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, R2 is selected from H, halogen, C1-3 alkyl and C1-3 alkoxy, n is 3 or 4, and m + n = 5. 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 450mAh / g or above, the lithium removal voltage is lower than 4.5 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 4.5 mAh / g at most.

Description

Technical Field

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

[0002] At present, with the rapid development of the energy field, lithium-ion batteries have become a key part in many important fields such as electric vehicles, consumer electronics, and large-scale energy storage due to their excellent performance and are widely used. However, as people's requirements for the performance of lithium-ion batteries continue to increase, problems such as capacity attenuation and limited cycle life have become increasingly prominent, becoming bottlenecks that urgently need to be broken through for their further development.

[0003] To overcome these problems, pre-lithiation technology has emerged, mainly divided into two ways: negative electrode lithium supplementation and positive electrode lithium supplementation. Multiple means are adopted for negative electrode lithium supplementation, such as physical lithium supplementation methods using lithium powder and lithium metal, chemical lithium supplementation methods using n-butyl lithium, and electrochemical lithium supplementation methods such as in-situ electrochemical lithium supplementation and non-in-situ electrochemical lithium supplementation. However, these methods all have serious drawbacks: lithium powder and lithium metal have too high chemical activity, bringing great safety risks; n-butyl lithium is highly toxic, harming the environment and human health; electrochemical lithium supplementation is not only complex in operation but also extremely costly, and these factors severely limit the large-scale application of negative electrode lithium supplementation technology.

[0004] In contrast, positive electrode lithium supplementation has obvious advantages. It usually adds a small amount of lithium supplement during the homogenization process of preparing the positive electrode sheet. During charging, lithium ions will be released from the high-capacity material to supplement the irreversible capacity loss during the first charge and discharge. Currently, common positive electrode lithium supplementation methods use materials such as 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 and Li 2 O), etc. However, they all have their own defects. For example, lithium-rich compounds such as Li 2 NiO 2 are prone to decomposition and have poor stability in air; although Li 5 FeO 4 has a high theoretical specific capacity, solid residues will remain after lithium supplementation, reducing the energy density of the battery. Although the lithium supplementation effect of binary lithium compounds is good, there are problems of gas generation, which will not only cause capacity attenuation but also pose safety hazards, and some de-lithiation potentials are too high, resulting in serious decomposition of the electrolyte.

[0005] In this context, organic lithium supplements have gradually come into the view of researchers and received attention. Organic lithium supplements have unique advantages. Their molecular structures are highly adjustable, and by designing specific functional groups and chemical bonds, the lithium supplementation performance can be precisely regulated. For example, some organic lithium supplements with specific structures can release lithium ions under relatively mild conditions, effectively reducing the risk brought by overly violent reactions. From the perspective of cost, the raw materials of organic lithium supplements are relatively easy to obtain, and the synthesis process is also relatively simple, which helps to reduce production costs. In addition, organic lithium supplements have good compatibility with existing battery manufacturing processes, can be well incorporated into the cathode material and electrolyte, and improve the overall performance and stability of the battery. However, there is still room for improvement in the specific capacity, conductivity, and chemical stability of organic lithium supplements, and further in-depth research and optimization are needed.

[0006] Patent CN109616629A discloses an organic lithium supplement. In the examples, only the lithium supplement containing nitro groups was studied, and the first charge-discharge efficiency of the battery was tested, while key indicators such as the specific capacity of the organic lithium supplement and the degree of improvement of the battery performance were not mentioned.

[0007] Although there are still some deficiencies in organic lithium supplements at present, their unique advantages and great potential cannot be ignored. In the future field of lithium-ion batteries, organic lithium supplements are expected to become an important development direction. Through continuous research and innovation to solve existing problems, organic lithium supplements are very likely to bring new breakthroughs to the improvement of lithium-ion battery performance and promote lithium-ion battery technology to a new height. Summary of the Invention

[0008] The purpose of the present invention is to solve at least one of the following technical problems existing in the existing organic lithium supplementation:

[0009] (1) The specific capacity is generally not high, less than 400 mAh / g;

[0010] (2) Poor air stability, easy to decompose in air;

[0011] (3) Continuous gas production during use, which is likely to cause battery safety hazards;

[0012] (4) High de-lithiation potential, for example, the de-lithiation voltage of conventional organic lithium supplement lithium oxalate is 4.7 V;

[0013] (5) When applied in batteries, the cycle performance and capacity density of the batteries are insufficient.

[0014] To this end, the present application provides an organic lithium supplement with a specific capacity higher than 450 mAh / g and a de-lithiation voltage lower than 4.5 V. Specifically, the organic lithium supplement provided by the present application has the following structure:

[0015] Among them, R1 Selected from -NH-Li or -S-Li, R 2 Selected from H, halogen, C 1～3 alkyl, C 1～3 alkoxy, n is 3 or 4, m + n = 5.

[0016] Preferably, n = 3. Excessive lithium hydroxide groups on the benzene ring will cause serious 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. Moreover, 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, thus reducing the rate performance and the actual available delithiated capacity of the battery.

[0017] Preferably, R 2 Selected from H, C 1～3 alkyl, C 1～3 alkoxy.

[0018] Compared with halogen, alkyl and alkoxy 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 delithiation process, lithium ions are more likely to be removed from lithium hydroxide, thus reducing the delithiation potential. While halogen atoms have a relatively large electronegativity and an electron-withdrawing inductive effect, which will reduce the electron cloud density on the benzene ring.

[0019] 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 hindering effect on the diffusion of lithium ions, making it impossible for lithium ions to be completely removed, reducing the delithiated capacity and increasing the delithiation 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.

[0020] Preferably, m is 2. When m = 2 and n = 3, the steric hindrance caused by excessive lithium hydroxide can be avoided.

[0021] In the specific embodiments of the present application, the organic lithium supplementing agent has at least one of the following structures:

[0022]

[0023]

[0024] In a second aspect, the organic lithium supplement agent can be prepared by the following method, the specific steps comprising:

[0025] 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:

[0026] Where R' 1 Selected from -NH 2 or -SH, R 2 Selected from H, halogen, C 1～3 Alkyl, C 1～3 Alkoxy, n is 3 or 4, m+n=5.

[0027] 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.

[0028] Wherein, the precursor is selected according to the pre-synthesized organic lithium supplement agent, for example:

[0029]

[0030] wait.

[0031] Wherein, the organic solvent is at least one of methanol, ethanol, tetrahydrofuran and N,N-dimethylformamide.

[0032] 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.

[0033] 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.

[0034] 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 lithium desorption 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 degree of irreversible lithium desorption 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.

[0035] In a fourth aspect, the present application provides a positive electrode material for a lithium battery, the positive electrode material comprising: the above-mentioned organic lithium supplement, a positive electrode active material, a conductive agent and a binder.

[0036] In a specific embodiment of the present application, in the positive electrode 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%.

[0037] In a specific embodiment of the present application, the positive electrode active material can be selected from the commonly used lithium positive electrode 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.

[0038] In a specific embodiment of the present application, the conductive agent can be selected from the commonly used 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.

[0039] Preferably, in the positive electrode material, the mass content of the conductive agent is 5-10%.

[0040] In a specific embodiment of the present application, the binder can be selected from the commonly used 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.

[0041] Preferably, in the positive electrode material, the mass content of the binder is 5-10%.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] (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.

[0044] (2) The organic lithium supplement provided by the present application has a high specific capacity while having a low lithium deintercalation voltage. The specific capacity of the lithium supplement in this application is above 450 mAh / g, and the lithium deintercalation voltage is lower than 4.5 V, which can increase the energy density of the lithium battery by up to 4.5 mAh / g.

[0045] (3) The organic lithium supplement provided by the present application has a simple synthesis process, a high reaction yield, is not easily decomposed after being placed in the air for 1 month, and has stable performance; and the product after lithium deintercalation of the organic lithium supplement is soluble in the electrolyte and will not affect the positive electrode active material.

[0046] (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

[0047] Figure 1 This is a scanning electron microscope image of the organic lithium supplement agent in Example 1;

[0048] Figure 2 This is a test diagram of the electrical properties of the organic lithium supplement in Example 1;

[0049] Figure 3 is the hydrogen nuclear magnetic resonance spectrum of the organic lithium supplement agent in Example 1;

[0050] Figure 4 This is a test diagram of the electrical properties of the organic lithium supplement in Comparative Example 1. DETAILED DESCRIPTION

[0051] 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.

[0052] 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.

[0053] 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.

[0054] In this application, when the name of a compound is inconsistent with the corresponding structural formula, the structural formula shall prevail.

[0055] The present invention is further described in detail below through specific embodiments.

[0056] Example 1

[0057] Synthesis of organic lithium supplement: Weigh lithium hydroxide and the precursor of formula I in a molar ratio of 4:1 and disperse them in 60 mL of ethanol respectively. Mix the two substances evenly and stir 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.

[0058] Figure 1 It is the scanning electron microscope image of the organic lithium supplement in Example 1.

[0059] Figure 2 It is the electrical property test chart of the organic lithium supplement in Example 1. It can be seen from the figure that the specific capacity of this lithium supplement is 511 mAh / g and the average de-lithiation voltage is 4.1 V.

[0060] Figure 3 It is the nuclear magnetic resonance hydrogen spectrum of the organic lithium supplement in Example 1.

[0061] The synthesis of the organic lithium supplement in the remaining examples refers to Example 1.

[0062] 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.

[0063] (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 coat the slurry evenly 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 coin cell half-cell. Correctly install the coin 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 discharging to 2.0 V at a discharging current of 0.1 C, and record the charging specific capacity.

[0064] (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 coat the slurry evenly 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 coin cell half-cell, and perform the test using a coin cell test system. Read the average de-lithiation voltage on the test software.

[0065] (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.

[0066] Table 1: Performance test results of the organic lithium supplement

[0067]

[0068]

[0069]

[0070] As can be seen from Table 1, the specific capacity of the organic lithium supplement provided by this application is above 450 mAh / g, and the de-lithiation voltage is below 4.5 V. Compared with the organic lithium supplements in the prior art, both the specific capacity and de-lithiation voltage performance have been improved; and the organic lithium supplement provided by this application has good stability and no secondary gas generation, while in the comparative example, due to the instability of amino and mercapto groups, the stability of the lithium supplement is poor.

[0071] Preparation of the battery

[0072] Mix LiFePO 4 , the organic lithium supplements in the above-mentioned examples and comparative examples, SP, and PVDF evenly in a mass ratio of 88:5:3:4, and then obtain the positive electrode sheet through slurry mixing, coating, drying, and rolling. Mix artificial graphite, SP, sodium carboxymethyl cellulose CMC, and styrene-butadiene rubber SBR evenly in a mass ratio of 94.4:2:2:1.6, and then obtain the negative electrode sheet through slurry mixing, 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 test, and cycle performance improvement test 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 battery 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 energy density of the lithium battery by up to 4.5 mAh / g at most, and the cycling performance can be increased by up to 200% 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 solution 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, in the various specific technical features described in the above specific embodiments, they can be combined in any suitable way 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, R2 is selected from H, halogen, C 1～3 Alkyl, C 1～3 Alkoxy, n is 3 or 4, m+n=5.

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, wherein the precursor has the following structure: wherein R'1 is selected from -NH2 or -SH, R2 is selected from H, halogen, C 1～3 Alkyl, C 1～3 Alkoxy, n is 3 or 4, m+n=5.

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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