Low-temperature solid polymer electrolyte, preparation method and battery

Abstract

The invention discloses a low-temperature solid polymer electrolyte, a preparation method and a battery. The electrolyte is prepared from a polymer solvent and various lithium salts, the various lithium salts are lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethane) sulfonyl imide, lithium hexafluorophosphate, lithium difluoro (oxalato) borate and lithium nitrate; the polymer is poly (1, 3-dioxolame); and a plurality of different solvated structures are formed between the plurality of lithium salts and the polymer. Different solvated structures repel each other and are not easy to gather, so that the low-temperature solid polymer electrolyte has relatively small ion cluster particles, crystallization of a polymer is inhibited, the ionic conductivity of the low-temperature solid polymer electrolyte at low temperature is improved, and activation energy of lithium ion migration is reduced. The interaction among various solvation structures also reduces the activation energy of lithium ion desolvation, so that the lithium ions can move between the positive electrode and the negative electrode more easily.

Description

Technical Field

[0001] The present invention relates to the field of electrolyte technology, and in particular to a low-temperature solid polymer electrolyte, a preparation method and a battery. Background Art

[0002] Solid-state electrolytes have attracted widespread attention due to their inherent safety and reliability. Among solid-state electrolytes, solid polymer electrolytes (SPEs), with their superior processability and interfacial compatibility, have shown great application prospects. Compared with inorganic solid electrolytes (such as oxides, sulfides, and halides), SPEs exhibit superior interfacial compatibility and increased manufacturing feasibility. Furthermore, SPEs are highly plastic, can be combined with fillers, additives, or solvents, and are amenable to molecular design modifications (such as copolymerization, cross-linking, and grafting) to achieve a wide range of physicochemical properties. Therefore, SPEs exhibit excellent electrode wettability and processability and are considered promising candidates for next-generation electrolytes.

[0003] However, the existing technical solutions have at least the following technical problems: The single solvated structure in the solid polymer electrolyte will aggregate into larger ion clusters and crystals, which will lead to a rapid decrease in the ionic conductivity of the solid polymer electrolyte and an increase in the activation energy of lithium ion migration. This aggregation and crystallization is particularly obvious under low temperature conditions, resulting in a decrease in the coulombic efficiency and an increase in the capacity decay rate of batteries using solid polymer electrolytes. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a low-temperature solid polymer electrolyte, a preparation method and a battery, which solves the problem of poor performance of solid polymer electrolytes at low temperatures in the prior art, and achieves high coulombic efficiency and low capacity decay rate of the battery under low temperature conditions.

[0005] The technical solution adopted in the present invention is as follows: A low-temperature solid-state polymer electrolyte is composed of a polymer solvent and multiple lithium salts; the multiple lithium salts are lithium bis(fluorosulfonyl imide) (LiFSI), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium difluorooxalatoborate (LiDFOB), and lithium nitrate (LiNO3); the polymer is poly(1,3-dioxolane) (PDOL); and the multiple lithium salts and polymer form multiple different solvation structures. The different solvation structures repel each other and are less likely to aggregate, resulting in smaller ion clusters in the low-temperature solid-state polymer electrolyte and inhibiting polymer crystallization. This improves the ionic conductivity of the low-temperature solid-state polymer electrolyte and reduces the activation energy for lithium ion migration in the electrolyte. This allows the low-temperature solid-state polymer electrolyte to maintain good ionic conductivity within the range of 0°C to -20°C. At -20°C, the ionic conductivity of the low-temperature solid-state polymer electrolyte reaches 0.17 mS cm -1 The activation energy of lithium ion migration is reduced to 0.18eV. The interaction between multiple solvation structures also reduces the activation energy of lithium ion desolvation, reducing the desolvation activation energy of the low-temperature solid polymer electrolyte to 0.26eV. Higher ionic conductivity, lower lithium ion migration activation energy and desolvation activation energy mean that lithium ions can move more easily between the positive and negative electrodes.

[0006] A method for preparing the above-mentioned low-temperature solid polymer electrolyte comprises the following steps: (1) adding lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), lithium hexafluorophosphate, lithium difluorooxalatoborate and lithium nitrate to 1,3-dioxolane monomer and uniformly stirring to obtain a low-temperature solid polymer electrolyte prepolymer solution; (2) Adding the prepolymer solution as an electrolyte into a battery and allowing it to stand for a period of time to allow the prepolymer solution to polymerize and form a low-temperature solid polymer electrolyte.

[0007] Furthermore, the concentrations of lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), lithium hexafluorophosphate, lithium difluorooxalatoborate, and lithium nitrate in the 1,3-dioxolane monomer are 1 mol / L, 0.1 mol / L, 0.1 mol / L, 0.1 mol / L, and 0.1 mol / L, respectively.

[0008] Furthermore, the stirring temperature is 20°C.

[0009] A battery whose positive electrode active material is one or more of lithium iron phosphate (LFP), lithium nickel oxide (LNO), lithium cobalt oxide (LCO), lithium iron manganese phosphate (LMFP), lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), or nickel-cobalt-manganese ternary cathode (NCM); whose negative electrode material is one of lithium metal (Li), graphite (Gr), or silicon carbon; and whose electrolyte is the aforementioned low-temperature solid polymer electrolyte or the low-temperature solid polymer electrolyte produced by the aforementioned method. Batteries of various types, such as button batteries and soft-pack batteries, can be produced according to actual needs.

[0010] Compared with the prior art, the present invention has the following beneficial effects: The various lithium salts in the present invention can form a variety of different solvation structures with the polymer solvent. These different solvation structures repel each other and are less likely to aggregate, resulting in smaller ion clusters in the low-temperature solid polymer electrolyte and inhibiting polymer crystallization. This not only improves the ionic conductivity of the low-temperature solid polymer electrolyte but also reduces the activation energy for lithium ion migration within the low-temperature solid polymer electrolyte.

[0011] At the same time, the interaction between multiple solvation structures will weaken the interaction between lithium ions and solvent molecules in the solvation structure itself, making it easier for lithium ions to escape from the solvation structure at low temperatures, thereby reducing the activation energy of desolvation.

[0012] Therefore, the low-temperature solid polymer electrolyte of the present invention also has high ionic conductivity, low lithium ion migration activation energy and desolvation activation energy at low temperatures, which means that lithium ions can move more easily between the positive and negative electrodes. This allows batteries using the low-temperature solid polymer electrolyte of the present invention to have high coulombic efficiency and low capacity decay rate even at low temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a comparison chart of dynamic light scattering test results of the low-temperature solid polymer electrolyte provided in Example 1 and the solid polymer electrolyte provided in Comparative Example 1.

[0014] Figure 2 3 is a comparison chart of the two-dimensional wide-angle X-ray scattering results of the low-temperature solid polymer electrolyte provided in Example 1 and the solid polymer electrolyte provided in Comparative Example 1.

[0015] Figure 3 This is a comparison chart of the ionic conductivity of the low-temperature solid polymer electrolyte provided in Example 1 and the solid polymer electrolyte provided in Comparative Example 1.

[0016] Figure 4This is a comparison chart of lithium ion migration activation energy and desolvation activation energy of the low-temperature solid polymer electrolyte provided in Example 1 and the solid polymer electrolyte provided in Comparative Example 1.

[0017] Figure 5 This is a comparison chart of the coulombic efficiency of the lithium-copper battery provided in Example 2 and the lithium-copper battery provided in Comparative Example 2 under different temperature conditions.

[0018] Figure 6 This is a comparison chart of the changes in nominal specific capacity and coulombic efficiency of the full battery provided in Example 3 and the full battery provided in Comparative Example 3 during variable temperature cycling.

[0019] Figure 7 This is a performance diagram of the soft-pack lithium metal full battery provided in Example 4 after 470 cycles at -20°C. DETAILED DESCRIPTION

[0020] The technical solution of the present invention will be further explained in detail below with reference to the accompanying drawings and specific examples.

[0021] Unless otherwise specified, the raw materials used in the present invention are commonly available in the market. Example 1

[0022] A low-temperature solid polymer electrolyte, the specific preparation steps of which are as follows: (1) To 1 mL of 1,3-dioxolane monomer, add 1 mmol of lithium bis(fluorosulfonyl)imide, 0.1 mmol of lithium bis(trifluoromethanesulfonyl)imide, 0.1 mmol of lithium hexafluorophosphate, 0.1 mmol of lithium difluorooxalatoborate, and 0.1 mmol of lithium nitrate. Stir evenly at 20°C for 15 minutes to completely dissolve the lithium salt in the solvent to obtain a low-temperature solid-state polymer electrolyte prepolymer solution.

[0023] (2) When manufacturing a battery, the prepolymer solution is first added to the battery. After the battery is manufactured, the battery is left to stand for 24 hours. During this process, the 1,3-dioxolane monomer gradually polymerizes into poly-1,3-dioxolane. At this time, the electrolyte in the battery is the low-temperature solid polymer electrolyte. Example 2

[0024] A lithium-copper battery, the specific preparation steps of which are as follows: The battery negative electrode housing, gasket, current collector, lithium metal, the low-temperature solid polymer electrolyte prepolymer prepared in Example 1, separator, solid polymer electrolyte prepolymer prepared in Example 1, copper sheet, current collector, and battery positive electrode housing are stacked together in order. The entire battery is placed in a hydraulic press and pressed to obtain a button battery.

[0025] The battery needs to be left to stand for 24 hours before use to allow the polymer to polymerize. Example 3

[0026] A lithium metal full battery, the specific preparation steps of which are as follows: The battery negative electrode housing, gasket, current collector, lithium metal, the low-temperature solid polymer electrolyte prepolymer solution prepared in Example 1, separator, solid polymer electrolyte prepolymer solution prepared in Example 1, lithium iron phosphate positive electrode sheet, current collector, and battery positive electrode housing are stacked together in order. The entire battery is placed in a hydraulic press and pressed to obtain a button battery.

[0027] The battery needs to be left to stand for 24 hours before use to allow the polymer to polymerize. Example 4

[0028] A lithium metal full battery, the specific preparation steps of which are as follows: (1) Weld the nickel tabs to the lithium-plated copper foil and aluminum foil.

[0029] (2) The lithium-plated copper foil with nickel tabs, the low-temperature solid polymer electrolyte prepolymer prepared in Example 1, the separator, the lithium iron phosphate electrode, and the aluminum foil with nickel tabs are stacked together in order.

[0030] (3) Wrap the assembly with aluminum-plastic film, evacuate the film, and then heat-seal the opening to obtain a soft-pack battery.

[0031] (4) The battery needs to be left to stand for 24 hours before use to allow the polymer to polymerize. Comparative Example 1

[0032] A solid polymer electrolyte, the specific preparation steps of which are as follows: (1) Add 1 mmol of lithium bis(fluorosulfonyl)imide to 1 mL of 1,3-dioxolane monomer. Stir the mixed solution evenly for 15 minutes at 20°C to completely dissolve the lithium salt in the solvent to obtain a solid polymer electrolyte prepolymer solution.

[0033] (2) When making a battery, first add the prepolymer solution to the battery. After the battery is made, let it sit for 24 hours. During this process, the 1,3-dioxolane monomer will gradually polymerize into poly-1,3-dioxolane, and the electrolyte in the battery will now be a solid polymer electrolyte. Comparative Example 2

[0034] A lithium-copper battery, the specific preparation steps of which are as follows: The battery negative electrode housing, gasket, current collector, lithium metal, the solid polymer electrolyte prepolymer solution prepared in Comparative Example 1, separator, the solid polymer electrolyte prepolymer solution prepared in Comparative Example 1, copper sheet, current collector, and battery positive electrode housing are stacked together in order. The entire battery is placed in a hydraulic press and pressed to obtain a button battery.

[0035] The battery needs to be left to stand for 24 hours before use to allow the polymer to polymerize. Comparative Example 3

[0036] A lithium-copper battery, the specific preparation steps of which are as follows: The battery negative electrode housing, gasket, current collector, lithium metal, solid polymer electrolyte prepolymer solution prepared in Comparative Example 1, separator, solid polymer electrolyte prepolymer solution prepared in Comparative Example 1, copper sheet, lithium iron phosphate positive electrode sheet, and battery positive electrode housing are stacked together in order. The entire battery is placed in a hydraulic press and pressed to obtain a button battery.

[0037] The battery needs to be left to stand for 24 hours before use to allow the polymer to polymerize.

[0038] Figure 1 This is a comparison chart of dynamic light scattering test results of the low-temperature solid polymer electrolyte provided in Example 1 and the solid polymer electrolyte provided in Comparative Example 1. The average cluster size of the low-temperature solid polymer electrolyte provided in Example 1 is smaller than that of the solid polymer electrolyte provided in Comparative Example 1.

[0039] Figure 2 This figure compares the two-dimensional wide-angle X-ray scattering results of the low-temperature solid polymer electrolyte provided in Example 1 and the solid polymer electrolyte provided in Comparative Example 1. The scattering rings of the low-temperature solid polymer electrolyte provided in Example 1 are more diffuse than those of the solid polymer electrolyte provided in Comparative Example 1, indicating a decrease in crystallinity and confirming an increase in entropy.

[0040] Figure 3 This is a comparison chart of the ionic conductivity of the low-temperature solid polymer electrolyte provided in Example 1 and the solid polymer electrolyte provided in Comparative Example 1. The ionic conductivity of the low-temperature solid polymer electrolyte provided in Example 1 is generally higher than that of the solid polymer electrolyte provided in Comparative Example 1. In the low temperature range of 0°C to -20°C, the ionic conductivity of the low-temperature solid polymer electrolyte provided in Example 1 is improved even more. At -20°C, the ionic conductivity of the low-temperature solid polymer electrolyte provided in Example 1 is 8.5 times that of the solid polymer electrolyte provided in Comparative Example 1, reaching 0.17 mS cm -1 .

[0041] Figure 4This figure compares the lithium ion migration activation energy and desolvation activation energy of the low-temperature solid polymer electrolyte provided in Example 1 with the solid polymer electrolyte provided in Comparative Example 1. The lithium ion migration activation energy of the low-temperature solid polymer electrolyte provided in Example 1 is 0.18 eV, which is lower than the 0.27 eV of the solid polymer electrolyte provided in Comparative Example 1. Furthermore, the desolvation activation energy of the low-temperature solid polymer electrolyte provided in Example 1 is 0.26 eV, which is also lower than the 0.39 eV of the solid polymer electrolyte provided in Comparative Example 1.

[0042] Figure 5 The coulombic efficiency comparison chart of the lithium copper battery provided in Example 2 and the lithium copper battery provided in Comparative Example 2 under different temperature conditions, using the Aurbach test method (0.5 mA cm -2 ,5mAh cm -2 At room temperature, 0°C, and -20°C, the coulombic efficiency of the lithium-copper battery provided in Example 2 was higher than that of the lithium-copper battery provided in Comparative Example 2. The difference between the two increased as the temperature dropped. The coulombic efficiency of the lithium-copper battery provided in Example 2 reached 97.42% at -20°C.

[0043] Figure 6 This figure compares the nominal specific capacity and coulombic efficiency of the full battery provided in Example 3 and the full battery provided in Comparative Example 3 during temperature cycling. The positive electrode uses lithium iron phosphate, and the negative electrode uses lithium metal (N / P = 4). The battery provided in Example 3 has an initial room temperature capacity of 163.3 mAh / g. When the temperature drops to -20°C, the capacity remains at 52.5% of the room temperature capacity, 13 times that of the comparative example.

[0044] Figure 7 This is the performance graph of the soft-pack lithium metal full battery provided in Example 4 after 470 cycles at -20°C. The positive electrode of the soft-pack lithium metal full battery uses lithium iron phosphate material and the negative electrode uses lithium metal. Figure 7 The long cycle test shown shows that even under high cathode loading (N / P=4) and harsh ambient temperature (-20°C), the battery can still maintain 93.56% of its initial capacity after 470 cycles.

[0045] The low-temperature solid polymer electrolyte provided in Example 1 of the present application includes poly 1,3-dioxolane (PDOL), lithium bis(fluorosulfonyl imide) (LiFSI), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium difluorooxalatoborate (LiDFOB), and lithium nitrate (LiNO3).

[0046] The low-temperature solid polymer electrolyte contains a variety of lithium salts, which can form a variety of different solvation structures with the polymer solvent. These different solvation structures repel each other and are less likely to aggregate, resulting in smaller ion clusters and inhibited polymer crystallization.

[0047] like Figure 1 、 Figure 2 As shown, the average cluster size of the low-temperature solid polymer electrolyte provided by Example 1 is smaller than that of the solid polymer electrolyte provided by Comparative Example 1; the scattering rings of the low-temperature solid polymer electrolyte provided by Example 1 are more diffuse than those of the solid polymer electrolyte provided by Comparative Example 1, which indicates that the crystallinity is reduced; the ionic conductivity of the low-temperature solid polymer electrolyte provided by Example 1 is higher than that of the solid polymer electrolyte provided by Comparative Example 1 as a whole. Smaller ion clusters and lower degree of crystallization improve the ionic conductivity of the low-temperature solid polymer electrolyte. Figure 3 As shown, the ionic conductivity of the solid polymer electrolyte provided in Example 1 is higher than that of the solid polymer electrolyte provided in Comparative Example 1. At -20°C, the ionic conductivity of the solid polymer electrolyte provided in Example 1 is 8.5 times that of the solid polymer electrolyte provided in Comparative Example 1. At the same time, the smaller ion clusters and lower degree of crystallization also reduce the activation energy of lithium ion migration in the low-temperature solid polymer electrolyte. Figure 4 As shown in FIG1 , the lithium ion migration activation energy of the low-temperature solid polymer electrolyte provided in Example 1 is 0.18 eV, which is lower than the 0.27 eV of the solid polymer electrolyte provided in Comparative Example 1. The interaction between multiple solvation structures will also weaken the interaction between lithium ions and solvent molecules in the solvation structure itself, making it easier for lithium ions to escape from the solvation structure at low temperatures, thereby reducing the activation energy of desolvation. Figure 4 As shown, the desolvation activation energy of the low-temperature solid polymer electrolyte provided in Example 1 is 0.26 eV, which is also lower than the 0.39 eV of the solid polymer electrolyte provided in Comparative Example 1. Higher ionic conductivity, lower lithium ion migration activation energy and desolvation activation energy mean that lithium ions can move more easily between the positive and negative electrodes.

[0048] With the above advantages, the battery using the low-temperature solid polymer electrolyte provided in Example 1 can have better performance than the battery using the solid polymer electrolyte provided in Comparative Example 1, especially under low temperature conditions. Figure 5As shown in the figure, under three different temperature conditions, room temperature, 0°C, and -20°C, the coulombic efficiency of the lithium-copper battery provided in Example 2 is higher than that of the lithium-copper battery provided in Comparative Example 2. The lower the temperature, the greater the difference between the two. The coulombic efficiency of the lithium-copper battery provided in Example 2 can reach 97.42% under the condition of -20°C. For large-capacity soft-pack batteries, the low-temperature solid polymer electrolyte also performs well. Figure 6 As shown, during the entire temperature change cycle, the coulombic efficiency of the full battery provided by Example 3 is higher than that of the full battery provided by Comparative Example 3, and the advantage is more obvious under low temperature conditions. Figure 7 As shown, the capacity decay rate of the soft-pack lithium metal full battery provided in Example 4 at -20°C is extremely low, only 0.01% per cycle.

[0049] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A low-temperature solid polymer electrolyte, characterized in that: The invention is composed of a polymer solvent and a plurality of lithium salts; the plurality of lithium salts are lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), lithium hexafluorophosphate, lithium difluorooxalatoborate and lithium nitrate; the polymer is poly(1,3-dioxolane); and a plurality of different solvation structures are formed between the plurality of lithium salts and the polymer.

2. A method for preparing the low-temperature solid polymer electrolyte according to claim 1, characterized in that: The following steps are involved: (1) adding lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), lithium hexafluorophosphate, lithium difluorooxalatoborate and lithium nitrate to 1,3-dioxolane monomer and uniformly stirring to obtain a low-temperature solid polymer electrolyte prepolymer solution; (2) Adding the prepolymer solution as an electrolyte into a battery and allowing it to stand for a period of time to allow the prepolymer solution to polymerize and form a low-temperature solid polymer electrolyte.

3. The method for preparing a low-temperature solid polymer electrolyte according to claim 2, characterized in that: The concentrations of lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), lithium hexafluorophosphate, lithium difluorooxalatoborate, and lithium nitrate in the 1,3-dioxolane monomer are 1 mol / L, 0.1 mol / L, 0.1 mol / L, 0.1 mol / L, and 0.1 mol / L, respectively.

4. The method for preparing a low-temperature solid polymer electrolyte according to claim 2, wherein: The stirring temperature is 20°C.

5. A battery, characterized in that: The active material of the positive electrode plate of the battery cell is one or more of lithium iron phosphate, lithium nickelate, lithium cobaltate, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel manganese oxide, and nickel cobalt manganese ternary positive electrode; the negative electrode material is one of lithium metal, graphite, and silicon carbon; the electrolyte is the low-temperature solid polymer electrolyte as described in claim 1 or the low-temperature solid polymer electrolyte prepared by the method of any one of claims 2 to 4.

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