Composite negative electrode and preparation method thereof

Abstract

The present application provides a kind of composite negative electrode and its preparation method, the composite negative electrode includes polymer fiber membrane, and the polymer fiber membrane is deposited with conductive material layer;And metal lithium / lithium alloy layer, the metal lithium / lithium alloy layer is compounded on one side or two sides of polymer fiber membrane, wherein the fiber diameter of the polymer fiber membrane is 100nm-20 μm, and the pore area ratio between fibers is in the range of 10-70%, preferably 20-50%.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium metal batteries, in particular to a polymer fiber film material and lithium composite product for the negative electrode of a lithium metal battery. BACKGROUND

[0002] Lithium metal batteries are considered to be the development direction of the next generation of energy storage batteries due to their high specific capacity, high energy density and other advantages. However, the metal lithium negative electrode has problems such as volume expansion and lithium dendrite growth during charging and discharging, which can easily lead to short circuit of the battery and cause safety hazards.

[0003] Currently, the metal lithium negative electrode mainly adopts the form of pure lithium strip or lithium-copper composite strip, but the pure lithium strip has low strength and is easy to deform, while the lithium-copper composite strip uses a copper foil with high density as the substrate (the density of the copper foil is 8.9 g / cm 3 ), which increases the weight of the battery and reduces the specific energy of the battery.

[0004] The use of carbon nanotube film materials or carbon fiber film materials can reduce the weight of the battery, but these two materials have high cost and are difficult to form into rolls, and cannot be mass-produced.

[0005] Metal fibers, semiconductor fibers and inorganic oxide fibers cannot be used as supporting materials due to their high weight and high cost.

[0006] The polymer fiber film material process is simple, and the cost is suitable, but the polymer fiber itself is not conductive. If the polymer fiber film is directly used as a support material, the battery performance will quickly decay in the later stage of the cycle because the support material does not have conductivity. A layer of metal material needs to be deposited on the polymer fiber film to reduce the sheet resistance of the polymer fiber film to less than or equal to 100 mΩ (resistance per square centimeter area). Considering the weight, cost and process feasibility of the material, a simple process of conductive plating is used, and the material itself has conductivity, which is expected to be used as a support material for metal lithium. By depositing lithium-philic site materials such as gold, silver, zinc oxide, tin oxide, cobalt oxide, molybdenum oxide, etc. on the surface and / or inside of the polymer fiber film, a composite material can be obtained in which liquid / gaseous metal lithium is immersed in the inside and / or surface of the polymer fiber film skeleton. However, during the electrochemical charging and discharging process, the metal lithium is released from the inside of the polymer fiber skeleton during discharging, and the metal lithium is deposited in the inside of the polymer fiber skeleton during charging. The newly deposited metal lithium is not as dense as the original liquid / gaseous metal lithium immersed in the polymer fiber film, which causes the polymer fiber film to be expanded by the newly deposited metal lithium in the limited space of the polymer fiber film, resulting in the destruction of the structure of the polymer fiber film and the deterioration of the cycle performance of the battery. In addition, the lithium-philic site and the metal lithium react, for example, using lithium-philic zinc oxide, lithium and zinc oxide react to form lithium-zinc alloy and lithium oxide, and the lithium-philic zinc oxide particles are detached from the surface of the polymer fiber film, resulting in a decrease in the adhesion of the metal lithium to the polymer fiber film material. With the extension of time, the metal lithium layer will be detached from the polymer fiber film material. SUMMARY

[0007] The inventors of the present application found that the fiber diameter of the currently rolled polymer fiber membrane is large (the fiber diameter is greater than 20 μm), and some use a fiber and fiber bundle weaving method to form a membrane. The polymer fiber membrane formed by the above method has a relatively thick thickness (the thickness is much greater than 20 μm), a heavy mass, a high cost, a large battery volume, and no advantage in replacing copper foil materials. In addition, the overlap between the fibers during spinning is random, the pores between the fibers are many, and the pore area ratio is large. When such materials are used as the support material of the metal lithium negative electrode, in the early stage of battery cycling, because there is composite metal lithium on the surface of the polymer fiber, the metal lithium will slowly supplement the lithium loss in the battery cycling process, and the metal lithium will slowly thin out. The battery has good early cycle performance and good consistency. In the later stage of battery cycling, the initially compounded metal lithium will be consumed. In the later stage of battery cycling, because the fiber diameter is thick and the pores between the fibers are many, the substrate for depositing metal lithium is very uneven and uneven, which is not conducive to the uniform deposition of metal lithium. In addition, some metal lithium will be deposited into the pores between the fibers, causing the fibers to be separated, torn and pulled apart, resulting in damage to the support material during the later stage of battery cycling, which cannot effectively play the role of current collection and support, and the performance of the battery deteriorates. In addition, the polymer fiber membrane (with conductivity) and the metal lithium / lithium alloy are compounded together, which requires a large pressure to tightly fit, and the tensile strength of the membrane material is very high. If the membrane material is easily stretched and deformed, and the elongation at break is large (greater than 20%), the polymer fiber membrane material is easily stretched and deformed during the pressure compounding of lithium, resulting in a problem of stretching and shrinking of the polymer fiber membrane lithium compound product, and many pits or wrinkles appear on the product.

[0008] In view of the above problems of the material, the inventors of the present application have continuously experimented and explored the fiber diameter of the polymer fiber membrane, the fiber and fiber overlap method, and the pore area between the fibers, and found that the fiber diameter is 100 nm-20 μm, the fiber and fiber overlap method is orderly, and the pore area ratio between the fibers is 10-70%, preferably 20-50%. Such a structure of the material plays a positive role in the deposition of metal lithium in the later stage of battery cycling.

[0009] The newly synthesized polymer fiber membrane has the advantages of light weight, tensile resistance, small elongation at break, and the like. A layer of metal conductive layer is deposited on the surface of the polymer fiber membrane, which enhances the conductivity of the material. In addition, due to its low density, high tensile strength, small elongation at break, and small sheet resistance, it is more suitable as a support material for metal lithium negative electrodes. By designing the fiber diameter, the pore area ratio between the fibers, and the fiber overlap or weaving method, a good substrate structure can be provided for the uniform deposition of lithium ions, thereby improving the cycle life of the battery.

[0010] Therefore, the present application proposes the following technical solutions.

[0011] According to one aspect of the present application, there is provided a composite negative electrode, comprising a polymer fiber membrane, a layer of conductive material deposited on the polymer fiber membrane; and a metal lithium / lithium alloy layer, the metal lithium / lithium alloy layer being compounded on one side or both sides of the polymer fiber membrane, wherein the polymer fiber membrane is composed of polymer fibers with a fiber diameter of 100 nm-20 μm, the angle between fibers and fibers is greater than 5 degrees to 90 degrees, the porosity area ratio between fibers is in the range of 10-70%, preferably 20-50%.

[0012] Optionally, the polymer fiber membrane is made of at least one material of polyester fiber, polyamide fiber, polyimide fiber, polyarylate fiber, polyacrylonitrile fiber, aramid fiber, polytetrafluoroethylene fiber, and polyurethane fiber.

[0013] Optionally, the polymer fiber membrane has a fiber diameter of 100 nm-20 μm, preferably 1-15 μm; the fibers and the fibers are arranged in an ordered oblique cross arrangement, the angle of fiber intersection is in the range of greater than 5 degrees to 90 degrees; the porosity area ratio between fibers is in the range of 20-60%.

[0014] Optionally, after the polymer fibers are formed into a film, at least one of the conductive copper, nickel, silver, tin, and gold materials is deposited on the polymer fibers, and the thickness of the formed metal layer is 200 nm-2 μm. The metal layer can be deposited on the surface of the fibers constituting the polymer fiber membrane by physical vapor deposition or electroplating. In the present application, any one of the above methods is used to form the metal layer, which is simple in process, low in cost, firm and reliable in plating, good in conductivity, and small in sheet resistance.

[0015] Physical vapor deposition parameters: high-purity target material (copper, nickel, silver, tin, or gold, purity 99.99%) in a vacuum degree of 10 -3 -10 - 4 Pa, power 300-500 W, target base distance 60-100 mm, deposition time 20-40 minutes; or an evaporated metal source (copper, nickel, silver, tin, or gold, purity 99.99%) is selected, a vacuum degree of 10 -3 -10 -4 Pa, electron beam power 8-12 kV, 200-300 mA, deposition time 5-10 minutes.

[0016] Electroplating parameters: current density 2-6 A / dm 2 , temperature 20-60°C, electroplating time 30-100 s.

[0017] Optionally, the thickness of the polymer fiber membrane is 3-25 μm, and the density is 0.5-2.5 g / cm 3The tensile strength is 50-200 MPa, the elongation at break is 1-20%, and the resistance per square centimeter is 1-100 mΩ.

[0018] Optionally, the thickness of the metal lithium / lithium alloy layer is 1-50 um, preferably 5-20 um.

[0019] Optionally, the lithium alloy layer is an alloy layer formed by metal lithium and any one or at least two of Ag, Au, Sn, Si, Zn, Al, Mg, In, Ga, B, Mn, Sb, Cr, C, V, Cu, Fe or Ti.

[0020] Another aspect of the present application provides a method for preparing a composite electrode, comprising the following steps:

[0021] First step: obtaining an initial polymer fiber film by electrospinning, melt-blowing spinning, spun-bonding, wet-laid or weaving, controlling the fiber diameter to be in the range of 100 nm-20 um, preferably 500 nm-15 um, the angle between fibers to be in the range of greater than 5 degrees to 90 degrees, and the fiber interstitial pore area ratio to be in the range of 10-70%, preferably 20-50%; the initial polymer fiber is subjected to hot rolling, with the temperature range being 100-200 DEG C and the pressure being 0.5-3 MPa, to obtain a polymer fiber film.

[0022] Second step: forming a conductive layer on the polymer fiber film by physical vapor deposition or electroplating;

[0023] Third step: tightly combining one side or both sides of the polymer fiber film and the metal lithium / lithium alloy layer by rolling or flat pressing to obtain a composite negative electrode.

[0024] Optionally, the parameters of electrospinning include: the humidity RH is controlled in the range of 30-50%, the polymer concentration of the spinning solution is 3-10 wt%, 0.1-1 wt% of ferroferric oxide nanoparticles (particle size 20-50 nm) can also be added to the spinning solution, at least one liquid spraying head, voltage 20-30 KV, flow rate 0.3-1 mL / h, needle nozzle diameter 22G-27G, receiving distance 15-25 cm.

[0025] Optionally, melt-blown spinning parameters: ambient temperature 20-25℃, humidity RH controlled at 40-60%, melt-blown liquid polymer concentration 3-10wt%, 0.1-1wt% ferroferric oxide nanoparticles (particle size 20-50nm) can also be added to the melt-blown liquid, melt temperature 200-300 degrees, melt pressure 10-15MPa, spinneret diameter 0.05mm-0.5mm, spinneret hole spacing 0.5-1.5mm, die temperature slightly higher than the melt temperature 5-10℃, airflow hot air temperature 250-350 degrees, airflow pressure 0.2-1.0MPa, airflow velocity 0.5-1.5 Mach, screw speed 50-150rpm, receiving distance 10-30cm.

[0026] Optionally, a drum with an angle is used for collection (the drum can rotate at any angle from 0 to 90 degrees), the speed of the receiving roller is 100-1000r / min, and the initial polymer fiber is obtained (high-speed collection can straighten the fibers of different angles into fibers with consistent direction); non-woven fabric and magnetic field assisted collection can also be used, and after winding, the non-woven fabric is separated to obtain the initial polymer fiber film.

[0027] The drum is wound, the drum position is fixed (fixed position) according to the receiving distance, the fibers of different directions are straightened and overlapped into fibers with consistent orientation by the rapid rotation of the drum; the drum is rotated at an angle for the first time, any angle within 5-90°, for example, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, 90°, etc., the fibers formed by the first rotation and the fibers obtained from the fixed position form a film material with a certain angle; the drum is rotated at an angle for the second time, any angle within 5-90°, the polymer fiber film formed by the second rotation is regularly overlapped between the fibers formed by the first rotation and the fibers formed by the fixed position.

[0028] It should be noted that the drum is rotated at an angle at least once, and the orientation of the fibers wound by the drum each time is consistent, and there will be a certain angle (5-90°) between the fibers formed by different times, forming a double or multi-layer regular angle initial polymer fiber film.

[0029] Optionally, non-woven fabric and magnetic field assisted winding are used to collect the fibers directly onto one side of the non-woven fabric to obtain polymer fiber film 1; continue spinning, rewind the polymer fiber film 1, rotate the angle of the magnetic field within any angle within 5-90°, obtain polymer fiber film 2; continue spinning, rewind the polymer fiber film 2, rotate the angle of the magnetic field within any angle within 5-90°, obtain the initial polymer fiber film.

[0030] It should be noted that the angle of the rotating magnetic field is at least once, and the orientation of the fiber wound each time is consistent, and there is a certain angle (5-90°) between the fibers formed between different times, which forms a double or multi-layer regular angle polymer fiber membrane. The above initial polymer fiber is further hot rolled at a temperature of 100-200°C and a pressure of 0.5-3MPa, and at the same time, the non-woven fabric material is torn off to obtain a polymer fiber membrane.

[0031] The purpose of hot rolling is to make the fibers and the fibers contact more closely and the material thickness thinner. On the other hand, thermal motion is beneficial to the rearrangement of the fibers and the fibers (the angle between the fibers and the fibers is almost unchanged during rearrangement), and after rearrangement, the porosity between the fibers and the fibers is smaller, and the thickness of the material is more uniform. The strength of the material is enhanced after hot rolling.

[0032] The polymer film material obtained by magnetic field assisted winding contains iron oxide nanoparticles, and the polymer fiber membrane obtained by winding needs to be pickled in dilute sulfuric acid and dilute nitric acid with a concentration of 0.5-1wt%, then washed with water, and vacuum dried to obtain the final polymer film material.

[0033] After the polymer fiber membrane is hot rolled, the overlap between the fibers and the fibers is basically shaped, and subsequent operations such as depositing a conductive layer and pickling have no effect on the overlap mode of the fibers and the fibers.

[0034] Optionally, the preparation method of the composite negative electrode applied to the metal lithium battery specifically comprises:

[0035] Step 1, preparing a polymer fiber membrane base material, and optimizing the structure parameters during preparation, including adjusting the fiber diameter, the pore ratio between the fibers, and the overlap mode;

[0036] Step 2, depositing a metal conductive layer on the polymer fiber membrane base material;

[0037] Step 3, combining the material of step 2 with metal lithium to prepare a metal lithium battery negative electrode.

[0038] Optionally, the step 1 comprises:

[0039] Step 101, selecting a high molecular / polymer fiber material with a density less than 2.5g / cm 3 and high strength;

[0040] Step 102, using advanced preparation processes such as electrospinning, melt-blowing spinning, spun-bonding, wet-laid or weaving to prepare a polymer fiber membrane base material with a fiber diameter of 100nm-20μm, preferably 500nm-15μm;

[0041] Step 103, the lapping mode of the polymer fiber membrane base material is optimized, including the skew cross mode, the control of the angle between the fibers and the pore area ratio between the fibers of 10%-70%, etc., to provide a suitable base structure for uniform deposition of lithium ions.

[0042] Optionally, the step 2 comprises:

[0043] Step 201, a metal conductive layer with a thickness of 200nm-2um is deposited on the surface of the polymer fiber membrane base material by physical vapor deposition, electroplating, etc., and the metal conductive layer material is copper, nickel, silver, tin, gold, etc.

[0044] Step 202, the deposition process parameters are optimized to improve the dispersibility and conductivity of the metal conductive layer on the surface of the polymer fiber membrane base material.

[0045] The composite negative electrode material prepared by the above method not only has conductivity, but also uses a lightweight and high-strength polymer fiber membrane material as a base, which is lighter and thinner than the traditional copper foil current collector, and can improve the energy density of the battery.

[0046] The application also relates to the application of the composite negative electrode in a metal lithium battery.

[0047] Optionally, the metal lithium battery can include a liquid or solid lithium ion secondary battery.

[0048] The positive electrode of the secondary battery can be selected from NCM (nickel-cobalt-manganese) ternary, NCA (nickel-cobalt-aluminum ternary), lithium iron phosphate, S positive electrode, V2O5 positive electrode, etc.; the liquid electrolyte can be selected from at least one of ether, ester electrolyte, local high-concentration electrolyte, ionic liquid; the solid electrolyte can be selected from at least one of oxide solid electrolyte, sulfide solid electrolyte, polymer solid electrolyte; and the negative electrode is the composite negative electrode material described above.

[0049] Compared with the prior art, the composite negative electrode applied to the metal lithium battery provided by the application has at least one of the following beneficial effects:

[0050] 1. The lightweight and high-strength polymer fiber membrane is used as a base, a metal conductive layer is deposited on the surface of the base, the conductivity of the material itself is enhanced, and the material itself has low density, high strength and small elongation at break, which is more suitable as a supporting material for the metal lithium negative electrode. Compared with the traditional copper foil current collector, the composite material is lighter and thinner, and the energy density of the battery can be increased by 5-10%.

[0051] 2. By optimizing the structural parameters of the polymer fiber membrane, such as the fiber diameter size, the inter-fiber pore area ratio, and the lapping method, a good substrate structure is provided for the uniform deposition of lithium ions, which is beneficial to improve the cycle life of the battery.

[0052] 3. By using advanced preparation processes such as vapor deposition or electroplating, the dispersibility and conductivity of the metal conductive layer on the surface of the polymer fiber membrane can be effectively improved, thereby improving the overall electrochemical performance of the composite material.

[0053] 4. The preparation process of the composite material is simple, low in cost, and the material has good consistency and reliability, which is beneficial to realize industrialized application. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 is an SEM image of the polymer fiber membrane of Example 1;

[0055] Figure 2 is a photo of the electrode sheet disassembled at the later stage of battery cycle of battery group 1-4, 6;

[0056] Figure 3 is a photo of the electrode sheet disassembled at the later stage of battery cycle of battery group 5;

[0057] Figure 4 shows the state of the composite negative electrode 6, composite negative electrode 7 (Comparative Examples 3, 4) just after being made;

[0058] Figure 5 shows the state of the composite negative electrode 6, composite negative electrode 7 after being left for 12 hours;

[0059] Figure 6 is a battery cycle performance graph of battery group 1-6 (Examples 1-4 and Comparative Examples 1-2). DETAILED DESCRIPTION

[0060] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0061] Example 1:

[0062] The present embodiment provides a preparation method of a composite negative electrode applied to a metal lithium battery, comprising the following steps:

[0063] Step 1, preparing a polymer fiber membrane base material;

[0064] The polyethylene terephthalate (PET) raw material is used, the density is less than 2g / cm 3 , the strength is higher;

[0065] The electrostatic spinning process is adopted, the environmental humidity is 40%, the PET is dissolved in the trifluoroacetic acid and dichloromethane solution (volume ratio 6:4), a solution with a concentration of 5wt% is prepared, two parallel nozzles are adopted, the voltage is 23kV, the flow rate is 0.5mL / h, the needle nozzle diameter is 24G, the receiving distance is 20cm, the drum winding is adopted, the winding speed of the drum is 200m / min, first, the position of the drum is fixed (referred to as the fixed position), the spinning is wound at a speed of 200m / min, the spinning is straightened in the same direction during the winding process; then the first rotation of the drum position is 30° from the fixed position, the high-speed winding at the same speed is continued, the fiber with an angle of 10-50° from the fiber wound in the fixed position is obtained; then the second rotation of the drum position is 60° from the fixed position, the high-speed winding at the same speed is continued, the fiber with an angle of 40-80° from the fiber wound in the fixed position is obtained, the initial polymer fiber membrane is obtained, at this time, the average thickness of the polymer fiber membrane is 20μm, the thickness tolerance is ±3μm, the pore area between the fibers accounts for about 85% of the total area of the polymer fiber membrane material, and the tensile strength is 46.2MPa.

[0066] The polymer fiber membrane is rolled by a 120℃ hot roller, the pressure is set to 1MPa, and the speed is 1m / min, to obtain the final polymer fiber membrane, the thickness of the polymer fiber membrane is changed to 12μm, the thickness tolerance is changed to ±1μm, the pore area between the fibers accounts for about 30% of the total area of the polymer fiber membrane material, and the tensile strength is 74.5MPa. After hot rolling, the material is thinner, more uniform, has smaller porosity, and greater strength; the polymer fiber membrane base material with a fiber diameter in the range of 5-10μm is prepared, the fibers are staggered and overlapped between the fibers, and the angle between the pore area between the fibers and the horizontal and vertical fibers is 10-80°. Figure 1 The physical map of the polymer fiber membrane is shown.

[0067] Step 2, depositing a metal conductive layer on the above polymer fiber membrane base material;

[0068] After the polymer fiber membrane is treated by oil removal, roughening, sensitization and activation, a gas deposition process is adopted, a nickel target with a purity of about 99.99% is used, the vacuum degree is controlled at 10 -4Pa, heating power 300W, evaporation source temperature 1400℃, target base distance 100mm, deposition base temperature control at 200℃, depositing about 30nm thick metal nickel on the surface of the polymer fiber membrane; then preparing the electroplating solution, the electroplating solution composition is CuSO4·5H2O (15g / L) + potassium sodium tartrate (40g / L) + NaOH (12g / L) + formaldehyde (10mL / L), pH=12.5, the membrane material with the above nickel plating layer is slowly placed in the plating solution through the unwinding equipment, the current density is 3A / dm 2 , 40℃ water bath heating, slow stirring for 15 minutes, after winding, the polymer fiber membrane with about 300nm thick copper plating layer on the fiber is obtained; in order to prevent the oxidation of the copper plating layer, a nickel layer is continuously deposited on the surface of the copper plating layer by gas phase deposition, and the above nickel plating layer is deposited in the same way, about 60nm thick metal nickel is deposited on the surface of the copper plating layer, and a conductive polymer fiber membrane with a thickness of 13μm and a density of 1.43g / cm 3 , the tensile strength is 76.5MPa, the elongation at break is 1.19%, and the resistance per square centimeter area is 25.8mΩ.

[0069] Step 3, the 15μm thick pure lithium belt, the conductive polymer fiber membrane and the 15μm thick pure lithium belt are three layers, which are compounded together by means of winding and unwinding and pressure equipment, and a 5MPa pressure is obtained. Composite negative electrode 1.

[0070] Example 2:

[0071] The embodiment provides a preparation method of a composite negative electrode applied to a metal lithium battery, comprising the following steps:

[0072] Step 1, preparing a polymer fiber membrane base material;

[0073] The raw material nylon 6 particles have a density less than 2g / cm 3 , and high strength;

[0074] The nylon 6 particles and the iron tetroxide powder (particle size 20-50nm) are dissolved into a formic acid and acetic acid mixed solution, the volume ratio of the formic acid and the acetic acid is 6:4, a solution with a polymer concentration of 6wt% (wherein the content of the iron tetroxide is 0.8wt%) is prepared, mechanical stirring is carried out for 5 hours (rotation speed 300r / min), and a uniform mixed solution is obtained.

[0075] A melt-blowing spinning process is adopted, the ambient temperature is 25℃, the humidity is controlled to be 40%, the solution temperature is heated to 200℃, the solution pressure is set to be 10MPa, the spinning hole diameter is 0.1mm, the hole spacing of the spinning hole is 1.0mm, the temperature of the die head is 205℃, the air flow hot air temperature is 250 degrees, the air flow pressure is 0.8MPa, the air flow speed is 1.0 Mach, the screw rotation speed is 120rpm, and the receiving distance is 20cm.

[0076] The non-woven fabric and the magnetic field are used for auxiliary winding. The non-woven fabric is first unwound. The magnetic field is arranged in parallel with the direction of the non-woven fabric. The force direction of the magnetic field is perpendicular to the direction of the non-woven fabric. The polymer fiber membrane 1 is obtained.

[0077] The polymer fiber membrane 1 is rewound. The direction of the magnetic field is changed to 50° with the direction of the non-woven fabric. The polymer fiber membrane 1 continues to spin fibers. The initial polymer fiber membrane is obtained. The thickness is 30 μm. The thickness tolerance is ± 6 μm. The pore area between the fibers accounts for 90% of the total area of the polymer fiber membrane material. The tensile strength of the membrane material is 56.3 MPa.

[0078] The initial polymer fiber membrane is subjected to hot rolling by means of the winding and unwinding device. The temperature is 200°C. The pressure is 2 MPa. The speed is 1.5 m / min. The non-woven fabric layer is synchronously torn off. The polymer fiber membrane material is obtained. The thickness is 15 μm. The thickness tolerance becomes ± 1 μm. The pore area between the fibers accounts for about 30% of the total area of the polymer fiber membrane material. The tensile strength is 102.4 MPa. After the hot rolling, the material thickness becomes thinner. The thickness is more uniform. The porosity is smaller.

[0079] The polymer membrane material roll is immersed in hydrochloric acid with a concentration of 1 wt% for 2 hours. The ferroferric oxide is removed. The polymer membrane material is obtained after being washed with distilled water for 3 times and vacuum dried at 80°C for 6 hours. The pore area between the fibers accounts for about 30% of the total area of the polymer fiber membrane material. The polymer fiber membrane base material with a fiber diameter in the range of 4-10 microns is prepared. The fibers are staggered and overlapped. The angle between the horizontal and vertical fibers is 20-80°.

[0080] Step 2, depositing a metal conductive layer on the polymer fiber membrane base material

[0081] Referring to step 2 of embodiment 1, the polymer fiber membrane with a thickness of about 40 nm of Ni, about 1 μm of copper, and about 70 nm of Ni is obtained. The polymer fiber membrane with a metal layer is obtained. The thickness is 16 μm. The density is 1.36 g / cm 3 . The tensile strength is 102.6 MPa. The elongation at break is 13.4%. The resistance per square centimeter area is 31.3 mΩ.

[0082] Step 3, the 15 μm thick lithium-magnesium alloy strip (magnesium content is 5%), the conductive polymer fiber membrane, and the 15 μm thick lithium-magnesium alloy strip (magnesium content is 5%) are compounded together by means of the unwinding and winding and pressure equipment under the pressure of 5 MPa. The composite negative electrode 2 is obtained.

[0083] Embodiment 3:

[0084] The embodiment provides a preparation method of a composite negative electrode applied to a metal lithium battery.

[0085] Step 1, preparing a polymer fiber membrane base material;

[0086] Polyacrylonitrile is selected as a raw material, the density of which is less than 2 g / cm 3 , and the tensile strength is large;

[0087] An electrostatic spinning process is adopted, the environmental humidity is controlled to be 30%, polyacrylonitrile is dissolved into N,N-dimethylformamide, the concentration of the solution is 8 wt%, the uniform solution is obtained by magnetic stirring for 6 hours, three parallel nozzles are adopted, the voltage is set to be 23 kV, the flow rate is 0.5 mL / h, the needle nozzle diameter is 25G, the receiving distance is 20 cm, a roller is adopted for winding, the winding speed of the roller is 100 m / min, first, the position of the roller is fixed (referred to as a fixed position), the spinning is wound at the speed of 100 m / min, and the spinning is straightened in the same direction during the winding process; then the position of the roller is rotated for the first time by 20 degrees from the fixed position, the high-speed winding is continuously carried out at the same speed, and the fibers wound with the fixed position are obtained to be 10-50 degrees; then the position of the roller is rotated for the second time by 50 degrees from the fixed position, the high-speed winding is continuously carried out at the same speed, and the fibers wound with the fixed position are obtained to be 30-80 degrees, an initial polymer fiber membrane is obtained, the thickness is 30 mu m, the thickness tolerance is ± 3 mu m, the pore area between the fibers accounts for about 87% of the total area of the polymer fiber membrane material, and the tensile strength is 46.7 MPa.

[0088] The initial polymer fiber membrane is rolled by a hot roller, the temperature is 200 DEG C, the pressure is set to be 2 MPa, and the speed is 1 m / min, a final polymer fiber membrane is obtained, the thickness is 18 mu m, the thickness tolerance is ± 1 mu m, the pore area between the fibers accounts for about 35% of the total area of the polymer fiber membrane material, the tensile strength is 87.6 MPa, a polymer fiber membrane base material with fiber diameters in the range of 130-200 nm is prepared, the fibers are staggered and overlapped, and the angle between the fibers is 10-80 degrees.

[0089] Step 2, depositing a metal conductive layer on the polymer fiber membrane base material;

[0090] Referring to step 2 in embodiment 1, a polymer fiber membrane with a Ni layer of about 50 nm in thickness, a copper layer of about 1 mu m in thickness and a Ni layer of about 70 nm in thickness is obtained, a polymer fiber membrane with a metal layer is obtained, the membrane material thickness is 19 mu m, the density of the membrane material is 1.23 g / cm 3 , the tensile strength is 88.9 MPa, the elongation at break is 10.83%, and the resistance per square centimeter area is 30.3 m omega.

[0091] Step 3, 15 μm thick pure lithium belt, conductive polymer fiber film and 15 μm thick pure lithium belt three layers are compounded together by means of unwinding and winding and pressure equipment, using a pressure of 5 MPa, to obtain a composite negative electrode 3.

[0092] Example 4: The material is prepared by using the step 1 of example 1, the difference is that the step 1 uses a roller to collect the fibers, the position of the roller is fixed all the time, the collected fibers are all arranged in the same direction, the fibers are arranged in parallel between the fibers, and the parallel arranged fibers are woven into a fiber film to obtain an initial polymer fiber film, at this time the average thickness of the polymer fiber film is 30 μm, the thickness tolerance is ± 3 μm, the pore area between the fibers accounts for about 80% of the total area of the polymer fiber film material, and the tensile strength is 50.3 MPa.

[0093] The polymer fiber film is further rolled by a 120℃ hot roller, the pressure is set to 1 MPa, and the speed is 1 m / min, to obtain a final polymer fiber film, the thickness of the polymer fiber film is changed to 13 μm, the thickness tolerance is changed to ± 1 μm, the pore area between the fibers accounts for about 30% of the total area of the polymer fiber film material, the tensile strength is 104.5 MPa, after the hot roller, the material is thinner, the thickness is more uniform, the porosity is smaller, and the strength is greater.

[0094] Step 2, depositing a metal conductive layer on the polymer fiber film base material;

[0095] Referring to step 2 of example 1, a polymer fiber film with a layer of metal is obtained, the thickness of the film material is 14 μm, the density of the film material is 1.93 g / cm 3 , the tensile strength is 118.9 MPa, the elongation at break is 15.83%, and the resistance per square centimeter area is 30.3 mΩ.

[0096] Step 3, 15 μm thick pure lithium belt, conductive polymer fiber film and 15 μm thick pure lithium belt three layers are compounded together by means of unwinding and winding and pressure equipment, using a pressure of 5 MPa, to obtain a composite negative electrode 3.

[0097] Comparative example 1: lithium copper composite belt

[0098] A 15 μm thick pure lithium belt, a 6 μm thick copper foil (the density of the copper foil is 8.9 g / cm 3 ) and a 15 μm thick pure lithium belt are compounded together by means of unwinding and winding and pressure equipment, using a pressure of 5 MPa, to obtain a lithium copper composite belt.

[0099] Comparative example 2:

[0100] The comparative example provides a preparation method of a composite negative electrode applied to a metal lithium battery, comprising the following steps:

[0101] Step 1, preparing a polymer fiber membrane base material;

[0102] A polypropylene (PP) raw material is used, which has a density less than 2 g / cm 3 , and a high strength.

[0103] An electrostatic spinning process is adopted, and the PP is dissolved in a dimethylbenzene and cyclohexanone solution (volume ratio 5:1) to obtain a solution with a concentration of 15 wt%. An electrostatic spinning process is adopted, a voltage of 10 kV, a receiving distance of 8 cm, and a flow rate of 0.5 mL / h are adopted to prepare a polymer fiber membrane base material with a fiber diameter of 21-30 μm. The pore area between the fibers accounts for 82% of the total area of the polymer fiber membrane material, and the overlap between the fibers has no regularity.

[0104] Step 2, depositing a metal conductive layer on the above polymer fiber membrane base material;

[0105] Referring to step 2 of example 1, a polymer fiber membrane with a thickness of about 40 nm of Ni + a thickness of about 1 μm of copper + a thickness of about 70 nm of Ni is obtained, and a polymer fiber membrane with a metal layer is obtained. The thickness of the membrane material is 28 μm, the density is 1.26 g / cm 3 , the tensile strength is 68.2 MPa, the elongation at break is 14.32%, and the resistance per square centimeter area is 29.5 mΩ.

[0106] Step 3, three layers of 15 μm thick pure lithium strips, conductive polymer fiber membranes, and 15 μm thick pure lithium strips are compounded together by means of a take-up and release and pressure device, and a pressure of 5 MPa is adopted to obtain a composite negative electrode 5.

[0107] Comparative example 3:

[0108] The comparative example provides a preparation method of a composite negative electrode applied to a metal lithium battery, comprising the following steps:

[0109] Step 1, selecting a polyethylene fiber membrane base material;

[0110] A polyethylene fiber membrane on the market is adopted.

[0111] Step 2, referring to step 2 of example 1, a polymer fiber membrane with a thickness of about 40 nm of Ni + a thickness of about 1 μm of copper + a thickness of about 70 nm of Ni is obtained, and a conductive polymer fiber membrane is obtained. The thickness is 18 μm, the density is 1.25 g / cm 3 , the tensile strength is 67 MPa, the elongation at break is 25.8%, and the resistance per square centimeter area is 31.8 mΩ.

[0112] Step 3, the 15 um thick pure lithium belt, polymer fiber film and 15 um thick pure lithium belt three layers are compounded together by means of take-up and pressure equipment with a pressure of 5 MPa to obtain a composite negative electrode 6, the just-made state of the composite negative electrode 6 is shown in Figure 4 , the surface of the composite product is flat; the state after standing for 12 hours is shown in Figure 5 , because the elongation at break of the polyethylene fiber film material is large (25.8%), the polymer fiber film has been stretched and deformed in the process of compounding lithium under a pressure of 5 MPa, and the stretched and deformed part of the material will shrink after standing for a period of time. The surface-composited metallic lithium is also soft and very thin, which cannot limit the shrinkage of the polymer fiber film, and many pits and wrinkles appear on the surface of the composite material, which cannot be used for battery electrode sheets.

[0113] Comparative Example 4:

[0114] The materials are prepared by steps 1 and step 2 of Example 1, the difference is that the fibers are collected by a roller in step 1, and the position of the roller is fixed all the time, and the collected fibers are arranged in the same direction, and the fibers are arranged in parallel with each other. The thickness of the final polymer fiber film is 14 um, the density is 1.42 g / cm 3 , the tensile strength is 60.7 MPa, the elongation at break is 25.3%, and the resistance per square centimeter area is 26.3 mΩ.

[0115] Step 3, the 15 um thick pure lithium belt, polymer fiber film and 15 um thick pure lithium belt three layers are compounded together by means of take-up and pressure equipment with a pressure of 5 MPa to obtain a composite negative electrode 6, the just-made state of the composite negative electrode 6 is shown in Figure 5 , because the polymer fiber is easy to be stretched and deformed in the same direction, and the elongation at break is large, resulting in many pits and wrinkles on the composite product, which cannot be used for battery electrode sheets.

[0116] Electrochemical performance test

[0117] The above examples and comparative examples are used as negative electrodes, the positive electrode is a nickel-cobalt-manganese 811 ternary positive electrode, the areal density of the double-sided coated surface is 40.3 mg / cm 2 , the separator is a single-sided ceramic-coated (coating thickness 2 um) polyethylene (thickness 12 um), the electrolyte is 1 mol / L LiFSI DOL (1,3-dioxolane) / DOE (ethylene glycol dimethyl ether) (volume ratio 1:1) + 5% FEC + 0.2M LiNO3, the positive electrode sheet size is 43*56 mm, the negative electrode sheet size is 45*58 mm, a 650 mAh capacity battery cell is assembled, the liquid injection amount is 2.5 g, the charging rate is 0.2C, the discharging rate is 1C, the cycle performance of the battery is tested, and the electrode sheet state is observed after disassembling the battery cell in the later cycle.

[0118] Table 1 Battery data and electrode condition after disassembly for different groups

[0119]

[0120] The data in the table above shows that, compared to battery group 5, the lithium-copper composite strip battery using the negative electrode has the lowest specific energy. Battery group 1 shows a 7.3% increase in specific energy, battery group 2 a 5.36% increase, battery group 3 a 6.09% increase, battery group 4 a 5.09% increase, and battery group 6 also shows an increase in specific energy. However, due to the coarse fibers in the polymer fiber membrane substrate, the large pores between the fibers, and the irregular, spiderweb-like arrangement of the fibers, uneven deposition of metallic lithium on the fiber membrane substrate occurs in the later stages of cycling. Furthermore, the lithium deposited in the pores expands during volume expansion, damaging the substrate material and causing surface unevenness and breakage. Figure 3 As shown. The electrode plates from battery packs 1, 2, 3, 4, and 5, after being disassembled during the later stages of battery cycling, are as follows. Figure 2 As shown, the electrode surface is flat and the electrode is not damaged.

[0121] pass Figure 6 As can be seen from the battery cycle performance diagram, the performance of the polymer fiber membrane substrate material in Comparative Example 2 deteriorates after 70 cycles. In the later stages of the cycle, the metallic lithium in the lithium-ion replenishment layer will be depleted. The metallic lithium deposited on the negative electrode during charging will be directly deposited on the polymer fiber membrane substrate material. Because the fibers of the substrate material are coarse and have large pores, and the fibers are arranged irregularly like a spider web, the metallic lithium deposition is uneven. Some metallic lithium will be deposited in the pores between the fibers, causing damage to the polymer fiber substrate and deteriorating battery performance.

[0122] It should be understood that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite negative electrode, characterized by, The composite negative electrode comprises: a polymer fiber membrane having a conductive material layer deposited thereon; and a metal lithium / lithium alloy layer, which is compounded on one side or both sides of the polymer fiber membrane, The diameter of the polymer fiber is 100 nm-20 μm, the fiber-to-fiber porosity area ratio is in the range of 10-70%, the fibers and the fibers between them are orderly overlapped to form a double-layer or multi-layer regular angle polymer fiber membrane, wherein the fibers in the same layer are oriented consistently, and the angle between the fibers of another layer is in the range of greater than 5 degrees to 90 degrees.

2. The composite negative electrode according to claim 1, characterized by The material of the polymer fiber membrane is at least one of polyester fiber, polyamide fiber, polyimide fiber, polyarylate fiber, polyacrylonitrile fiber, aramid fiber, polytetrafluoroethylene fiber, and polyurethane fiber.

3. The composite negative electrode according to claim 1, characterized by The polymer fiber film has a thickness of 3-25 μm, a density of 0.5-2.5 g / cm 3 , a tensile strength of 50-200 MPa, an elongation at break of 1%-20%, and a resistance of 1-100 mΩ per square centimeter.

4. The composite anode according to claim 1, characterized by The fiber diameter of the polymer fiber membrane is 1 μm-15 μm.

5. The composite anode according to claim 1, wherein The conductive material layer comprises at least one of conductive copper, nickel, silver, tin, and gold, and the thickness of the conductive material layer is 200 nm-2 μm.

6. The composite anode according to claim 1, wherein The thickness of the metal lithium / lithium alloy layer is 1-50 μm. The lithium alloy layer is an alloy layer formed by metal lithium and any one or at least two elements of Ag, Au, Sn, Si, Zn, Al, Mg, In, Ga, B, Mn, Sb, Cr, C, V, Cu, Fe, or Ti.

7. A method for producing the composite negative electrode according to any one of claims 1 to 6, characterized by, The method comprises the following steps: First step: obtaining an initial polymer fiber membrane by electrospinning, melt-blowing, spun-bonding, wet-laying, or weaving, and then performing hot roller pressing on the initial polymer fiber to obtain a polymer fiber membrane, wherein the fiber diameter is in the range of 100 nm-20 μm, the fibers and the fibers between them are orderly overlapped to form a double-layer or multi-layer regular angle polymer fiber membrane, wherein the fibers in the same layer are oriented consistently, and the overlapping angle between the fibers of another layer is in the range of 5 degrees to 90 degrees, and the fiber-to-fiber porosity area ratio is in the range of 10-70%; Second step: forming a conductive layer on the polymer fiber membrane by physical vapor deposition or electroplating; Third step: tightly combining one side or both sides of the polymer fiber membrane and the metal lithium / lithium alloy layer by roller pressing or flat pressing to obtain a composite negative electrode.

8. The method of claim 7, wherein, In the first step, at least one of electrospinning, melt-blowing, spun-bonding, wet-laying, or weaving is adopted, and the overlapping angle of the fibers between the two layers is controlled by adjusting the rotation angle of the winding drum during the collection of the two-layer fiber membrane, or by adjusting the angle of the magnetic field in the case of magnetic field-assisted winding.

9. The method of claim 7, wherein, The hot roller pressing parameters are: temperature 100-200 ℃, and pressure 0.5-3 MPa.

10. Application of the composite negative electrode according to any one of claims 1 to 6 in a metal lithium battery.

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