 900 nm, 1 μm, 3 μm, 5 μm, 7 μm, or 10 μm, but not limited to the listed values, and other values not listed in the range are also applicable, and optionally 100 nm-1 μm.

[0022] In the present application, the median particle size of the lithium storage material is 60 nm-10 μm. If the particle size is too large, the negative electrode film roughness is poor, and large particles are easily pulverized during the charge and discharge cycle. If the particle size is too small, it is easy to agglomerate and not easy to disperse uniformly.

[0023] In one embodiment, the median particle size of the nucleation material is 30-100 nm, for example 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm, but not limited to the listed values, and other values not listed in the range are also applicable.

[0024] In the present application, the median particle size of the nucleation material is 30-100 nm. If the particle size is too large, the negative electrode film roughness is poor, and large particles are easily pulverized during the charge and discharge cycle. If the particle size is too small, it is easy to agglomerate and not easy to disperse uniformly.

[0025] In one embodiment, the carbon material includes any one or a combination of at least two of single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), or carbon fibers (VGCF), wherein a typical but non-limiting combination includes a combination of SWCNT and MWCNT, a combination of SWCNT and CGCF, a combination of MWCNT and CGCF, or a combination of SWCNT, MWCNT, and CGCF.

[0026] In the present application, the carbon material not only plays a role in constructing a porous skeleton structure, but also provides a network transmission channel for electron transmission, improving the transmission efficiency of electrons and enabling uniform deposition of lithium ions.

[0027] In one embodiment, the binder comprises a water-based binder.

[0028] In one embodiment, the water-based binder comprises any one or a combination of at least two of polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), or styrene butadiene rubber (SBR), wherein a typical but non-limiting combination comprises a combination of polyacrylic acid and sodium carboxymethyl cellulose, a combination of sodium carboxymethyl cellulose and styrene butadiene rubber, or a combination of polyacrylic acid, sodium carboxymethyl cellulose, and styrene butadiene rubber, and the like.

[0029] In the present application, the binder not only plays a role in bonding the various material components in the negative electrode sheet, achieving lapping between carbon materials, promoting the distribution of lithium storage materials and nucleation materials on carbon materials and between carbon materials, but also can form a porous framework structure together with carbon materials, thereby improving the stability of the self-supporting lithium-free negative electrode sheet. At the same time, the binder can achieve the bonding of the self-supporting lithium-free negative electrode sheet and the current collector, so that the self-supporting lithium-free negative electrode sheet is not easy to peel off.

[0030] In a second aspect, the present application provides a preparation method of the self-supporting lithium-free negative electrode sheet of the first aspect, and the preparation method comprises the following steps:

[0031] The carbon material and the lithium storage material are mixed to obtain a first mixture; then the nucleation material and the pore-forming agent are mixed with the first mixture to obtain a second mixture; then the binder and the solvent are mixed with the second mixture to obtain a slurry; the slurry is coated on the surface of the current collector, dried first, washed with water, and then dried second to obtain the self-supporting lithium-free negative electrode sheet.

[0032] In the present application, the carbon material is fully mixed with the lithium storage material as a conductive agent, and then the nucleation material and the pore-forming agent are uniformly mixed. After that, the binder and the solvent are added, and under the action of the solvent, the binder is dissolved and forms a uniform slurry with the carbon material, the lithium storage material, the nucleation material, and the pore-forming agent. The slurry is coated on the current collector to form a thin film, and the thin film is dried and then washed with water. After washing, the pore-forming agent is washed away after dissolving in water, so that pores are formed in the structure inside and on the surface of the thin film. The thin film forms a porous framework structure after the pore-forming is successful, that is, the carbon material in the thin film not only serves as a conductive network but also forms a porous framework structure together with the binder, thereby providing space for the deposition of lithium ions and achieving the effect of relieving the volume expansion of the negative electrode. The lithium storage material provides lithium storage capacity and nucleation sites, thereby improving the energy density of the lithium ion battery. The nucleation material and the lithium storage material can further reduce the lithium ion nucleation barrier and induce the uniform deposition of metallic lithium, thereby avoiding the volume expansion problem caused by the deposition of metallic lithium only on the surface of the negative electrode, and being conducive to improving the initial efficiency and capacity of the lithium battery.

[0033] Exemplarily, when the porous framework structure is arranged on one side of the current collector, the slurry is coated on the surface of one side of the current collector, and then the first drying, water washing and second drying are sequentially performed to obtain the self-supporting lithium-free negative electrode sheet.

[0034] Exemplarily, when the porous framework structure is arranged on both sides of the current collector, the slurry is coated on the surface of one side of the current collector, and then the first drying, water washing and second drying are sequentially performed to complete the arrangement of the porous framework structure on one side; the coating, first drying and second drying are repeated to arrange the porous framework structure on both sides of the current collector to obtain the self-supporting lithium-free negative electrode sheet.

[0035] In one embodiment, the mixing method of the carbon material and the lithium storage material comprises a first ball milling.

[0036] In one embodiment, the first ball milling is performed in a planetary ball mill.

[0037] In one embodiment, the rotation speed of the first ball milling is 100-300 rpm, for example, 100 rpm, 150 rpm, 200 rpm, 250 rpm or 300 rpm, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0038] The rotation speed of the first ball milling in the present application refers to the rotation speed of the planetary ball mill.

[0039] In one embodiment, the time of the first ball milling is 6-10 h, for example, 6 h, 7 h, 8 h, 9 h or 10 h, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0040] In one embodiment, the mixing method of the nucleating material and the first mixture comprises a second ball milling.

[0041] In one embodiment, the second ball milling is performed in a planetary ball mill.

[0042] In one embodiment, the rotation speed of the second ball milling is 100-300 rpm, for example, 100 rpm, 150 rpm, 200 rpm, 250 rpm or 300 rpm, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0043] The rotation speed of the second ball milling in the present application refers to the rotation speed of the planetary ball mill.

[0044] In one embodiment, the time of the second ball milling is 6-10 h, for example, 6 h, 7 h, 8 h, 9 h or 10 h, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0045] In an embodiment, the method of mixing the binder, the solvent, and the second mixture comprises a third ball milling.

[0046] In an embodiment, the third ball milling is performed in a planetary ball mill.

[0047] In an embodiment, the third ball milling is performed at a rotation speed of 100-300 rpm, such as 100 rpm, 150 rpm, 200 rpm, 250 rpm, or 300 rpm, but not limited to the listed values, and other values not listed in the range are also applicable.

[0048] In the present application, the rotation speed of the third ball milling refers to the rotation speed of the planetary ball mill.

[0049] In an embodiment, the third ball milling is performed for a time of 10-15 h, such as 10 h, 11 h, 12 h, 13 h, 14 h, or 15 h, but not limited to the listed values, and other values not listed in the range are also applicable.

[0050] In an embodiment, the pore-forming agent comprises a water-soluble salt.

[0051] In an embodiment, the water-soluble salt comprises NaCl and / or KCl.

[0052] In an embodiment, the pore-forming agent is added in a mass of 10-30 wt% of the total mass of the carbon material, the lithium storage material, the nucleating material, and the binder, such as 10 wt%, 12 wt%, 14 wt%, 16 wt%, 18 wt%, 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, or 30 wt%, but not limited to the listed values, and other values not listed in the range are also applicable.

[0053] In the present application, the role of the pore-forming agent is to form pores for the negative electrode sheet, and the pore-forming agent is added in a mass of 10-30 wt% of the total mass of the carbon material, the lithium storage material, the nucleating material, and the binder. If the content of the pore-forming agent is too low, it is not possible to form a porous framework structure, and the space provided for lithium ions is reduced, and the role of the porous framework structure in relieving volume expansion cannot be played. If the content of the pore-forming agent is too high, a large number of pores are formed in the film, the content of the binder is reduced, and it is not possible to form a self-supporting network connection structure.

[0054] In an embodiment, the solvent comprises water.

[0055] In an embodiment, the solid content of the slurry is 14-20 wt%, for example 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or 20 wt%, but is not limited to the listed values, and other unlisted values within the range of values are also applicable.

[0056] The present application enables the solid content of the slurry to be within a suitable range, avoiding the defect that the negative electrode sheet is prone to breakage due to low strength during film formation, and also avoiding the defect that the pore-forming agent cannot be completely removed.

[0057] In an embodiment, the coating includes cast film formation.

[0058] The nucleating material and the like have a large weight, and can be distributed from bottom to top during the casting process. Due to the weight of the nucleating material itself, a part of the nucleating material is dispersed and distributed on the current collector. During the charging and discharging process, the nucleating material is more likely to obtain energy in the current collector, thereby gradually diffusing onto the current collector, and further inducing lithium to deposit from a position close to the current collector and penetrate into the skeleton structure, avoiding the deposition of lithium on the surface of the self-supporting lithium-free negative electrode sheet, and being conducive to improving the initial efficiency and lithium storage capacity.

[0059] In addition, the process of cast film formation is matched with the use of the binder of the present application, which can improve the stability of the obtained self-supporting lithium-free negative electrode sheet, and has certain compatibility with the existing lithium ion negative electrode preparation process.

[0060] The equipment used for cast film formation includes a doctor blade, and the height of the doctor blade for cast film formation is 100-300 pm, for example 100 pm, 120 pm, 140 pm, 160 pm, 180 pm, 200 pm, 220 pm, 240 pm, 260 pm, 280 pm, or 300 pm, but is not limited to the listed values, and other unlisted values within the range of values are also applicable.

[0061] In an embodiment, the current collector includes a copper foil.

[0062] In an embodiment, the temperature of the first drying is 70-90°C, for example 70°C, 75°C, 80°C, 85°C, or 90°C, but is not limited to the listed values, and other unlisted values within the range of values are also applicable.

[0063] In an embodiment, the time of the first drying is 10-15 h, for example 10 h, 11 h, 12 h, 13 h, 14 h, or 15 h, but is not limited to the listed values, and other unlisted values within the range of values are also applicable.

[0064] In the present application, the film is washed after the first drying, and the washing is to flush away the pore-forming agent to form a porous framework structure of the coated film. If the pore-forming is not performed, the porous framework structure cannot be formed.

[0065] In one embodiment, the temperature of the second drying is 110-130℃, for example 110℃, 115℃, 120℃, 125℃ or 130℃, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0066] In one embodiment, the time of the second drying is 10-15h, for example 10h, 11h, 12h, 13h, 14h or 15h, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0067] In a third aspect, the present application provides a lithium battery, comprising the self-supporting lithium-free negative electrode sheet of the first aspect.

[0068] Compared with the related art, the present application has at least the following beneficial effects:

[0069] (1) The framework structure in the self-supporting lithium-free negative electrode sheet provided by the present application provides necessary space for lithium storage, solves the problem of high volume shrinkage and expansion of the battery negative electrode during charging and discharging, and also provides a high-speed transmission channel for electrons, reduces ion concentration polarization, and is beneficial to lithium ion deposition; the nucleation material and the energy storage material cooperate to reduce the nucleation barrier in the porous framework structure, induce rapid and uniform deposition of lithium from the bottom of the current collector to the electrolyte during preparation, promote lithium deposition in the framework of the porous framework structure, avoid the problem of easy volume expansion caused by lithium deposition outside the framework, and avoid the problem of uneven lithium ion deposition; the use of the binder can improve the stability of the self-supporting lithium-free negative electrode sheet, and avoid the problems of structure collapse and poor negative electrode adhesion;

[0070] (2) The lithium ion full-solid-state battery assembled by the self-supporting three-dimensional network lithium-free negative electrode sheet prepared by the present application has a coulombic efficiency of 98% or more after 100 cycles, a nucleation overpotential of 30mV or less, and a volume change rate of 2% or less. The polarization voltage of the symmetrical battery is 0.15V or less after 100 cycles.

[0071] Other aspects can be apparent to those skilled in the art after reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0072] The accompanying drawings are used to provide a further understanding of the technical solutions of the present application, and constitute a part of the specification, and together with the embodiments of the present application, are used to explain the technical solutions of the present application, and do not constitute a limitation on the technical solutions of the present application.

[0073] Figure 1 is a SEM image of the porous framework structure in the self-supporting lithium-free negative electrode sheet obtained in Example 1;

[0074] Figure 2 is a nucleation overpotential graph of Example 1;

[0075] Figure 3 is a nucleation overpotential graph of Example 6;

[0076] Figure 4 is a nucleation overpotential graph of Comparative Example 1. DETAILED DESCRIPTION

[0077] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations of the present application.

[0078] Example 1

[0079] The present embodiment provides a self-supporting lithium-free negative electrode sheet, which comprises a copper foil, a porous framework structure arranged on one side of the copper foil, and a lithium storage material and a nucleation material distributed on the porous framework structure;

[0080] The porous framework structure comprises a carbon material and a binder polyacrylic acid (Blue Whale Black Stone BA-290SPAA) lapped between the carbon material;

[0081] The lithium storage material is Si with a median particle size of 1 μm;

[0082] The nucleation material is Ag with a median particle size of 50 nm;

[0083] The carbon material is carbon fiber VGCF (Showa Denko VGCF-H);

[0084] The mass ratio of the lithium storage material to the carbon material is 1:7;

[0085] The mass of the nucleation material accounts for 4 wt% of the total mass of the lithium storage material and the carbon material;

[0086] The mass of the binder accounts for 5 wt% of the total mass of the lithium storage material and the carbon material;

[0087] The preparation method of the self-supporting lithium-free negative electrode sheet of the present embodiment comprises the following steps:

[0088] (1) First ball-mill mix the carbon material and the lithium storage material with a mass ratio of 1:7 to obtain a first mixture; the first ball-milling uses a planetary ball mill with a rotation speed of 200 rpm for 8 h;

[0089] (2) then the nucleation material and pore-forming agent NaCl are second ball-milled with the first mixture to obtain a second mixture; the pore-forming agent accounts for 20% of the total mass of the carbon material, lithium storage material, nucleation material and binder; the second ball-milling is planetary ball-milling at a speed of 200 rpm for 8 h;

[0090] (3) the binder, water and the second mixture are third ball-milled to obtain a slurry with a solid content of 17%; the third ball-milling is planetary ball-milling at a speed of 200 rpm for 13 h;

[0091] (4) the prepared slurry is coated on a copper foil to be cast into a film, then first dried at 80℃ in a vacuum drying oven for 12 h to obtain a thin film; the obtained thin film is then washed with deionized water to form pores; finally, the thin film after pore formation is second dried at 120℃ in a vacuum drying oven for 12 h to obtain a self-supporting lithium-free negative electrode sheet.

[0092] The SEM image of the porous framework structure in the self-supporting lithium-free negative electrode sheet obtained in this example is shown in FIG. 1.

[0093] Example 2

[0094] This example provides a self-supporting lithium-free negative electrode sheet, which comprises a copper foil, a porous framework structure arranged on one side of the copper foil, and a lithium storage material and a nucleation material distributed on the porous framework structure;

[0095] The porous framework structure comprises a carbon material and a binder carboxymethylcellulose sodium (Celloid CMC2200) bridged between the carbon material;

[0096] The lithium storage material is SiO with a median particle size of 100 nm;

[0097] The nucleation material is ZnO with a median particle size of 60 nm;

[0098] The carbon material is single-walled carbon nanotube (Merck single-arm carbon nanotube 755710);

[0099] The mass ratio of the lithium storage material to the carbon material is 1:5;

[0100] The mass of the nucleation material accounts for 1 wt% of the total mass of the lithium storage material and the carbon material;

[0101] The mass of the binder accounts for 2 wt% of the total mass of the lithium storage material and the carbon material;

[0102] The preparation method of the self-supporting lithium-free negative electrode sheet in this example comprises the following steps:

[0103] (1) first ball-mixing carbon material and lithium storage material to obtain a first mixture; the first ball-milling is planetary ball-milling, the rotation speed is 100 rpm, and the time is 10 h;

[0104] (2) then second ball-mixing nucleation material and pore-forming agent KCl with the first mixture to obtain a second mixture; the pore-forming agent accounts for 10% of the total mass of carbon material, lithium storage material, nucleation material and binder; the second ball-milling is planetary ball-milling, the rotation speed is 100 rpm, and the time is 10 h;

[0105] (3) third ball-mixing binder, water and the second mixture to obtain a slurry with a solid content of 14%; the third ball-milling is planetary ball-milling, the rotation speed is 100 rpm, and the time is 15 h;

[0106] (4) coating the prepared slurry on a copper foil to flow into a film, then first drying at 70℃ in a vacuum drying oven for 15 h to obtain a thin film; then rinsing the obtained thin film with deionized water to form pores; finally, the film after pore-forming is second dried at 110℃ in a vacuum drying oven for 15 h to obtain a self-supporting lithium-free negative electrode sheet.

[0107] Example 3

[0108] The self-supporting lithium-free negative electrode sheet provided in this embodiment includes a copper foil, a porous framework structure arranged on one side of the copper foil, and a lithium storage material and a nucleation material distributed on the porous framework structure;

[0109] The porous framework structure includes carbon material and binder SBR (Riken 430B) lapped between the carbon material;

[0110] The lithium storage material is a combination of CoSe and Co3O4 with a median particle size of 1 μm, and the mass ratio of CoSe to Co3O4 is 1:1;

[0111] The nucleation material is Mo2N with a median particle size of 60 nm;

[0112] The carbon material is multi-walled carbon nanotube (Merck single-arm carbon nanotube 755133);

[0113] The mass ratio of the lithium storage material to the carbon material is 1:10;

[0114] The mass of the nucleation material accounts for 8 wt% of the total mass of the lithium storage material and the carbon material;

[0115] The mass of the binder accounts for 8 wt% of the total mass of the lithium storage material and the carbon material;

[0116] The preparation method of the self-supporting lithium-free negative electrode sheet provided in this embodiment includes the following steps:

[0117] (1) First ball-milling of carbon material and lithium storage material to obtain a first mixture; the first ball-milling is performed by planetary ball-milling at a speed of 300 rpm for 6 h;

[0118] (2) Then, second ball-milling of nucleation material and pore-forming agent (KCl and NaCl at a mass ratio of 1:1) with the first mixture to obtain a second mixture; the pore-forming agent accounts for 30% of the total mass of carbon material, lithium storage material, nucleation material and binder; the second ball-milling is performed by planetary ball-milling at a speed of 300 rpm for 6 h;

[0119] (3) Third ball-milling of binder, water and the second mixture to obtain a slurry with a solid content of 20%; the third ball-milling is performed by planetary ball-milling at a speed of 300 rpm for 10 h;

[0120] (4) Casting the prepared slurry on a copper foil to form a film, then first drying at 90°C in a vacuum drying oven for 10 h to obtain a thin film; then rinsing the obtained thin film with deionized water to form pores; finally, second drying of the film with pores at 130°C in a vacuum drying oven for 10 h to obtain a self-supporting lithium-free negative electrode sheet.

[0121] Example 4

[0122] The self-supporting lithium-free negative electrode sheet of the present embodiment is different from that of Example 1 only in that the mass ratio of lithium storage material to carbon material is 1:4, and the rest is the same as that of Example 1.

[0123] Example 5

[0124] The self-supporting lithium-free negative electrode sheet of the present embodiment is different from that of Example 1 only in that the mass ratio of lithium storage material to carbon material is 1:11, and the rest is the same as that of Example 1.

[0125] Example 6

[0126] The self-supporting lithium-free negative electrode sheet of the present embodiment is different from that of Example 1 only in that the nucleation material accounts for 0.5% of the total mass of carbon material and lithium storage material, and the rest is the same as that of Example 1.

[0127] Example 7

[0128] The self-supporting lithium-free negative electrode sheet of the present embodiment is different from that of Example 1 only in that the nucleation material accounts for 9% of the total mass of carbon material and lithium storage material, and the rest is the same as that of Example 1.

[0129] Example 8

[0130] The embodiment provides a self-supporting lithium-free negative electrode sheet, which is different from the embodiment 1 only in that the pore forming agent accounts for 5% of the total mass of the carbon material, the lithium storage material, the nucleating material and the binder, and the rest is the same as the embodiment 1.

[0131] Embodiment 9

[0132] The embodiment provides a self-supporting lithium-free negative electrode sheet, which is different from the embodiment 1 only in that the pore forming agent accounts for 35% of the total mass of the carbon material, the lithium storage material, the nucleating material and the binder, and the rest is the same as the embodiment 1.

[0133] Embodiment 10

[0134] The embodiment provides a self-supporting lithium-free negative electrode sheet, which is different from the embodiment 1 only in that the binder accounts for 1% of the total mass of the carbon material and the lithium storage material, and the rest is the same as the embodiment 1.

[0135] Embodiment 11

[0136] The embodiment provides a self-supporting lithium-free negative electrode sheet, which is different from the embodiment 1 only in that the binder accounts for 9% of the total mass of the carbon material and the lithium storage material, and the rest is the same as the embodiment 1.

[0137] Embodiment 12

[0138] The embodiment provides a self-supporting lithium-free negative electrode sheet, which is different from the embodiment 1 only in that the third ball milling is mixed to obtain a slurry with a solid content of 10%, and the rest is the same as the embodiment 1.

[0139] Embodiment 13

[0140] The embodiment provides a self-supporting lithium-free negative electrode sheet, which is different from the embodiment 1 only in that the third ball milling is mixed to obtain a slurry with a solid content of 25%, and the rest is the same as the embodiment 1.

[0141] Comparative Example 1

[0142] The comparative example provides a lithium foil as a negative electrode material and a copper foil as a positive electrode material.

[0143] Comparative Example 2

[0144] The comparative example provides a negative electrode sheet and a preparation method thereof, which are different from the embodiment 1 only in that the nucleating material and the lithium storage material are not contained, and only the carbon material and the binder are contained, and the rest is the same as the embodiment 1.

[0145] Comparative Example 3

[0146] The comparative example provides a negative electrode sheet and a preparation method thereof, which are different from the embodiment 1 only in that the nucleating material is not contained, and the rest is the same as the embodiment 1.

[0147] Comparative Example 4

[0148] This comparative example provides a negative electrode sheet and a preparation method thereof, which is different from Example 1 only in that it does not contain a pore-forming agent, and the rest is the same as Example 1.

[0149] Comparative Example 5

[0150] This comparative example provides a negative electrode sheet and a preparation method thereof, which is different from Example 1 only in that it does not contain a lithium storage material, and the rest is the same as Example 1.

[0151] Performance test

[0152] The self-supporting lithium-free negative electrode sheet provided by the examples and comparative examples is subjected to the following performance test, and the test results are shown in Table 1 below.

[0153] Table 1

[0154] Among them, the test method is:

[0155] (1) Adhesion test: the side of the electrode sheet with active material is pasted on the stretching part with 401 quick-drying adhesive, the stretching part is pulled at an angle of 90°, and the pulling force F when the stretching part falls off is recorded;

[0156] (2) Charge-discharge coulombic efficiency, nucleation overpotential, volume change rate test:

[0157] First, assemble the half battery: use the lithium-free negative electrode sheet prepared by the above examples, comparative examples 2-5 as one end of the half battery, and use a lithium foil with a thickness of 50 μm as the other end, at the same time, the lithium foil is negative and the copper foil is positive in comparative example 1, and LiPSCl sulfide solid-state electrolyte (the ionic conductivity of the electrolyte used is > 1 mS / cm) is used as the electrolyte to assemble a full solid-state lithium ion half battery, and the full solid-state lithium ion half battery is assembled into a solid-state battery clamp, the pressure of the clamp on the half battery is 5 MPa, and the performance test is carried out at a charge-discharge current density of 1 mA / cm 2 , the charge-discharge capacity is 5 mAh / cm 2 , test the coulombic efficiency, nucleation overpotential (nucleation process is driven by electrochemistry, the initial peak value on the voltage curve represents the nucleation overpotential that needs to be overcome), and the volume change rate in the thickness direction of the whole battery before and after charge-discharge, wherein the unit of coulombic efficiency is %;

[0158] (3) Polarization voltage test: first assemble a symmetric battery: use the lithium-free negative electrode sheet prepared in the above examples, examples 2-5 as two sections of the symmetric battery, use LiPSCl sulfide solid-state electrolyte (the ionic conductivity of the electrolyte used is >1 mS / cm) as the electrolyte to assemble a full solid-state lithium ion symmetric battery, the pressure of the clamp on the whole battery is 5 MPa, the cycle performance test is carried out at a current of 1 mA / cm 2 The polarization voltage is tested by cycling 100 cycles with a current of 1 mA / cm

[0159] From the test results, it can be seen that:

[0160] (1) As can be seen from examples 1 to 3, figures 1-2 and table 1, the skeleton structure in the self-supporting lithium-free negative electrode sheet provided by the present application provides the necessary space for lithium storage, solves the problem of high volume shrinkage and expansion of the battery negative electrode during charging and discharging, and also provides a high-speed transmission channel for electrons, reduces the concentration polarization of ions, and is conducive to lithium ion deposition; the nucleation material and lithium storage material distributed on the porous skeleton structure can reduce the nucleation barrier in the porous skeleton structure, can induce rapid and uniform deposition of lithium from the bottom of the current collector to the electrolyte direction during charging and discharging, and can promote lithium deposition in the frame of the porous skeleton structure, avoiding the problem of easy expansion of volume caused by lithium deposition outside the frame, and also avoiding the problem of uneven lithium ion deposition; the use of the binder can improve the stability of the self-supporting lithium-free negative electrode sheet, avoiding the problems of structure collapse or poor negative electrode adhesion; the lithium ion full solid-state battery assembled by the self-supporting lithium-free negative electrode sheet has a coulomb efficiency of more than 98% after 100 cycles, the nucleation overpotential is below 30 mV, the volume change rate is below 2%, and the polarization voltage of the symmetric battery is below 0.15 V after 100 cycles;

[0161] (2) As can be seen from the comparison of example 1 and examples 4-5, by controlling the mass ratio of lithium storage material to carbon material to meet 1:(5-10), the lithium storage material is dispersed in the porous skeleton structure composed of carbon material to induce lithium deposition, which can provide a strong conductive framework, expand the reaction surface and adjust the Li + flux, provide the necessary space for lithium storage, and reduce the negative electrode expansion;

[0162] (3) As can be seen from examples 1 and examples 6-7 and figure 1-3, by controlling the mass of the nucleation material to be 1-8 wt% of the total mass of the lithium storage material and the carbon material, the nucleation barrier of lithium deposition can be reduced, ensuring uniform deposition under high rate conditions, and avoiding lithium deposition growth outside the porous skeleton structure;

[0163] (4) By comparing Example 1 with Examples 8-9, it can be seen that by controlling the mass of the binder to account for 2-8wt% of the total mass of the lithium storage material and the carbon material, the stability of the porous framework structure and the lapping and distribution of the lithium storage material and the nucleation material on the porous framework structure can be improved without affecting the conductivity of the porous framework structure;

[0164] (5) By comparing Example 1 with Examples 10-11, it can be seen that by controlling the mass of the pore-forming agent to account for 10-30wt% of the total mass of the carbon material, the lithium storage material, the nucleation material, and the binder, sufficient space can be provided for lithium storage, promoting the lithium storage material and the nucleation material to induce lithium deposition to grow under the current collector within the porous framework structure, avoiding lithium deposition to accumulate and grow on the surface of the porous framework structure, and reducing the swelling of the negative electrode;

[0165] (6) By comparing Example 1 with Examples 12-13, it can be seen that by controlling the solid content of the slurry to be 14-20wt%, the defect of low strength and easy fragmentation of the negative electrode sheet during film formation can be avoided, and the defect of incomplete removal of the pore-forming agent can also be avoided, improving the uniformity of the film-forming slurry and the stability of the negative electrode sheet;

[0166] (7) By comparing Example 1 with Comparative Example 1 and Figures 1, 2, and 4, it can be seen that, compared with the traditional lithium foil as the negative electrode, the self-supporting three-dimensional network-shaped lithium-free negative electrode sheet prepared by the application can well improve the coulombic effect of the battery, reduce the nucleation overpotential of the battery, reduce the nucleation barrier of lithium ions, accelerate the uniform deposition of lithium ions, and significantly improve the volume expansion of the battery, and the long cycle stability of the battery is well improved;

[0167] (8) By comparing Example 1 with Comparative Examples 2 and 3 and Figures 1-2, it can be seen that by adding the nucleation material and the lithium storage material in the application, the nucleation barrier of lithium ions during the charging and discharging process of the battery can be significantly reduced, the lithium can be induced to deposit rapidly and uniformly from the bottom of the current collector to the electrolyte direction during the preparation process, the lithium can be deposited within the framework of the porous framework structure, and problems such as easy volume expansion caused by lithium deposition outside the framework and uneven deposition of lithium ions can be avoided;

[0168] (9) By comparing Example 1 with Comparative Example 4, it can be seen that by adding the pore-forming agent, the negative electrode sheet forms a porous framework structure, providing space for the deposition of lithium ions and achieving the effect of relieving the volume expansion of the negative electrode;

[0169] (10) By comparing Example 1 with Comparative Example 5, it can be seen that by adding the lithium storage material, the lithium is promoted to deposit within the framework of the porous framework structure, reducing the volume expansion of the battery and promoting the uniform deposition of lithium.

[0170] In summary, the porous framework structure in the self-supporting lithium-free anode sheet provided in this application provides the necessary space for lithium storage, solving the problem of high volume shrinkage and expansion of the battery anode during charging and discharging. It also provides a high-speed electron transport channel, reducing ion concentration polarization and facilitating lithium-ion deposition. The synergistic effect of the nucleating material and the lithium storage material in the porous framework structure lowers the nucleation barrier, inducing rapid and uniform lithium deposition from the bottom of the current collector towards the electrolyte during charging and discharging. This promotes lithium deposition within the framework of the porous framework, avoiding problems such as easy volume expansion caused by lithium deposition outside the framework, and preventing uneven lithium-ion deposition. The use of a binder enhances the stability of the self-supporting lithium-free anode sheet, preventing structural collapse or poor anode bonding.

[0171] The applicant declares that the above description is only a specific implementation of this application, but the protection scope of this application is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application fall within the protection and disclosure scope of this application.

Claims

1. A self-supporting lithium-free negative electrode sheet, comprising a current collector, a porous framework structure disposed on at least one side of the current collector, and a lithium storage material and a nucleation material distributed on the porous framework structure. The porous framework structure comprises a carbon material and a binder bridging between the carbon materials. The lithium storage material comprises any one or a combination of at least two of Si, SiO, CoSe or Co 3 O 4. The nucleation material comprises any one or a combination of at least two of Ag, ZnO, MgO or Mo 2 N. The mass ratio of the lithium storage material to the carbon material is 1: (5-10). The mass of the nucleation material accounts for 1-8 wt% of the total mass of the lithium storage material and the carbon material. The mass of the binder accounts for 2-8 wt% of the total mass of the lithium storage material and the carbon material.

2. The self-supporting lithium-free negative electrode sheet according to claim 1, wherein The median particle size of the lithium storage material is 60 nm-10 μm.

3. The self-supporting lithium-free negative electrode sheet according to claim 1, wherein The median particle size of the nucleation material is 30-100 nm.

4. The self-supporting lithium-free negative electrode sheet of claim 1, wherein, The carbon material comprises any one or a combination of at least two of single-walled carbon nanotubes, multi-walled carbon nanotubes or carbon fibers.

5. The self-supporting lithium-free negative electrode sheet of claim 1, wherein, The binder comprises a water-based binder. 6.A method for preparing the self-supporting lithium-free negative electrode sheet according to any one of claims 1-5, comprising the following steps: mixing the carbon material and the lithium storage material to obtain a first mixture; then mixing the nucleation material and a pore-forming agent with the first mixture to obtain a second mixture; then mixing the binder, a solvent and the second mixture to obtain a slurry; coating the slurry on the surface of the current collector, performing a first drying, then water washing, and then performing a second drying to obtain the self-supporting lithium-free negative electrode sheet.

7. The production method according to claim 6, wherein The pore-forming agent comprises a water-soluble salt. The added mass of the pore-forming agent accounts for 10-30 wt% of the total mass of the carbon material, the lithium storage material, the nucleation material and the binder.

8. The production method according to claim 6, wherein The solid content of the slurry is 14-20 wt%. The temperature of the first drying is 70-90 ℃, and the time is 10-15 h. The temperature of the second drying is 110-130 ℃, and the time is 10-15 h.

9. The production method according to claim 6, wherein The coating method comprises flow casting.

10. A lithium battery wherein, The lithium battery comprises the self-supporting lithium-free negative electrode sheet according to any one of claims 1-5.

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