An organic lithium supplementing agent, a preparation method thereof and application thereof in a positive electrode material

Abstract

The application provides an organic lithium supplementing agent, which has the following structure: wherein R1 is selected from -COOLi, -O-COOLi, -NH-COOLi, -C=C-Li, p is 2 or 3, R2 is selected from H, halogen, C 1～3 alkyl, C 1～3 alkoxy, n is 3 or 4, and m+n+p=6. The organic lithium supplementing agent provided by the application has high specific capacity and low delithiation voltage, the specific capacity is higher than 450 mAh / g, and the delithiation voltage is lower than 4.7 V, which is obviously superior to conventional organic lithium supplementing agents. When the organic lithium supplementing agent is applied to a battery, the energy density of the lithium battery can be increased by 4 mAh / g.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to an organic lithium supplementing agent, a preparation method thereof and application thereof in a positive electrode material. BACKGROUND

[0002] In the current wave of rapid development in the field of energy, lithium ion batteries have become an indispensable key element due to their excellent performance, and are widely used in electric vehicles, consumer electronics and large-scale energy storage and many other important fields. However, with the continuous improvement of the performance requirements of lithium ion batteries, the problems of capacity attenuation and limited cycle life have become increasingly prominent, becoming a bottleneck that needs to be broken through.

[0003] To overcome these difficulties, pre-lithiation technology has emerged, mainly including negative electrode lithium supplementing and positive electrode lithium supplementing. Negative electrode lithium supplementing uses various means, such as physical lithium supplementing (lithium powder, lithium metal), chemical lithium supplementing (n-butyl lithium) and electrochemical lithium supplementing (in-situ electrochemical lithium supplementing and non-in-situ electrochemical lithium supplementing). However, these methods have many serious drawbacks, such as the high chemical activity of lithium powder and lithium metal, which poses a great safety risk, the strong toxicity of n-butyl lithium, which is harmful to the environment and human health, and the complex operation and high cost of electrochemical lithium supplementing, which all limit its widespread application.

[0004] In comparison, positive electrode lithium supplementing has certain advantages. It usually involves adding a small amount of positive electrode lithium supplementing agent during the slurry preparation of the positive electrode sheet, and lithium ions are released from the high-capacity material during charging to supplement the irreversible capacity loss of the first charge and discharge. The current common positive electrode lithium supplementing methods include lithium-rich compounds (such as Li2NiO2, Li5FeO4), binary lithium compounds (such as Li3N, Li2O2 and Li2O) and the like. However, these methods each have their own defects. Taking the lithium-rich compound Li2NiO2 as an example, it is prone to decomposition and has poor air stability; Li5FeO4 has a high theoretical specific capacity, but produces solid residues after lithium supplementing, reducing the energy density of the battery. Binary lithium compounds have good lithium supplementing effect, but have the problem of gas production, leading to capacity attenuation and safety hazards, and some have high delithiation potentials, which will cause severe decomposition of the electrolyte.

[0005] In this context, organic lithium supplementing agents have gradually attracted attention. Organic lithium supplementing agents have unique advantages. Their molecular structures are highly adjustable, allowing precise control of lithium supplementing performance through the design of functional groups and chemical bonds. For example, organic lithium supplementing agents with specific structures can release lithium ions under relatively mild conditions, reducing the risk of violent reactions. In terms of cost, the raw materials for organic lithium supplementing agents are relatively easy to obtain, and the synthesis process is relatively simple, which helps to reduce production costs. In addition, organic lithium supplementing agents have good compatibility with existing battery manufacturing processes and can be well integrated into positive electrode materials and electrolytes, improving the overall performance and stability of batteries. However, organic lithium supplementing agents still need to be improved in terms of specific capacity, electrical conductivity, and chemical stability, and further research and optimization are needed.

[0006] CN109616629A discloses an organic lithium supplementing agent. In the examples, only lithium supplementing agents containing nitro groups are studied, and the first charge-discharge efficiency of the battery is tested. However, the specific capacity of the organic lithium supplementing agent, the improvement range of the battery performance, and other aspects are not mentioned.

[0007] Although there are some deficiencies in organic lithium supplementing agents at present, they have unique advantages and potential and are expected to become an important development direction in the field of lithium-ion batteries in the future. Through continuous research and innovation, current problems can be solved, and new breakthroughs in lithium-ion battery performance improvement can be made, promoting the further development of lithium-ion battery technology. SUMMARY

[0008] The present application aims to solve at least one of the following technical problems of existing organic lithium supplementing agents:

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

[0010] (2) Poor air stability, easily decomposed in air;

[0011] (3) Continuous gas production during use, which can easily cause safety hazards to the battery;

[0012] (4) High delithiation potential, for example, the delithiation voltage of conventional organic lithium supplementing agent lithium oxalate is 4.7 V;

[0013] (5) When applied in batteries, the cycle performance and capacity density of the battery are not enough.

[0014] Therefore, the present application provides an organic lithium supplementing agent with a specific capacity higher than 450 mAh / g and a delithiation voltage lower than 4.7 V. Specifically, the organic lithium supplementing agent provided by the present application has the following structure:

[0015] wherein R1 is selected from -COOLi, -O-COOLi, -NH-COOLi, -C=C-Li, and p is 2 or 3; R2 is selected from H, halogen, C1～3 alkyl, C 1～3 alkoxy, n is 3 or 4, and m+n+p=6.

[0016] Preferably, R1 is selected from -COOLi, -O-COOLi, and -NH-COOLi.

[0017] Compared with -C≡C-Li, -COOLi, -O-COOLi, and -NH-COOLi are all strong electron-donating groups, and due to their electron-donating effect, the electron cloud density on the benzene ring is increased, and in turn, the electron cloud density on the lithium hydroxide (-OLi) is also increased, the binding force between the lithium ion and the oxygen atom is weakened, and the delithiation potential is reduced. However, the electron-donating abilities of the three are different, which is related to the strength of the electron-donating conjugation effect of the groups. On the other hand,

[0018] The introduction of O or N atoms in -O-COOLi and -NH-COOLi not only increases the relative molecular mass, but also increases the steric hindrance of the molecular structure. In the process of lithium deintercalation, the larger steric hindrance will hinder the diffusion and migration of lithium ions, so that the lithium ions need to overcome a larger energy barrier to be extracted from the lithium supplement agent. Therefore, R1 is preferably -COOLi.

[0019] Preferably, p=2. Too many lithium carboxylates on the benzene ring will cause serious steric hindrance, which will hinder the diffusion channel of lithium ions in the process of lithium ion deintercalation.

[0020] Preferably, R2 is selected from H, C 1～3 alkyl, C 1～3 alkoxy.

[0021] Compared with halogen, alkyl and alkoxy are electron-donating groups, which will increase the electron cloud density on the benzene ring, and in turn, the electron cloud density of the lithium hydroxide connected to the benzene ring is also relatively increased. After the electron cloud density is increased, the binding force between the lithium ion and the oxygen atom is weakened, and in the delithiation process, the lithium ion is more easily extracted from the lithium hydroxide, thereby reducing the delithiation potential. The electronegativity of halogen atom is larger, and has an electron-withdrawing inductive effect, which will reduce the electron cloud density on the benzene ring.

[0022] Further, if the vacant position on the benzene ring is substituted, the substituent will occupy a certain space on the benzene ring, which will hinder the diffusion of lithium ions, so that the lithium ions cannot be completely extracted, which will reduce the delithiation capacity and increase the delithiation voltage. Secondly, after the vacant position on the benzene ring is substituted, the relative molecular mass of the structure is increased, and even if the lithium ion is completely deintercalated, its specific capacity will also be reduced compared with the unsubstituted. Therefore, R2 is preferably H.

[0023] Preferably, n = 3. Too many hydroxyl lithium groups on the benzene ring will cause serious steric hindrance, each hydroxyl lithium group occupies a certain space, and they form a crowded structure around the benzene ring. During the lithium ion deintercalation process, this steric hindrance will hinder the diffusion channel 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 too many hydroxyl lithium groups will increase the intermolecular force, and the crystallinity of the material may be improved, which will make the diffusion path of lithium ions in the material longer and more tortuous, increase the resistance of lithium ion diffusion, and is not conducive to the rapid deintercalation of lithium ions during the charging and discharging process, thereby reducing the rate performance and actual available deintercalation capacity of the battery.

[0024] In some embodiments of the present application, p = 2, n = 3, and m = 1.

[0025] In some other embodiments of the present application, p = 3, n = 3, and m = 0.

[0026] In some other embodiments of the present application, p = 2, n = 4, and m = 0.

[0027] In specific embodiments of the present application, the organic lithium supplementing agent has at least one of the structures shown below:

[0028]

[0029]

[0030] In a second aspect, the organic lithium supplementing agent can be prepared by the following method, and the specific steps include:

[0031] The precursor and the lithium source are dissolved in an organic solvent respectively, mixed and reacted, filtered and dried after the reaction is completed, and the above-mentioned organic lithium supplementing agent is obtained. The precursor has the structure shown below:

[0032] wherein R'1 is selected from -COOH, -O-COOH, -NH-COOH, -C≡CH, p is 2 or 3; R2 is selected from H, halogen, C 1～3 alkyl, C 1～3 alkoxy, n is 3 or 4, and m + n + p = 6.

[0033] The lithium source includes but is not limited to lithium carbonate, lithium bicarbonate, lithium hydroxide, metallic lithium, lithium hydride, organic Li reagent (such as tert-butyllithium, n-butyllithium, diphenyl lithium, naphthalene lithium), etc.

[0034] The precursor is selected according to the pre-synthesized organic lithium supplementing agent, for example:

[0035]

[0036] etc.

[0037] The organic solvent is at least one of methanol, ethanol, tetrahydrofuran, and N,N-dimethylformamide.

[0038] The reaction time is 6-24 hours, and the drying is vacuum drying for 6-24 hours at a drying temperature of 60-150°C.

[0039] In a third aspect, the application provides an application of the organic lithium supplementing agent in a lithium battery cathode material.

[0040] When the organic lithium supplementing agent of the application is applied in the cathode material, the energy density of the lithium battery can be increased by 5 mAh / g due to the high specific capacity and low delithiation voltage of the organic lithium supplementing agent, and the product after delithiation is soluble in the electrolyte, does not affect the cathode active material, has high irreversible delithiation degree, and the gas generated in the formation process can be discharged at one time and will not continuously generate gas to cause battery safety problems.

[0041] In a fourth aspect, the application provides a lithium battery cathode material, which comprises the organic lithium supplementing agent, a cathode active material, a conductive agent, and a binder.

[0042] In the specific embodiment of the application, the mass content of the organic lithium supplementing agent in the cathode material is 2-20%, preferably 2-5%. For example, the mass content of the organic lithium supplementing agent is 2%, 5%, 6%, 8%, 10%, 12%, 14%, 15%, 18%, 20%, or any value between 2% and 20%.

[0043] In the specific embodiment of the application, the cathode active material can be selected from commonly used lithium cathode materials in the art, including but not limited to at least one of a lithium iron phosphate material or a carbon-coated lithium iron phosphate material, a lithium nickel cobalt manganese ternary material or a lithium nickel cobalt manganese ternary material modified by doping and coating, a lithium manganese iron phosphate material, a lithium cobaltate material, a lithium manganate material, etc.

[0044] In the specific embodiment of the application, the conductive agent can be selected from 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.

[0045] Preferably, the mass content of the conductive agent in the cathode material is 5-10%.

[0046] In specific embodiments of this application, the adhesive may be selected from adhesives commonly used 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.

[0047] Preferably, the binder content in the positive electrode material is 5-10% by mass.

[0048] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0049] (1) The organic lithium supplement provided in this application has a sheet-like structure. The two-dimensional planar characteristics of the sheet-like structure are conducive to the diffusion and transport of substances. In the battery electrode, charged particles such as lithium ions can migrate more quickly in the plane of the sheet-like material, thereby improving the charging and discharging speed and efficiency of the battery.

[0050] (2) The organic lithium supplement provided in this application contains a carboxyl group. After the -COOH is replaced by Li, the electron-withdrawing ability decreases, which is conducive to the decrease of the delithiation potential. In addition, the lithium content on the benzene ring increases, which is also conducive to the decrease of the delithiation potential.

[0051] (3) The organic lithium replenishing agent provided in this application has a high specific capacity and a low delithiation voltage. The specific capacity of the lithium replenishing agent in this application is above 450 mAh / g and the delithiation voltage is below 4.7 V, which can increase the energy density of lithium batteries by up to 4 mAh / g.

[0052] (4) The organic lithium supplement provided in this application has a simple synthesis process, high reaction yield, is not easily decomposed after being placed in the air for 1 month, and has stable performance; and the product of the organic lithium supplement after delithiation is soluble in the electrolyte and will not affect the positive electrode active material.

[0053] (5) The organic lithium replenishing agent provided in this application has a high degree of irreversible delithiation, and the gas produced can be discharged in one go during the formation process, and will not continue to produce gas to cause battery safety problems. Attached Figure Description

[0054] Figure 1 This is a scanning electron microscope image of the organic lithium supplement in Example 1;

[0055] Figure 2 The graph shows the electrical performance test results of the organic lithium supplement in Example 1.

[0056] Figure 3 The 1H NMR spectrum of the organic lithium supplement in Example 1;

[0057] Figure 4 The graph shows the electrical performance test results of the organic lithium supplement in Comparative Example 1. Detailed Implementation

[0058] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not intended to limit the present application.

[0059] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges are provided as a separate value from but are included in the range. For values which are less than or greater than a stated range, the range is intended to include all values and sub-ranges between the stated values or sub-ranges. For values which are less than or greater than a maximum or minimum limit, the range is intended to include all values and sub-ranges between the maximum or minimum limit and the value.

[0060] In the description of the present application, the term "comprising" or "including" or any other variant is intended to cover non-exclusive inclusions, so that a process, method, article or apparatus including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such a process, method, article or apparatus. Without more limitations, the element defined by the statement "including a" does not exclude the presence of other identical elements in the process, method, article or apparatus including the element.

[0061] In the present application, when the compound name is inconsistent with the corresponding structural formula, the structural formula is preferred.

[0062] The present application will be further described in detail below through specific embodiments.

[0063] Example 1

[0064] Synthesis of organic lithium supplementing agent: lithium hydroxide and compound of formula (I) were weighed in a molar ratio of 5:1, respectively dispersed in 60 mL of ethanol, uniformly mixed and stirred, the stirring speed was 500 rpm, and the stirring time was 12 h; the obtained turbid liquid was suction filtered, and the filter cake was vacuum dried at 110°C for 12 h, ground after natural cooling to obtain the organic lithium supplementing agent shown in formula (5).

[0065] The synthesis of organic lithium supplementing agent in Examples 2-4 refers to Example 1.

[0066] The structures of the organic lithium supplementing agents in the examples and comparative examples are shown in Table 1, and the specific capacity, average delithiation voltage and air stability of each were tested.

[0067] (1) Specific capacity test: the organic lithium supplement agent to be tested, PVDF and conductive agent SP are dissolved in solvent NMP at a mass ratio of 90:5:5, uniformly mixed and stirred to prepare a slurry, then the slurry is uniformly coated on an aluminum foil positive electrode current collector, and a positive electrode sheet is obtained after drying. The positive electrode sheet and lithium sheet are assembled into a half battery. The half battery is correctly installed on the clamp of the battery test system, and charged at a constant current of 0.1C to a voltage of 4.5V. After standing for 15 min, it is discharged at a constant current of 0.1C to 2.0V, and the charging specific capacity is recorded.

[0068] (2) Average delithiation voltage test: the organic lithium supplement agent to be tested, PVDF and conductive agent SP are dissolved in solvent NMP at a mass ratio of 90:5:5, uniformly mixed and stirred to prepare a slurry, then the slurry is uniformly coated on an aluminum foil positive electrode current collector, and a positive electrode sheet is obtained after drying. The positive electrode sheet and lithium sheet are assembled into a half battery, and the average delithiation voltage is read on the test software using the half battery test system.

[0069] (3) Air stability test: first, the organic lithium supplement agent to be tested, PVDF and conductive agent SP are mixed at a mass ratio of 90:5:5, and the positive electrode material sample is placed in a specific air environment. After 30 days of exposure, the sample is weighed again, the weight difference is calculated, and the air stability of the material is evaluated according to the size of the weight change. Then, the organic lithium supplement agent before and after air exposure is prepared into a positive electrode sheet and assembled into a battery, and the charging and discharging test is carried out respectively. According to the capacity change, the air stability is further judged by the charging and discharging efficiency.

[0070] Table 1: Performance test results of organic lithium supplement agent

[0071]

[0072]

[0073] As can be seen from Table 1, the specific capacity of the organic lithium supplement agent provided by the application is above 450 mAh / g, and the delithiation voltage is below 4.7V. Compared with the organic lithium supplement agent in the prior art, the specific capacity and delithiation voltage performance are improved. And the organic lithium supplement agent provided by the application has good stability and no secondary gas generation. In the comparative example, the carboxyl group is easily oxidized, so the stability is poor.

[0074] Preparation of battery

[0075] LiFePO4, the organic lithium supplementing agent in the above examples and comparative examples, SP and PVDF were mixed uniformly according to a mass ratio of 88:5:3:4, and then a positive electrode sheet was obtained by slurry mixing, coating, drying, and rolling. Artificial graphite, SP, sodium carboxymethyl cellulose (CMC) and polystyrene butadiene (SBR) were mixed uniformly according to a mass ratio of 94.4:2:2:1.6, and then a negative electrode sheet was obtained by slurry mixing, coating, drying, and rolling. After assembling the positive and negative electrode sheets, a lithium ion battery was obtained, and lithium supplementing of the negative electrode material was realized in the first charge and discharge cycle. Then, the battery was subjected to gas production amount testing, capacity density improvement testing, and cycle performance improvement testing, and the results are shown in Table 2 below.

[0076] (4) Battery gas production amount testing: a. After the soft pack battery was once formed, the charge and discharge test was carried out, and the generated gas was collected into a gas collection bag through a pipeline; b. The collected gas was injected into a gas chromatograph for analysis to obtain the composition and content of the gas; c. According to the composition and content of the gas, and the volume of the container, the gas production amount of the soft pack battery was calculated.

[0077] (5) Cycle performance testing: after the lithium ion battery was formed, in an environment at 25°C, after discharge, once charge and discharge were carried out, after constant current charging to a voltage of 3.65V at a charge current of 1C, constant voltage charging was carried out at 3.65V with a charge cutoff current of 0.05C, and after standing for 15 min, constant current discharge was carried out at a discharge current of 1C to 2.0V, and the discharge capacity of the first cycle was recorded as C1; then 1000 cycles of charge and discharge were carried out, and the discharge capacity of the 1000th cycle C1000 was recorded, and C1000 / C1x100% was the discharge capacity retention rate of the battery core in 1000 cycles.

[0078] (6) Battery capacity density improvement testing: according to the above battery preparation method, the difference is that no organic lithium supplementing agent is added, and after the battery is formed, in an environment at 25°C, after discharge, once charge and discharge are carried out, after constant current charging to a voltage of 3.65V at a charge current of 1C, constant voltage charging is carried out at 3.65V with a charge cutoff current of 0.05C, and after standing for 15 min, constant current discharge is carried out at a discharge current of 1C to 2.0V, and the discharge capacity of the first cycle is recorded as C2, the discharge capacity of the first cycle in the cycle performance testing is recorded as C1, and the capacity density improvement amount ΔV = C1-C2.

[0079] Table 2: Effect of organic lithium supplementing agent on battery performance

[0080]

[0081]

[0082] As can be seen from Table 2, compared with no addition of the lithium supplement, the organic lithium supplement provided by the application can increase the capacity density of the lithium battery by 4 mAh / g at most, and the cycle performance can be increased by 200% at most, which is obviously superior to the comparative examples.

[0083] The above describes the specific embodiments of the application in detail, but the application is not limited to the specific details in the above embodiments, and various simple modifications can be made to the technical solutions of the application within the technical concept of the application, and these simple modifications all belong to the protection scope of the application.

[0084] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the application will not further describe various possible combinations.

[0085] In addition, various different embodiments of the application can also be combined in any manner, as long as it does not deviate from the idea of the application, and it should also be considered as disclosed by the application.

Claims

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

2. A method for preparing the organic lithium supplement according to claim 1, characterized in that, include: The precursor and lithium source are dissolved separately in an organic solvent, mixed, and then reacted. After the reaction is complete, the mixture is filtered and dried to obtain the organic lithium supplement. The precursor has the following structure: ， R'1 is selected from -COOH, -O-COOH, and -NH-COOH, and p is 2 or 3; R2 is selected from H, halogens, and C. 1~3 Alkyl, C 1~3 Alkoxy groups, 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, lithium metal, lithium hydride, tert-butyllithium, n-butyllithium, biphenyl lithium, and naphthalene lithium.

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

5. The application 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 the cathode material of lithium battery.

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

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

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

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