CN110429243A - A kind of preparation method of high specific energy secondary cell lithium anode - Google Patents

Abstract

The invention discloses a method for preparing a metal lithium negative electrode of a high specific energy secondary battery. First, the metal lithium negative electrode is completely immersed in a phosphorus-containing treatment solution with a solid content of 2%-20%, and the standing reaction time is 2-60 Minutes, the reaction temperature is 25-100 °C; then the binder solution with curing effect is evenly added dropwise on the surface of the metal lithium negative electrode to obtain a high specific energy secondary battery metal lithium negative electrode containing a lithium phosphide protective layer. The invention can regulate the amount of lithium phosphide generated in situ on the surface by controlling the concentration of the phosphorus-containing solution and the immersion time, which is very suitable for batch processing of metal lithium negative electrodes, and is conducive to promoting the industrialization of high specific energy secondary batteries . In the metal lithium battery system assembled with the metal lithium negative electrode containing the lithium phosphide protective layer of the present invention, the metal lithium is stable and compatible with the liquid electrolyte or solid electrolyte, thereby improving the electrochemical performance of the assembled metal lithium secondary battery, so it can be greatly improved. Significantly improve the cycle stability of the battery.

Description

A kind of preparation method of metal lithium negative electrode of high specific energy secondary battery

technical field

The invention relates to chemical power source technology, belongs to the preparation of a secondary battery, and specifically refers to a method for preparing a metal lithium negative electrode of a high specific energy secondary battery.

Background technique

Metal lithium secondary batteries are one of the candidates for next-generation high specific energy storage secondary batteries. When metal lithium is used as the negative electrode of lithium secondary batteries, the uneven dissolution-deposition of metal lithium will lead to the growth of lithium dendrites during charging and discharging, which will lead to serious safety hazards in lithium metal secondary batteries. The success of lithium-ion batteries with lithium-intercalated carbon materials as negative electrodes has greatly inhibited researchers from researching and developing metal lithium secondary batteries. However, with the development of technology, the energy density of lithium-ion batteries with carbon materials as the negative electrode has reached a bottleneck. Due to the urgent market demand for high-energy secondary batteries, the research and development boom of lithium-ion secondary batteries with metal lithium as the negative electrode has begun to appear again. . Although the current metal lithium secondary battery technology is still not comparable to lithium-ion battery technology, from a long-term point of view, metal lithium secondary battery is one of the best choices to break through the existing energy density bottleneck. Therefore, in recent years, many research institutes at home and abroad have begun to conduct research and development of high specific energy lithium metal secondary batteries with metal lithium as the negative electrode.

At present, researchers mainly suppress the growth of lithium dendrites and improve the Coulombic efficiency of metal lithium dissolution and deposition by constructing a three-dimensional structure of metal lithium anode or building a stable SEI film on the surface of metal lithium anode. In terms of constructing a metal lithium anode with a three-dimensional structure, Wang et al. (wang et al., Adv. Energy Mater. 2018, 1802720) used the connected tubular carbon material obtained after carbonization of eggplant as a carrier, loaded metal lithium into it, and obtained A metal lithium negative electrode supported by a three-dimensional skeleton structure, its mass specific capacity can reach 91% of that of metal lithium, and the Coulombic efficiency of the electrode is as high as 99.1%. In terms of building a stable SEI film, Cheng et al. (Cheng et al., Chem, 2017, 2, 258–270) used a lithium-sulfur battery electrolyte containing 0.02M Li ₂ S ₅ to pretreat the metal lithium electrode for 1 cycle, Thus, a stable SEI film is constructed on the surface of lithium metal anode to inhibit the growth of dendrite lithium. However, this method is not suitable for the treatment of large-area lithium metal anodes, and it is difficult to achieve industrial applications. Guo et al proposed in the patent (CN 105280886 B) to use a phosphoric acid solution to construct a lithium phosphate surface protection layer on the surface of lithium metal, and achieved good results. However, the main component of their protective layer is lithium phosphate, which is an electronic insulator, and its room temperature lithium ion conductivity is also very low (<10 ^-8 S cm ^-1 ), which is not conducive to the rapid transmission of lithium ions. Black phosphorus (P) has good electronic conductivity and is also a negative electrode material for lithium batteries with very good thermal stability. The _Li3P product generated after it reacts with lithium metal has a very high room temperature lithium ion conductivity ( ~10 ⁻⁴ S cm ⁻¹ ).

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, provide a kind of preparation method of metal lithium negative pole of secondary battery of high specific energy, mainly solve the direct contact between metal lithium electrode and electrolyte (liquid electrolyte or solid electrolyte) in the prior art. The electrochemical stability and other problems that exist during contact, the method is simple and suitable for large-scale batch preparation of lithium metal negative electrodes with lithium phosphide protective layers, so as to realize the assembly of lithium metal negative electrodes into high specific energy secondary batteries industrialization.

The purpose of the present invention is achieved through the following technical solutions:

A method for preparing a metal lithium negative electrode of a high specific energy secondary battery, characterized in that: the method for preparing a metal lithium negative electrode containing a lithium phosphide protective layer, the steps and process conditions thereof are as follows:

Step 1: completely immerse the metal lithium negative electrode in the phosphorus-containing treatment solution with a solid content of 2%-20%, let it stand for a reaction time of 2-60 minutes, and a reaction temperature of 25-100°C, and dry it for later use;

Step 2: polymerize the prepared LiTFSI/DOL saturated solution with an initiator, and after complete polymerization, dissolve the solid in a tetrahydrofuran solution with a solid content of 0.1-1% by mass to obtain a curing binder solution;

Step 3: Take out the metal lithium negative electrode and wash it with a solvent to remove impurities in the surface protective layer, then evenly drop the cured binder solution obtained in step 2 on the surface of the metal lithium negative electrode in step 1, and then heat to remove The solvent is used to obtain a lithium metal negative electrode of a high specific energy secondary battery containing a lithium phosphide protective layer.

The lithium metal negative electrode refers to lithium metal, lithium-boron alloy or lithium metal negative electrode supported by a three-dimensional structure.

The phosphorus-containing treatment liquid is divided into a solvent and a solute, wherein the solvent is tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), ethyl methyl carbonate (EMC), ethylene carbonate (EC), dimethyl carbonate One of esters (DMC) or their mixed solvent; the solute is one of phosphorus triiodide (PI ₃ ), phosphorus tribromide (PBr ₃ ), and phosphorus trichloride (PCl ₃ ).

The binder solution with curing function is ring-opening polymer of 1,3-ethylene oxide/tetrahydrofuran (PDOL/THF).

The drying temperature in the first step is preferably 60°C.

Compared with the prior art, the present invention has the following remarkable features and positive effects:

1. The present invention uses a phosphorus-containing solution to treat the surface of lithium metal, and constructs a layer of electrochemically stable protective layer (Li ₃ P) with high ionic conductivity in situ on the surface of the lithium metal electrode. This protective layer can conduct lithium ions rapidly in addition to In addition to its functions, it can also realize the physical isolation of metal lithium electrodes and liquid electrolytes (or solid electrolytes), solve the problem of chemical or electrochemical instabilities between electrolytes (or solid electrolytes) and metal lithium, and at the same time inhibit The role of lithium dendrite growth.

2. The method for in-situ generation of a lithium phosphide protective layer on the surface of metallic lithium provided by the present invention, since the surface of metallic lithium is treated with a phosphorus-containing solution, the phosphating generated in situ on the surface can be regulated by controlling the concentration of the phosphorus-containing solution and the immersion time The amount of lithium is very suitable for batch processing of metal lithium negative electrodes, and is conducive to promoting the industrialization of high specific energy secondary batteries.

3. After the metal lithium negative electrode containing lithium phosphide protective layer of the present invention is paired with the positive electrode material to assemble the metal lithium battery system, the metal lithium is stable and compatible with the liquid electrolyte or solid electrolyte, thereby improving the secondary performance of the assembled metal lithium. The electrochemical performance of the battery can greatly improve the cycle stability of the battery.

Description of drawings

Fig. 1 is the cycle stability test comparison diagram of the liquid lithium symmetric battery assembled by lithium phosphide protective layer metal lithium negative electrode and blank electrode in embodiment 2;

Fig. 2 is a comparison chart of the cycle stability test of the composite solid electrolyte high specific energy secondary battery assembled with the metal lithium negative electrode containing the lithium phosphide protective layer and the blank electrode in Example 3.

Detailed ways

The present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings, but the implementation of the present invention is not limited thereto.

Example 1

The steps and process conditions of the preparation method of the metal lithium negative electrode of the high specific energy secondary battery described in this embodiment are as follows:

Step 1: In an inert atmosphere glove box, cut out a lithium metal sheet of a suitable size, and then press it onto the surface of a stainless steel disc. Next, it was immersed in a phosphorus triiodide (PI ₃ )/tetrahydrofuran (THF) treatment solution with a solid content of 2%, and was left to react at a temperature of 25° C. for 60 minutes. Then the negative plate was taken out, and washed with an organic solvent (EMC:EC:DMC mixed solvent, volume ratio 1:1:1) several times to remove soluble substances (such as elemental iodine), and dried at 60°C for later use.

Step 2: Polymerize the prepared LiTFSI/DOL saturated solution with an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, (BMIm)BF ₄ ) initiator, and after complete polymerization, take a certain amount The solid is dissolved in tetrahydrofuran, and a solution with a solid content of 0.1% by mass is prepared to obtain a curing binder solution of ring-opening polymer of 1,3-ethylene oxide/tetrahydrofuran (PDOL/THF), which is ready for use.

Step 3: Add 150 μl of the solidified binder solution (PDOL/THF) obtained in Step 2, and evenly drop it onto the surface of the metal lithium negative electrode obtained in Step 1, and then heat to remove the solvent to obtain a lithium phosphide-containing protective electrode. Layered high specific energy secondary battery lithium metal negative electrode.

The lithium phosphide protective layer containing lithium phosphide protective layer prepared in this example is a lithium negative electrode for secondary batteries with high specific energy. The results of the scanning electron microscope characterization test show that the surface of the electrode is very smooth, and the element distribution diagram also shows that phosphorus is evenly distributed on the surface of the electrode. .

The metal lithium electrode containing the lithium phosphide protective layer prepared in step 3 is used as the negative electrode, the solution of 1MLiPF ₆ EC:DMC:EMC is used as the electrolyte and celegard is used as the diaphragm, and NMC:SP:PVDF=8:1: The electrode sheet of 1 is a positive electrode, and a 2032 button battery is assembled.

The organic liquid metal lithium secondary battery (Li-B|1M LiPF ₆ EC:DMC:EMC|NCM) assembled by the metal lithium negative electrode containing lithium phosphide protective layer obtained in this example has been tested for cycle stability, and the results It shows that the cycle stability of the battery assembled with the lithium metal negative electrode containing the lithium phosphide protective layer has been significantly improved compared with the battery assembled with the blank lithium metal negative electrode, indicating that the protective layer has a positive effect on the secondary effect between the lithium metal and the electrolyte. The reaction has obvious inhibitory and slowing effect.

Example 2

The preparation method of the metal lithium negative electrode of the high specific energy secondary battery described in this embodiment, that is, the lithium-boron alloy negative electrode containing the lithium phosphide protective layer, its steps and process conditions are as follows:

Step 1: In an inert atmosphere glove box, cut out a lithium-boron alloy sheet of a suitable size, polish it to remove surface impurities, and then press it onto the surface of a stainless steel disc. Next, it was immersed in a phosphorous-containing treatment solution of phosphorus triiodide (PI ₃ )/tetrahydrofuran (THF) with a solid content of 10%, and stood to react for 20 minutes at a temperature of 50°C. Then the negative electrode sheet was taken out, washed with an organic solvent (EMC:EC:DMC mixed solvent, volume ratio 1:1:1) multiple times to remove soluble substances, and dried at 60°C for later use.

Step 2: polymerize the prepared LiTFSI/DOL saturated solution with an ionic liquid (BMIm) BF ₄ initiator, after complete polymerization, take a certain amount of solid and dissolve it in tetrahydrofuran to prepare a solution with a solid content of 0.5% by mass, Obtain the ring-opening polymer of 1,3-ethylene oxide ring-opening polymer/tetrahydrofuran (PDOL/THF) as a binder solution with curing effect, and set it aside.

Step 3: Take 50 μl of the solidified binder solution obtained in Step 2, and evenly drop it onto the surface of the lithium-boron alloy negative electrode obtained in Step 1, and then heat to remove the solvent to obtain a lithium phosphide-containing protective layer. Boron alloy negative electrode.

The lithium-boron alloy negative electrode containing lithium phosphide protective layer prepared in this example, the results of the scanning electron microscope characterization test show that the electrode surface is very smooth, and the element distribution diagram also shows that phosphorus is evenly distributed on the electrode surface.

The lithium-boron alloy negative electrode containing lithium phosphide protective layer obtained in step 3 is positive and negative, and 1MLiTFSI DOL:DME (DME is ethylene glycol dimethyl ether) electrolyte and diaphragm containing 1% _LiNO3 are used to assemble the 2032 button Organic liquid metal lithium symmetric battery.

As shown in Figure 1, it is the cycle stability data of the organic liquid symmetric battery (Li-B|1M LiTFSI DOL:DME|Li-B) obtained in this example, at 0.5mA cm ^-2 , 0.5mAh cm ^-2 Under certain conditions, its cycle stability exceeds 1000 hours, while the cycle stability of the battery assembled with blank electrodes is less than 600 hours.

Example 3

The steps and process conditions of the preparation method of the lithium-boron alloy negative electrode containing the lithium phosphide protective layer described in this embodiment are as follows:

Step 1: In an inert atmosphere glove box, cut out a lithium-boron alloy sheet of a suitable size, polish it to remove surface impurities, and then press it onto the surface of a stainless steel disc. Next, it was immersed in a phosphorous-containing treatment solution of phosphorus triiodide (PI ₃ )/tetrahydrofuran (THF) with a solid content of 20%, and allowed to stand at 100° C. for 2 minutes for reaction. Then the negative electrode sheet was taken out, washed with an organic solvent (EMC:EC:DMC mixed solvent, volume ratio 1:1:1) multiple times to remove soluble substances, and dried at 60°C for later use.

Step 2: Polymerize the prepared LiTFSI/DOL saturated solution with an ionic liquid (BMIm) BF ₄ initiator. After complete polymerization, take a certain amount of solid and dissolve it in tetrahydrofuran to prepare a solution with a solid content of 1% by mass. Obtain the ring-opening polymer of 1,3-ethylene oxide ring-opening polymer/tetrahydrofuran (PDOL/THF) as a binder solution with curing effect, and set it aside.

Step 3: Take 25 μl of the solidified binder solution obtained in Step 2, and evenly drop it onto the surface of the metal lithium negative electrode obtained in Step 1, and then heat to remove the solvent to obtain lithium boron containing a lithium phosphide protective layer. Alloy negative electrode.

The lithium-boron alloy electrode with lithium phosphide protective layer prepared in this embodiment is the negative electrode, the electrode sheet using LiFePO ₄ :SP:PEO=7:1:2 is the positive electrode, and LAGP:LiTFSI/PEO (LAGP is lithium aluminum germanium Phosphorus inorganic solid electrolyte powder, mass percentage is 85%, wherein Li:EO=8:1mol/mol in LiTFSI/PEO polymer electrolyte) is composite solid electrolyte. Assemble the 2032 button cell.

As shown in Figure 2, the composite solid electrolyte metal lithium secondary battery (Li-B|LAGP:LiTFSI/PEO|LiFePO ₄ ) assembled with the lithium-boron alloy negative electrode containing the lithium phosphide protective layer obtained in this example is at 55°C The cycle stability test was carried out under the conditions, and the results showed that the cycle stability of the battery assembled with the lithium-boron alloy negative electrode containing the lithium phosphide protective layer was significantly improved compared with the battery assembled with the blank lithium-boron alloy negative electrode. It shows that the protective layer containing lithium phosphide greatly improves the compatibility and stability of the composite solid electrolyte and metal lithium, and at the same time, it can significantly inhibit the growth of metal lithium dendrites.

Example 4

The steps and process conditions of the preparation method of the lithium metal negative electrode of the high specific energy secondary battery, that is, the three-dimensional skeleton structure metal lithium negative electrode containing lithium phosphide protective layer described in this embodiment are as follows:

Step 1: In an inert atmosphere glove box, cut out a suitable size of copper foam, clean it to remove surface impurities, and then inject molten lithium metal into the pores of the foam copper under an inert atmosphere to prepare a three-dimensional structure supported lithium metal anode ,spare. After the negative electrode is completely cooled, immerse it in a phosphorus-containing treatment solution with a solid content of 10% (PBr ₃ is dissolved in a mixed solvent THF:DMSO, and the solvent volume ratio is 1:1), and stand at 25°C for 20 minutes. . Then the negative electrode sheet was taken out, and washed with an organic solvent (EMC:EC:DMC mixed solvent, volume ratio 1:1:1) several times to remove soluble substances, and dried at 60°C for later use.

Step two, step three are the same as embodiment 2

The three-dimensional skeleton metal lithium negative electrode containing lithium phosphide protective layer in this embodiment is adopted, and the electrode sheet composed of NCA:SP:PVDF=8:1:1 is the positive electrode, and the electrode sheet is composed of PPC (polypropylene carbonate) polymer Containing 6% of 1M LiPF ₆ EC:DMC:EMC as gel electrolyte and fiber separator as support, assemble 2032 button cells.

The gel electrolyte metal lithium secondary battery (Li|PPC Gel electrolyte|NCA) assembled by the three-dimensional structure of the lithium phosphide protective layer supported by the metal lithium negative electrode obtained in this example was tested for cycle stability, and the results showed that the phosphide-containing Compared with the battery assembled with the blank three-dimensional metal lithium anode, the battery assembled by the three-dimensional structure of the lithium protective layer supports the lithium metal anode, and its cycle stability has been significantly improved, indicating that the protective layer has a certain effect on the growth of metal lithium dendrites. inhibition.

Example 5

The steps and process conditions of the preparation method of the metal lithium negative electrode of the high specific energy secondary battery, that is, the phosphorus-containing protective layer lithium-boron alloy negative electrode described in this embodiment are as follows:

Step 1: In an inert atmosphere glove box, cut out a lithium-boron alloy sheet of a suitable size, polish it to remove surface impurities, and then press it onto the surface of a stainless steel disc. Next, it is immersed in a phosphorus-containing treatment solution (PCl ₃ is dissolved in a mixed solvent EMC:EC:DMC, and the solvent volume ratio is 1:1:1) with a solid content of 10% phosphorus trichloride (PCl ₃ ), Under the condition that the temperature is 25° C., the reaction was left to stand for 30 minutes. Then the negative electrode sheet was taken out, washed with an organic solvent (EMC:EC:DMC mixed solvent, volume ratio 1:1:1) multiple times to remove soluble substances, and dried at 60°C for later use.

Step two, step three are the same as embodiment 2

A method for preparing a high specific energy metal lithium secondary battery assembled with the phosphorus-containing protective layer lithium-boron alloy negative electrode prepared in this embodiment. A lithium-boron alloy containing a lithium phosphide protective layer is used as the negative electrode, and an electrode sheet composed of LiFePO ₄ :SP:PEO=7:1:2 is used as the positive electrode, and LLZO (LLZO is lithium lanthanum zirconium oxygen inorganic solid electrolyte) with a thickness of 150 microns ) The ceramic sheet is a solid electrolyte, and a 2032 button battery is assembled.

The solid-state lithium battery (Li|LLZO|LiFePO ₄ ) assembled with the metal lithium negative electrode containing the lithium phosphide protective layer obtained in this example was tested at 55°C, and the results showed that the protective layer containing lithium phosphide Compared with batteries assembled with blank lithium-boron alloy negative electrodes, the cycle stability of batteries assembled with lithium-boron alloy negative electrodes has been significantly improved, indicating that the protective layer containing lithium phosphide has greatly improved the performance of inorganic ceramic solid electrolytes and The compatibility and stability of metal lithium can significantly inhibit the growth of metal lithium dendrites.

Claims (5)

1. A preparation method for a lithium metal negative pole of a high specific energy secondary battery, characterized in that: the preparation method of a lithium metal negative pole containing a lithium phosphide protective layer, its steps and process conditions thereof are as follows: Step 1: completely immerse the metal lithium negative electrode in the phosphorus-containing treatment solution with a solid content of 2%-20%, let it stand for a reaction time of 2-60 minutes, and a reaction temperature of 25-100°C, and dry it for later use; Step 2: polymerize the prepared LiTFSI/DOL saturated solution with an initiator, and after complete polymerization, dissolve the solid in a tetrahydrofuran solution with a solid content of 0.1-1% by mass to obtain a curing binder solution; Step 3: Take out the metal lithium negative electrode and wash it with a solvent to remove impurities in the surface protective layer, then evenly drop the cured binder solution obtained in step 2 on the surface of the metal lithium negative electrode in step 1, and then heat to remove The solvent is used to obtain a lithium metal negative electrode of a high specific energy secondary battery containing a lithium phosphide protective layer. 2 . The method for preparing a metal lithium negative electrode of a high specific energy secondary battery according to claim 1 , wherein the metal lithium negative electrode refers to metal lithium, a lithium-boron alloy or a metal lithium negative electrode supported by a three-dimensional structure. 3. according to claim 1 or 2 described a kind of preparation method of metal lithium negative electrode of high specific energy secondary battery, it is characterized in that: phosphorus-containing treatment liquid is divided into solvent and solute, wherein said solvent is tetrahydrofuran (THF), One of dimethyl sulfoxide (DMSO), ethyl methyl carbonate (EMC), ethylene carbonate (EC), dimethyl carbonate (DMC) or their mixed solvent; the solute is phosphorus triiodide One of (PI ₃ ), phosphorus tribromide (PBr ₃ ), and phosphorus trichloride (PCl ₃ ). 4. The preparation method of a metal lithium negative electrode of a high specific energy secondary battery according to claim 1, characterized in that: the binder solution with curing effect is the ring-opening of 1,3-oxirane Polymer/tetrahydrofuran (PDOL/THF). 5 . The method for preparing a metal lithium negative electrode of a high specific energy secondary battery according to claim 1 , wherein the drying temperature in step 1 is 60° C.