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

Abstract

The invention provides a self-assembled molecular layer, an alkali metal ion battery positive electrode modification method and application thereof, and belongs to the technical field of alkali metal ion batteries. Monomer molecules of the self-assembled molecular layer are composed of anchoring groups, middle groups and terminal groups, the anchoring groups are combined with transition metal or other surface groups in the positive electrode material of the alkali metal ion battery, and chemical and electrochemical reactions at an interface are adjusted through the middle groups and the terminal groups; the preparation method of the self-assembled molecular layer comprises the following steps: putting an alkali metal ion battery positive electrode material or a positive electrode plate into a monomer molecular solution, soaking for a certain time, taking out, cleaning the electrode plate with a pure solvent, and drying. When the self-assembled molecular layer provided by the invention is used for modifying the positive electrode of the alkali metal ion battery, the side reaction between the positive electrode and electrolyte can be inhibited, a stable interface phase can be formed, and the interface resistance can be reduced, so that the polarization growth and the capacity fading in the battery circulation process can be relieved, and the service life of the battery can be prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of alkali metal ion batteries, and in particular relates to a self-assembled molecular layer, an alkali metal ion battery positive electrode modification method and applications thereof. Background Art

[0002] Alkali metal ion batteries store and release electrical energy through reversible electrochemical reactions. Represented by lithium batteries with 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 unable to meet the growing battery performance requirements of modern applications.

[0003] Achieving high energy density essentially relies on the use of a cathode with a high operating voltage and high specific capacity. However, high voltage or deep delithiation is often accompanied by an unstable interface between the cathode and the electrolyte. The electrolyte undergoes irreversible oxidative decomposition under the catalysis of high voltage and transition metal elements of the cathode, and produces harmful gases and byproducts; the cathode-electrolyte interlayer formed under uncontrollable interfacial side reactions cannot effectively passivate the interface between the cathode and the electrolyte. Under continuous side reactions, the electrolyte is continuously consumed and accompanied by repeated destruction and generation of the interfacial phase; the corrosion effect of the electrolyte on the cathode will also intensify, resulting in changes in the near-surface crystal structure of the cathode and particle destruction, which in turn leads to kinetic damage and capacity decay. The above instabilities are ultimately reflected in the loss of energy efficiency, shortened cycle life and reduced safety of the battery.

[0004] Cathode surface modification is an effective method to alleviate the interface problem between the cathode and the electrolyte and improve the performance of alkali metal ion batteries. However, the design and selection of modified materials and modification methods face multiple challenges: it is necessary to find modified materials that can effectively inhibit side reactions without causing significant negative impacts on the cathode kinetics and capacity; surface modified materials need to minimize the increase in thickness and mass to achieve higher energy density; surface modification processes need to be simple, efficient and scalable for application in actual production; in addition, the economy of modified materials and processes is also important to ensure commercial competitiveness. Summary of the invention

[0005] The present invention is based on the above background technology and aims to provide a self-assembled molecular layer, an alkali metal ion battery positive electrode modification method and applications thereof.

[0006] The invention provides a self-assembled molecular layer, which has the following characteristics: it is formed by self-assembly, adsorption and regular arrangement of monomer molecules on the surface of the positive electrode material of an alkali metal ion battery, wherein the monomer molecules include: an anchoring group, which spontaneously adsorbs and bonds with a transition metal or a surface group thereof in the positive electrode material of the alkali metal ion battery, wherein 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, and includes any one or more of an alkyl group, a halogenated alkyl group, an alkenyl group, a halogenated alkenyl group, an alkynyl group, a halogenated alkynyl group, a nitro group, a cyano group, a sulfonyl fluoride group, an aryl group, a halogenated aryl group or a carboxyl group, wherein in the alkali metal ion battery, when the monomer molecules are adsorbed on the surface of the positive electrode material, the terminal group faces the electrolyte of the alkali metal ion battery.

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

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

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

[0010] The self-assembled molecular layer provided by the present invention may also have the following characteristics: 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.

[0011] The present invention also provides a method for modifying the positive electrode of an alkali metal ion battery, which has the following characteristics, using any of the aforementioned self-assembled molecular layers and their corresponding monomer molecules, and includes the following steps: S10, placing the positive electrode material of the alkali metal ion battery in a solution of monomer molecules and soaking it for a period of time, so that the monomer molecules are self-assembled and adsorbed on the surface of the positive electrode material and arranged regularly to form a self-assembled molecular layer; S20, taking out the positive electrode material treated in step S10, washing and drying it to complete the modification of the positive electrode material.

[0012] In the alkali metal ion battery positive electrode modification method provided by the present invention, it can also have the following characteristics: wherein, 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 alkali metal ion battery positive electrode modification method provided by the present invention may also have the following characteristics: wherein, in step S10, the corresponding monomer molecule concentration in the monomer molecule solution is 0.5 mmol / L to 10 mmol / L, and the immersion time is 2 h to 24 h.

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

[0015] Functions and Effects of the Invention

[0016] The self-assembled molecular layer provided in the present invention has a structure of organic monomer molecules that is diverse and designable, and thus this feature can be fully utilized to design surface properties, thereby specifically regulating the interface according to the characteristics of the positive electrode and the battery system.

[0017] The self-assembled molecular layer provided by the present invention is used to modify the positive electrode of the alkali metal ion battery, which can effectively improve the interface stability between the positive electrode and the electrolyte, construct a stable passivating positive electrode-electrolyte intermediate phase, alleviate the structural and interface degradation related to the interface side reaction, and effectively improve the battery's cycle stability, capacity retention rate and energy efficiency maintenance ability.

[0018] The self-assembled molecular layer and the method for modifying the positive electrode material of an alkali metal ion battery using the self-assembled molecular layer provided by the present invention can realize a uniform modified layer with molecular-level thickness, while the cost of the materials involved is controllable, the process is simple and efficient, and has the potential for large-scale application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 TEM images and SS energy spectrum images of active material particles in the NCM811 pole piece before modification and the NCM811 pole piece after modification (sample 1) in Example 3 of the present invention;

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

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

[0022] Figure 4 It is NCM811||SiO in Example 3 of the present invention. x Comparison of the cycling performance of Battery 3 and Battery 4 of / C soft-pack full battery. DETAILED DESCRIPTION

[0023] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the following embodiments and drawings specifically describe a self-assembled molecular layer, an alkali metal ion battery positive electrode modification method and its application of the present invention.

[0024] <Example 1>

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

[0026] The monomer molecule includes an anchor group and a terminal group. 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 group in the positive electrode 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.

[0028] The terminal group is directly connected to the anchoring group, including any one or more of an alkyl group, a halogenated alkyl group, an alkenyl group, a halogenated alkenyl group, an alkynyl group, a halogenated alkynyl group, a nitro group, a cyano group, a sulfonyl fluoride group, an aryl group, a halogenated aryl group or a carboxyl group. In an alkali metal ion battery, 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 self-assembly, adsorption and regular arrangement of monomer molecules on the surface of the positive electrode material of the alkali metal ion battery.

[0031] The monomer molecule includes an anchor group, an intermediate group and a terminal group. 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.

[0032] The anchoring group spontaneously adsorbs and bonds with the transition metal or its surface group in the positive electrode 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.

[0033] The intermediate group is connected between the anchor group and the terminal group and serves as the skeleton of the monomer molecule. The intermediate group includes a saturated hydrocarbon group and / or an unsaturated hydrocarbon group. The saturated hydrocarbon group includes an alkyl group, a cycloalkyl group, a halogenated alkyl group or a halogenated cycloalkyl group; the unsaturated hydrocarbon group includes an alkenyl group, a halogenated alkenyl group, an aryl group or a halogenated aryl group.

[0034] The terminal group is connected to the intermediate group, including any one or more of an alkyl group, a halogenated alkyl group, an alkenyl group, a halogenated alkenyl group, an alkynyl group, a halogenated alkynyl group, a nitro group, a cyano group, a sulfonyl fluoride group, an aryl group, a halogenated aryl group or a carboxyl group. In an alkali metal ion battery, 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 positive electrode of an alkali metal ion battery, using the self-assembled molecular layer and the corresponding monomer molecules in Embodiment 1 and / or Embodiment 2, comprising the following steps:

[0037] S10, soaking the positive electrode material of the alkali metal ion battery in a 0.5 mmol / L to 10 mmol / L monomer molecule solution for 6 hours, so that the monomer molecules are self-assembled and adsorbed on the surface of the positive electrode material and arranged regularly to form a self-assembled molecular layer.

[0038] In alkali metal ion batteries: (1) When the monomer molecule is composed of an anchor group and a terminal group connected to each other, the anchor group spontaneously adsorbs to the transition metal or its surface group in the positive electrode material, and the terminal group serves as the skeleton of the monomer molecule and faces the electrolyte of the alkali metal ion battery. (2) When the monomer molecule is composed of an anchor group, an intermediate group and a terminal group connected in sequence, the anchor group spontaneously adsorbs to the transition metal or its surface group in the positive electrode material, and the intermediate group connects the anchor group to the terminal group and serves as the skeleton of the monomer molecule, and the terminal group faces the electrolyte of the alkali metal ion battery.

[0039] S20, taking out the positive electrode material treated in step S10, washing and drying it to complete the modification of the positive electrode material, and then placing it in an inert atmosphere or a dry environment for standby use.

[0040] Specifically, this embodiment controls the experimental parameters in the alkali metal ion battery positive electrode modification method to prepare 14 different modified positive electrodes, which are respectively recorded 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 the above Table 1, 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-benzenedicarboxylic 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 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 for LiNi 0.6 Co 0.2 Mn 0.2 O2.

[0046] Figure 1 These are the transmission electron microscope images and SS energy spectrum images of the active material particles in the NCM811 pole piece before modification and the NCM811 pole piece after modification (sample 1) in Example 3 of the present invention.

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

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

[0049] like Figure 2As shown, the intensity of the characteristic groups from FPSH decreases rapidly as the bombardment proceeds, 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 surface of NCM811.

[0050] This embodiment also provides an application of a positive electrode modification method for an alkali metal ion battery in an alkali metal ion battery.

[0051] The alkali metal ion battery comprises a battery 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 by 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 are assembled, which are respectively recorded 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 positive electrodes of these 20 alkali metal ion batteries are common positive electrode materials or the modified positive electrode 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 1 is a comparison of the cycle performances of Battery 1 and Battery 2 of the NCM811||Li button half-cell in Example 3 of the present invention.

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

[0059] Figure 4 It is NCM811||SiO in Example 3 of the present invention. x Comparison of the cycling performance of Battery 3 and Battery 4 of / C soft-pack full battery.

[0060] As shown in Table 2 and Figure 4As shown, NCM811||SiO with an N / P ratio of 1.12 x The cycle performance of the / C soft-pack full battery was tested at a charge cut-off voltage of 4.25V and 4.45V, and the current density during the cycle was 1C rate. Figure 4 It can be seen that the capacity retention rate and discharge voltage maintenance ability of the NCM811 positive electrode modified with the self-assembled molecular layer (battery 3) at two cut-off voltages are significantly better than those of the control sample using unmodified NCM811 (battery 4).

[0061] In the above Table 2, the test conditions of the Li||LCO button cells of cells 5 to 10 are: 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 up to 200 cycles.

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

[0063] In the above Table 2, the test conditions of the Li||NCM90 button batteries of batteries 11 to 17 are: 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 up to 100 cycles.

[0064] As shown in the specific materials, parameters and battery performance data of batteries 11 to 17 in Table 2, when using NCM90 modified with a self-assembled molecular layer constructed with BuDA, BeDA, SPA or NBSF as the positive electrode, the Li||NCM90 button batteries all have a significantly higher cycle capacity retention rate than the control sample (battery 17) using unmodified NCM90.

[0065] In the above Table 2, the test conditions of the Li||NCM622 button batteries of batteries 18 to 20 are: 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 up to 200 cycles.

[0066] As shown in the specific materials, parameters and battery performance data of batteries 18 to 20 in Table 2, when NCM622 modified with a self-assembled molecular layer constructed by FOMS or FBPMS is used as the positive electrode, the Li||NCM622 button batteries 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 the groups of each part of the monomer molecule, the self-assembled molecular layer modification strategy provided in this embodiment can be used to modify the positive electrodes of various alkali metal ion batteries, and its performance is significantly better than that of batteries using unmodified positive electrodes.

[0068] Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A self-assembled molecular layer, characterized in that: It is formed by self-assembly of monomer molecules adsorbed and regularly arranged on the surface of the positive electrode material of the alkali metal ion battery, and the monomer molecules include: An anchoring group that spontaneously adsorbs and bonds with a transition metal or a surface group thereof in a positive electrode material of an alkali metal ion battery, wherein 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 The terminal group is directly or indirectly connected to the anchor group, including any one or more of an alkyl group, a haloalkyl group, an alkenyl group, a haloalkenyl group, an alkynyl group, a haloalkynyl group, a nitro group, a cyano group, a sulfonyl fluoride group, an aryl group, a haloaryl group or a carboxyl group, In the alkali metal ion battery, 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.

2. The self-assembled molecular layer according to claim 1, characterized in that: in, The monomer molecule also includes an intermediate group, The intermediate group is connected between the anchor group and the terminal group and serves as the skeleton of the monomer molecule. The intermediate group includes a saturated hydrocarbon group and / or an unsaturated hydrocarbon group.

3. The self-assembled molecular layer according to claim 2, characterized in that: in, The saturated hydrocarbon group includes an alkyl group, a cycloalkyl group, a halogenated alkyl group or a halogenated cycloalkyl group.

4. The self-assembled molecular layer according to claim 2, characterized in that: in, The unsaturated hydrocarbon group includes an alkenyl group, a halogenated alkenyl group, an aryl group or a halogenated aryl group.

5. The self-assembled molecular layer according to any one of claims 1 to 4, characterized in that: in, The total number of atoms excluding 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.

6. A method for modifying the positive electrode of an alkali metal ion battery, characterized in that: The self-assembled molecular layer according to any one of claims 1 to 5 and the corresponding monomer molecules thereof are used, comprising the following steps: S10, placing the positive electrode material of the alkali metal ion battery in the solution of the monomer molecules and soaking it for a period of time, so that the monomer molecules are self-assembled, adsorbed and regularly arranged on the surface of the positive electrode material to form the self-assembled molecular layer; S20, taking out the positive electrode material processed in step S10, washing and drying it to complete the modification of the positive electrode material.

7. The method for modifying the positive electrode of an alkali metal ion battery according to claim 6, characterized in that: in, 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.

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

9. Application of a method for modifying a positive electrode of an alkali metal ion battery in an alkali metal ion battery, characterized in that: in, The alkali metal ion battery comprises a battery negative electrode, a separator, an electrolyte and a modified positive electrode. The modified positive electrode is obtained by modifying the positive electrode material of an alkali metal ion battery through the alkali metal ion battery positive electrode modification method according to any one of claims 6 to 8.

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