A positive electrode lithium supplementing agent, a preparation method thereof and a positive electrode sheet

Abstract

This invention relates to the field of lithium-ion battery technology, and in particular to a positive electrode lithium replenishment agent, its preparation method, and a positive electrode sheet, comprising lithium-rich lithium iron phosphate and lithium nitrobenzene. The positive electrode lithium replenishment agent provided by this invention uses LFO as the main lithium source and combines it with lithium nitrobenzene to form a protective layer in situ on the surface of lithium-rich lithium iron phosphate particles, reducing interfacial side reactions and gas generation, achieving efficient active lithium compensation, and thus improving the overall performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a positive electrode lithium replenishing agent, its preparation method, and the positive electrode sheet. Background Technology

[0002] During the initial charge and discharge of lithium-ion batteries, the formation of the solid electrolyte interphase (SEI) film at the negative electrode irreversibly consumes active lithium ions in the battery system, leading to a lower initial coulombic efficiency and a loss of actual reversible capacity. To compensate for this irreversible lithium loss and improve the overall energy density and cycle performance of the battery, introducing lithium replenishing agents into the electrodes has become a key technical approach. Lithium replenishing agents are used to release additional active lithium ions during battery activation or the first charge to compensate for the initial depletion of lithium reserves. Among these, positive electrode lithium replenishing agents have attracted widespread attention due to their relative stability, low cost, ease of operation, and high safety.

[0003] Currently, many different types of cathode lithium replenishing agents have been reported. For example, invention patent application CN202410721790.6 discloses a cathode lithium replenishing material Li2NiO2 and its preparation method. This lithium-rich nickel oxide has a high specific capacity (≥400mAh / g) and a high voltage plateau (4.2~4.5V), making it suitable for applications requiring high energy density. Another example is invention patent application CN202511189482.4, which discloses a lithium-rich lithium iron ferrite lithium replenishing agent and its preparation method. The main component of this lithium-rich lithium iron ferrite lithium replenishing agent is Li5FeO4 (LFO), which has a higher initial charge capacity (>700mAh / g) and a lower initial coulombic efficiency (<10%), thus also exhibiting good lithium-ion replenishment effects.

[0004] However, these lithium replenishers still have the following problems in practical applications: Due to the surface tension of the cathode material, there is a large interfacial impedance between the lithium replenisher particles and the cathode substrate, which means that the lithium replenisher cannot be completely delithiated during the formation process, and some lithium remains trapped in the lithium replenisher, resulting in the waste of some active lithium. Furthermore, because the delithiation potential of the cathode lithium replenisher is inconsistent with that of the cathode material, the battery voltage will rise to a high delithiation potential during the first charge, inducing irreversible precipitation of oxygen in the bulk lattice of the material. This precipitated oxygen reacts with the electrolyte, destroying the stable SEI film between the cathode and the electrolyte, thereby deteriorating the battery's stability and ultimately reducing the battery's cycle stability and energy density. In addition, the synthesis of lithium replenishers like Li₂NiO₂ requires precise control of reaction conditions and has drawbacks such as complex reactions and high processing and purification costs, resulting in a high overall preparation cost for existing lithium replenishers. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a positive electrode lithium replenishing agent, its preparation method, and a positive electrode sheet. The positive electrode lithium replenishing agent uses LFO as the main lithium source and combines it with lithium nitrobenzene to form a protective layer in situ on the surface of lithium-rich lithium iron phosphate particles, reducing interfacial side reactions and gas generation, achieving efficient active lithium compensation, and thus improving the overall performance of the battery.

[0006] The technical solution to the problem of the present invention is as follows: Firstly, a positive electrode lithium replenishing agent is provided, comprising lithium iron ferrite rich in lithium and lithium nitrobenzene.

[0007] This application uses LFO as the main lithium source to improve the lithium replenishment capacity, and adds lithium nitrobenzene as a key functional additive. The decomposition products of lithium nitrobenzene (such as carbonaceous materials containing aromatic rings, Li2O, etc.) can form a dense, ionicly conductive but electronically insulating protective layer in situ on the surface of lithium iron phosphate particles. This protective film can physically isolate the lithium iron phosphate from direct contact with the electrolyte, and prevent the electrolyte from contacting the inside of the lithium replenishment agent or the decomposition products, thereby ensuring interface stability and protecting the SEI film from erosion, achieving efficient active lithium compensation, and thus improving the battery's first coulombic efficiency, cycle stability and safety.

[0008] Preferably, the lithium-rich lithium iron oxide includes at least one of Li5FeO4 and Li5Fe5O8.

[0009] Preferably, the lithium nitrobenzene comprises at least one of lithium p-nitrobenzene, lithium o-nitrobenzene, lithium m-nitrobenzene, lithium 2,3-dinitrobenzene, lithium 2,4-dinitrobenzene, lithium 2,5-dinitrobenzene, lithium 2,6-dinitrobenzene, lithium 3,4-dinitrobenzene, and lithium 3,5-dinitrobenzene.

[0010] Preferably, the mass ratio of the lithium iron phosphate to the lithium nitrobenzene is 1:(1~4).

[0011] Preferably, the lithium iron ferrite rich in lithium is prepared by the following method:

[0012] Weigh out 32-64 parts by mass of 1,1'-bis(dimethylsilyl)ferrocene, 60-80 parts by mass of toluene, 10-20 parts by mass of 3-(thiophen-2-yl)acrylonitrile, 0.003-0.04 parts by mass of allylphenylselenide, and 0.03-0.3 parts by mass of chloroplatinic acid catalyst and place them into a reaction vessel to obtain a reaction mixture; cool the reaction mixture to room temperature and remove toluene by vacuum distillation to obtain the lithium-rich lithium ferrite.

[0013] Preferably, the temperature in the reaction vessel is 80~90℃, and the reaction time is 2~4h.

[0014] Preferably, the lithium nitrobenzene is prepared by the following method:

[0015] Nitrobenzoic acid and lithium source are mixed evenly in a solvent to obtain a mixture; the mixture is heated under continuous stirring to react and obtain a reaction solution; the reaction solution is filtered and vacuum dried to obtain lithium nitrobenzene.

[0016] Preferably, the lithium source includes at least one of lithium carbonate, lithium carbonate-6Li2, lithium formate, lithium oxalate, lithium acetate, lithium cobalt oxide, lithium manganese oxide, lithium borate, lithium oxide, and lithium hydroxide.

[0017] Preferably, the solvent includes at least one of water, anhydrous ethanol, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0018] Preferably, the stirring rate is 50~1500 r / min, the heating temperature is 45~90℃, and the reaction time is 0.5~8h.

[0019] Preferably, the vacuum drying temperature is 45~90℃, and the vacuum drying time is 8~48h.

[0020] Secondly, the present invention also provides a method for preparing the positive electrode lithium replenishing agent as described above, comprising the following steps:

[0021] S1. Dissolve lithium iron ferrite, polyvinylpyrrolidone and lithium carboxymethyl cellulose in water to obtain the first dispersion;

[0022] S2. Lithium nitrate is added to the first dispersion and dispersed to obtain a second dispersion;

[0023] S3. The second dispersion is subjected to a hydrothermal reaction, and after the reaction is cooled to room temperature, it is washed and dried to obtain the precursor;

[0024] S4. The precursor is calcined to obtain a positive electrode lithium replenishing agent.

[0025] In the above preparation process, polyvinylpyrrolidone (PVP), as a polymeric dispersant and steric stabilizer, effectively prevents the aggregation of nano / submicron particles in water through steric hindrance, ensuring the formation of a uniform and stable suspension. This is the foundation for the subsequent uniform composite of lithium nitrobenzene and lithium-rich lithium ferrite. Lithium carboxymethyl cellulose (CMC-Li), as a viscosity modifier and auxiliary lithium source, can prevent particle sedimentation, maintain dispersion stability, and act as a soft template under the high temperature and high pressure environment of the subsequent hydrothermal reaction, influencing the microstructure of the product and forming a more stable interface layer.

[0026] Preferably, in step S1, the mass ratio of lithium iron ferrite, polyvinylpyrrolidone, and lithium carboxymethyl cellulose is 4:3:3.

[0027] Preferably, in step S3, the conditions for the hydrothermal reaction include: a reaction temperature of 0~180℃ and a reaction time of 6~8h.

[0028] Preferably, in step S3, the washing includes washing the solid with distilled water and anhydrous ethanol four times, respectively.

[0029] Preferably, in step S3, the drying conditions include: a drying temperature of 55~65℃ and a drying time of 5~7h.

[0030] Preferably, in step S4, the calcination conditions include: a calcination temperature of 400~600℃ and a calcination time of 3~5h.

[0031] Thirdly, the present invention also provides a positive electrode sheet, comprising a current collector and a positive electrode film layer located on the current collector, the positive electrode film layer comprising a positive electrode active material and a positive electrode lithium supplement agent as described in any of the preceding claims.

[0032] Preferably, the mass percentage of the positive electrode lithium supplement is 0.5 wt% to 10 wt% based on the total mass of the positive electrode film.

[0033] Preferably, the positive electrode active material includes at least one of lithium iron phosphate, lithium cobalt oxide, ternary positive electrode material, quaternary positive electrode material, and lithium-rich manganese-based positive electrode material.

[0034] Preferably, the positive electrode film layer further includes a conductive agent and a binder.

[0035] Preferably, the conductive agent includes at least one of carbon nanotubes, carbon black, conductive graphite, carbon fiber, and graphene.

[0036] Preferably, the adhesive comprises at least one of polyvinylidene fluoride, sodium alginate, polyvinyl alcohol, polymethyl methacrylate, hydrogenated nitrile rubber, polytetrafluoroethylene, and polyacrylic acid.

[0037] The beneficial effects of this invention are as follows:

[0038] 1. The positive electrode lithium replenishing agent provided in this application uses LFO as the main lithium source and combines it with the protective layer formed in situ on the surface of lithium-rich lithium iron phosphate particles by lithium nitrobenzene. This prevents the electrolyte from contacting the inside of the lithium replenishing agent or decomposition products when the lithium replenishing agent is completely delithiated for the first time, thereby reducing the side reactions and gas generation at the interface and achieving efficient active lithium compensation.

[0039] 2. The preparation method of this application is based on hydrothermal method, which has the advantages of simple operation and low cost.

[0040] 3. The positive electrode sheet prepared using the positive electrode lithium supplement provided in this application has good comprehensive performance, and the battery using the positive electrode sheet has good initial coulombic efficiency, cycle stability and safety. Detailed Implementation

[0041] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0042] Example 1

[0043] (1) Synthesis of Li5FeO4

[0044] 40 parts of 1,1'-bis(dimethylsilyl)ferrocene, 70 parts of toluene, 15 parts of 3-(thiophen-2-yl)acrylonitrile, 0.02 parts of allylphenylselenide, and 0.1 parts of chloroplatinic acid catalyst were weighed and placed in a reaction vessel. The reaction mixture was stirred at 85°C for 3 hours. After the reaction was completed, the mixture was cooled to room temperature, and toluene was removed by vacuum distillation to obtain a brownish-red solid intermediate. The intermediate was calcined at 500°C for 4 hours under an argon atmosphere to obtain Li5FeO4 powder.

[0045] (2) Synthesis of lithium p-nitrobenzoate

[0046] Lithium carbonate and p-nitrobenzoic acid were weighed in a molar ratio of 1:1 and added to a reaction flask. Deionized water was added as a solvent, and the solid-liquid ratio was 1:10. The mixture was stirred at a stirring rate of 2500 r / min for 2 h, and then reacted in an 80℃ water bath at a stirring rate of 500 r / min for 12 h. After the reaction was completed, the reaction solution was hot filtered, the filter cake was washed twice with hot water, and then vacuum dried at 80℃ for 16 h to obtain lithium p-nitrobenzoate.

[0047] (3) Preparation of positive electrode lithium supplement

[0048] Four parts of Li5FeO4 powder, three parts of polyvinylpyrrolidone, and three parts of lithium carboxymethyl cellulose were weighed and added to 200 mL of deionized water. The mixture was magnetically stirred for 2 hours to obtain a uniform first dispersion. Four parts of lithium p-nitrobenzoate were weighed and added to the first dispersion. The mixture was ultrasonically treated for 1 hour to form a second dispersion. This dispersion was transferred to a hydrothermal reactor and reacted at 160 °C for 7 hours. After cooling, the mixture was centrifuged, and the solid product was washed with deionized water and ethanol. It was then dried at 80 °C for 12 hours to obtain the precursor. The precursor was calcined at 500 °C for 4 hours in argon to obtain the positive electrode lithium supplement LNFO-1.

[0049] (4) Preparation of positive electrode sheet

[0050] 1.90% LNFO-3, 95.10% lithium iron phosphate (COP) active material, 0.6% conductive carbon black, and 0.6% carbon nanotubes were added to a first mixing tank and stirred until homogeneous. 1.8% binder (polyvinylidene fluoride dissolved in N-methylpyrrolidone) was added to a second mixing tank and stirred until homogeneous. The mixture from the first mixing tank was then added to the second mixing tank and stirred to form a uniform slurry with a viscosity of 6500 mPa·s. This slurry was coated onto aluminum foil, dried at 120℃, rolled, and slit to obtain the positive electrode sheet with an areal density controlled at 250 g / m². 2 .

[0051] (5) Battery manufacturing

[0052] The positive electrode, negative electrode, separator, and shell are assembled, dried, and then injected with electrolyte to obtain a battery cell. The battery cell is left to stand for 48 hours, and then subjected to formation treatment at 40℃ and a magnetic field strength of 1500mT. After standing, evacuation, capacity testing, and K-value testing, a lithium-ion battery is obtained.

[0053] Example 2

[0054] The process is basically the same as in Example 1, except that in step (3), 8 parts of lithium p-nitrobenzoate are weighed and added to the first dispersion. The resulting positive electrode lithium replenishing agent is denoted as LNFO-2.

[0055] Example 3

[0056] The process is basically the same as in Example 1, except that in step (3), 12 parts of lithium p-nitrobenzoate are weighed and added to the first dispersion. The resulting positive electrode lithium replenishing agent is denoted as LNFO-3.

[0057] Example 4

[0058] The process is basically the same as in Example 1, except that in step (3), 16 parts of lithium p-nitrobenzoate are weighed and added to the first dispersion. The resulting positive electrode lithium replenishing agent is designated as LNFO-4.

[0059] Example 5

[0060] The process is basically the same as in Example 1, except that in step (4), 0.96% of LNFO-1, 96.04% of lithium iron phosphate positive electrode active material, 0.6% of conductive carbon black, and 0.6% of carbon nanotubes are added to the first stirring tank and stirred evenly.

[0061] Example 6

[0062] The process is basically the same as in Example 1, except that in step (4), 3.28% LNFO-1, 94.17% lithium iron phosphate positive electrode active material, 0.6% conductive carbon black, and 0.6% carbon nanotubes are added to the first stirring tank and stirred evenly.

[0063] Comparative Example 1

[0064] (1) Preparation of positive electrode sheet

[0065] 97.00% of lithium iron phosphate, dissolved in N-methylpyrrolidone, was added to a first mixing tank and stirred until homogeneous. 0.6% conductive carbon black and 0.6% carbon nanotubes were added to the first mixing tank and stirred until homogeneous. 1.8% binder (polyvinylidene fluoride dissolved in N-methylpyrrolidone) was added to a second mixing tank and stirred until homogeneous. The mixture from the first mixing tank was then added to the second mixing tank and stirred to form a uniform slurry with a viscosity of 6500 mPa·s. This slurry was coated onto aluminum foil, dried at 120°C, rolled, and slit to obtain the positive electrode sheet, with an areal density controlled at 250 g / m². 2 .

[0066] (2) Battery preparation

[0067] The positive electrode, negative electrode, separator, and shell are assembled, dried, and then injected with electrolyte to obtain a battery cell. The battery cell is left to stand for 48 hours, and then subjected to formation treatment at 40℃ and a magnetic field strength of 1500mT. After standing, evacuation, capacity testing, and K-value testing, a lithium-ion battery is obtained.

[0068] Comparative Example 2

[0069] The process is basically the same as Comparative Example 1, except that 1.90% of lithium p-nitrobenzoate, 95.10% of lithium iron phosphate (positive electrode active material), 0.6% of conductive carbon black, and 0.6% of carbon nanotubes are added to the first mixing tank and stirred until homogeneous.

[0070] Comparative Example 3

[0071] The process is basically the same as Comparative Example 1, except that: 1.90% Li5FeO4, 95.10% lithium iron phosphate positive electrode active material, 0.6% conductive carbon black, and 0.6% carbon nanotubes were added to the first stirring tank and stirred until homogeneous.

[0072] Performance testing

[0073] The capacity, gas production volume, and cycle life of the batteries in Examples 1-6 and Comparative Examples 1-3 were tested. The test results are shown in Table 1.

[0074] Example 1 173.8 156.9 3.4% 108.23% Example 2 173.5 155.6 3.0% 107.01% Example 3 172.9 155.2 2.0% 106.89% Example 4 170.8 152.4 1.9% 105.86% Example 5 171.9 152.7 1.7% 105.98% Example 6 173.2 155.0 2.1% 107.46% Comparative Example 1 164.4 150.9 1.6% 104.20% Comparative Example 2 169.4 152.3 1.9% 105.36% Comparative Example 3 173.7 156.4 7.0% 107.42%

[0075] As shown in Table 1, Example 1 achieved a capacity retention of 108.23% and a discharge capacity of 156.9 mAh / g after 300 cycles. This indicates that the positive electrode lithium replenisher is more effective than the batteries provided by Comparative Examples 2 and 3, which contain traditional lithium replenishers. Furthermore, compared to Comparative Example 3 (which only added Li5FeO4), although the difference in lithium replenishment effect and cycle performance is small, the gas production volume stored in Comparative Example 3 is much larger than that in Example 1. This indicates that the gas production of the present invention is much lower than that of traditional lithium iron ferrite lithium replenishers.

[0076] Furthermore, as shown in Example 5, reducing the amount of positive electrode lithium replenisher slightly reduces the charge / discharge capacity and cycle performance of the battery, but significantly reduces the amount of gas produced during storage, which is lower than that of Comparative Example 2, which added lithium p-nitrobenzoate as a lithium replenisher, and even close to that of Comparative Example 1, which served as a blank example.

Claims

1. A positive electrode lithium replenishing agent, characterized in that, Including lithium iron ferrite rich in lithium and lithium nitrobenzene.

2. The positive electrode lithium replenishing agent according to claim 1, characterized in that, The lithium-rich lithium iron ferrite includes at least one of Li5FeO4 and Li5Fe5O8.

3. The positive electrode lithium replenishing agent according to claim 1, characterized in that, The lithium nitrobenzene includes at least one of lithium p-nitrobenzene, lithium o-nitrobenzene, lithium m-nitrobenzene, lithium 2,3-dinitrobenzoate, lithium 2,4-dinitrobenzoate, lithium 2,5-dinitrobenzoate, lithium 2,6-dinitrobenzoate, lithium 3,4-dinitrobenzoate, and lithium 3,5-dinitrobenzoate.

4. The positive electrode lithium replenishing agent according to claim 1, characterized in that, The mass ratio of the lithium iron ferrite rich in lithium to the lithium nitrobenzene is 1:(1~4).

5. A method for preparing a positive electrode lithium supplement agent as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Dissolve lithium iron ferrite, polyvinylpyrrolidone and lithium carboxymethyl cellulose in water to obtain the first dispersion; S2. Lithium nitrate is added to the first dispersion and dispersed to obtain a second dispersion; S3. The second dispersion is subjected to a hydrothermal reaction, and after the reaction is cooled to room temperature, it is washed and dried to obtain the precursor; S4. The precursor is calcined to obtain a positive electrode lithium replenishing agent.

6. The method for preparing the positive electrode lithium replenishing agent according to claim 5, characterized in that, In step S3, the conditions for the hydrothermal reaction include: a reaction temperature of 0~180℃ and a reaction time of 6~8h.

7. The method for preparing the positive electrode lithium replenishing agent according to claim 5, characterized in that, In step S3, the washing includes washing the solid with distilled water and anhydrous ethanol four times each.

8. The method for preparing the positive electrode lithium replenishing agent according to claim 5, characterized in that, In step S4, the calcination conditions include: a calcination temperature of 400~600℃ and a calcination time of 2~6h.

9. A positive electrode plate, characterized in that, It includes a current collector and a positive electrode film layer located on the current collector, the positive electrode film layer comprising a positive electrode active material and a positive electrode lithium supplement as described in any one of claims 1-4.

10. The positive electrode lithium replenishing agent according to claim 9, characterized in that, The mass percentage of the positive electrode lithium supplement is 0.5 wt% to 10 wt% based on the total mass of the positive electrode film.