CN108550808A - A kind of composition metal cathode of lithium and preparation method thereof - Google Patents

Abstract

The invention provides a composite metal lithium negative electrode, which includes a primary network structure formed by polymers; a secondary network structure formed by filling nano-scale carbon materials into the primary network structure; and a secondary network structure formed by filling lithium metal into the secondary network structure. three-level composite structure. Firstly, the secondary network structure filled with carbon materials is obtained by accumulative rolling method, and then metal lithium is embedded in the secondary network structure filled with carbon materials by cumulative rolling method, electrodeposition lithium or evaporation lithium plating to obtain a composite metal lithium anode. The negative electrode with this structure can improve the morphology of lithium deposition and solve the problem of lithium dendrite growth, thereby improving the cycle performance and safety of the battery.

Description

A kind of composite metal lithium negative electrode and preparation method thereof

technical field

The invention belongs to the field of lithium ion secondary batteries, in particular to a composite metal lithium negative electrode and a preparation method thereof.

Background technique

Lithium-ion secondary batteries use lithium ions to move between the positive and negative electrodes to provide electrical energy to the outside. Improving the specific energy of lithium-ion secondary batteries is the main development direction of lithium-ion secondary batteries at present. One of the effective methods is to use lithium metal as the negative electrode. This is because metal lithium per unit weight or volume can release the most energy during the discharge process when it migrates from the negative electrode to the positive electrode, that is, metal lithium is the negative electrode active material with the highest weight or volume specific energy. However, metal lithium will grow lithium dendrites on the surface during the charge-discharge cycle, which will lead to the pulverization of the lithium negative electrode, increase the internal resistance of the battery, reduce the battery capacity, and affect the service life. What's more serious is that lithium dendrites will continue to grow, which can pierce the separator, contact with the positive electrode, and cause an internal short circuit, which brings serious safety problems. Therefore, solving the growth of lithium dendrites is a problem that must be solved for the practical application of lithium anodes.

In order to suppress the growth of lithium dendrites, scientists and engineers have made a lot of research and efforts. These works mainly focus on the following aspects. (1) According to the disclosure of documents Energy Environ.Sci.2014,7,513 and Adv.Sci.2016,3,1500213, and patent CN103531839, by adding additives in the electrolyte, the SEI composition and morphology of the metal lithium negative electrode surface are regulated to form A stable SEI inhibits dendrite growth. (2) Constructing an in-situ artificial SEI to protect the lithium metal anode. (3) Polymer electrolyte or all-solid electrolyte is used to block the formation of lithium dendrites. Yet these method measures all have very big deficiency. During the charge-discharge cycle of lithium metal anode, it will experience a large volume change, so neither the electrolyte additive nor the in-situ artificial SEI has enough strength and toughness to withstand the volume change of lithium metal cycle without breaking. This is especially true when the current density increases. According to theoretical calculations, only when the electrolyte strength exceeds 6Gpa, can the lithium dendrite puncture be completely blocked. However, none of the existing polymer electrolytes has reached such a high strength. In addition, lithium dendrites will diffuse along the grain boundaries of the all-solid electrolyte, thereby short-circuiting through the all-solid electrolyte. Therefore, polymer electrolytes and all-solid-state electrolytes cannot solve the problem of lithium dendrite growth.

In addition to solving from the direction of SEI and electrolyte, there are also some works focusing on the structural optimization of lithium metal anodes. Patent CN105845891A discloses a double-layer metal lithium negative electrode structure. There is a covering layer on the surface of the lithium metal, and the covering layer is composed of one or more of carbon materials, polymer materials, and glass fibers. The capping layer affects the electrochemical environment during lithium deposition, thereby inhibiting the growth of lithium dendrites. However, according to the research of the inventors, it is found that the thickness of the covering layer must be thick enough to change the electrochemical environment of lithium deposition and achieve the effect of suppressing dendrites. The covering layer will reduce the energy density of the battery, increase the internal resistance of the battery, and affect the performance of the battery. In addition, the invention cannot realize the double-layer structure through a mass production process. The document NATURE NANOTECHNOLOGYVOL 11, 2016, 7 proposes a new solution. The multilayer graphene oxide is immersed in liquid lithium, and a multilayer structure of graphene sheet/metal lithium is formed through capillary action. The metal lithium anode with this structure has good electrochemical activity during cyclic charge and discharge, and can inhibit the growth of dendrites. However, the process is complicated, and the required graphene oxide sheets cannot be produced continuously, and can only be produced in a small area by suction filtration. In particular, it is necessary to use molten liquid lithium, which can only be operated under the protection of Ar gas. Overall, this method does not have the significance and value of amplification and practical application.

Contents of the invention

The object of the present invention is to address the deficiencies of the prior art and provide a composite metal lithium negative electrode of a lithium-ion secondary battery, which avoids electrode pulverization and internal short circuit in the battery charge-discharge cycle.

The technical solution adopted in the present invention is to provide a metal lithium negative electrode with a three-level composite structure, the composite metal lithium negative electrode includes: a primary network structure composed of polymers; nano-scale carbon materials are filled into the primary network structure to form The secondary network structure; the lithium metal is filled into the secondary network structure to form a tertiary composite structure.

The pore diameter range of the primary network structure of the composite metal lithium negative electrode is 0.1 μm to 1 mm, and the porosity is 10% to 99%; the pore diameter range of the secondary network structure is 10nm to 1mm, and the porosity is 9% to 98%. The range of pore diameter in the tertiary composite structure is 0nm-0.1mm, and the porosity is 0%-50%.

The preferred tertiary composite structure of the composite metal lithium negative electrode is: the pore size in the primary network structure is 0.2 μm to 2 μm, and the porosity is 60% to 95%; the pore size in the secondary network structure is 0.05 μm to 1 μm, and the porosity is 50% to 85%; the pore diameter in the tertiary composite structure is 0nm to 100nm, and the porosity is 0% to 5%.

The thickness of the composite metal lithium negative electrode is 0.05 μm to 1 mm.

The polymer described in the composite metal lithium negative electrode is polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyimide, polyacrylonitrile, polyaniline, polylactic acid, cellulose acetate and polylactic acid glycolic acid copolymer One or more of them, preferably polytetrafluoroethylene, with a mass content of 2% to 20%.

The nanoscale carbon material described in the composite metal lithium negative electrode is one or more of natural graphite, artificial graphite, modified graphite, graphitized carbon, activated carbon, hard carbon, soft carbon, and graphene, with a mass content of 15% ~70%.

The mass content of the lithium metal in the composite metal lithium negative electrode is 20%-80%.

The present invention also provides a preparation method for the composite metal lithium negative electrode, specifically: using the cohesiveness of the polymer, rolling with a metal rolling method, the amount of deformation under compression is 10% to 50%, and obtaining a three-dimensional Network polymer; the carbon material is spread on the surface of the three-dimensional network polymer, and then rolled, and the compression deformation is 20% to 50%, and the carbon is filled into the three-dimensional network structure to obtain a secondary structure filled with carbon; the metal Lithium is tiled on the surface of the secondary structure, and then rolled, with a deformation of 20% to 50% under pressure, a part of the metal lithium is embedded in the carbon material, and a part of the metal lithium is filled in the gap of the three-dimensional structure, and the first composite metal lithium is obtained For the negative electrode, the composite lithium metal negative electrode is cut, laminated, and rolled for 3 to 20 times to obtain a composite lithium metal negative electrode with a uniform microstructure.

Further, the preparation method of the composite metal lithium negative electrode is: using electrodeposited lithium to embed metal lithium into a carbon material to fill the secondary network structure or using evaporation lithium plating to embed metal lithium into a carbon material to fill the secondary network structure.

The inventors have studied the formation and growth of lithium dendrites by consulting literature and conducting related experiments. During the charging process, lithium ions will electrochemically react on the surface of the negative electrode. When the electrochemical potential of the surface is lower than the Li ⁺ /Li potential, lithium ionization will occur on the surface of the negative electrode. The electrochemical potential of the anode surface is affected by various factors, such as the Li ⁺ concentration, the average potential of the anode, and the microscopic topography of the electrode surface, etc. Among them, the influence of electrode surface morphology on lithium deposition is particularly obvious: in areas with small curvature radii on the electrode surface, such as defect edges, protrusions, etc., charges are more likely to be enriched, resulting in a lower potential than other areas, and lithium deposition is often preferential; the deposited metal Lithium in turn exacerbates the inconsistency of the surface morphology, leading to lithium dendrite growth.

Existing technologies solve the above problems from chemical and thin-film manufacturing technologies, but chemical methods have the problems of complex process, difficult regulation, and low degree of practicality, and the degree of improving the cycle performance of batteries is limited; thin-film manufacturing technologies have high costs and low The environmental requirements are harsh and practical problems are difficult. None of them can completely solve the problems of lithium pulverization and lithium dendrites in the lithium negative electrode.

Beneficial effect:

The compound metal lithium negative electrode structure provided by the present invention can improve the lithium deposition morphology and solve the problem of lithium dendrite growth, thereby improving the cycle performance and safety of the battery: first, the micron-scale polymer framework has high stability and electrical It is chemically inert and will not affect the performance of the battery. Moreover, the carbon and lithium distributed in the network structure can ensure that the structure has good electronic conductivity and ensure the normal deposition/dissolution of lithium; secondly, lithium is evenly distributed in the network structure. The lithium carbon layer acts as a lithium source during the lithium dissolution process to provide part of the capacity; the lithium carbon layer can balance the surface potential of the negative electrode and inhibit the growth of dendrites during lithium deposition; third, the micron-scale polymer skeleton in the composite lithium negative electrode structure can be lithium The deposition/dissolution provides space, alleviates the volume change of the negative electrode, and improves the structural stability.

Description of drawings

Fig. 1 is the schematic diagram of composite metal lithium negative electrode structure of the present invention;

Fig. 2 is the cycle diagram that adopts composite metal lithium negative electrode of the present invention to make symmetrical battery;

Figure 3 is a cycle result diagram of a symmetrical battery made of a conventional lithium metal negative electrode;

Detailed ways

Example 1

The polymer content in the composite metal lithium negative electrode is 2%, the nano-scale carbon material content is 25%, and the lithium metal content is 73%.

The composite metal lithium negative electrode is obtained by accumulative rolling method. The specific method is: using the cohesiveness of the polymer PTFE, rolling by the metal rolling method, and the deformation of the lower pressure is 10% to 50%, to obtain a three-dimensional rolling after one rolling Network polymer; the carbon material is spread on the surface of the three-dimensional network polymer, and then rolled, and the compression deformation is 20% to 50%, and the carbon is filled into the three-dimensional network structure to obtain a secondary structure filled with carbon; the metal Lithium is tiled on the surface of the secondary structure, and then rolled, with a deformation of 20% to 50% under pressure, a part of the metal lithium is embedded in the carbon material, and a part of the metal lithium is filled in the gap of the three-dimensional structure, and the first composite metal lithium is obtained negative electrode. Cutting, stacking, and rolling the above composite lithium metal negative electrode are repeated 3 to 20 times to obtain a composite metal lithium negative electrode with a uniform microstructure. According to the easily deformable characteristics of polymer, nano-scale carbon and lithium metal, this technology uses the huge shear force generated by the polymer during severe plastic deformation to form a skeleton, and disperses carbon materials and lithium metal in it. A three-level composite structure composite lithium metal negative electrode composed of micron-scale polymer/nano-scale carbon/metal lithium is formed, which has a unique microstructure and excellent mechanical properties.

Figures 2 and 3 show that the overpotential of the composite metal lithium negative electrode of the present invention is obviously lower than that of conventional lithium negative electrodes, and the cycle stability is better.

Example 2

The polymer content in the composite metal lithium negative electrode is 10%, the nano-scale carbon material content is 50%, and the lithium metal content is 40%.

The composite metal lithium negative electrode was obtained by accumulative rolling method, and the specific method was the same as in Example 1.

Example 3

The polymer content in the composite metal lithium negative electrode is 20%, the nano-scale carbon material content is 30%, and the lithium metal content is 50%.

The composite metal lithium negative electrode was obtained by accumulative rolling method, and the specific method was the same as in Example 1.

Example 4

The specific method of obtaining the composite metal lithium negative electrode is: using the cohesiveness of polymer PTFE, rolling by metal rolling method, and the deformation amount under compression is 10% to 50%, to obtain a three-dimensional network polymer after one rolling; The carbon material is tiled on the surface of the three-dimensional network polymer, and then rolled, and the compression deformation is 20% to 50%, and the carbon is filled into the three-dimensional network structure to obtain a secondary structure filled with carbon; then the metal is deposited by electrodepositing lithium. Lithium is intercalated into the secondary network structure filled with carbon materials to prepare a composite metal lithium negative electrode with a tertiary composite structure.

Example 5

The specific method of obtaining the composite metal lithium negative electrode is: using the cohesiveness of polymer PTFE, rolling by metal rolling method, and the deformation amount under compression is 10% to 50%, to obtain a three-dimensional network polymer after one rolling; The carbon material is spread on the surface of the three-dimensional network polymer, and then rolled, and the compression deformation is 20% to 50%, and the carbon is filled into the three-dimensional network structure to obtain a secondary structure filled with carbon; Lithium is intercalated into the secondary network structure filled with carbon materials to prepare a composite metal lithium negative electrode with a tertiary composite structure.

comparative example

Patent CN 106784635 A provides a method for preparing a composite lithium negative electrode for solid-state batteries. Lithium metal is deposited in the voids of three-dimensional carbon materials or porous foam materials by thermal infusion or electrodeposition to prepare a composite lithium negative electrode. The three-dimensional skeleton The application of the pre-storage lithium in the preparation process provides sufficient space and provides a carrier for receiving metal lithium during the battery cycle, which can inhibit the growth of lithium dendrites during the battery cycle, stabilize the volume change of the electrode, and have good cycle stability and use. The advantage of long life.

The structure of the composite metal lithium negative electrode in the patent of the present invention uses a polymer as a three-dimensional skeleton, which is better in strength and toughness than the carbon skeleton, so the structure is more stable; it can be realized by various methods, and has strong machinability; and it can be adjusted by The structure of the material is controlled by the components of polymer, carbon and metal lithium, and the structure is variable and controllable; more importantly, because the polymer skeleton is more stable than the carbon skeleton, it can better stabilize the electrode volume change , good cycle stability and longer service life.

The above descriptions are preferred implementation modes of the present invention, and the scope of rights of the present invention cannot be defined by them. It should be pointed out that for those skilled in the art, modifications or equivalent replacements to the technical solutions of the present invention will not depart from the protection scope of the present invention.

Claims (9)

1. a kind of composition metal cathode of lithium, it is characterised in that：The cathode includes：The primary network station structure set up by polymer； Nano-scale carbon material is filled into the two grade network structure constituted in primary network station structure；Lithium metal is filled into two grade network structure The three-level composite construction of composition forms composition metal cathode of lithium.

2. composition metal cathode of lithium according to claim 1, it is characterised in that：Aperture in the primary network station structure is 0.1 μm~1mm, porosity is 10%~99%；Aperture in two grade network structure is 10nm~1mm, porosity is 9%~ 98%；Aperture in three-level composite construction is 0nm~0.1mm, and porosity is 0%~50%.

3. composition metal cathode of lithium according to claim 2, it is characterised in that：Aperture in the primary network station structure is 0.2 μm~2 μm, porosity is 60%~95%；Aperture in two grade network structure is 0.05 μm~1 μm, porosity 50% ~85%；Aperture in three-level composite construction is 0nm~100nm, and porosity is 0%~5%.

4. composition metal cathode of lithium according to claim 1, it is characterised in that：The thickness of the composition metal cathode of lithium For 0.05 μm~1mm.

5. composition metal cathode of lithium according to claim 1, it is characterised in that：The polymer is polytetrafluoroethylene (PTFE), Kynoar, polyimides, polyacrylonitrile, polyaniline, polylactic acid, in cellulose acetate and polylactide glycolate copolymer One or more, content is 2%~20%.

6. composition metal cathode of lithium according to claim 1, it is characterised in that：The nano-scale carbon material is natural stone Ink, artificial graphite, modified graphite, graphitized carbon, activated carbon, hard carbon, soft carbon, one or more in graphene, content is 15%~70%.

7. composition metal cathode of lithium according to claim 1, it is characterised in that：The content of the lithium metal be 20%~ 80%.

8. a kind of preparation method of composition metal cathode of lithium according to claim 1, it is characterised in that：The preparation method For：Polymer is rolled using metal rolled method, it is 10%~50% to push deflection, obtains the three dimensional network by once rolling Network polymer；Carbon material is laid in three-dimensional network polymer surfaces, is rolled, pushes deflection 20%~50%, carbon is filled out It is charged in three-dimensional net structure, obtains the secondary structure filled by carbon；Lithium metal is laid in secondary structure surface, is then carried out Rolling pushes deflection 20%~50%, and a part of lithium metal is embedded in carbon material, and a part of lithium metal is filled into three-dimensional structure Gap in, obtain first of composition metal cathode of lithium, above-mentioned composition metal cathode of lithium is cut out, is overlapped, roll, repeatedly 3~20 times, obtain the uniform composition metal cathode of lithium of microstructure.

9. the preparation method of composition metal cathode of lithium according to claim 8, it is characterised in that：The composite metal lithium is negative The preparation method of pole is：Using electro-deposition lithium by the two grade network structure of lithium metal insertion carbon material filling or using evaporation plating lithium By the two grade network structure of lithium metal insertion carbon material filling.