A lithium metal negative electrode and its preparation method and application

Abstract

The present invention provides a lithium metal anode, a preparation method, and an application thereof. The active layer of the lithium metal anode includes a hollow active material and a solid electrolyte. The pores within the hollow active material contain lithium metal. The hollow active material is doped with a lithium-philic substance and / or the internal pore walls are loaded with a lithium-philic layer. In the lithium metal anode of the present invention, the lithium metal is located in the pores within the hollow active material. In combination with the solid electrolyte, this prevents lithium deposition on the surface of the lithium metal anode. The lithium metal also has sufficient expansion space for deposition and dissolution, which can relieve the stress of lithium deposition. Therefore, the lithium metal anode of the present invention improves the safety and electrochemical performance of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a lithium metal negative electrode and a preparation method and application thereof. Background Art

[0002] In recent years, with the demand for high-energy-density and highly safe chemical power sources in electronics such as smartphones, tablets, and electric vehicles, the energy density of commercial lithium-ion secondary batteries with graphite as the negative electrode has been limited and has almost reached its limit. Among lithium-ion secondary batteries, metallic lithium has the most negative electrode potential (-3.045V) and the highest specific capacity (3860mAh / g), which can meet the high energy density requirements of electrode materials. In addition, the organic electrolytes currently used in lithium-ion secondary batteries have safety issues such as flammability, corrosion, and poor thermal stability, which have restricted the development of traditional lithium-ion batteries. All-solid-state batteries can address these safety risks, making all-solid-state batteries with lithium as the negative electrode a hot topic of research.

[0003] However, when metallic lithium is used as the negative electrode, the cycle life of the lithium secondary battery is limited by the metallic lithium negative electrode. During the cycle, dendrites will form on the surface of the metallic lithium negative electrode. On the one hand, the dendrites will come into contact with the electrolyte and consume the electrolyte, causing battery failure. On the other hand, the consumption of metallic lithium will lead to low coulombic efficiency of the negative electrode. Moreover, lithium dendrites may pierce the diaphragm, causing internal short circuit of the battery, causing battery safety problems.

[0004] In the existing technology, lithium dendrites are often suppressed by preparing a protective layer or a three-dimensional lithium negative electrode. However, the protective layer will increase the internal resistance of the battery, increase the migration distance of lithium ions, and reduce the ionic and electronic conductivity, thereby affecting the performance of the battery. In addition, the production efficiency of the protective layer or the three-dimensional lithium negative electrode is low, the processing technology is complex, and it is difficult to achieve large-scale negative electrode production. At the same time, when preparing the lithium metal negative electrode, lithium deposition stress exists, which will affect the dissolution and deintercalation of lithium ions in the lithium metal negative electrode during the charge and discharge process.

[0005] Based on the above research, it is necessary to provide a lithium metal negative electrode, which has sufficient expansion space for lithium deposition and dissolution, can inhibit the growth of lithium dendrites, improve the safety of the battery, and at the same time has a simple preparation process, high production efficiency, and can be used on a large scale. Summary of the Invention

[0006] The purpose of the present invention is to provide a lithium metal negative electrode and its preparation method and application. The lithium metal in the lithium metal negative electrode is deposited inside the hollow active material, which not only reduces or avoids the formation of lithium dendrites, but also releases the stress of lithium deposition, thereby improving the electrochemical performance and safety performance of the battery.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a lithium metal negative electrode, wherein the active layer of the lithium metal negative electrode comprises a hollow active material and a solid electrolyte, wherein the pores of the hollow active material comprise lithium metal;

[0009] The hollow active material is doped with a lithium-philic substance and / or the internal pore wall is loaded with a lithium-philic layer.

[0010] In the lithium metal negative electrode described in the present invention, lithium metal and an active material with a porous hollow structure are matched with each other, so that the lithium metal can be located inside the active layer compared to the hollow active material. The lithium metal located inside the active layer can avoid lithium precipitation on the surface of the lithium metal negative electrode, thereby improving the safety performance of the battery; at the same time, the hollow active material of the present invention has a lithium-philic layer and / or is doped with a lithium-philic substance, which not only improves the affinity for lithium and increases the lithium loading capacity, but also has a high lithium-philicity compared to the surface of the material, so that the lithium metal can be located in the pores of the hollow active material after deposition, thereby avoiding the growth of lithium dendrites on the negative electrode surface; and the porous structure can also provide expansion space for the deposition and dissolution of lithium metal, release the stress of lithium deposition, and thus facilitate the function of lithium metal.

[0011] The lithium metal negative electrode of the present invention also contains a solid electrolyte. The loaded solid electrolyte can be matched with the hollow active material and the lithium metal in the pores to improve the transmission rate of lithium ions, further inhibit the growth of lithium dendrites of the lithium metal in the pores of the hollow active material, reduce the impedance of the battery, and improve the cycle stability of the battery.

[0012] Preferably, the solid electrolyte is coated on the surface of the active layer and is infiltrated and loaded inside the active layer.

[0013] Preferably, the surface of the hollow active material is coated with a solid electrolyte.

[0014] The lithium metal negative electrode of the present invention also contains a solid electrolyte, which is loaded on the surface and inside of the active layer. It not only coats the active layer, but the internally loaded solid electrolyte can also coat the hollow active material, further inhibiting the growth of lithium dendrites, reducing the impedance of the battery, and improving the cycle stability of the battery.

[0015] Preferably, the hollow active material has a spherical or quasi-spherical morphology and a particle diameter of 200-2000 nm, for example, 200 nm, 400 nm, 600 nm, 800 nm, 1000 nm, 1200 nm, 1400 nm, 1600 nm, 1800 nm or 2000 nm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0016] The particle diameter of the hollow active material described in the present invention will affect the lithium metal loading capacity, lithium consumption during the cycle, lithium metal deposition and dissolution rate, etc., thereby affecting the performance of the battery; when the particle diameter of the hollow active material is too large, the lithium metal deposition and dissolution rate will become smaller, which is not conducive to the material rate performance. When the particle diameter of the hollow active material is too small, the lithium loading capacity will be reduced, and the specific surface area will increase, thereby increasing the lithium loss during the cycle.

[0017] Preferably, the hollow active material has at least one hole, for example, 1, 2, 3, 4, 5, 6, 7 or 8 holes, and a diameter of 50-1990 nm, for example, 50 nm, 100 nm, 300 nm, 500 nm, 700 nm, 900 nm, 1100 nm, 1200 nm, 1300 nm, 1500 nm, 1700 nm or 1900 nm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0018] The hollow active material of the present invention includes at least one pore. Since the lithium metal is located inside the pore, the size of the pore will affect the content of stored lithium metal. If the diameter of the pore is too small, the lithium metal content in the pore of the hollow active material is too low, resulting in too low a lithium metal content in the active layer of the lithium metal negative electrode, thereby leading to problems such as a decrease in the specific capacity of the negative electrode. If the diameter of the pore is too large, although more metallic lithium can be stored, the structural stability of the hollow active material will be reduced, resulting in a decrease in the cycle performance of the battery.

[0019] Preferably, the volume of the lithium metal accounts for 5-90% of the internal pore volume of the hollow active material, for example, it can be 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] Preferably, based on the content of the active layer, the content of the solid electrolyte is 1-20wt%, for example, it can be 1wt%, 5wt%, 7wt%, 9wt%, 11wt%, 13wt%, 15wt%, 17wt%, 19wt% or 20wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] Preferably, the thickness of the lithium-philic layer is 1-10 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] Preferably, the content of the doped lithium-philic substance in the hollow active material is 1-5wt%, for example, it can be 1wt%, 2wt%, 3wt%, 4wt% or 5wt%, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0023] Preferably, the thickness of the active layer is 20-150 μm, for example, 20 μm, 40 μm, 80 μm, 100 μm, 130 μm or 150 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] Preferably, the hollow active material comprises a conductor of electrons and ions.

[0025] Preferably, the hollow active material includes any one or a combination of at least two of porous hollow carbon spheres, porous hollow lithium titanate spheres or porous hollow tin spheres. Typical but non-limiting combinations include a combination of porous hollow carbon spheres and porous hollow lithium titanate spheres, or a combination of porous hollow lithium titanate spheres and porous hollow tin spheres.

[0026] Preferably, the lithiophilic layer comprises a transition metal oxide and / or a transition metal sulfide.

[0027] Preferably, the transition metal oxide includes any one or a combination of at least two of ZnO, CuO, SnO or NiO. Typical non-limiting combinations include a combination of ZnO and CuO, or a combination of SnO and NiO.

[0028] Preferably, the transition metal sulfide includes any one or a combination of at least two of ZnS, CuS, SnS or NiS. Typical but non-limiting combinations include a combination of ZnS and CuS, and a combination of ZnS and SnS.

[0029] Preferably, the lithiophilic species comprises nitrogen and / or sulfur.

[0030] When the hollow active material of the present invention is a porous hollow carbon sphere, a lithiophilic substance source, such as a nitrogen source and / or a sulfur source, can be incorporated into the porous hollow carbon sphere during its preparation, so that nitrogen and / or sulfur serving as lithiophilic substances are doped into the porous hollow carbon sphere.

[0031] Preferably, the solid electrolyte includes any one or a combination of at least two of a polymer solid electrolyte, an oxide solid electrolyte, a LiPON-type electrolyte, a sulfide crystalline solid electrolyte, a sulfide glassy electrolyte or a glass ceramic solid electrolyte.

[0032] Preferably, the polymer solid electrolyte includes any one of polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polypropylene oxide (PPO) or polyvinylidene chloride (PVDC) or a combination of at least two; the oxide solid electrolyte includes a crystalline electrolyte including any one of perovskite type, NASICON type, LISICON type or garnet type or a combination of at least two; the sulfide crystalline solid electrolyte LISICON; the sulfide glass electrolyte includes any one of Li2S-P2S5, Li2S-SiS2 or Li2S-B2S3 or a combination of at least two.

[0033] Preferably, the active layer further includes a conductive agent and a binder.

[0034] Preferably, the mass ratio of the hollow active material, the conductive agent and the binder is (92-95):(2-4):(3-4), for example, it can be 92:4:4, 93:4:3 or 95:2:3, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] The conductive agent, binder and hollow active material in the active layer of the present invention constitute a complete conductive network, wherein the conductive agent includes any one of conductive carbon black, conductive carbon nanotubes, acetylene black, Ketjen black or conductive carbon fibers, or a combination of at least two of them. Typical but non-limiting combinations include a combination of conductive carbon black and conductive carbon nanotubes, or a combination of acetylene black and conductive carbon nanotubes. The binder includes any one of polyvinylidene fluoride, styrene-butadiene rubber or sodium carboxymethyl cellulose, or a combination of at least two of them. Typical but non-limiting combinations include a combination of polyvinylidene fluoride and styrene-butadiene rubber, or a combination of styrene-butadiene rubber and sodium carboxymethyl cellulose.

[0036] Preferably, the lithium metal negative electrode further comprises a current collector, and the active layer is disposed on at least one side of the current collector.

[0037] Preferably, the current collector comprises copper or porous copper.

[0038] Preferably, the thickness of the current collector is 4-50 μm, for example, it can be 4 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] In a second aspect, the present invention provides a method for preparing a lithium metal negative electrode as described in the first aspect, the preparation method comprising the following steps:

[0040] (1) doping the hollow active material with a lithiophilic substance and / or preparing a lithiophilic layer on the pore wall of the hollow active material to obtain an internally lithiophilic active material;

[0041] (2) slurrying and coating the internal lithium-philic active material in step (1) to obtain an active layer, and then depositing lithium metal to obtain the lithium metal negative electrode;

[0042] The active layer further comprises the step of loading a solid electrolyte on the surface and inside of the active layer before depositing lithium metal and / or after depositing lithium metal.

[0043] In the preparation process of the lithium metal negative electrode described in the present invention, a lithium-philic substance is first doped into the hollow active material, and / or a lithium-philic layer is deposited on the pore wall. Then, the hollow active material is slurried with a conductive agent, a binder and a solvent, and coated on the current collector to form a complete conductive network. Then, lithium metal is deposited. Since the interior of the hollow active material has a higher lithium-philicity and contains pores, the internal specific surface area is larger. Therefore, after the lithium metal is deposited, the lithium metal can be loaded in the pores of the hollow active material, and will not be loaded on the surface of the active layer or only a very small amount is loaded on the surface of the active layer.

[0044] The present invention can load the solid electrolyte before or after depositing lithium metal. Loading before depositing lithium metal is more advantageous. If the solid electrolyte is loaded after depositing lithium metal, the solid electrolyte will not penetrate completely due to the inevitable deposition of some lithium in the gaps between the hollow active materials, making the solid electrolyte coating the hollow active materials uneven.

[0045] Preferably, the method of loading the solid electrolyte in step (2) includes a tape casting method, a spraying method or a sputtering deposition method.

[0046] When loading the solid electrolyte, the present invention prepares a slurry of the solid electrolyte, lithium salt and additives, applies the slurry on the active layer, and draws air below the active layer so that the solid electrolyte covers the active layer and penetrates into the active layer. At the same time, the solid electrolyte penetrated into the active layer can also cover the hollow active material and fill the gaps in the hollow active material. The lithium salt includes any one of LiPF6, LiBF4 or LiTFSI or a combination of at least two of them, and the additive includes any one of a plasticizer, a coupling agent or a binder or a combination of at least two of them.

[0047] Preferably, the plasticizer includes any one or a combination of at least two of di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP) or diethyl phthalate (DEP); the coupling agent includes a silane coupling agent and / or a titanate coupling agent; and the binder includes but is not limited to PVDF.

[0048] Preferably, the method for depositing lithium metal in step (2) includes electrochemical deposition or melting method.

[0049] Preferably, the method for preparing the lithium-philic layer in step (1) includes any one of a template method, a vapor phase chemical deposition method, a liquid phase chemical deposition method or a high temperature reaction method.

[0050] Preferably, the method for preparing the hollow active material in step (1) includes any one of a template method, a vapor phase chemical deposition method, a liquid phase chemical deposition method or a high temperature reaction method.

[0051] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises the following steps:

[0052] (1) doping the hollow active material with a lithiophilic substance, and / or preparing a lithiophilic layer on the pore wall of the hollow active material by a template method, a vapor phase chemical deposition method, a liquid phase chemical deposition method, or a high temperature reaction method, to obtain an internally lithiophilic active material;

[0053] (2) After the internal lithium-philic active material of step (1) is slurried and coated to obtain an active layer, a solid electrolyte is loaded on the surface and inside of the active layer by a casting method, a spraying method or a sputtering deposition method, and then lithium metal is deposited by an electrochemical deposition method or a melting method to obtain the lithium metal negative electrode.

[0054] In a third aspect, the present invention provides a solid-state battery, comprising the lithium metal negative electrode as described in the first aspect.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] (1) The lithium metal in the lithium metal negative electrode of the present invention is inside the hollow active material, which not only prevents lithium deposition on the surface of the lithium metal negative electrode and improves the safety performance of the battery, but also provides expansion space for the deposition and dissolution of lithium metal, thereby releasing the stress of lithium deposition;

[0057] (2) The lithium metal negative electrode of the present invention further includes a solid electrolyte, which can coat the active layer and the porous hollow active material, further improving the safety performance of the lithium metal negative electrode, while reducing the impedance of the battery and improving the cycle stability of the battery;

[0058] (3) The lithium metal negative electrode preparation process of the present invention is simple. When preparing the lithium metal negative electrode, the porous hollow active material is slurried and coated on the current collector to provide a deposition site for the lithium metal. Therefore, compared with the conventional lithium metal negative electrode, only one more step of slurrying and coating is required, which can make the lithium metal negative electrode have excellent performance and high production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 Schematic diagram of the structure of the hollow active material according to Example 1 of the present invention;

[0060] Figure 2 Schematic diagram of the structure of the lithium metal negative electrode according to Example 1 of the present invention;

[0061] Among them, 1-hollow active material, 2-pore, 3-solid electrolyte, 4-current collector. DETAILED DESCRIPTION

[0062] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0063] Example 1

[0064] This embodiment provides a lithium metal negative electrode, the lithium metal negative electrode is as follows Figure 2 As shown, it includes a current collector 4 and an active layer with a thickness of 20 μm on the surface of the current collector 4, the active layer includes a hollow active material 1, conductive carbon black SP, CMC and SBR in a mass ratio of 93:2:2:3, and the surface and interior of the active layer also include a solid electrolyte 3;

[0065] The hollow active material 1 is a porous hollow carbon sphere with a diameter of 1580 nm. The structural diagram is shown in FIG. Figure 1 As shown, the interior includes one pore 2 with a diameter of 200 nm, one pore 2 with a diameter of 250 nm, and two pores 2 with diameters of 300 nm. The interior of the pore 2 is loaded with lithium metal, which accounts for 60% of the volume of the pore 2. The porous hollow carbon sphere is doped with 1 wt% nitrogen.

[0066] The solid electrolyte 3 is PEO (polyethylene oxide), and its content is 10 wt% based on the content of the active layer; the current collector 4 is porous copper with a thickness of 20 μm;

[0067] The preparation method of the lithium metal negative electrode comprises the following steps:

[0068] (1) The porous hollow carbon spheres were heat-treated in an ammonia atmosphere for 2 h to obtain nitrogen-doped porous hollow carbon spheres;

[0069] (2) mixing the nitrogen-doped porous hollow carbon spheres, conductive carbon black SP, CMC, SBR and water described in step (1) to form a slurry, and coating the slurry on the porous copper to obtain an active layer;

[0070] (3) PEO, LiTFSI and dibutyl phthalate are dissolved in methanol, and the obtained solution is cast on the active layer described in step (2) by a tape casting method, and the lower part of the active layer is evacuated by an exhaust platform. After drying, lithium metal is deposited by an electrochemical deposition method to obtain the lithium metal negative electrode.

[0071] Example 2

[0072] This embodiment provides a lithium metal negative electrode, comprising a current collector and an active layer with a thickness of 80 μm on the surface of the current collector, wherein the active layer comprises a hollow active material, acetylene black, and PVDF in a mass ratio of 95:2:3, and further comprises a solid electrolyte on the surface and inside of the active layer;

[0073] The hollow active material is a hollow tin ball with a diameter of 2000nm, which includes a pore with a diameter of 1990nm. The interior of the pore is loaded with lithium metal accounting for 5% of the pore volume, and the pore wall is loaded with a 1nm CuS lithium-philic layer.

[0074] The solid electrolyte is LIPON, and its content is 2 wt% based on the content of the active layer; the current collector is porous copper with a thickness of 4 μm;

[0075] The preparation method of the lithium metal negative electrode comprises the following steps:

[0076] (1) The CuS hollow sphere shell is prepared using a template method, that is, using PS carbon spheres as templates, vapor-depositing CuS on the surface of PS microspheres, and then heating and burning off the PS microspheres to obtain a hollow CuS hollow sphere shell. Metal tin is deposited outside the CuS shell by chemical deposition to obtain an internal lithium-philic active material;

[0077] (2) mixing the internal lithium-philic active material, acetylene black, PVDF and water in step (1) to form a slurry, and coating the slurry on the porous copper to obtain an active layer;

[0078] (3) LIPON is loaded on the surface and inside of the active layer by magnetron sputtering, and lithium metal is deposited by electrochemical deposition to obtain the lithium metal negative electrode.

[0079] Example 3

[0080] This embodiment provides a lithium metal negative electrode, comprising a current collector and an active layer with a thickness of 150 μm on the surface of the current collector, wherein the active layer comprises a hollow active material, conductive carbon black SP, CMC, and SBR in a mass ratio of 93:2:2:3, and the surface and interior of the active layer further comprise a solid electrolyte;

[0081] The hollow active material is a porous hollow carbon sphere with a diameter of 200 nm, which includes two pores with a diameter of 50 nm each. The interior of the pores is loaded with lithium metal, which accounts for 85% of the pore volume. The pore walls are loaded with a 1 nm SnO lithium-philic layer. The porous hollow carbon sphere is also doped with 3% nitrogen.

[0082] The solid electrolyte is LATP, and its content is 15 wt% based on the content of the active layer; the current collector is a copper foil with a thickness of 50 μm;

[0083] The preparation method of the lithium metal negative electrode comprises the following steps:

[0084] (1) After nitrogen doping during the preparation of porous hollow carbon spheres, a SnO lithium-philic layer is prepared on the pore wall by vapor phase chemical deposition to obtain an internal lithium-philic active material;

[0085] (2) mixing the internal lithium-philic active material, conductive carbon black SP, CMC, SBR and water in step (1) to form a slurry, and coating the slurry on a copper foil to obtain an active layer;

[0086] (3) LATP, LiPF6 and vinylene carbonate are dissolved in ethanol, and the obtained solid electrolyte solution is sprayed on the active layer described in step (2). At the same time, the lower part of the active layer is evacuated by an exhaust platform. After drying, lithium metal is deposited by electrochemical deposition to obtain the lithium metal negative electrode.

[0087] Example 4

[0088] This embodiment provides a lithium metal negative electrode, comprising a current collector and an active layer with a thickness of 20 μm on the surface of the current collector, wherein the active layer comprises a hollow active material, Ketjen black, and SBR in a mass ratio of 92:4:4, and further comprises a solid electrolyte on the surface and inside of the active layer;

[0089] The hollow active material is a hollow lithium titanate sphere with a diameter of 2000nm, which includes a pore with a diameter of 1500nm. The interior of the pore is loaded with lithium metal accounting for 30% of the pore volume, and the pore wall is loaded with a 1nm ZnS lithium-philic layer;

[0090] The solid electrolyte is PEO (polyethylene oxide), and its content is 20 wt% based on the content of the active layer; the current collector is porous copper with a thickness of 4 μm;

[0091] The preparation method of the lithium metal negative electrode comprises the following steps:

[0092] (1) A ZnS lithium-philic layer is prepared on the pore wall of a hollow lithium titanate sphere by liquid phase chemical deposition to obtain an internal lithium-philic active material;

[0093] (2) mixing the internal lithium-philic active material of step (1), Ketjen black, SBR and N-methylpyrrolidone to form a slurry, and coating the slurry on the porous copper to obtain an active layer;

[0094] (3) After electrochemically depositing lithium metal on the active layer in step (2), PEO, LiTFSI and fluoroethylene carbonate are dissolved in methanol, and the obtained solid electrolyte solution is cast on the active layer after the lithium metal is deposited by a casting method, and at the same time, the bottom of the active layer is evacuated by an exhaust platform. After drying, the lithium metal negative electrode is obtained.

[0095] Example 5

[0096] This embodiment provides a lithium metal negative electrode, which is the same as that of Example 1 except that in step (3) of the preparation method, lithium metal is first electrochemically deposited and then a solid electrolyte is loaded to change the lithium metal negative electrode accordingly.

[0097] Example 6

[0098] This embodiment provides a lithium metal negative electrode. The lithium metal negative electrode is the same as that of embodiment 1 except that the content of the solid electrolyte is 0.5 wt %.

[0099] Example 7

[0100] This embodiment provides a lithium metal negative electrode. The lithium metal negative electrode is the same as that of embodiment 1 except that the content of the solid electrolyte is 30 wt %.

[0101] Example 8

[0102] This embodiment provides a lithium metal negative electrode, which is the same as that of embodiment 1 except that the diameter of the hollow active material is 2200 nm.

[0103] Example 9

[0104] This embodiment provides a lithium metal negative electrode, which is the same as that of embodiment 1 except that the diameter of the hollow active material is 180 nm and correspondingly includes one 150 nm pore.

[0105] Example 10

[0106] This embodiment provides a lithium metal negative electrode, which is the same as that of embodiment 1 except that the diameter of the pores in the hollow active material is 45 nm.

[0107] Example 11

[0108] This embodiment provides a lithium metal negative electrode, which is the same as that of embodiment 1 except that the number of holes in the hollow active material is 1 and the diameter is 1500 nm.

[0109] Example 12

[0110] This embodiment provides a lithium metal negative electrode, which is the same as that of embodiment 1 except that the hollow active material only includes one 250 nm pore.

[0111] Example 13

[0112] This embodiment provides a lithium metal negative electrode. The lithium metal negative electrode is the same as that of embodiment 1 except that the hollow active material includes 6 pores each with a diameter of 250 nm.

[0113] Example 14

[0114] This embodiment provides a lithium metal negative electrode, which is the same as that of Example 1 except that the hollow active material is a porous lithium titanate ball loaded with a corresponding lithium-philic layer.

[0115] Example 15

[0116] This embodiment provides a lithium metal negative electrode, which is the same as that of Example 1 except that the hollow active material is a porous tin ball and carries a corresponding lithium-philic layer.

[0117] Comparative Example 1

[0118] This comparative example provides a lithium metal negative electrode, which includes a current collector and an active layer with the same thickness as that in Example 1. The current collector is porous copper with a thickness of 20 μm, and the active layer is lithium metal, which is obtained by electrochemical deposition on the surface of the current collector.

[0119] Comparative Example 2

[0120] This comparative example provides a lithium metal negative electrode, which is the same as Example 1 except that the active material carbon balls are solid and do not include pores, and the lithium metal is located on the outermost surface of the active layer.

[0121] Comparative Example 3

[0122] This comparative example provides a lithium metal negative electrode, which is the same as Example 1 except that it does not include a solid electrolyte.

[0123] The lithium metal negative electrode described in the above embodiments and comparative examples was assembled with a positive electrode sheet and a solid electrolyte into a lithium battery, and the cycle performance was tested; wherein the positive electrode sheet was an NCM523 positive electrode, SP and PVDF with a mass ratio of 95.7:2.5:1.8, and the slurry was coated on aluminum foil and then baked and roller-pressed to obtain a positive electrode sheet; the solid electrolyte was LATP; and the cycle performance test conditions were 25°C 1C / 1C cycle.

[0124] The test results are shown in Table 1:

[0125] Table 1

[0126]

[0127]

[0128] From Table 1, we can see the following points:

[0129] (1) It can be seen from the examples and comparative examples that the present invention loads lithium metal inside the hollow active material, which can inhibit lithium plating from the lithium metal negative electrode. Since the main failure mechanism of lithium metal batteries is the short circuit caused by the growth of lithium dendrites, if there is a short circuit, the cycle will end, and the lithium metal battery will show a deterioration in cycle performance. Therefore, excellent cycle performance can represent excellent safety performance. The lithium metal negative electrode of the present invention can improve the safety performance and cycle performance of the battery; it can be seen from Examples 1 and 5 that a lithium metal negative electrode with excellent performance can be obtained by first depositing lithium metal and then loading a solid electrolyte during the preparation process; it can be seen from Examples 1 and 6-7 that if the content of the solid electrolyte is too much or too little, the performance of the battery will decrease. Since the solid electrolyte is coated on the surface of the active layer and penetrates into the interior of the active layer and coated on the surface of the hollow active material, it plays a role in further inhibiting the growth of lithium dendrites, reducing internal resistance and improving cycle performance in combination with the lithium negative electrode.

[0130] (2) It can be seen from Example 1 and Examples 8-9 that when the diameter of the hollow active material is too large, on the one hand, it is not conducive to the deposition and dissolution of lithium metal, and on the other hand, it increases the migration distance of lithium ions. When the diameter of the hollow active material is too small, the diameter of the corresponding internal pores is small, which reduces the amount of lithium stored in the pores. Therefore, when the diameter of the hollow active material is within a reasonable range, it can ensure that the lithium metal negative electrode is loaded with a reasonable amount of lithium metal and does not affect the function of the lithium metal. It can be seen from Example 1 and Examples 10-11 that when the pore diameter in the hollow active material is too small, the processing capacity in the pores is also reduced, but an excessively large pore diameter will greatly reduce the structural stability of the hollow active material and affect the cycle performance of the battery. It can be seen from Example 1 and Examples 12-13 that when the pore diameter is significantly different from that of the hollow active material, if the number of pores is small, the lithium storage capacity will be too small, and when the number of pores is too large, the stability of the material will decrease. Therefore, the diameter, pore diameter and number of the hollow active material of the present invention are matched with each other, so that the lithium metal negative electrode has excellent electrochemical properties and high stability.

[0131] (3) It can be seen from Example 1 and Examples 14-15 that when the hollow active material is porous lithium titanate or porous tin balls, the performance is better than that of hollow carbon balls, because porous lithium titanate has stronger ion conductivity, porous tin has stronger conductivity, and is more compatible with lithium, so it is less likely to precipitate lithium; it can be seen from Example 1 and Comparative Example 1 that the present invention can inhibit the formation of lithium dendrites compared to conventional lithium metal negative electrodes, and significantly improve the safety performance and cycle performance of the battery; it can be seen from Example 1 and Comparative Example 2 that when the active material matched with lithium metal does not have pores, the deposited lithium metal can only be on the surface of the active material and cannot enter the interior, and there will also be the problem of lithium dendrites forming on the surface of the lithium negative electrode. Therefore, the lithium metal negative electrode of the present invention is matched with the active material having a porous hollow structure, which greatly improves the performance of the battery; it can be seen from Example 1 and Comparative Example 3 that the solid electrolyte loaded in the lithium metal negative electrode can be matched with the lithium metal in the pores, further improving the safety performance of the negative electrode, and can reduce the impedance of the battery and improve the cycle stability of the battery.

[0132] In summary, the present invention provides a lithium metal negative electrode and its preparation method and application. The lithium metal in the lithium metal negative electrode is deposited inside the hollow active material, which not only inhibits the formation of lithium dendrites, but also releases the stress of lithium deposition, greatly improving the electrochemical performance and safety performance of the battery.

[0133] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A lithium metal negative electrode, characterized in that The active layer of the lithium metal negative electrode includes a hollow active material and a solid electrolyte, and the pores inside the hollow active material include lithium metal; The hollow active material is doped with a lithiophilic substance and / or the inner pore wall is loaded with a lithiophilic layer; The solid electrolyte is coated on the surface of the active layer and is infiltrated and loaded inside the active layer; The surface of the hollow active material is coated with a solid electrolyte; The content of the solid electrolyte is 1-20 wt % based on the content of the active layer.

2. The lithium metal negative electrode according to claim 1, characterized in that The hollow active material has a spherical or quasi-spherical shape, and a particle diameter of 200-2000 nm.

3. The lithium metal negative electrode according to claim 1, characterized in that In the hollow active material, there is at least one hole with a diameter of 50-1990 nm.

4. The lithium metal negative electrode according to claim 1, characterized in that The volume of the lithium metal accounts for 5-90% of the internal pore volume of the hollow active material.

5. The lithium metal negative electrode according to claim 1, characterized in that The thickness of the lithium-philic layer is 1-10 nm.

6. The lithium metal negative electrode according to claim 1, characterized in that In the hollow active material, the content of the doped lithium-philic substance is 1-5 wt %.

7. The lithium metal negative electrode according to claim 1, characterized in that The thickness of the active layer is 20-150 μm.

8. The lithium metal negative electrode according to claim 1, characterized in that The hollow active material includes a conductor of electrons and ions.

9. The lithium metal negative electrode according to claim 1, characterized in that The hollow active material includes any one of porous hollow carbon spheres, porous hollow lithium titanate spheres or porous hollow tin spheres, or a combination of at least two of them.

10. The lithium metal negative electrode according to claim 1, characterized in that The lithiophilic layer includes a transition metal oxide and / or a transition metal sulfide.

11. The lithium metal negative electrode according to claim 10, characterized in that The transition metal oxide includes any one of ZnO, CuO, SnO or NiO, or a combination of at least two thereof.

12. The lithium metal negative electrode according to claim 10, characterized in that The transition metal sulfide includes any one of ZnS, CuS, SnS or NiS, or a combination of at least two thereof.

13. The lithium metal negative electrode according to claim 1, characterized in that The lithiophilic species include nitrogen and / or sulfur.

14. The lithium metal negative electrode according to claim 1, characterized in that The solid electrolyte includes any one or a combination of at least two of a polymer solid electrolyte, an oxide solid electrolyte, a LiPON type electrolyte, a sulfide crystalline solid electrolyte, a sulfide glassy electrolyte or a glass ceramic solid electrolyte.

15. The lithium metal negative electrode according to claim 1, characterized in that The active layer also includes a conductive agent and a binder.

16. The lithium metal negative electrode according to claim 1, characterized in that The lithium metal negative electrode further includes a current collector, and the active layer is disposed on at least one side of the current collector.

17. The lithium metal negative electrode according to claim 16, characterized in that The thickness of the current collector is 4-50 μm.

18. A method for preparing a lithium metal negative electrode according to any one of claims 1 to 17, characterized in that: The preparation method comprises the following steps: (1) doping the hollow active material with a lithiophilic substance and / or preparing a lithiophilic layer on the pore wall of the hollow active material to obtain an internally lithiophilic active material; (2) slurrying and coating the internal lithium-philic active material in step (1) to obtain an active layer, and then depositing lithium metal to obtain the lithium metal negative electrode; The method further includes the step of loading a solid electrolyte on the surface and inside of the active layer before and / or after depositing the lithium metal.

19. The preparation method according to claim 18, characterized in that The method of loading the solid electrolyte in step (2) includes a tape casting method, a spraying method or a sputtering deposition method.

20. The preparation method according to claim 18, characterized in that The method for depositing lithium metal in step (2) includes electrochemical deposition or melting method.

21. The preparation method according to claim 18, characterized in that The method for preparing the lithium-philic layer in step (1) includes any one of a template method, a vapor phase chemical deposition method, a liquid phase chemical deposition method or a high temperature reaction method.

22. The preparation method according to claim 18, characterized in that The preparation method comprises the following steps: (1) doping the hollow active material with a lithiophilic substance, and / or preparing a lithiophilic layer on the pore wall of the hollow active material by a template method, a vapor phase chemical deposition method, a liquid phase chemical deposition method, or a high temperature reaction method, to obtain an internally lithiophilic active material; (2) After the internal lithium-philic active material of step (1) is slurried and coated to obtain an active layer, a solid electrolyte is loaded on the surface and inside of the active layer by a casting method, a spraying method or a sputtering deposition method, and then lithium metal is deposited by an electrochemical deposition method or a melting method to obtain the lithium metal negative electrode.

23. A solid-state battery, characterized in that: The solid-state battery comprises the lithium metal negative electrode according to any one of claims 1 to 17.

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