Organic lithium supplement agent, preparation method thereof and application of organic lithium supplement agent in positive electrode material

Abstract

The invention provides an organic lithium supplement agent, which has the following structure: # imgabs0 #, in which R1 is selected from-NH-Li or-S-Li, and p is 2 or 3; r2 is selected from H, halogen, C1-3 alkyl and C1-3 alkoxy, n is 3 or 4, and m + n + p = 6. The organic lithium supplement agent provided by the invention has high specific capacity and low lithium removal voltage, the specific capacity of the organic lithium supplement agent is 480mAh / g or above, the lithium removal voltage is lower than 4.7 V, the organic lithium supplement agent is obviously superior to a conventional organic lithium supplement agent, and after the organic lithium supplement agent is applied to a battery, the energy density of the lithium battery can be increased by 4.55 mAh / g at most.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly to an organic lithium supplement and its preparation method and application in cathode materials. Background Art

[0002] In the context of the booming development of the current energy industry, lithium-ion batteries have become the core technology in fields such as electric vehicles, consumer electronics, and large-scale energy storage due to their excellent energy density, efficient charge and discharge performance, and long service life. However, with the continuous expansion of market demand, the requirements for battery performance have become increasingly stringent, especially problems such as capacity attenuation and short cycle life have become increasingly prominent, seriously restricting their further development. Therefore, exploring and optimizing advanced lithium supplementation technologies to improve battery performance has become the focus of attention in the academic and industrial circles.

[0003] In response to this challenge, pre-lithiation technology has emerged, mainly divided into two strategies: negative electrode lithium supplementation and positive electrode lithium supplementation. The methods of negative electrode lithium supplementation are relatively diverse, and common solutions include physical lithium supplementation (using lithium powder or lithium metal), chemical lithium supplementation (such as n-butyllithium), and electrochemical lithium supplementation (including in-situ and non-in-situ electrochemical lithium supplementation). However, these methods all have significant drawbacks. For example, lithium powder and lithium metal have safety hazards due to their high activity, the toxicity of n-butyllithium may harm the environment and human health, and electrochemical lithium supplementation is difficult to apply on a large scale due to its complex process and high cost.

[0004] In contrast, the positive electrode lithium supplementation strategy has received extensive attention due to its simple operation and high safety. Generally, this method compensates for the irreversible capacity loss during the first charge and discharge process by adding a small amount of lithium supplement during the homogenization process of the positive electrode sheet, so that lithium ions are precipitated from high-capacity materials during battery charging. Currently, the mainly studied positive electrode lithium supplement materials mainly include lithium-rich compounds (such as Li 2 NiO 2 , Li 5 FeO 4 ) and binary lithium compounds (such as Li 3 N, Li 2 O 2 , Li 2 O), but these materials still have certain limitations. For example, Li 2 NiO 2 has poor stability in air and is prone to decomposition; Li 5 FeO 4Although it has a high theoretical specific capacity, solids may remain after lithium supplementation, affecting the energy density. Binary lithium compounds, although having a high lithium supplementation efficiency, may cause problems with by-product gases, which not only affect the battery life but also pose safety hazards. In addition, some binary lithium compounds have a high de-lithiation potential, which may accelerate the decomposition of the electrolyte and further reduce the battery stability.

[0005] Under this background, organic lithium supplements have gradually gained the favor of researchers due to their superior adjustable molecular structure, low synthesis cost, and good system compatibility. Their core advantage lies in that by regulating functional groups and chemical bonds, precise release of lithium ions can be achieved, and the lithium supplementation process can be completed under relatively mild conditions, thereby reducing safety risks. Patent CN109616629A discloses an organic lithium supplement containing nitro groups and tests its effect on the first charge-discharge efficiency of the battery, but does not conduct in-depth research on the optimization of specific capacity and long-term performance, and further exploration is still needed.

[0006] Although the current organic lithium supplements are still in the development stage, their unique application potential cannot be ignored. In the future, by continuously optimizing the molecular structure and lithium supplementation mechanism, this technology is expected to drive lithium-ion batteries to a higher performance level and provide a new breakthrough for the development of next-generation energy storage technologies. Summary of the Invention

[0007] The purpose of the present invention is to solve at least one of the following technical problems existing in the existing organic lithium supplementation:

[0008] (1) The specific capacity is generally not high, less than 400 mAh / g;

[0009] (2) Poor air stability, easy to decompose in air;

[0010] (3) Continuous gas production during use, easily causing battery safety hazards;

[0011] (4) High de-lithiation potential, for example, the de-lithiation voltage of the conventional organic lithium supplement lithium oxalate is 4.7 V;

[0012] (5) When applied in a battery, the cycle performance and capacity density of the battery are insufficient.

[0013] To this end, the present application provides an organic lithium supplement with a specific capacity higher than 480 mAh / g and a de-lithiation voltage lower than 4.7 V. Specifically, the organic lithium supplement provided by the present application has the following structure:

[0014] Wherein, R 1 is selected from -NH-Li or -S-Li, and p is 2 or 3; R 2 is selected from H, halogen, C 1～3 alkyl, C 1～3An alkoxy group, n is 3 or 4, and m + n + p = 6.

[0015] Preferably, p = 2. Excessive lithium amide or lithium mercaptan on the benzene ring will cause severe steric hindrance. During the insertion and extraction of lithium ions, this steric hindrance will block the diffusion channels of lithium ions.

[0016] Preferably, R 2 is selected from H, C 1～3 alkyl, C 1～3 alkoxy group.

[0017] Compared with halogen, alkyl and alkoxy groups are electron-donating groups, which will increase the electron cloud density on the benzene ring, and then relatively increase the electron cloud density of lithium hydroxide connected to the benzene ring. After the electron cloud density increases, the binding force between lithium ions and oxygen atoms will weaken. During the de-lithiation process, lithium ions are more likely to be removed from lithium hydroxide, thereby reducing the de-lithiation potential. Halogen atoms have a relatively large electronegativity and an electron-withdrawing inductive effect, which will reduce the electron cloud density on the benzene ring.

[0018] Furthermore, if the vacant positions on the benzene ring are substituted, the substituents will occupy a certain space on the benzene ring, which will have a certain hindrance effect on the diffusion of lithium ions, making it impossible for lithium ions to be completely removed, reducing the de-lithiation capacity and increasing the de-lithiation voltage. Secondly, after the vacant positions on the benzene ring are substituted, the relative molecular mass of the structure increases. Even if lithium ions are completely inserted and extracted, its specific capacity will be lower than that without substitution. Therefore, R 2 is preferably H.

[0019] Preferably, n = 3. Excessive lithium hydroxide on the benzene ring will cause severe steric hindrance. Each lithium hydroxide group occupies a certain space, and they form a crowded structure around the benzene ring. During the insertion and extraction of lithium ions, this steric hindrance will block the diffusion channels of lithium ions, making it difficult for lithium ions to diffuse from the inside of the material to the surface or from the surface to the electrolyte. And excessive lithium hydroxide will increase the intermolecular force, and the crystallinity of the material may increase, resulting in a longer and more tortuous diffusion path of lithium ions in the material, increasing the resistance to lithium ion diffusion, which is not conducive to the rapid insertion and extraction of lithium ions during charge and discharge, thereby reducing the rate performance and the actual available de-lithiation capacity of the battery.

[0020] In some embodiments of the present application, p = 2, n = 3, m = 1.

[0021] In other embodiments of the present application, p = 3, n = 3, m = 0.

[0022] In other embodiments of the present application, p = 2, n = 4, m = 0.

[0023] In a specific embodiment of the present application, the organic lithium supplement has at least one of the following structures:

[0024]

[0025]

[0026] In a second aspect, the organic lithium supplement agent can be prepared by the following method, the specific steps comprising:

[0027] The precursor and the lithium source are dissolved in an organic solvent respectively, mixed and reacted, and filtered and dried after the reaction is completed to obtain the above-mentioned organic lithium supplement, wherein the precursor has the following structure:

[0028] Where R' 1 Selected from -NH 2 or -SH, p is 2 or 3; R 2 Selected from H, halogen, C 1～3 Alkyl, C 1～3 Alkoxy, n is 3 or 4, m+n+p=6.

[0029] The lithium source includes, but is not limited to, lithium carbonate, lithium bicarbonate, lithium hydroxide, metallic lithium, lithium hydride, organic Li reagents (such as tert-butyl lithium, n-butyl lithium, biphenyl lithium, naphthalene lithium), and the like.

[0030] Wherein, the precursor is selected according to the pre-synthesized organic lithium supplement agent, for example:

[0031]

[0032] wait.

[0033] Wherein, the organic solvent is at least one of methanol, ethanol, tetrahydrofuran and N,N-dimethylformamide.

[0034] Wherein, the reaction time is 6 to 24 hours; the drying is vacuum drying for 6 to 24 hours, and the drying temperature is 60 to 150°C.

[0035] In a third aspect, the present application provides an application of the above-mentioned organic lithium supplement agent in a positive electrode material of a lithium battery.

[0036] When the organic lithium supplement agent of the present application is used in the positive electrode material, due to its high specific capacity and low delithiation voltage, the energy density of the lithium battery can be increased by up to 4.5 mAh / g. In addition, the product after delithiation can be dissolved in the electrolyte and will not affect the positive electrode active material. The irreversible delithiation degree is high, and the gas produced can be discharged once during the formation process, and there will be no continuous gas production to cause battery safety problems.

[0037] Fourthly, the present application provides a cathode material for a lithium battery, which includes the above-mentioned organic lithium supplement, cathode active material, conductive agent and binder.

[0038] In a specific embodiment of the present application, in the cathode material, the mass content of the organic lithium supplement is 2-20%, preferably 2-5%. For example, the mass content of the organic lithium supplement is 2%, 5%, 6%, 8%, 10%, 12%, 14%, 15%, 18%, 20% or any value between 2-20%.

[0039] In a specific embodiment of the present application, the cathode active material can be selected from common lithium cathode materials in the art, including but not limited to lithium iron phosphate materials or carbon-coated lithium iron phosphate materials, nickel cobalt manganese lithium ternary materials or doped and coated modified nickel cobalt manganese lithium ternary materials, lithium manganese iron phosphate materials, lithium cobalt oxide materials, lithium manganese oxide materials, etc.

[0040] In a specific embodiment of the present application, the conductive agent can be selected from common conductive agents in the art, including but not limited to at least one of super conductive carbon black, Ketjen black, acetylene black, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, and graphene oxide.

[0041] Preferably, in the cathode material, the mass content of the conductive agent is 5-10%.

[0042] In a specific embodiment of the present application, the binder can be selected from common binders in the art, including but not limited to at least one of polyvinylpyrrolidone, polyvinylidene fluoride, polyethylene oxide, polytetrafluoroethylene, sodium carboxymethyl cellulose, and copolymers of styrene and butadiene.

[0043] Preferably, in the cathode material, the mass content of the binder is 5-10%.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] (1) The organic lithium supplement provided by the present application has a flaky structure. The two-dimensional planar characteristics of the flaky structure are conducive to the diffusion and transmission of substances. In the battery electrode, charged particles such as lithium ions can migrate more quickly within the plane of the flaky material, thereby improving the charging and discharging speed and efficiency of the battery;

[0046] (2) The organic lithium supplement provided by the present application has a high specific capacity and a low de-lithiation voltage. The specific capacity of the lithium supplement in the present application is above 480 mAh / g, and the de-lithiation voltage is lower than 4.7 V, which can increase the energy density of the lithium battery by up to 4.55 mAh / g;

[0047] (3) The organic lithium supplement provided by the present application has a simple synthesis process, a high reaction yield, is not easy to decompose after being placed in the air for 1 month, and has stable performance; and the product of the organic lithium supplement after lithium removal is soluble in the electrolyte and will not affect the positive electrode active material;

[0048] (4) The organic lithium supplement provided in the present application has a high degree of irreversible lithium desorption, and the gas produced can be discharged once during the formation process, and will not continue to produce gas to cause battery safety problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a scanning electron microscope image of the organic lithium supplement agent in Example 1;

[0050] Figure 2 This is a test diagram of the electrical properties of the organic lithium supplement in Example 1;

[0051] Figure 3 This is the hydrogen nuclear magnetic resonance spectrum of the organic lithium supplement agent in Example 1. DETAILED DESCRIPTION

[0052] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0053] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0054] In the description of the present invention, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0055] In this application, when the name of a compound is inconsistent with the corresponding structural formula, the structural formula shall prevail.

[0056] The present invention is further described in detail below through specific examples.

[0057] Example 1

[0058] Synthesis of the organic lithium supplement: Weigh lithium hydroxide and the precursor of Formula I with a molar ratio of 5:1 and disperse them in 60 mL of ethanol respectively. Uniformly mix and stir the two substances at a stirring speed of 500 rpm for 12 h. Filter the obtained turbid liquid by suction filtration, and vacuum-dry the filter cake at 110 °C for 12 h. After natural cooling, grind it to obtain the organic lithium supplement shown in Formula 1.

[0059] Figure 1 It is the scanning electron microscope image of the organic lithium supplement in Example 1.

[0060] Figure 2 It is the graph of the electrical performance test of the organic lithium supplement in Example 1. It can be seen from the graph that the specific capacity of this lithium supplement is 575 mAh / g and the average de-lithiation voltage is 4.57 V.

[0061] Figure 3 It is the nuclear magnetic resonance hydrogen spectrum of the organic lithium supplement in Example 1.

[0062] The synthesis of the organic lithium supplement in the remaining examples refers to Example 1.

[0063] The structures of the organic lithium supplements in the examples and comparative examples are shown in Table 1, and their specific capacities, average de-lithiation voltages and air stabilities are tested respectively.

[0064] (1) Specific capacity test: Dissolve the organic lithium supplement to be tested, PVDF and the conductive agent SP in a mass ratio of 90:5:5 in the solvent NMP, mix and stir evenly to make a slurry, then evenly coat the slurry on the positive current collector aluminum foil, and dry it to obtain a positive electrode sheet. Assemble the positive electrode sheet and the lithium sheet into a button cell half-cell. Correctly install the button cell half-cell on the fixture of the battery test system, and perform constant current charging to a voltage of 4.5 V at a charging current of 0.1 C. After standing for 15 min, perform constant current discharge to 2.0 V at a discharge current of 0.1 C, and record the charging specific capacity.

[0065] (2) Average de-lithiation voltage test: Dissolve the organic lithium supplement to be tested, PVDF and the conductive agent SP in a mass ratio of 90:5:5 in the solvent NMP, mix and stir evenly to make a slurry, then evenly coat the slurry on the positive current collector aluminum foil, and dry it to obtain a positive electrode sheet. Assemble the positive electrode sheet and the lithium sheet into a button cell half-cell, and perform the test using a button cell test system. Read the average de-lithiation voltage on the test software.

[0066] (3) Air stability test: First, mix the organic lithium supplement to be tested, PVDF, and conductive agent SP in a mass ratio of 90:5:5. Place the positive electrode material sample in a specific air environment. After 30 days of exposure, weigh the sample again, calculate the weight difference, and evaluate the air stability of the material based on the magnitude of the weight change. Then, prepare the organic lithium supplement before and after air exposure into electrode sheets and assemble them into batteries, and conduct charge and discharge tests respectively. Further judge its air stability based on the capacity change and charge-discharge efficiency.

[0067] Table 1: Performance test results of the organic lithium supplement

[0068]

[0069]

[0070] As can be seen from Table 1, the specific capacity of the organic lithium supplement provided in this application is above 480 mAh / g, and the lithium extraction voltage is below 4.7V. Compared with the organic lithium supplement in the prior art (Comparative Example 1), both the specific capacity and lithium extraction voltage performance have been improved; and the organic lithium supplement provided in this application has good stability and no secondary gas generation.

[0071] Preparation of the battery

[0072] Mix LiFePO 4 , the organic lithium supplement, SP, and PVDF in the above embodiments and comparative examples respectively in a mass ratio of 88:5:3:4, mix them evenly, and obtain the positive electrode sheet through slurry adjustment, coating, drying, and rolling. Mix artificial graphite, SP, sodium carboxymethyl cellulose CMC, and styrene-butadiene SBR respectively in a mass ratio of 94.4:2:2:1.6, mix them evenly, and obtain the negative electrode sheet through slurry adjustment, coating, drying, and rolling. Assemble the positive and negative electrode sheets to obtain a lithium-ion battery, and realize lithium supplementation of the negative electrode material in the first charge-discharge cycle. Then, conduct gas generation amount test, capacity density improvement, and cycle performance improvement tests on the battery, and the results are shown in Table 2 below.

[0073] (4) Battery gas generation amount test: a. Conduct charge and discharge tests on the soft-pack battery after the first formation, and collect the generated gas into a gas collection bag through a pipeline; b. Inject the collected gas into a gas chromatograph for analysis to obtain the composition and content of the gas; c. Calculate the gas generation amount of the soft-pack battery based on the composition and content of the gas and the volume of the container.

[0074] (5) Cycling performance test: After the lithium-ion battery is formed, in an environment of 25 °C, after discharging, it is charged and discharged once. At a charging current of 1C, it is constantly charged at a constant current until the voltage reaches 3.65V, and then at a constant voltage of 3.65V, the charging cut-off current is 0.05C. After standing for 15 minutes, it is constantly discharged at a discharging current of 1C until 2.0V. Record the discharging capacity of the first cycle as C1; then perform 1000 charging and discharging cycles, record the discharging capacity C1000 of the 1000th cycle, and C1000 / C1×100% is recorded as the discharging capacity retention rate of the cell for 1000 cycles.

[0075] (6) Battery capacity density improvement test: Referring to the above battery preparation method, the difference is that no organic lithium supplement agent is added. After the battery is formed, in an environment of 25 °C, after discharging, it is charged and discharged once. At a charging current of 1C, it is constantly charged at a constant current until the voltage reaches 3.65V, and then at a constant voltage of 3.65V, the charging cut-off current is 0.05C. After standing for 15 minutes, it is constantly discharged at a discharging current of 1C until 2.0V. Record the discharging capacity of the first cycle as C2, and record the discharging capacity of the first cycle in the cycling performance test as C1. The capacity density improvement amount ΔV = C1 - C2.

[0076] Table 2: Influence of organic lithium supplement agent on battery performance

[0077]

[0078]

[0079] As can be seen from Table 2, compared with not adding a lithium supplement agent, the organic lithium supplement agent provided by the present application can increase the capacity density of the lithium battery by up to 4.55 mAh / g at most, and the cycling performance can be increased by up to 210% at most, which is significantly better than the comparative example.

[0080] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0081] In addition, it should be noted that, among the various specific technical features described in the above specific embodiments, they can be combined in any appropriate manner without conflict. In order to avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0082] In addition, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, it should also be regarded as the content disclosed by the present invention.

Claims

1. An organic lithium supplement, characterized in that: It has the following structure: wherein R1 is selected from -NH-Li or -S-Li, and p is 2 or 3; R2 is selected from H, halogen, C 1～3 Alkyl, C 1～3 Alkoxy, n is 3 or 4, m+n+p=6.

2. A method for preparing the organic lithium supplement agent according to claim 1, characterized in that: include: The precursor and the lithium source are dissolved in an organic solvent respectively, mixed and reacted, and filtered and dried after the reaction is completed to obtain the organic lithium supplement agent, wherein the precursor has the following structure: Wherein R'1 is selected from -NH2 or -SH, and p is 2 or 3; R2 is selected from H, halogen, C 1～3 Alkyl, C 1～3 Alkoxy, n is 3 or 4, m+n+p=6.

3. The preparation method according to claim 2, characterized in that: The lithium source is at least one of lithium carbonate, lithium bicarbonate, lithium hydroxide, metallic lithium, lithium hydride, tert-butyl lithium, n-butyl lithium, biphenyl lithium, and naphthalene lithium.

4. The preparation method according to claim 2, characterized in that: The organic solvent is at least one of methanol, ethanol, tetrahydrofuran and N,N-dimethylformamide.

5. Use of the organic lithium supplement agent according to claim 1 or the organic lithium supplement agent obtained by the preparation method according to any one of claims 2 to 4 in positive electrode materials for lithium batteries.

6. A positive electrode material for a lithium battery, comprising an organic lithium supplement, a positive electrode active material, a conductive agent and a binder, characterized in that: The organic lithium supplement is the organic lithium supplement according to claim 1 or the organic lithium supplement obtained by the preparation method according to any one of claims 2 to 4.

7. The positive electrode material according to claim 6, characterized in that In the positive electrode material, the mass content of the organic lithium supplement is 2-20%.

8. The positive electrode material according to claim 6, characterized in that In the positive electrode material, the positive electrode active material is at least one of lithium iron phosphate material or carbon-coated lithium iron phosphate material, nickel cobalt lithium manganese oxide ternary material or doped coated modified nickel cobalt lithium manganese oxide ternary material, lithium manganese iron phosphate material, lithium cobalt oxide material, and lithium manganese oxide material.

9. The positive electrode material according to claim 6, characterized in that In the positive electrode material, the conductive agent is at least one of super conductive carbon black, Ketjen black, acetylene black, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, and graphene oxide.

10. The positive electrode material according to claim 6, characterized in that In the positive electrode material, the binder is at least one of polyvinyl pyrrolidone, polyvinylidene fluoride, polyethylene oxide, polytetrafluoroethylene, sodium carboxymethyl cellulose, and a copolymer of styrene and butadiene.

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