Self-assembled molecular layer, alkali metal ion battery cathode modification method and application thereof

Abstract

The application provides a self-assembled molecular layer, a modification method of a positive electrode of an alkali metal ion battery and application thereof, and belongs to the technical field of alkali metal ion batteries.The monomer molecule of the self-assembled molecular layer is composed of an anchoring group, an intermediate group and a terminal group, the anchoring group is combined with transition metals or other surface groups in the positive electrode material of the alkali metal ion battery, and the intermediate group and the terminal group are used for adjusting chemical and electrochemical reactions at the interface; the preparation method of the self-assembled molecular layer is as follows: the positive electrode material or the positive electrode sheet of the alkali metal ion battery is put into a monomer molecule solution, taken out after soaking for a certain time, cleaned with a pure solvent and dried after drying.The self-assembled molecular layer provided by the application is used for modifying the positive electrode of the alkali metal ion battery, which is helpful for inhibiting side reactions between the positive electrode and the electrolyte, forming a stable interface phase, reducing interface resistance, relieving polarization growth and capacity attenuation in the battery cycle process, and prolonging the service life of the battery.

Description

Technical Field

[0001] This invention belongs to the field of alkali metal ion battery technology, specifically relating to a self-assembled molecular layer, a method for modifying the cathode of an alkali metal ion battery, and their applications. Background Technology

[0002] Alkali metal ion batteries store and release electrical energy through reversible electrochemical reactions. Represented by lithium batteries, which boast high energy density, long cycle life, and no memory effect, alkali metal ion batteries have been widely used in portable electronic devices, electric vehicles, and even renewable energy storage systems. However, the energy density of existing alkali metal ion batteries is gradually becoming insufficient to meet the growing performance demands of modern applications.

[0003] Achieving high energy density essentially relies on using a cathode with high operating voltage and high specific capacity. However, high voltage or deep delithiation often leads to interfacial instability between the cathode and electrolyte. Under high voltage and the catalysis of transition metal elements in the cathode, the electrolyte undergoes irreversible oxidative decomposition, producing harmful gases and byproducts. The cathode-electrolyte interlayer formed under uncontrolled interfacial side reactions cannot effectively passivate the interface between the cathode and electrolyte. Under continuous side reactions, the electrolyte is constantly consumed, accompanied by repeated destruction and formation of the interfacial phase. The corrosive effect of the electrolyte on the cathode is also intensified, leading to changes in the near-surface crystal structure and particle destruction of the cathode, resulting in impaired kinetics and capacity decay. These instabilities ultimately manifest as energy efficiency loss, shortened cycle life, and reduced safety in the battery.

[0004] Cathode surface modification is an effective method to alleviate interfacial problems between the cathode and electrolyte and improve the performance of alkali metal ion batteries. However, the design and selection of modification materials and methods face multiple challenges: it is necessary to find modification materials that can effectively suppress side reactions without significantly negatively impacting cathode kinetic performance and capacity; surface modification materials need to minimize thickness and mass gain to achieve higher energy density; surface modification processes need to be simple, efficient, and scalable for practical application; in addition, the economics of modification materials and processes are also important to ensure commercial competitiveness. Summary of the Invention

[0005] This invention is based on the above background technology and aims to provide a self-assembled molecular layer, a method for modifying the cathode of an alkali metal ion battery, and its application.

[0006] This invention provides a self-assembled molecular layer characterized by being formed by the self-assembly, adsorption, and regular arrangement of monomer molecules on the surface of the positive electrode material of an alkali metal ion battery. The monomer molecules include: an anchoring group, which spontaneously adsorbs and bonds with a transition metal or its surface groups in the positive electrode material of the alkali metal ion battery; the anchoring group includes any one or more of –SH, –COOH, –PO3H2, –SO3H, –C≡N, –NO2, –SiCl3, –Si(OCH3)3, or –Si(OH)3; and a terminal group, which is directly or indirectly connected to the anchoring group, including any one or more of alkyl, haloalkyl, alkenyl, haloalkenyl, alkynyl, haloalkynyl, nitro, cyano, sulfonylfluoride, aryl, haloaryl, or carboxyl groups. In the alkali metal ion battery, when the monomer molecules are adsorbed on the surface of the positive electrode material, the terminal groups face the electrolyte of the alkali metal ion battery.

[0007] The self-assembled molecular layer provided by the present invention may also have the following features: wherein the monomer molecule further includes an intermediate group, which is connected between the anchoring group and the terminal group and serves as the backbone of the monomer molecule, and the intermediate group includes saturated hydrocarbon groups and / or unsaturated hydrocarbon groups.

[0008] The self-assembled molecular layer provided by the present invention may also have the following feature: wherein the saturated hydrocarbon group includes alkyl, cycloalkyl, haloalkyl or halocycloalkyl.

[0009] The self-assembled molecular layer provided by the present invention may also have the following feature: wherein the unsaturated hydrocarbon group includes alkenyl, haloalkenyl, aryl or haloaryl.

[0010] The self-assembled molecular layer provided by the present invention may also have the following characteristics: the total number of atoms other than hydrogen atoms and halogen atoms in the monomer molecule is not less than 4 and the relative molecular mass of the monomer molecule is not greater than 500.

[0011] This invention also provides a method for modifying the cathode of an alkali metal ion battery, characterized by using the self-assembled molecular layer and its corresponding monomer molecules as described above, comprising the following steps: S10, immersing the cathode material of the alkali metal ion battery in a solution of monomer molecules for a period of time, so that the monomer molecules self-assemble, adsorb, and arrange themselves regularly on the surface of the cathode material to form a self-assembled molecular layer; S20, taking out the cathode material treated in step S10, washing and drying it to complete the modification of the cathode material.

[0012] The method for modifying the cathode of an alkali metal ion battery provided by the present invention may also have the following feature: in step S10, the solvent corresponding to the solution of the monomer molecules includes any one or more of methanol, ethanol, isopropanol, acetone, dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, tetrahydrofuran, cyclohexane, dimethyl carbonate, or octane.

[0013] The method for modifying the cathode of an alkali metal ion battery provided by the present invention may also have the following features: in step S10, the concentration of the monomer molecules in the solution is 0.5 mmol / L to 10 mmol / L, and the soaking time is 2h to 24h.

[0014] The present invention also provides an application of the method for modifying the positive electrode of an alkali metal ion battery in an alkali metal ion battery, characterized in that: the alkali metal ion battery includes a negative electrode, a separator, an electrolyte, and a modified positive electrode, wherein the modified positive electrode is obtained by modifying the positive electrode material of the alkali metal ion battery by the method for modifying the positive electrode of an alkali metal ion battery according to any one of claims 6 to 8.

[0015] The role and effect of invention

[0016] The self-assembled molecular layer provided in this invention has a diverse and designable structure of organic monomer molecules. Therefore, this feature can be fully utilized for surface property design, thereby enabling targeted interface control based on the characteristics of the cathode and battery system.

[0017] Modifying the cathode of an alkali metal ion battery using the self-assembled molecular layer provided by this invention can effectively improve the interfacial stability between the cathode and the electrolyte, construct a stable passivating cathode-electrolyte intermediate phase, alleviate structural and interfacial degradation related to interfacial side reactions, and effectively improve the battery's cycle stability, capacity retention, and energy efficiency maintenance capabilities.

[0018] The self-assembled molecular layer and the method for modifying alkali metal ion battery cathode materials using the self-assembled molecular layer provided by this invention can achieve a uniform, molecular-level thickness modification layer, while the cost of the materials involved is controllable, the process is simple and efficient, and it has the potential for large-scale application. Attached Figure Description

[0019] Figure 1 These are transmission electron microscope (TEM) images and SS energy dispersive spectroscopy (EDS) images of active material particles in the NCM811 electrode sheet before modification and the modified NCM811 electrode sheet (sample 1) in Example 3 of the present invention.

[0020] Figure 2 These are the time-of-flight secondary ion mass spectrometry test data of the modified NCM811 electrode (sample 1) in Example 3 of the present invention;

[0021] Figure 3 This is a comparison of the cycle performance of battery 1 and battery 2 of the NCM811||Li button half-cell in Embodiment 3 of the present invention;

[0022] Figure 4 In Embodiment 3 of the present invention, NCM811||SiO x Comparison of cycle performance of battery 3 and battery 4 in / C soft-pack full battery. Detailed Implementation

[0023] To make the technical means, creative features, objectives and effects of this invention easier to understand, the following embodiments, in conjunction with the accompanying drawings, specifically illustrate a self-assembled molecular layer, a method for modifying the cathode of an alkali metal ion battery, and its applications.

[0024] <Example 1>

[0025] This embodiment provides a self-assembled molecular layer, which is formed by the self-assembly, adsorption, and regular arrangement of monomer molecules on the surface of the positive electrode material of an alkali metal ion battery.

[0026] The monomer molecule includes anchoring groups and terminal groups. The total number of atoms in the monomer molecule, excluding hydrogen atoms and halogen atoms, is not less than 4, and the relative molecular mass of the monomer molecule is not greater than 500.

[0027] The anchoring group spontaneously adsorbs and bonds with the transition metal or its surface groups in the cathode material of the alkali metal ion battery. The anchoring group includes any one or more of –SH, –COOH, –PO3H2, –SO3H, –C≡N, –NO2, –SiCl3, –Si(OCH3)3 or –Si(OH)3.

[0028] The terminal group is directly connected to the anchoring group, including any one or more of alkyl, haloalkyl, alkenyl, haloalkenyl, alkynyl, haloalkynyl, nitro, cyano, sulfonyl fluoride, aryl, haloaryl, or carboxyl groups. In alkali metal ion batteries, when the monomer molecule is adsorbed on the surface of the positive electrode material, the terminal group faces the electrolyte of the alkali metal ion battery.

[0029] <Example 2>

[0030] This embodiment provides a self-assembled molecular layer, which is formed by the self-assembly, adsorption, and regular arrangement of monomer molecules on the surface of the positive electrode material of an alkali metal ion battery.

[0031] Monomer molecules include anchoring groups, intermediate groups, and terminal groups. The total number of atoms in a monomer molecule, excluding hydrogen atoms and halogen atoms, is not less than 4, and the relative molecular mass of the monomer molecule is not greater than 500.

[0032] The anchoring group spontaneously adsorbs and bonds with the transition metal or its surface groups in the cathode material of the alkali metal ion battery. The anchoring group includes any one or more of –SH, –COOH, –PO3H2, –SO3H, –C≡N, –NO2, –SiCl3, –Si(OCH3)3 or –Si(OH)3.

[0033] The intermediate group connects the anchoring group and the terminal group and serves as the backbone of the monomer molecule. The intermediate group includes saturated hydrocarbon groups and / or unsaturated hydrocarbon groups. Saturated hydrocarbon groups include alkyl, cycloalkyl, haloalkyl, or halocycloalkyl groups; unsaturated hydrocarbon groups include alkenyl, haloalkenyl, aryl, or haloaryl groups.

[0034] The terminal group is connected to the intermediate group, including any one or more of alkyl, haloalkyl, alkenyl, haloalkenyl, alkynyl, haloalkynyl, nitro, cyano, sulfonyl fluoride, aryl, haloaryl, or carboxyl groups. In alkali metal ion batteries, when the monomer molecule is adsorbed on the surface of the positive electrode material, the terminal group faces the electrolyte of the alkali metal ion battery.

[0035] <Example 3>

[0036] This embodiment provides a method for modifying the cathode of an alkali metal ion battery, using the self-assembled molecular layers and their corresponding monomer molecules from Example 1 and / or Example 2, including the following steps:

[0037] S10: The positive electrode material of the alkali metal ion battery is immersed in a solution of monomer molecules of 0.5 mmol / L to 10 mmol / L for 6 hours, so that the monomer molecules self-assemble and adsorb on the surface of the positive electrode material and arrange themselves regularly to form a self-assembled molecular layer.

[0038] In alkali metal ion batteries: (1) When a monomer molecule is composed of interconnected anchoring groups and terminal groups, the anchoring groups spontaneously adsorb onto the transition metals in the cathode material or their surface groups, and the terminal groups serve as the backbone of the monomer molecule and face the electrolyte of the alkali metal ion battery. (2) When a monomer molecule is composed of sequentially connected anchoring groups, intermediate groups, and terminal groups, the anchoring groups spontaneously adsorb onto the transition metals in the cathode material or their surface groups, the intermediate groups connect the anchoring groups and terminal groups and serve as the backbone of the monomer molecule, and the terminal groups face the electrolyte of the alkali metal ion battery.

[0039] S20: Take out the positive electrode material processed in step S10, wash and dry it to complete the modification of the positive electrode material, and then place it in an inert atmosphere or dry environment for later use.

[0040] Specifically, in this embodiment, by controlling the experimental parameters in the method for modifying the cathode of an alkali metal ion battery, 14 different modified cathodes were prepared, which are respectively denoted as Sample 1, Sample 2, Sample 3, Sample 4, Sample 5, Sample 6, Sample 7, Sample 8, Sample 9, Sample 10, Sample 11, Sample 12, Sample 13, and Sample 14.

[0041] The specific parameters of samples 1 to 14 during the preparation process are shown in Table 1 below.

[0042] Table 1 (Specific parameters of samples 1 to 14 during the preparation process)

[0043]

[0044] In Table 1 above, FPSH is 4,4,5,5,5-pentafluoro-1-pentanethiol, BA is benzoic acid, CBA is 4-chlorobenzoic acid, FBA is 4-fluorobenzoic acid, PPA is phenylphosphonic acid, CBSA is 4-chlorobenzenesulfonic acid, BuDA is 1,4-succinic acid, BeDA is 1,4-phthalic acid, SPA is 3-mercaptopropionic acid, NBSF is 4-nitrobenzenesulfonyl fluoride, MBSA is 4-methylbenzenesulfonic acid, SSA is styrenesulfonic acid, FOMS is tridecafluorooctyltrimethoxysilane, and FBPMS is pentafluorophenylpropyltrimethoxysilane.

[0045] NCM811 is for LiNi 0.8 Co 0.1 Mn 0.1 O2, LCO is LiCoO2, NCM90 is LiNi 0.9 Co 0.05 Mn 0.05 O2, NCM622 is LiNi 0.6 Co 0.2 Mn 0.2 O2.

[0046] Figure 1 These are transmission electron microscopy (TEM) images and energy dispersive spectroscopy (EDS) images of the active material particles in the NCM811 electrode sheet before modification and the modified NCM811 electrode sheet (sample 1) in Example 3 of the present invention.

[0047] like Figure 1 As shown, the modified NCM811 particles have an additional amorphous layer with a thickness of about 2 nm on the surface, and the S and F elements from FPSH are uniformly distributed on the surface.

[0048] Figure 2 These are the time-of-flight secondary ion mass spectrometry test data of the modified NCM811 electrode (sample 1) in Example 3 of the present invention.

[0049] like Figure 2As shown, the intensity of the characteristic groups from FPSH decreases rapidly with bombardment, while the intensity of the groups from the NCM811 crystal itself increases rapidly, proving that FPSH molecules form a self-assembled molecular layer on the NCM811 surface.

[0050] This embodiment also provides an application of an alkali metal ion battery cathode modification method in alkali metal ion batteries.

[0051] An alkali metal ion battery includes a negative electrode, a separator, an electrolyte, and a modified positive electrode. The modified positive electrode is obtained by modifying the positive electrode material of the alkali metal ion battery using the alkali metal ion battery positive electrode modification method provided in this embodiment.

[0052] Specifically, in this embodiment, a total of 20 alkali metal ion batteries were assembled, which are respectively labeled as battery 1, battery 2, battery 3, battery 4, battery 5, battery 6, battery 7, battery 8, battery 9, battery 10, battery 11, battery 12, battery 13, battery 14, battery 15, battery 16, battery 17, battery 18, battery 19 and battery 20.

[0053] The cathodes of these 20 alkali metal ion batteries are ordinary cathode materials or modified cathode materials prepared as described above (samples 1 to 14).

[0054] The specific materials, parameters, and battery performance of batteries 1 to 20 in this embodiment are shown in Table 2 below.

[0055] Table 2 (Specific materials, parameters, and battery performance of batteries 1 to 20)

[0056]

[0057] Figure 3 This is a comparison of the cycle performance of battery 1 and battery 2 of the NCM811||Li button half-cell in Embodiment 3 of the present invention.

[0058] As shown in Table 2 and Figure 3 As shown, the NCM811||Li button cell has a set charge / discharge voltage range of 2.7V to 4.4V. It is first cycled 3 times at a 0.1C rate, then cycled up to 150 times at a 0.2C rate. (See Table 2 and...) Figure 3 It can be seen that the self-assembled molecular layer modified half-cell constructed by FPSH has higher cycle capacity retention and smaller polarization growth.

[0059] Figure 4 In Embodiment 3 of the present invention, NCM811||SiO x Comparison of cycle performance of battery 3 and battery 4 in / C soft-pack full battery.

[0060] As shown in Table 2 and Figure 4As shown, NCM811||SiO has an N / P ratio of 1.12. x The cycle performance of the / C pouch full cell was tested at charging cutoff voltages of 4.25V and 4.45V, with a 1C rate current density during cycling. (See Table 2 and...) Figure 4 It can be seen that the NCM811 cathode modified with self-assembled molecular layers (battery 3) has significantly better capacity retention and discharge voltage maintenance capabilities under both cutoff voltages than the control sample (battery 4) using unmodified NCM811.

[0061] In Table 2 above, the test conditions for Li||LCO button cells of batteries 5 to 10 are as follows: within the charge and discharge voltage range of 3.0V to 4.55V, first cycle at a rate of 0.1C for 3 cycles, and then cycle at a rate of 0.2C for 200 cycles.

[0062] As shown in Table 2, the specific materials, parameters and battery performance data of batteries 5 to 10 show that when LCO modified by self-assembled molecular layers constructed with BA, CBA, FBA, PPA or CBSA is used as the positive electrode, Li||LCO coin cells all have significantly higher cycle capacity retention rates compared with the control sample (battery 10) using unmodified LCO.

[0063] In Table 2 above, the test conditions for Li||NCM90 button cells of batteries 11 to 17 are as follows: within the charge and discharge voltage range of 3.0V to 4.4V, first cycle at a rate of 0.1C for 3 cycles, and then cycle at a rate of 0.2C for 100 cycles.

[0064] As shown in Table 2, the specific materials, parameters and battery performance data of batteries 11 to 17 show that when NCM90 modified by self-assembled molecular layers constructed with BuDA, BeDA, SPA or NBSF is used as the positive electrode, the Li||NCM90 coin cells all have significantly higher cycle capacity retention rates compared with the control sample (battery 17) using unmodified NCM90.

[0065] In Table 2 above, the test conditions for Li||NCM622 button cells of batteries 18 to 20 are as follows: within the charge and discharge voltage range of 3.0-4.5V, first cycle at a rate of 0.1C for 3 cycles, and then cycle at a rate of 0.2C for 200 cycles.

[0066] As shown in Table 2, the specific materials, parameters and battery performance data of batteries 18 to 20 show that when using NCM622 modified by self-assembled molecular layers constructed by FOMS or FBPMS as the positive electrode, the Li||NCM622 coin cells all have a higher cycle capacity retention rate than the control sample (battery 20) using unmodified NCM622.

[0067] As shown in Table 2 above, by utilizing the flexible selection and combination of functional groups in each part of the monomer molecule, the self-assembled molecular layer modification strategy provided in this embodiment can be used to modify the cathodes of various alkali metal ion batteries, and its performance is significantly better than that of batteries using unmodified cathodes.

[0068] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for modifying the cathode of an alkali metal ion battery, comprising the following steps: S10, the positive electrode material of the alkali metal ion battery is immersed in a solution of monomer molecules for a period of time, so that the monomer molecules self-assemble and adsorb on the surface of the positive electrode material and arrange themselves regularly to form a self-assembled molecular layer. S20: Take out the positive electrode material processed in step S10, wash and dry it to complete the modification of the positive electrode material. The cathode material is any one of NCM90, NCM622, NCM811, and LCO. The monomer molecules include: An anchoring group spontaneously adsorbs and bonds with the transition metal or its surface groups in the cathode material of the alkali metal ion battery, and the anchoring group includes any one or more of –SH, –COOH, –PO3H2, –SO3H, –C≡N, –NO2, –SiCl3, –Si(OCH3)3 or –Si(OH)3; The terminal group, indirectly connected to the anchoring group, includes any one or more of alkyl, haloalkyl, alkenyl, haloalkenyl, alkynyl, haloalkynyl, nitro, cyano, sulfonylfluoride, aryl, haloaryl, or carboxyl groups; and An intermediate group, which is connected between the anchoring group and the terminal group and serves as the backbone of the monomer molecule, comprising saturated hydrocarbon groups and / or unsaturated hydrocarbon groups. In the alkali metal ion battery, when the monomer molecules are adsorbed onto the surface of the positive electrode material, the terminal groups face the electrolyte of the alkali metal ion battery, forming the self-assembled molecular layer.

2. The method for modifying the cathode of an alkali metal ion battery according to claim 1, characterized in that: in, The saturated hydrocarbon group includes alkyl, cycloalkyl, haloalkyl, or halocycloalkyl.

3. The method for modifying the cathode of an alkali metal ion battery according to claim 1, characterized in that: in, The unsaturated hydrocarbon group includes alkenyl, haloalkenyl, aryl, or haloaryl.

4. The method for modifying the cathode of an alkali metal ion battery according to any one of claims 1 to 3, characterized in that: in, The total number of atoms other than hydrogen and halogen atoms in the monomer molecule is not less than 4, and the relative molecular mass of the monomer molecule is not greater than 500.

5. The method for modifying the cathode of an alkali metal ion battery according to claim 1, characterized in that: in, In step S10, the solvent corresponding to the solution of the monomer molecule includes any one or more of methanol, ethanol, isopropanol, acetone, dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, tetrahydrofuran, cyclohexane, dimethyl carbonate, or octane.

6. The method for modifying the cathode of an alkali metal ion battery according to claim 1, characterized in that: in, In step S10, the concentration of the monomer molecules in the solution is 0.5 mmol / L to 10 mmol / L. Soaking time is 2 h to 24 h.

7. The application of a method for modifying the cathode of an alkali metal ion battery in alkali metal ion batteries, characterized in that: in, The alkali metal ion battery includes a negative electrode, a separator, an electrolyte, and a modified positive electrode. The modified cathode is obtained by modifying the cathode material of an alkali metal ion battery using the alkali metal ion battery cathode modification method described in any one of claims 1 to 6.

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