Lithium metal composite negative electrode and preparation method and application thereof

Abstract

The present application relates to a kind of lithium metal composite negative electrode and its preparation method and application, the lithium metal composite negative electrode includes polymer substrate layer, composite layer and lithium metal layer from inside to outside sequentially, the composite layer includes second polymer and lithium alloy, the lithium alloy is LiM x , M is selected from one or more of Ag, Al, Ba, Bi, Ga, Ge, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, Mg, Mn. The above-mentioned lithium metal composite negative electrode can be prepared by simple melting, casting and hot rolling, suitable for industrial production;The lithium metal composite negative electrode prepared by the above preparation method has a conductive, lithium gradient composite layer, which can effectively inhibit the lithium deposition at the interface between the negative electrode and the separator. The above-mentioned lithium metal composite negative electrode is used in lithium metal battery, not only can improve the energy density of battery, and can effectively inhibit the problem of negative electrode lithium dendrite, is conducive to realizing the long-term stable cycle of high energy density lithium battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a lithium metal composite anode, its preparation method, and its application. Background Technology

[0002] Copper foil is one of the commonly used materials for the negative electrode current collector in lithium metal batteries. As an inactive component, copper foil accounts for approximately 20% of the total mass of a lithium battery, but contributes no capacity. Therefore, replacing traditional copper foil with lightweight components is expected to significantly improve the energy density of lithium batteries. For example, sputtering an ultrathin copper layer onto a polymer substrate as a composite current collector can effectively reduce weight and thus improve the energy density of lithium batteries.

[0003] However, the interaction between the polymer substrate and the copper layer in existing composite current collectors is usually weak, and the copper layer and polymer substrate are prone to separation. This results in extremely poor structural stability and high internal resistance of the composite current collector, which limits the reversibility and kinetics of the lithium metal deposition-stripping process. Furthermore, lithium metal anodes prepared from such composite current collectors are prone to lithium dendrite formation at the interface between the anode and the separator, which seriously affects the safety and cycle life of the battery and restricts the performance improvement and rapid iteration of lithium batteries. Summary of the Invention

[0004] To address the problems of poor interfacial stability and easy formation of lithium dendrites at the interface between the negative electrode and the separator in lithium metal anodes prepared using traditional composite current collectors, this invention provides a lithium metal composite anode, its preparation method, and its application. By constructing a composite layer containing polymer and lithium alloy between the polymer substrate layer and the lithium metal layer, the interfacial stability of the negative electrode and the internal resistance of the negative electrode can be effectively improved, thereby enhancing the reversibility and kinetics of the lithium metal deposition-stripping process in the negative electrode. Furthermore, this invention controls the distribution of lithium content in the composite layer to create a dual gradient of conductivity and lithiophilicity, thereby regulating the lithium nucleation tendency at the composite layer (at the interface with the polymer substrate layer) to be better than that at the surface of the lithium metal layer. This effectively suppresses lithium deposition at the interface between the negative electrode and the separator, enabling lithium metal batteries containing this lithium metal composite anode to have high energy density and long-term stable cycling at high rates.

[0005] Specifically, the following technical solutions are provided:

[0006] The first aspect of the present invention provides a lithium metal composite anode, the lithium metal composite anode comprising a polymer substrate layer, a composite layer and a lithium metal layer;

[0007] The polymer base layer comprises a first polymer;

[0008] The composite layer is disposed on at least one side of the polymer substrate along the thickness direction, and the composite layer comprises a second polymer and a lithium alloy, wherein the lithium alloy is LiM xWhere M is selected from one or more of Ag, Al, Ba, Bi, Ga, Ge, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, Mg, and Mn, and x is 0.01-2;

[0009] The lithium metal layer is disposed on the side of the composite layer away from the polymer substrate layer.

[0010] Furthermore, in the composite layer, the lithium alloy has a three-dimensional network structure and is in interactive contact with the second polymer.

[0011] Furthermore, the lithium content in the lithium metal composite negative electrode gradually decreases along a first direction, where the first direction is the direction from the lithium metal layer to the polymer substrate layer; more preferably, the lithium content in the composite layer is 25%-75%, such as 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, etc., including but not limited to the content percentages listed above.

[0012] Further, the first polymer may be selected from one or more of polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polyimide (PI), polyamide (PA), and polytetrafluoroethylene (PTFE); the second polymer may be selected from one or more of polyethylene terephthalate, polyethylene, polypropylene, polyimide, polyamide, and polytetrafluoroethylene; more preferably, the first polymer and the second polymer are the same polymer.

[0013] Furthermore, the thickness of the first polymer substrate layer is preferably 4-8 μm, such as 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, etc., including but not limited to the thicknesses listed above.

[0014] Furthermore, the thickness of the composite layer is preferably 0.5-5μm, such as 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, etc., including but not limited to the thicknesses listed above.

[0015] Furthermore, the thickness of the lithium metal layer is preferably 0.1-15μm, such as 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, etc., including but not limited to the layer thicknesses listed above.

[0016] A second aspect of the present invention provides a method for preparing the lithium metal composite anode described in the first aspect, comprising the following steps:

[0017] S1. Provide material A, which contains a first polymer, and material B, which contains a second polymer and source M.

[0018] S2. Material A and material B are melted to form melt A and melt B respectively, and then stacked in an AB or BAB arrangement to form a composite film layer by casting; the composite film layer includes film layer A and film layer B.

[0019] S3. Apply lithium metal strips to the surface of the composite film layer B, and perform roll forming to obtain the lithium metal composite negative electrode.

[0020] Further, in step S1, the source of M is elemental M and / or oxide M, wherein M is selected from one or more of Ag, Al, Ba, Bi, Ga, Ge, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, Mg, and Mn.

[0021] Further, in step S1, the M source is in the form of one or more of nanoparticles, nanowires, and nanofibers; more preferably, the particle size of the nanoparticles is 5-1000 nm, and the cross-sectional diameter of the nanowires and nanofibers is 5-100 nm.

[0022] Further, in step S1, the mass percentage of the second polymer in the material B is 1%-30%, such as 1%, 5%, 10%, 15%, 20%, 25%, 30%, etc., including but not limited to the mass percentages listed above.

[0023] Furthermore, in step S2, the melt A and the melt B are extruded through a die head arranged in a certain pattern, so that the melts are stacked in an AB or BAB arrangement.

[0024] Furthermore, in step S2, the thickness of the A film layer is preferably 4-8 μm, such as 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, etc., including but not limited to the layer thicknesses listed above.

[0025] Further, in step S2, the thickness of the B film layer is preferably 0.5-5μm, such as 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, etc., including but not limited to the layer thicknesses listed above.

[0026] Further, in step S3, the thickness of the lithium metal strip is preferably 5-20 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc., including but not limited to the layer thicknesses listed above.

[0027] Further, in step S3, the lithium metal strip is transferred onto the surface of the B film layer of the composite film layer.

[0028] Further, in step S3, the pressure of the roller pressing is preferably 0.1-100 MPa, and the temperature is preferably 25-100℃.

[0029] A third aspect of the present invention provides a lithium metal battery comprising a negative electrode sheet, wherein the negative electrode sheet is a lithium metal composite negative electrode as described in the first aspect or a lithium metal composite negative electrode prepared by the preparation method described in the second aspect.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. This invention uses a polymer layer as the substrate, a composite layer containing polymer and lithium alloy as the conductive current collector, and the lithium alloy in the composite layer and the lithium metal layer disposed on the side of the composite layer away from the substrate together as the negative electrode active material, forming an integrated lithium metal composite negative electrode. This integrated lithium metal composite negative electrode is lightweight, which can effectively improve energy density. Moreover, the composite layer containing polymer and lithium alloy has strong interaction forces with the polymer substrate and lithium metal layer, good interface stability, and low internal resistance, which can effectively improve the reversibility and kinetics of lithium metal deposition-stripping process in the negative electrode and reduce the phenomenon of uneven lithium deposition on the lithium metal negative electrode. In addition, at the beginning of battery charging, lithium ions preferentially deposit on the uniformly dispersed conductive lithium alloy sites, thereby forming uniformly distributed lithium nucleation sites. During the continued charging process, lithium ions will be uniformly deposited based on these uniform nucleation sites, thereby further suppressing the formation of lithium dendrites and improving battery safety and cycle life.

[0032] 2. This invention controls the lithium content distribution of the composite layer in the above-mentioned lithium metal composite anode, so that the lithium content gradually decreases along the direction from the lithium metal layer to the polymer substrate layer, forming a dual gradient of conductivity and lithiophilicity (limonophilicity gradually increases and conductivity gradually decreases along the direction from the lithium metal layer to the polymer substrate layer). The conductivity gradient regulates the lithium nucleation tendency on the surface of the lithium metal layer to be worse than that at the bottom of the composite layer (at the interface with the polymer substrate layer), while the lithiophilic gradient regulates the lithium nucleation tendency at the bottom of the composite layer to be better than that at the surface of the lithium metal layer. Under the synergistic effect of the above dual gradient structure, the lithium nucleation tendency at the bottom of the composite layer is much better than that at the surface of the lithium metal layer, thereby effectively suppressing lithium deposition at the interface between the anode and the separator, and greatly reducing the risk of short circuit in lithium metal batteries.

[0033] 3. This invention also provides a method for preparing the above-mentioned lithium metal composite anode. A lithium metal composite anode with a tightly bonded polymer substrate layer, composite layer, and lithium metal layer can be obtained through melting, casting, and rolling. This preparation method is simple, low-cost, and easy to industrialize, exhibiting strong adaptability and universality. Furthermore, the prepared lithium metal composite anode has a stable structure and can effectively suppress the formation of lithium dendrites. Specifically, this invention utilizes the diffusion of lithium metal elements into the composite layer under rolling conditions and the in-situ alloying reaction with the uniformly dispersed M source in the B film layer to form a lithium alloy with a three-dimensional structure and a dual gradient of conductivity and lithiophilicity. The lithium alloy with a three-dimensional network structure forms interactive contact with the polymer in the composite layer, which is beneficial to improving the interfacial compatibility and adhesion between the polymer and the lithium alloy with the dual gradient of conductivity and lithiophilicity. This effectively addresses the changes in volume, internal stress, and electrode structure of lithium metal batteries caused by charge-discharge cycles, thus improving the battery's coulombic efficiency and cycle life. Moreover, the lithium alloy with a three-dimensional structure can further reduce the internal resistance of the anode and improve the battery's rate performance. In summary, the lithium metal composite anode prepared by the above method is beneficial for achieving long-term stable cycling of high-energy-density lithium metal batteries at high rates.

[0034] 4. The lithium metal battery composed of the lithium metal composite anode and the high-nickel ternary cathode provided by this invention has a capacity retention rate of not less than 90% after 1000 charge-discharge cycles, and a capacity retention rate of not less than 85% after 1750 charge-discharge cycles. This is far superior to the cycle life of lithium metal batteries assembled with lithium metal composite anodes prepared with traditional composite copper foil as current collectors (the battery capacity retention rate is only 22.3% after 500 charge-discharge cycles). Attached Figure Description

[0035] Figure 1 A schematic diagram of the lithium metal composite anode provided by the present invention;

[0036] Figure 2 Cycle performance diagram of a lithium metal battery assembled with a high-nickel ternary cathode and a lithium metal composite anode prepared in Example 1;

[0037] Icons: 1 represents the polymer substrate, 2 represents the composite layer, and 3 represents the lithium metal layer. Detailed Implementation

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. "Comprising" or "containing" as used herein means that it may include or contain other components in addition to the stated components. "Comprising" or "containing" as used herein may also be replaced with the closed form "is" or "consisting of".

[0039] As described in the background section, using a lightweight composite current collector as the negative electrode current collector for lithium metal batteries is beneficial to improving the energy density of lithium batteries. However, existing composite current collectors (polymer substrate + copper layer) have poor structural stability and high internal resistance. Furthermore, the negative electrode using this composite current collector is prone to generating lithium dendrites at the interface between the negative electrode and the separator during battery charging and discharging, which seriously affects the safety and cycle life of the battery.

[0040] To address the above problems, embodiments of the present invention provide a lithium metal composite anode, such as... Figure 1 As shown, the lithium metal composite anode comprises a polymer substrate layer 1, a composite layer 2, and a lithium metal layer 3; the polymer substrate layer 1 comprises a first polymer; the composite layer 2 is disposed on at least one side of the polymer substrate layer 1 along its thickness direction, and the composite layer 2 comprises a second polymer and a lithium alloy, wherein the lithium alloy is LiM x M is selected from one or more of Ag, Al, Ba, Bi, Ga, Ge, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, Mg, and Mn, and x is 0.01-2; the lithium metal layer 3 is disposed on the side of the composite layer 2 away from the polymer substrate layer 1.

[0041] To address the issues of poor structural stability, high internal resistance, and the tendency for lithium dendrites to form at the interface between the negative electrode and the separator in current composite current collectors, this invention uses a polymer layer as the substrate and a composite layer containing polymer and lithium alloy as the conductive current collector. The lithium alloy in the composite layer and the lithium metal layer disposed on the side of the composite layer away from the polymer substrate together serve as the negative electrode active material, forming an integrated lithium metal composite negative electrode. This integrated lithium metal composite negative electrode is lightweight, effectively improving energy density. Furthermore, the strong interaction between the composite layer containing polymer and lithium alloy, the polymer substrate layer, and the lithium metal layer results in good interface stability and low internal resistance, effectively improving the reversibility and kinetics of the lithium metal deposition-stripping process at the negative electrode and reducing uneven lithium deposition on the lithium metal negative electrode. In addition, at the beginning of battery charging, lithium ions preferentially deposit on uniformly dispersed, conductive, lithium-loving lithium alloy sites, forming uniformly distributed lithium nucleation sites. During continued charging, lithium ions will deposit uniformly based on these uniform nucleation sites, further suppressing lithium dendrite formation and improving battery safety and cycle life.

[0042] In this invention, the lithium alloy forms a three-dimensional network structure in the composite layer, interacting with the second polymer in the composite layer. This is beneficial to improving the interfacial compatibility and adhesion between the second polymer and the conductive and lithium-loving dual-gradient lithium alloy. It can effectively cope with the changes in volume, internal stress and electrode structure of lithium metal batteries caused by charge and discharge cycles, which is beneficial to improving the coulombic efficiency and cycle life of the battery. In addition, the lithium alloy with a three-dimensional structure can further reduce the internal resistance of the negative electrode and improve the rate performance of the battery.

[0043] In this invention, to further suppress lithium deposition at the interface between the lithium metal anode and the separator, the lithium content in the lithium metal composite anode is controlled so that the lithium content in the lithium metal composite anode gradually decreases along a first direction, the first direction being the direction from the lithium metal layer to the polymer substrate layer; preferably, the lithium content in the composite layer is 25%-75%, such as 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, etc., including but not limited to the content percentages listed above.

[0044] The lower the resistance on the lithium metal anode, the greater the probability of lithium deposition. In anodes prepared using traditional composite current collectors, the lithium-ion concentration is high at the interface between the anode surface and the separator, leading to preferential lithium deposition at this interface and increasing the risk of battery short circuits. This invention controls the lithium content distribution of the composite layer in the aforementioned lithium metal composite anode, causing the lithium content to gradually decrease along the direction from the lithium metal layer to the polymer substrate layer. This creates a dual gradient of conductivity and lithiophilicity (lithiophilicity gradually increases and conductivity gradually decreases along the direction from the lithium metal layer to the polymer substrate layer). The conductivity gradient controls the lithium nucleation tendency at the surface of the lithium metal layer to be inferior to that at the bottom of the composite layer (at the interface with the polymer substrate layer), while the lithiophilic gradient controls the lithium nucleation tendency at the bottom of the composite layer to be superior to that at the surface of the lithium metal layer. Under the action of this dual gradient structure, the lithium nucleation tendency at the bottom of the composite layer is far superior to that at the surface of the lithium metal layer, thereby effectively suppressing lithium deposition at the interface between the anode and the separator and significantly reducing the risk of short circuits in lithium metal batteries.

[0045] In this invention, the first polymer may be selected from one or more of polyethylene terephthalate, polyethylene, polypropylene, polyimide, polyamide, and polytetrafluoroethylene; the second polymer may be selected from one or more of polyethylene terephthalate, polyethylene, polypropylene, polyimide, polyamide, and polytetrafluoroethylene; more preferably, the first polymer and the second polymer are the same polymer, thereby improving the interfacial compatibility and adhesion between the polymer substrate layer and the composite layer.

[0046] In this invention, the thickness of the first polymer substrate layer is preferably 4-8 μm, such as 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, etc.; the thickness of the composite layer is preferably 0.5-5 μm, such as 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc.; the thickness of the lithium metal layer is preferably 0.1-15 μm, such as 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc.; the thickness of each of the above layers includes, but is not limited to, the thicknesses listed above.

[0047] The present invention also provides a method for preparing the above-mentioned lithium metal composite anode, comprising the following steps:

[0048] S1. Provide material A, which contains a first polymer, and material B, which contains a second polymer and source M.

[0049] S2. Material A and material B are melted to form melt A and melt B respectively, and then stacked in an AB or BAB arrangement to form a composite film layer by casting; the composite film layer includes film layer A and film layer B.

[0050] S3. Apply lithium metal strips to the surface of the composite film layer B, and perform hot rolling treatment to obtain the lithium metal composite negative electrode.

[0051] This invention utilizes a melting, casting, and rolling process to form a lithium alloy with a three-dimensional structure and a dual gradient of conductivity and lithiophilicity. This is achieved through in-situ alloying reactions between lithium metal elements diffused into the composite layer under rolling conditions and the uniformly dispersed M source in the B film layer. This results in a lithium metal composite anode with a tightly bonded polymer substrate layer, composite layer, and lithium metal layer. The above preparation method is simple to operate, low in cost, and easily scalable for industrial production, exhibiting strong adaptability and universality. Furthermore, the lithium metal composite anode prepared by this method has a stable structure and effectively suppresses the formation of lithium dendrites, which is beneficial for achieving long-term stable cycling of high-energy-density lithium metal batteries at high rates.

[0052] In some preferred embodiments, in step S1, the source of M is elemental M and / or oxide M, wherein M is selected from one or more of Ag, Al, Ba, Bi, Ga, Ge, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, Mg, and Mn.

[0053] In some preferred embodiments, in step S1, the form of the M source is one or more of nanoparticles, nanowires, and nanofibers; preferably, the particle size of the M source nanoparticles is 5-1000 nm, and the cross-sectional diameter of the M source nanowires and M source nanofibers is 5-100 nm, for example, silver nanowires with a cross-sectional diameter D50 of about 50 nm.

[0054] In some preferred embodiments, in step S2, melt A and melt B are extruded through a die arranged in a certain pattern, so that the melts are stacked in an AB or BAB arrangement.

[0055] In some preferred embodiments, in step S2, the thickness of film layer A is preferably 4-8 μm, such as 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, etc.; the thickness of film layer B is preferably 0.5-5 μm, such as 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc., including but not limited to the layer thicknesses listed above.

[0056] In some preferred embodiments, in step S3, the thickness of the lithium metal strip is preferably 5-20 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc., including but not limited to the layer thicknesses listed above.

[0057] In some preferred embodiments, in step S3, the lithium metal strip can be transferred onto the surface of the B film layer of the composite film.

[0058] In some preferred embodiments, in step S3, the pressure of the roller pressing is preferably 0.1-100 MPa, and the temperature is preferably 25-100°C.

[0059] The present invention also provides a lithium metal battery comprising a lithium metal composite negative electrode prepared by the above-described preparation method.

[0060] In some preferred embodiments, the above-mentioned lithium metal composite negative electrode is used as the negative electrode sheet, and together with the high-nickel ternary positive electrode, a high-energy-density lithium metal battery is formed, which exhibits excellent cycle stability during charge and discharge cycles.

[0061] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0062] Example 1

[0063] This embodiment relates to the preparation of a lithium metal composite anode, as detailed below:

[0064] (1) Provide polymer PI material and a mixture of polymer PI and silver nanowires (cross-sectional diameter D50 is 50nm) at a mass ratio of 15:85;

[0065] (2) The polymer PI material and the mixture are respectively fed to the extrusion system. After melting, the melt is extruded from the upper, middle and lower dies. The melt of the polymer PI material is extruded from the middle die, and the melt of the mixture is extruded from the upper and lower dies. After casting, a composite film is formed with a PI layer with a thickness of 6μm in the middle and a mixture layer with a thickness of 1.5μm on the upper and lower sides.

[0066] (3) A lithium metal strip with a thickness of 15 μm is coated on both sides of the composite film obtained in step (2) and hot-rolled. The rolling pressure is set to 25 MPa and the temperature is set to 45 °C. Under the action of hot rolling, the lithium metal and the uniformly dispersed Ag nanowires in the mixture layer form a composite layer with a thickness of 5.5 μm containing a conductive, lithiophilic dual gradient and a three-dimensional structure lithium-silver alloy (the thickness of the interactive contact layer formed by the lithium-silver alloy and the composite layer is 2 μm). The thickness of the lithium metal layer is 10 μm, and a lithium metal composite anode is obtained.

[0067] Example 2

[0068] This embodiment relates to the preparation of a lithium metal composite anode, and the specific operations are as follows:

[0069] (1) Provide polymer PI material and a mixture of polymer PI and nano SiO2 particles (particle size D50 is 180nm) uniformly mixed at a mass ratio of 15:85;

[0070] (2) The polymer PI material and the mixture are respectively fed to the extrusion system. After melting, the melt is extruded from the upper, middle and lower dies. The melt of the polymer PI material is extruded from the middle die, and the melt of the mixture is extruded from the upper and lower dies. After casting, a composite film is formed with a PI layer with a thickness of 6μm in the middle and a mixture layer with a thickness of 1.5μm on the upper and lower sides.

[0071] (3) A lithium metal strip with a thickness of 15 μm is coated on both sides of the composite film obtained in step (2) and hot rolling is performed. The rolling pressure is set to 25 MPa and the temperature is set to 45 °C. Under the action of hot rolling, the lithium metal and the uniformly dispersed nano SiO2 particles in the mixture layer form a composite layer with a thickness of 5.5 μm containing conductive, lithiophilic dual gradient and three-dimensional structure lithium silicon alloy (the thickness of the interactive contact layer formed by the lithium silicon alloy and the composite layer is 2 μm). The thickness of the lithium metal layer is 10 μm, and a lithium metal composite negative electrode is obtained.

[0072] Example 3

[0073] This embodiment relates to the preparation of a lithium metal composite anode, and the specific operations are as follows:

[0074] (1) Provide polymer PP material and a mixture of polymer PP and nano SiO2 particles (particle size D50 is 180nm) uniformly mixed at a mass ratio of 20:80;

[0075] (2) The polymer PP material and the mixture are respectively fed to the extrusion system. After melting, the melt is extruded from the upper, middle and lower dies. The melt of the polymer PP material is extruded from the middle die, and the melt of the mixture is extruded from the upper and lower dies. After casting, a composite film is formed with a PP layer with a thickness of 6μm in the middle and a mixture layer with a thickness of 1μm on the upper and lower sides.

[0076] (3) A lithium metal strip with a thickness of 15 μm is coated on both sides of the composite film obtained in step (2) and hot rolling is performed. The rolling pressure is set to 20 MPa and the temperature is set to 45 °C. Under the action of hot rolling, the lithium metal and the uniformly dispersed nano SiO2 particles in the mixture layer form a composite layer with a thickness of 4.5 μm containing conductive, lithiophilic dual gradient and three-dimensional structure lithium silicon alloy (the thickness of the interactive contact layer formed by the lithium silicon alloy and the composite layer is 1.3 μm). The thickness of the lithium metal layer is 11 μm, and a lithium metal composite negative electrode is obtained.

[0077] Comparative Example 1

[0078] This comparative example relates to the preparation of a lithium-free alloy polymer lithium metal composite anode. The difference from Example 1 is that the preparation of the mixture layer is not included, but the rest of the operations are the same. The lithium metal strip is directly coated on the PI layer and hot rolling is used to prepare the lithium-free alloy polymer lithium metal composite anode. The lithium metal composite anode includes a polymer PI layer and a lithium metal layer stacked sequentially from the inside to the outside.

[0079] Comparative Example 2

[0080] This comparative example relates to the preparation of a lithium metal composite anode. The difference from Example 1 is that: silver is directly magnetron sputtered onto the upper and lower sides of the polymer PI layer to prepare a composite film; the rest of the operations are the same, and a lithium metal composite anode containing a lithium-silver alloy is prepared. The lithium metal composite anode includes a polymer PI layer, a silver-lithium alloy layer (formed during hot rolling), and a lithium metal layer stacked sequentially from the inside to the outside.

[0081] Comparative Example 3

[0082] This comparative example relates to the preparation of a lithium metal composite anode, which differs from Example 1 in that: copper is directly magnetron sputtered onto the upper and lower sides of the polymer PI layer to prepare a composite copper foil current collector; lithium metal strip is rolled onto the composite copper foil (rolling pressure set to 25 MPa, temperature set to 45°C) to obtain a lithium metal composite anode, which includes a polymer PI layer, a copper metal layer and a lithium metal layer stacked sequentially from the inside to the outside.

[0083] Application and performance testing

[0084] (1) The peel strength of the lithium metal composite anodes prepared in the above examples and comparative examples was tested. The specific operation is as follows:

[0085] The lithium metal composite anodes prepared in each embodiment and comparative example were cut into strips of 20×150mm. Tensile tests were performed at room temperature at a rate of 250mm / min, and the peel strength between the polymer substrate layer and the metal layer was recorded.

[0086] The test results are shown in Table 1 below:

[0087] Table 1

[0088]

[0089]

[0090] As shown in Table 1, compared with conventional composite copper foil current collectors, the peel strength between the metal layer and the polymer substrate layer in the lithium metal composite anode prepared in Examples 1-3 is significantly improved, exceeding 300 times. This indicates that the lithium metal composite anode provided by the present invention has strong interfacial bonding between the polymer layer and the metal layer and good structural stability.

[0091] As can be seen from Example 1 and Comparative Example 1, introducing a composite layer containing polymer and lithium alloy between the polymer substrate layer and the lithium metal layer can effectively improve the peel strength of the lithium metal composite anode. However, Comparative Example 2 directly introduces a silver metal layer on the polymer substrate layer by magnetron sputtering, and then alloys it with lithium metal to form a lithium-silver alloy to prepare a lithium metal composite anode. Unlike Example 1, the lithium-silver alloy layer in the lithium metal composite anode prepared in Comparative Example 2 only contains silver and lithium, and does not contain polymer. It is impossible to improve the interfacial bonding force between the metal and the polymer by forming an apparent three-dimensional structure between the lithium-silver alloy and the polymer. Therefore, the interface between the lithium alloy and the polymer substrate layer in the lithium metal composite anode prepared in Comparative Example 2 still exhibits low adhesion, and the peel strength is much lower than that of the lithium metal composite anode prepared in Example 1.

[0092] (2) The lithium metal composite anodes prepared in the above examples and comparative examples were used as lithium metal battery anodes to construct lithium metal batteries, and the electrical performance of each lithium metal battery was tested. The specific operation is as follows:

[0093] Construction of lithium metal batteries: A bare cell is obtained by stacking a high-nickel ternary positive electrode, a separator, and a lithium metal composite negative electrode. Positive and negative electrode tabs are then welded together, the bare cell is encapsulated in an aluminum-plastic film battery case, electrolyte is injected, it is sealed, allowed to stand, formed, and capacity tested to obtain the lithium metal battery. Only the negative electrode differs among various lithium metal batteries; all other aspects are identical.

[0094] Cyclic performance tests were conducted on lithium metal batteries constructed with different lithium metal battery anodes: Under normal temperature conditions, each lithium metal battery was charged at a constant current of 1C to 4.25V, then charged at a constant voltage of 4.25V until the current reached 0.05C cutoff, and then discharged at 0.33C to 2.8V. The initial discharge capacity was recorded. Then, 500, 1000, and 1750 charge-discharge cycles were performed, and the discharge capacity at the 500th, 1000th, and 1750th cycles was recorded respectively. The capacity retention rate was calculated as (discharge capacity corresponding to the number of cycles / initial discharge capacity) × 100%.

[0095] The test results are shown in Table 2 below:

[0096] Table 2

[0097]

[0098] As shown in Table 2, the lithium metal batteries prepared using the lithium metal composite anodes prepared in Examples 1-3 of this invention as anode plates exhibit long-term cycle stability, with a capacity retention rate of no less than 1000 cycles after 1000 charge-discharge cycles, and a capacity retention rate of over 85% after 1750 charge-discharge cycles. In contrast, the lithium metal batteries constructed using the lithium metal composite anodes prepared in Comparative Examples 1-3 show a capacity decrease to less than 30% of the initial discharge capacity after only 500 charge-discharge cycles.

[0099] Therefore, it can be seen that by introducing a composite layer containing polymer and lithium alloy between the polymer substrate layer and the lithium metal layer, the present invention can effectively improve the cycle life of lithium metal batteries, enabling lithium metal batteries to have high energy density while maintaining long-term stable cycling at high rates.

[0100] The embodiments described above are merely preferred examples to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A lithium metal composite anode, characterized by, The lithium metal composite negative electrode comprises a polymer substrate layer, a composite layer and a lithium metal layer; The polymer substrate layer comprises a first polymer; The composite layer is disposed on at least one side of the polymer base layer along the thickness direction, and the composite layer comprises a second polymer and a lithium alloy, wherein the lithium alloy is LiM x wherein M is selected from one or more of Ag, Al, Ba, Bi, Ga, Ge, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, Mg, Mn, and x is 0.01-2. The lithium metal layer is arranged on the side of the composite layer away from the polymer substrate layer; The preparation method of the lithium metal composite negative electrode comprises the following steps: S1, providing a material A and a material B, the material A comprises a first polymer, and the material B comprises a second polymer and an M source; S2, forming a melt A and a melt B by melting the material A and the material B respectively, stacking the melt A and the melt B in an AB or BAB arrangement, and forming a composite film layer by casting; the composite film layer comprises an A film layer and a B film layer; S3, covering a lithium metal strip on the side of the composite film layer where the B film layer is located, and performing a rolling treatment to obtain the lithium metal composite negative electrode.

2. The lithium metal composite anode of claim 1, wherein, In the composite layer, the lithium alloy has a three-dimensional network structure and is in interactive contact with the second polymer; The content of lithium elements in the lithium metal composite negative electrode gradually decreases along a first direction, and the first direction is the direction in which the lithium metal layer points to the polymer substrate layer; The content of lithium elements in the composite layer accounts for 25%-75%.

3. The lithium metal composite anode of claim 1, wherein, The first polymer is selected from one or more of polyethylene terephthalate, polyethylene, polypropylene, polyimide, polyamide and polytetrafluoroethylene; The second polymer is selected from one or more of polyethylene terephthalate, polyethylene, polypropylene, polyimide, polyamide and polytetrafluoroethylene. 4.The lithium metal composite anode according to claim 1 or 3, characterized in that, The first polymer and the second polymer are the same polymer.

5. The lithium metal composite anode of claim 1, wherein the lithium metal composite anode is characterized by, The thickness of the first polymer substrate layer is 4-8 μm; The thickness of the composite layer is 0.5-5 μm; The thickness of the lithium metal layer is 0.1-15 μm.

6. The lithium metal composite anode of claim 1, wherein, In the step S1, the M source is an M element and / or an M oxide, wherein M is selected from one or more of Ag, Al, Ba, Bi, Ga, Ge, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, Mg and Mn; The form of the M source is one or more of nanoparticles, nanowires and nanofibers; the particle size of the nanoparticles is 5-1000 nm, and the cross-sectional diameter of the nanowires and the nanofibers is 5-100 nm; The mass content of the second polymer in the material B is 1%-30%.

7. The lithium metal composite anode of claim 1, wherein, In the step S2, the thickness of the A film layer is 4-8 μm; The thickness of the B film layer is 0.5-5 μm.

8. The lithium metal composite anode of claim 1, wherein, In the step S3, the thickness of the lithium metal strip is 5-20 μm; The pressure of the rolling is 0.1-100 MPa, and the temperature is 25-100 ℃.

9. A lithium metal battery comprising a negative electrode sheet, characterized by, The negative electrode tab is the lithium metal composite negative electrode according to any one of claims 1-8.

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