Low-temperature solid-state polymer electrolyte, preparation method and battery

Abstract

The application discloses a low-temperature solid-state polymer electrolyte, a preparation method and a battery. The electrolyte is composed of a polymer solvent and multiple lithium salts. The multiple lithium salts are lithium bisfluorosulfonylimide, lithium bistrifluoromethanesulfonimide, lithium hexafluorophosphate, lithium difluoro(oxalato)borate and lithium nitrate. The polymer is poly-1,3-dioxolane. Multiple different solvation structures are formed between the multiple lithium salts and the polymer. Different solvation structures repel each other and are not easy to aggregate, so that the low-temperature solid-state polymer electrolyte has smaller ion cluster particles, the crystallization of the polymer is inhibited, the ionic conductivity of the low-temperature solid-state polymer electrolyte at low temperature is improved, and the activation energy of lithium ion migration is reduced. The interaction between multiple solvation structures also reduces the activation energy of lithium ion desolvation, so that lithium ions can move more easily between the positive and negative electrodes.

Description

Technical Field

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

[0002] Solid-state electrolytes have attracted widespread attention due to their inherent safety and reliability. Among solid-state electrolytes, solid polymer electrolytes, with their superior processability and interfacial compatibility, show great promise for applications. Compared to inorganic solid electrolytes (such as oxides, sulfides, and halides), solid polymer electrolytes exhibit superior interfacial compatibility and greater manufacturing feasibility. Furthermore, solid polymer electrolytes possess high plasticity, allowing them to be combined with fillers, additives, or solvents, and can be molecularly modified (e.g., copolymerization, crosslinking, and grafting) to achieve a wide range of physicochemical properties. Therefore, solid polymer electrolytes, with their excellent electrode wettability and processability, are considered promising candidates for next-generation electrolytes.

[0003] However, the existing technical solutions have at least the following technical problems:

[0004] In solid polymer electrolytes, a single solvated structure can aggregate into larger ion clusters and crystals, leading to a rapid decrease in the ionic conductivity and an increase in the lithium-ion migration activation energy. This aggregation and crystallization are particularly pronounced at low temperatures, resulting in reduced coulombic efficiency and increased capacity degradation in batteries using solid polymer electrolytes. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a low-temperature solid polymer electrolyte, its 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 degradation rate of the battery under low-temperature conditions.

[0006] The technical solution adopted in this invention is as follows:

[0007] A low-temperature solid-state polymer electrolyte comprises a polymer solvent and multiple lithium salts; the lithium salts are lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium difluorooxalate borate (LiDFOB), and lithium nitrate (LiNO3); the polymer is poly(1,3-dioxolane) (PDOL); the lithium salts and the polymer form various solvation structures. These different solvation structures repel each other and are less prone to aggregation, resulting in smaller ion clusters in the low-temperature solid-state polymer electrolyte, and suppressing polymer crystallization. This improves the ionic conductivity of the low-temperature solid-state polymer electrolyte and lowers the activation energy for lithium-ion migration in the electrolyte. This allows the low-temperature solid-state polymer electrolyte to maintain good ionic conductivity in 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 lithium-ion migration activation energy is reduced to 0.18 eV. The interactions between various solvation structures also lower the lithium-ion desolvation activation energy, resulting in a desolvation activation energy of 0.26 eV for the low-temperature solid polymer electrolyte. The higher ionic conductivity and lower lithium-ion migration and desolvation activation energies mean that lithium ions can move more easily between the positive and negative electrodes.

[0008] A method for preparing the above-mentioned low-temperature solid polymer electrolyte includes the following steps:

[0009] (1) Add lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium difluorooxalateborate and lithium nitrate to 1,3-dioxolane monomer, stir evenly to obtain low-temperature solid polymer electrolyte prepolymer solution.

[0010] (2) The prepolymer liquid is added to the battery as an electrolyte and left to stand for a period of time to allow the prepolymer liquid to polymerize and form a low-temperature solid polymer electrolyte.

[0011] Furthermore, the concentrations of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium difluorooxalateborate, 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.

[0012] Furthermore, the stirring temperature is 20°C.

[0013] A battery, wherein the active material of the positive electrode of the battery cell is one or more selected from lithium iron phosphate (LFP), lithium nickel oxide (LNO), lithium cobalt oxide (LCO), lithium manganese iron phosphate (LMFP), lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), and nickel-cobalt-manganese ternary cathode (NCM); the negative electrode material is one of lithium metal (Li), graphite (Gr), and silicon carbon; and the electrolyte is the above-mentioned low-temperature solid polymer electrolyte or a low-temperature solid polymer electrolyte prepared by the above method. Depending on actual needs, corresponding button, pouch, and other types of batteries can be manufactured.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] In this invention, various lithium salts can form a variety of solvation structures with polymer solvents. These different solvation structures repel each other and are less prone to aggregation, resulting in smaller ion clusters in the low-temperature solid-state polymer electrolyte and inhibiting polymer crystallization. This not only improves the ionic conductivity of the low-temperature solid-state polymer electrolyte but also lowers the activation energy for lithium-ion migration within it.

[0016] Meanwhile, the interaction between various solvation structures weakens the interaction between lithium ions and solvent molecules in the solvation structure itself, making it easier for lithium ions to be released from the solvation structure at low temperatures and reducing the activation energy of desolvation.

[0017] Therefore, the low-temperature solid-state polymer electrolyte of this invention possesses high ionic conductivity and low lithium-ion migration activation energy and desolvation activation energy even at low temperatures. This means that lithium ions can move more easily between the positive and negative electrodes. This results in batteries using the low-temperature solid-state polymer electrolyte of this invention exhibiting high coulombic efficiency and low capacity degradation rate even at low temperatures. Attached Figure Description

[0018] Figure 1 This is a comparison chart of the dynamic light scattering experimental results of the low-temperature solid polymer electrolyte provided in Example 1 and the solid polymer electrolyte provided in Comparative Example 1.

[0019] Figure 2 This is a comparison diagram 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.

[0020] 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.

[0021] Figure 4This is a comparison graph of the 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.

[0022] Figure 5 The graph shows a comparison 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.

[0023] Figure 6 The graph shows a comparison of the nominal specific capacity and coulombic efficiency changes of the full cell provided in Example 3 and the full cell provided in Comparative Example 3 during temperature cycling.

[0024] Figure 7 The graph shows the performance of the pouch lithium metal full battery provided in Example 4 after 470 cycles at -20°C. Detailed Implementation

[0025] The technical solution of the present invention will be further explained clearly and in detail below with reference to the accompanying drawings and specific examples.

[0026] Unless otherwise specified, all raw materials used in this invention are commercially available in the field. Example 1

[0027] A low-temperature solid polymer electrolyte, the specific preparation steps of which are as follows:

[0028] (1) Add 1 mmol of lithium difluorosulfonylimide, 0.1 mmol of lithium ditrifluoromethanesulfonylimide, 0.1 mmol of lithium hexafluorophosphate, 0.1 mmol of lithium difluorooxalateborate, and 0.1 mmol of lithium nitrate to 1 mL of 1,3-dioxolane monomer. Stir evenly for 15 minutes at 20°C to completely dissolve the lithium salt in the solvent and obtain a low-temperature solid polymer electrolyte prepolymer solution.

[0029] (2) When manufacturing the battery, the prepolymer solution is first added to the battery. After the battery is manufactured, it is left to stand for 24 hours. During this process, the 1,3-dioxolane monomer will gradually polymerize into poly1,3-dioxolane, and the electrolyte in the battery at this time is the low-temperature solid polymer electrolyte. Example 2

[0030] The specific preparation steps of a lithium-copper battery are as follows:

[0031] The battery negative electrode casing, gasket, current collector, lithium metal, low-temperature solid polymer electrolyte prepolymer solution prepared in Example 1, separator, solid polymer electrolyte prepolymer solution prepared in Example 1, copper sheet, current collector, and battery positive electrode casing are added and stacked together in sequence. The entire battery is placed in a hydraulic press and pressed to obtain a button battery.

[0032] Before use, the battery should be left to stand for 24 hours to allow the polymer to polymerize before use. Example 3

[0033] The specific preparation steps of a lithium metal full battery are as follows:

[0034] The battery negative electrode casing, gasket, current collector, lithium metal, 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 casing are added and stacked together in sequence. The entire battery is placed in a hydraulic press and pressed to obtain a button battery.

[0035] Before use, the battery should be left to stand for 24 hours to allow the polymer to polymerize before use. Example 4

[0036] The specific preparation steps of a lithium metal full battery are as follows:

[0037] (1) Weld the nickel tabs onto lithium-plated copper foil and aluminum foil.

[0038] (2) Stack the lithium-plated copper foil with nickel tabs, the low-temperature solid polymer electrolyte prepolymer liquid prepared in Example 1, the separator, the lithium iron phosphate electrode sheet, and the aluminum foil with nickel tabs together in sequence.

[0039] (3) Wrap the assembly with aluminum-plastic film, evacuate the vacuum, and then heat seal the opening to obtain a soft-pack battery.

[0040] (4) The battery should be left to stand for 24 hours before use to allow the polymer to polymerize. Comparative Example 1

[0041] A solid polymer electrolyte, the specific preparation steps of which are as follows:

[0042] (1) Add 1 mmol of lithium difluorosulfonyl imide to 1 mL of 1,3-dioxolane monomer, and stir the mixture at 20 °C for 15 minutes to completely dissolve the lithium salt in the solvent to obtain a solid polymer electrolyte prepolymer solution.

[0043] (2) When making the battery, the prepolymer solution is added to the battery first. After the battery is made, it is left to stand for 24 hours. During this process, the 1,3-dioxolane monomer will gradually polymerize into poly1,3-dioxolane, and the electrolyte in the battery is a solid polymer electrolyte. Comparative Example 2

[0044] The specific preparation steps of a lithium-copper battery are as follows:

[0045] The negative electrode casing, 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, current collector, and positive electrode casing are added and stacked together in sequence. The entire battery is placed in a hydraulic press and pressed to obtain a button cell battery.

[0046] Before use, the battery should be left to stand for 24 hours to allow the polymer to polymerize before use. Comparative Example 3

[0047] The specific preparation steps of a lithium-copper battery are as follows:

[0048] The battery negative electrode casing, 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 casing are added and stacked together in sequence. The entire battery is placed in a hydraulic press and pressed to obtain a button cell battery.

[0049] Before use, the battery should be left to stand for 24 hours to allow the polymer to polymerize before use.

[0050] Figure 1 The image shows a comparison of the dynamic light scattering experimental 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.

[0051] Figure 2 A comparison of two-dimensional wide-angle X-ray scattering results for the low-temperature solid polymer electrolyte provided in Example 1 and the solid polymer electrolyte provided in Comparative Example 1. The scattering ring of the low-temperature solid polymer electrolyte provided in Example 1 is more diffuse than that of the solid polymer electrolyte provided in Comparative Example 1, indicating a decrease in crystallinity and confirming an increase in entropy.

[0052] 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. Within the low-temperature range of 0°C to -20°C, the increase in ionic conductivity of the low-temperature solid polymer electrolyte provided in Example 1 is even greater. 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 .

[0053] Figure 4This is a comparison graph of the 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. 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. At the same time, 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.

[0054] Figure 5 The lithium copper battery provided in Example 2 and the lithium copper battery provided in Comparative Example 2 (coulombic efficiency comparison under different temperature conditions, using the Aurbach test method (0.5 mA cm⁻¹)) are shown in the figure. -2 5mAh cm -2 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. Furthermore, the lower the temperature, the greater the difference between the two. The lithium copper battery provided in Example 2 achieves a coulombic efficiency of 97.42% at -20°C.

[0055] Figure 6 This is a comparison chart showing the changes in nominal specific capacity and coulombic efficiency of the full cell provided in Example 3 and the full cell provided in Comparative Example 3 during temperature cycling. The positive electrode is made of lithium iron phosphate, and the negative electrode is made of lithium metal (N / P=4). The battery provided in Example 3 has an initial capacity of 163.3 mAh / g at room temperature, and when the temperature drops to -20 degrees Celsius, it retains 52.5% of its room temperature capacity, which is 13 times that of the comparative example.

[0056] Figure 7 The image shows the performance of the pouch-type lithium metal full cell provided in Example 4 after 470 cycles at -20°C. The positive electrode of this pouch-type lithium metal full cell is made of lithium iron phosphate, and the negative electrode is made of lithium metal. Figure 7 As shown in the long-cycle test, even under high positive electrode load (N / P=4) and harsh ambient temperature (-20°C), the battery can still maintain 93.56% of its initial capacity after 470 cycles.

[0057] The low-temperature solid polymer electrolyte provided in Example 1 of this application includes poly(1,3-dioxolane) (PDOL), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium difluorooxalateborate (LiDFOB), and lithium nitrate (LiNO3).

[0058] The low-temperature solid polymer electrolyte contains various lithium salts, which can form a variety of solvation structures with the polymer solvent. These different solvation structures repel each other and are less prone to aggregation, resulting in smaller ion clusters in the low-temperature solid polymer electrolyte and inhibiting polymer crystallization.

[0059] like Figure 1 , Figure 2 As shown, 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; the scattering ring of the low-temperature solid polymer electrolyte provided in Example 1 is more diffuse than that of the solid polymer electrolyte provided in Comparative Example 1, indicating a decrease in crystallinity; 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. Smaller ionic clusters and lower crystallinity 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 generally 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. Simultaneously, the smaller ion clusters and lower degree of crystallinity also reduce the activation energy for lithium ion migration in the aforementioned low-temperature solid polymer electrolyte. Figure 4 As shown, 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 interactions between various solvation structures also weaken the interaction between lithium ions and solvent molecules within the solvation structure itself, making it easier for lithium ions to escape from the solvation structure at low temperatures, thus 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. The higher ionic conductivity, lower lithium-ion migration activation energy, and lower desolvation activation energy mean that lithium ions can move more easily between the positive and negative electrodes.

[0060] Due to the aforementioned advantages, the battery using the low-temperature solid polymer electrolyte provided in Example 1 exhibits better performance than the battery using the solid polymer electrolyte provided in Comparative Example 1, especially under low-temperature conditions. Figure 5As shown, 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. Furthermore, the lower the temperature, the greater the difference between the two. The lithium copper battery provided in Example 2 achieves a coulombic efficiency of 97.42% at -20°C. The low-temperature solid-state polymer electrolyte also performs excellently for large-capacity pouch batteries. Figure 6 As shown, throughout the entire temperature cycling process, the coulombic efficiency of the full cell provided in Example 3 is higher than that of the full cell provided in Comparative Example 3, with the advantage being more pronounced under low-temperature conditions. Figure 7 As shown, the pouch lithium metal full battery provided in Example 4 exhibits an extremely low capacity degradation rate at -20°C, which is only 0.01% per cycle.

[0061] 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 it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A low-temperature solid polymer electrolyte, characterized in that, The electrolyte is composed of a polymer solvent and various lithium salts, including lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium difluorooxalate borate, and lithium nitrate. The polymer is poly(1,3-dioxolane). Various solvation structures are formed between the lithium salts and the polymer. The low-temperature solid polymer electrolyte exhibits an ionic conductivity of 0.17 mS / cm at -20°C. -1 ; The preparation method of the low-temperature solid polymer electrolyte includes the following steps: (1) Lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium difluorooxalate borate, and lithium nitrate were added to 1,3-dioxolane monomer and stirred evenly to obtain a low-temperature solid polymer electrolyte prepolymer solution; the concentrations of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium difluorooxalate borate, and lithium nitrate in 1,3-dioxolane monomer were 1 mol / L, 0.1 mol / L, 0.1 mol / L, 0.1 mol / L, and 0.1 mol / L, respectively. (2) The prepolymer liquid is added to the battery as an electrolyte and left to stand for 24 hours to allow the prepolymer liquid to polymerize and form a low-temperature solid polymer electrolyte.

2. The low-temperature solid polymer electrolyte according to claim 1, characterized in that, The stirring temperature is 20°C.

3. A battery, characterized in that, The active material of the positive electrode of the battery cell is one or more of lithium iron phosphate, lithium nickel oxide, lithium cobalt oxide, 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; and the electrolyte is a low-temperature solid polymer electrolyte as described in any one of claims 1-2.

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