Lithium battery material as well as preparation method and application thereof

Abstract

The invention provides a lithium battery material and a preparation method and application thereof, the lithium battery material comprises a polymer and lithium nitrate, the polymer contains polar groups, and the mass of the lithium nitrate is 1-30wt% of the mass of the polymer. The lithium battery material provided by the invention better solves the problem of poor dissolution when lithium nitrate is applied to a lithium battery, and when the material is applied to the lithium battery, a lithium nitrate library is introduced into a battery system, so that lithium nitrate and nitrate radicals can be slowly released in a circulating process, and the electrical performance of the lithium battery is better improved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more specifically, to a lithium battery material, its preparation method, and its application. Background Technology

[0002] As environmental pollution problems caused by traditional energy sources become increasingly prominent, the share of the new energy industry in the energy sector is rising year by year, driven by high market demand and supported by national policies. In the fields of transportation, energy storage, and digital electronics, there are higher requirements for the energy density, safety, and stability of batteries.

[0003] Lithium-ion rechargeable batteries are widely used due to their high energy density, high cycle stability, and long cycle life. When lithium salts dissolve in a solvent, lithium-ion-solvent complexes are formed. Typically, solvent reduction of metallic Li results in the formation of an organic-inorganic component, while reduction of inorganic anions only forms inorganic components. Lithium nitrate (LiNO3) has a higher reducing power than LiPF6, LiFSI, and LiTFSI, and can participate in the Li solvent sheath, forming an inorganic solid electrolyte interphase (SEI) layer on the Li metal anode, inhibiting lithium dendrite growth and improving cycle stability. Furthermore, nitrate anions (NO3)... - The activation energy of ions is lower than that of other types of anions. These anions will preferentially adsorb in the Helmholtz inner plane and can be reduced first to form inorganic SEI components such as Li₂O and LiN. x O y Li3N can improve the stiffness and ionic conductivity of the electrode interface.

[0004] However, lithium nitrate suffers from poor solubility in most electrolyte systems, such as carbonate solvents and some ether solvents, which greatly limits its widespread application. Although there are various methods to improve the compatibility of lithium nitrate in solvents, such as adding highly soluble solvents like methyl sulfoxide and γ-butyrolactone, these solutions can also react with the lithium anode to form an SEI composed mainly of organic components, which is detrimental to the stability of the anode side. Alternatively, lithium nitrate can be dissolved using the inorganic salt CuF2 as a co-solvent, which avoids the influence of the co-solvent on the SEI, but its application is limited to only a few solvent systems.

[0005] Therefore, finding an efficient, universal, and simple solution to introduce lithium nitrate into battery systems to meet the market demand for high-performance and high-stability lithium secondary batteries is an urgent problem to be solved. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a lithium battery material and its preparation method. This material is composed of a polymer containing dissolved lithium nitrate. The polymer contains polar groups that can dissociate and dissolve lithium nitrate, effectively solving the problem of poor dissolution of lithium nitrate when applied to lithium batteries. When applied to lithium batteries, this material introduces a "lithium nitrate library" into the battery system, which can slowly release lithium nitrate and nitrate ions during cycling, thus significantly improving the electrical performance of the lithium battery.

[0007] Firstly, one of the objectives of this invention is to provide a lithium battery material.

[0008] Specifically, the lithium battery material includes a polymer and lithium nitrate. The polymer contains polar groups that can dissolve lithium nitrate, wherein the mass of lithium nitrate is 1-30 wt% of the polymer mass, preferably 1-20 wt%. This invention utilizes a polymer as a medium to dissolve lithium nitrate into the separator, allowing the lithium nitrate to be released slowly during battery cycling, thus ensuring the stability of the lithium battery.

[0009] Furthermore, the polymer is selected from one of cross-linked polar polymers and polar group modified polymers.

[0010] Furthermore, the polar groups in the polymer are selected from one or a combination of ether groups (-O-), ester groups (-COO-), amide groups (-CONH-), fluoroether groups (-O-CF2-CF2-), sulfonic acid groups (-SO3H), and fluoroester groups (-COO-CF2-CF2-). When the polymer and lithium nitrate are mixed, the lithium nitrate is stably dissolved in the polymer network, and the polar groups contained in the polymer have a good dissociation effect on the lithium nitrate, enabling it to play a role in the battery system.

[0011] Secondly, another objective of this invention is to provide a method for preparing lithium battery materials, which is one of the objectives of this invention.

[0012] Specifically, the method includes the following steps:

[0013] Step 1: Under the protection of an inert gas, the monomer is dissolved in a solvent and polymerization is carried out under the initiation of an initiator. After reacting for a period of time, a crosslinking agent is added to continue the reaction and obtain the polymer.

[0014] Step 2: Mix the polymer and lithium nitrate and dissolve them to obtain the lithium battery material.

[0015] More specifically, the method includes the following steps:

[0016] Step 1: Under the protection of an inert gas, dissolve the monomer in a solvent and mix thoroughly. Then add an initiator to carry out the polymerization reaction at 65-90°C for 12-36 hours. Next, add a crosslinking agent to carry out the crosslinking reaction at 65-80°C for 10-20 hours to obtain a polymer solution.

[0017] Step 2: Add lithium nitrate to the above polymer solution and dissolve to obtain lithium battery material.

[0018] Further, the polymerizing monomer is selected from organic monomers containing double bonds; preferably, the polymerizing monomer is selected from at least two of ethylene carbonate, polyethylene glycol methacrylate, polyethylene glycol methyl ether methacrylate, ethylene glycol monoethyl ether acrylate, methoxy polyethylene glycol acrylate, lithium (4-styrenesulfonyl)(trifluoromethanesulfonyl)imide, lithium styrenesulfonate, perfluoroalkyl vinyl ether, perfluorooctyl acrylate, hexafluoropropylene, and vinylidene fluoride; more preferably, the polymerizing monomer is selected from a combination of ethylene carbonate and polyethylene glycol methacrylate, wherein the molar ratio of ethylene carbonate to polyethylene glycol methacrylate is 1:1 to 1:4. It is worth mentioning that the present invention utilizes free radical reactions or other polymerization reactions to obtain polymers with side chains containing polar groups capable of dissociating lithium nitrate; simultaneously, this polymer has a cross-linked polymer network, which can add lithium nitrate to the polymer network in a solvent environment, introducing a "lithium nitrate library" into the battery system, and slowly releasing nitrate ions through the dissociation of polar groups.

[0019] Further, the initiator is selected from one or a combination of azobisisobutyronitrile, azobisisobutyronitrile, benzoyl peroxide, and dicumyl peroxide. The amount of initiator used is the conventional amount used to initiate the free radical polymerization reaction of the polymer monomers; preferably, the amount of initiator is 0.05–5 wt% of the mass of the polymer monomers.

[0020] Further, the crosslinking agent is selected from isocyanate compounds, preferably from one or a combination of polyhexamethylene isocyanate, hexamethylene isocyanate, and 4,4-diphenylmethane diisocyanate. The amount of crosslinking agent used is the conventional amount for carrying out the crosslinking reaction; preferably, the amount of crosslinking agent is 0.5 to 2 wt% of the mass of the initiating polymer monomer.

[0021] Furthermore, the solvent is selected from one or a combination of N,N-dimethylformamide, tetrahydrofuran, toluene, dichloromethane, dimethyl sulfoxide, N-methylpyrrolidone, chloroform, and toluene.

[0022] Furthermore, the inert gas is selected from one or a combination of argon, nitrogen, and helium.

[0023] Thirdly, a third objective of this invention is to provide the application of the lithium battery material for one of the objectives of this invention.

[0024] Specifically, one of the objectives of this invention is to use lithium battery materials to modify the separators of lithium batteries.

[0025] Furthermore, the method of modifying the separator using lithium battery materials is as follows:

[0026] Under an inert gas atmosphere, a polymer solution containing dissolved lithium nitrate is loaded onto a substrate and transferred to a vacuum oven. The substrate is then heated at 60–120°C for 6–8 hours under a vacuum of -0.06 to -0.1 MPa to dry the solvent, yielding a lithium nitrate and polymer-modified separator. The loading method can be either impregnation or drop coating. The substrate material can be one of glass fiber, lithium-ion battery separator, ceramic-modified separator, electrospun material, or nonwoven fabric.

[0027] Preferably, the loading of lithium nitrate on the separator is 0.1% to 1% of the separator mass, and the loading of polymer on the separator is 10% to 40% of the separator mass.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. This invention solves the problem of lithium nitrate not dissolving in the electrolyte system by applying a polymer containing dissolved lithium nitrate to the lithium battery system. This invention directly applies lithium nitrate to the surface of the separator, and slowly releases lithium nitrate into the electrolyte system during battery cycling, thereby improving the stability of the battery.

[0030] 2. This invention utilizes free radical reactions or other polymerization reactions to obtain a polymer medium whose side chains contain polar groups capable of dissociating lithium nitrate. This polymer medium has a cross-linked polymer network. Lithium nitrate is added to this polymer network in a solvent environment to obtain a polymer mixture solution containing lithium nitrate. This mixture solution adheres to a separator, resulting in a separator modified with lithium nitrate and polymer. When this modified separator is placed in an electrolyte system, regardless of the solubility of lithium nitrate in the original electrolyte system, the addition of lithium nitrate can improve the cycle stability of the battery, making it suitable for various lithium battery systems.

[0031] 3. The process of this invention is simple, it significantly improves the cycle stability of lithium-ion secondary batteries, and it is low in cost, compatible with various electrolytes, has strong versatility, great industrialization potential, and broad application prospects. Attached Figure Description

[0032] Figure 1 This is a structural diagram of the polymer prepared in Example 1 of the present invention;

[0033] Figure 2 The NMR spectrum of the polymer prepared in Example 1 of this invention;

[0034] Figure 3 This is a structural diagram of the polymer prepared in Example 6 of the present invention;

[0035] Figure 4 The NMR spectrum of the polymer prepared in Example 6 of this invention;

[0036] Figure 5 This is an electron microscope image of the lithium battery material prepared in Example 1 of the present invention;

[0037] Figure 6 This is an electron microscope cross-sectional view of the lithium battery material prepared in Example 1 of the present invention;

[0038] Figure 7 Voltage window test of the lithium battery prepared in Comparative Application Example 2 of this invention;

[0039] Figure 8 This is a voltage window test diagram of the lithium battery prepared in Application Example 1 of the present invention;

[0040] Figure 9 The charge-discharge cycle performance of the lithium nitrate-containing polymer prepared in Application Example 1 of the present invention and the comparative application example 2 when applied to a lithium battery is compared. Detailed Implementation

[0041] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0042] The raw materials used in the following examples and comparative examples are not particularly limited in their source; they can all be purchased on the market or prepared by conventional methods known to those skilled in the art.

[0043] Example 1

[0044] The following describes the preparation of a polymer solution containing lithium nitrate. The specific preparation steps are as follows:

[0045] Under an inert gas atmosphere, 0.57 g of ethylene ethylene carbonate and 0.43 g of polyethylene glycol methacrylate were added to 10 mL of dimethylformamide, dissolved and mixed evenly, and then 16.4 mg of azobisisobutyronitrile was added. The mixture was stirred with a magnetic stirrer and heated in an oil bath at 65 °C for 12 h to polymerize.

[0046] Under an inert gas atmosphere, 1 mL of the above solution (0.1 g / mL) was placed in a dry, pressure-resistant bottle. 1 mL of anhydrous tetrahydrofuran was added to dilute the concentration of the above product solution to 0.05 g / mL. 0.025 g of polyhexamethylene diisocyanate was added. Under magnetic stirring, the mixture was placed in a 70°C oil bath for crosslinking reaction. Then, 0.01 g of lithium nitrate was added and transferred to a small bottle. The mixture was stirred for more than 15 minutes to fully dissolve the lithium nitrate polymer solution.

[0047] Figure 1 The diagram shows the structural formula of the polymer prepared in this embodiment. The polymer structure includes multiple ethoxy groups, amide groups, and ester groups.

[0048] Figure 2 The NMR spectra of the polymer prepared in this embodiment are shown. 1 The spectrum shows that 3.2–4.0 ppm is the characteristic peak of hydrogen on alkyl groups connected to O, and around 1.8 ppm is the characteristic peak of hydrogen on alkyl groups connected to ester groups.

[0049] Figure 5 The image shows a surface and cross-sectional view of the lithium battery material prepared in this embodiment, i.e., the polymer after dissolving lithium nitrate. As can be seen from the image, lithium nitrate is uniformly dissolved in the polymer.

[0050] The following describes the process of modifying a membrane with a polymer containing lithium nitrate:

[0051] Under an inert gas atmosphere, the Celgard membrane was placed in a polytetrafluoroethylene petri dish, and 40 μL of a lithium nitrate polymer solution was dropped onto the 16 mm diameter Celgard membrane (1 mg / cm²). 2 Then, it is transferred to a vacuum oven and heated at 80°C for 6 hours under vacuum conditions of -0.1MPa to dry the solvent.

[0052] Example 2

[0053] In this embodiment, the preparation method of the polymer solution containing lithium nitrate is the same as that of the polymer solution containing lithium nitrate in Example 1, except that the amount of lithium nitrate used in this embodiment is 0.005g.

[0054] In this embodiment, the method of modifying the separator with a polymer containing lithium nitrate is the same as in Example 1.

[0055] Example 3

[0056] In this embodiment, the preparation method of the polymer solution containing lithium nitrate is the same as that of the polymer solution containing lithium nitrate in Example 1, except that the amount of lithium nitrate used in this embodiment is 0.02g.

[0057] In this embodiment, the method of modifying the separator with a polymer containing lithium nitrate is the same as in Example 1.

[0058] Example 4

[0059] In this embodiment, the preparation method of the polymer solution containing lithium nitrate is the same as that of the polymer solution containing lithium nitrate in Example 1, except that the amount of lithium nitrate used in this embodiment is 0.03g.

[0060] In this embodiment, the method of modifying the separator with a polymer containing lithium nitrate is the same as in Example 1.

[0061] Example 5

[0062] In this embodiment, the preparation method of the polymer solution containing lithium nitrate is the same as that of the polymer solution containing lithium nitrate in Example 1, except that the amount of lithium nitrate used in this embodiment is 0.05g.

[0063] In this embodiment, the method of modifying the separator with a polymer containing lithium nitrate is the same as in Example 1.

[0064] Example 6

[0065] The following describes the preparation of a polymer solution containing lithium nitrate. The specific preparation steps are as follows:

[0066] Under an inert gas atmosphere, 0.52 g of perfluoropropyl vinyl ether (PPVE), 0.3 g of polyethylene glycol methacrylate, and 0.2 g of (4-styrenesulfonyl)(trifluoromethanesulfonyl)imide were added to 10 mL of dimethylformamide, dissolved and mixed evenly, and then 16.4 mg of azobisisobutyronitrile was added. The mixture was stirred magnetically and heated in an oil bath at 65 °C for 12 h for polymerization.

[0067] Under an inert gas atmosphere, 1 mL (0.1 g / mL) of the above solution was placed in a dry, pressure-resistant bottle. 1 mL of anhydrous tetrahydrofuran was added to dilute the product solution to 0.05 g / mL. 0.025 g of polyhexamethylene diisocyanate was added, and the mixture was placed in a 70°C oil bath with magnetic stirring to carry out the crosslinking reaction. Then, 0.01 g of lithium nitrate was added and transferred to a small vial, stirred for at least 15 minutes until fully dissolved, yielding a polymer solution of lithium nitrate.

[0068] Figure 3 The structural diagram of the polymer prepared in this embodiment is shown. The polymer structure includes multiple ethoxy groups, amide groups, ester groups, fluoroether groups, and benzenesulfonate groups.

[0069] Figure 4 The NMR spectra of the polymer prepared in this embodiment are shown. 1The spectrum shows that 3.2–4.0 ppm is the characteristic peak of hydrogen on alkyl groups connected to O, around 1.8 ppm is the characteristic peak of hydrogen on alkyl groups connected to ester groups, and 7.9, 7.2, and 6.5 ppm are the characteristic peaks of hydrogen on benzene rings.

[0070] Comparative Example 1

[0071] In this comparative example, the preparation method of the polymer solution is the same as that of the polymer solution in Example 1, except that the polymer solution in this comparative example does not contain lithium nitrate.

[0072] In this comparative example, the method of modifying the membrane with polymer is the same as in Example 1.

[0073] Application Example 1

[0074] In this application example, the separator prepared in Example 1 is used for battery assembly, and the assembly method is as follows:

[0075] In a glove box with a water oxygen content of <0.01ppm, a CR2032 lithium-ion button battery was assembled using lithium iron phosphate as the positive electrode and a 300μm thick lithium metal as the negative electrode. The electrolyte was a 1M lithium hexafluorophosphate solution dissolved in a mixed solvent of ethylene carbonate, diethyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1.

[0076] Application Example 2

[0077] In this application example, the battery assembly method is the same as in Application Example 1, except that the separator used in this application example is the separator prepared in Example 2.

[0078] Application Example 3

[0079] In this application example, the battery assembly method is the same as in Application Example 1, except that the separator used in this application example is the separator prepared in Example 3.

[0080] Application Example 4

[0081] In this application example, the battery assembly method is the same as in Application Example 1, except that the separator used in this application example is the separator prepared in Example 4.

[0082] Application Example 5

[0083] In this application example, the battery assembly method is the same as in Application Example 1, except that the separator used in this application example is the separator prepared in Example 5.

[0084] Application Example 6

[0085] In this application example, the battery assembly method is the same as in Application Example 1, except that the separator used in this application example is the separator prepared in Example 6.

[0086] Application Example 7

[0087] In this application example, the battery assembly method is the same as in Application Example 1, and the separator used is the same as in Example 1. The difference is that the electrolyte of the battery is 2M lithium bis(fluorosulfonyl)imide dissolved in DME solvent.

[0088] Comparative Application Example 1

[0089] In this comparative application example, the battery assembly method is the same as in application example 1, except that the separator used in this example is the same as the separator prepared in comparative example 1.

[0090] Comparative Application Example 2

[0091] In this comparative application example, the battery assembly method is the same as in application example 1, except that the battery separator is an unmodified Celgard separator.

[0092] Comparative Application Example 3

[0093] In this comparative application example, the battery assembly method is the same as in application example 7, except that the battery separator is an unmodified Celgard separator.

[0094] The batteries assembled in Application Examples 1 to 7 and Comparative Application Examples 1 to 3 were subjected to electrical performance tests. Charge-discharge cycle performance tests were conducted at a voltage of 2.8 to 4.2 V and a current density of 37 mA / g. The test results are shown in Table 1.

[0095] Table 1:

[0096] <![CDATA[Specific capacity / mAh g -1 > Coulomb efficiency / % Capacity retention rate / % Application Example 1 148.0 99.63 92.77 Application Example 2 146.7 99.03 88.66 Application Example 3 145.3 99.56 91.53 Application Example 4 137.4 99.47 85.83 Application Example 5 133.6 99.41 83.48 Application Example 6 133.0 99.63 92.77 Application Example 7 149.1 99.23 90.11 Comparative Application Example 1 130.6 98.81 85.39 Comparative Application Example 2 146.4 98.71 85.4 Comparative Application Example 3 148.4 97.9 86.4

[0097] As shown in Table 1, the coulombic efficiency and capacity retention were improved to varying degrees after the electrolyte system was modified with a polymer containing lithium nitrate.

[0098] Furthermore, as shown in Application Examples 1-5, maintaining an appropriate lithium nitrate content in the polymer helps improve the capacity retention of lithium-ion batteries. This is because lithium nitrate can be uniformly distributed across the negative electrode interface of the entire electrolyte system and reacts with the negative electrode interface to generate stable inorganic SEI components such as Li₂O, LiNxOy, and Li₃N, thereby improving the stiffness and ionic conductivity of the electrode interface, stabilizing lithium deposition, and enhancing coulombic efficiency. However, excessive amounts lead to a decrease in capacity retention. This is because when the amount of lithium nitrate added is too large, it exceeds the polymer's ability to dissociate it. Some lithium nitrate cannot dissolve, inevitably increasing the internal impedance of the electrolyte system, which adversely affects the battery's cycle performance and reduces the capacity retention.

[0099] Furthermore, as can be seen from Application Examples 1 and 7 and Comparative Application Examples 1 to 3, introducing lithium nitrate into the polymer can give the battery better overall performance, and both coulombic efficiency and capacity retention are significantly improved.

[0100] Furthermore, by Figure 7 and Figure 8 As can be seen, compared with application example 2 ( Figure 7 The voltage window of the lithium battery is displayed at around 4.2V, as shown in Application Example 1. Figure 8 The voltage window of the lithium battery is shown to be around 5.0V. It is evident that by introducing polymer modification containing lithium nitrate, the addition of lithium nitrate forms a stable interface, significantly and effectively improving the voltage window.

[0101] Furthermore, by Figure 9 It can be seen that the lithium battery in Application Example 1 (blue) has better electric cycle performance than the lithium battery in Comparative Application Example 2 (red).

[0102] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A lithium battery material comprising a polymer and lithium nitrate, wherein the polymer contains polar groups, and the mass of the lithium nitrate is 1 to 30 wt% of the polymer mass.

2. The lithium battery material according to claim 1, characterized in that, The mass of the lithium nitrate is 1 to 20 wt% of the polymer mass.

3. The lithium battery material according to claim 1, characterized in that, The polymer is selected from cross-linked polar polymers and polar group modified polymers.

4. The lithium battery material according to claim 1, wherein the polar group is selected from one or a combination of ether group, ester group, amide group, fluoroether group, sulfonic acid group, and fluoroester group.

5. A method for preparing lithium battery materials according to any one of claims 1 to 4, comprising the following steps: Step 1: Under the protection of an inert gas, the monomer is dissolved in a solvent and polymerization is carried out under the initiation of an initiator. After reacting for a period of time, a crosslinking agent is added to continue the reaction and obtain the polymer. Step 2: Mix the polymer and lithium nitrate and dissolve them to obtain the lithium battery material.

6. The method for preparing lithium battery material according to claim 5, characterized in that, The polymerizing monomer is selected from organic monomers containing double bonds; preferably, the polymerizing monomer is selected from at least two of ethylene carbonate, polyethylene glycol methacrylate, polyethylene glycol methyl ether methacrylate, ethylene glycol monoethyl ether acrylate, methoxy polyethylene glycol acrylate, lithium (4-styrenesulfonyl)(trifluoromethanesulfonyl)imide, lithium styrenesulfonate, perfluoroalkyl vinyl ether, perfluorooctyl acrylate, hexafluoropropylene, and vinylidene fluoride.

7. The method for preparing lithium battery material according to claim 5, characterized in that, The initiator is selected from one or a combination of azobisisobutyronitrile, azobisisobutyronitrile, benzoyl peroxide, and dicumyl peroxide.

8. The method for preparing lithium battery material according to claim 5, characterized in that, The crosslinking agent is selected from isocyanate compounds, preferably from one or a combination of polyhexamethylene isocyanate, hexamethylene isocyanate, and 4,4-diphenylmethane diisocyanate.

9. The application of the lithium battery material according to any one of claims 1 to 4, wherein the lithium battery material is used to modify a separator for a lithium battery.

10. The application of the lithium battery material according to claim 9, characterized in that, The method of modifying the separator with lithium battery materials is as follows: Under an inert gas atmosphere, the lithium battery material is loaded onto a substrate, and then heated and dried under vacuum to obtain a modified separator. Preferably, the substrate material can be one of glass fiber, lithium battery separator, ceramic modified separator, electrospun material, and nonwoven fabric; Preferably, the loading of lithium nitrate on the separator is 0.1% to 1% of the separator mass, and the loading of polymer on the separator is 10% to 40% of the separator mass.

Images