A lithium supplement suitable for high-voltage positive electrodes, a preparation method and application thereof

Abstract

The present application relates to a kind of lithium supplementing agent suitable for high-voltage positive electrode and its preparation method and application, the lithium supplementing agent is reduced graphene oxide modified Li 4+x Si 1‑x Fe x O4, 0.5≥x≥0.01.The present application not only can supplement the capacity loss of lithium ion battery in initial cycle, but also can supplement long-term cycle irreversible capacity loss, improve the available capacity of battery after multiple cycles, greatly prolong the service life of battery;The lithium supplementing agent additive of the present application can be applied to high-voltage layered positive electrode, such as LiNi x Co y Mn z O2 (x+y+z=1) positive electrode, compared with other positive electrode materials assembled battery has higher energy density, more practical, higher commercial value.The steps of the present application are simple and easy to implement, not only safe, pollution-free, the cost of equipment and post-processing is small, and with the current battery production process adaptation, suitable for large-scale amplification and can be quickly put into use.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion batteries, and relates to a lithium supplementing agent suitable for a high-voltage positive electrode and a preparation method and application thereof. BACKGROUND

[0002] In today's era, energy shortage and greenhouse effect have become major crises faced by mankind. In the face of the crisis, it is imperative to use clean and renewable energy to replace fossil energy, and renewable energy cannot be continuously and stably output. In order to solve this problem, it is necessary to develop high-performance energy storage systems, such as the highly concerned lithium ion battery system. Since Sony applied it to mobile phones in 1991, lithium ion batteries have rapidly occupied the battery market of electronic products. Up to now, the development of electric vehicles has further broadened the corresponding market.

[0003] However, the energy density of the existing lithium cobalt oxide-graphite (LiCoO2(LCO)-Gr) lithium ion battery system has approached the limit, while the requirements for energy density of power batteries and electronic product batteries are continuously increasing, and it is imperative to use a battery system with higher specific energy. The most promising high-energy-density battery system for commercial application at present is a high-voltage positive electrode-composite negative electrode system, such as a LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811) positive electrode-SiO / C+graphite composite negative electrode system. The system uses an NCM811 positive electrode with a reversible capacity of about 200 mAh / g (LCO positive electrode is 170 mAh / g) and a SiO / C+graphite composite negative electrode (in which the reversible capacity of the SiO / C negative electrode is about 1400 mAh / g, and the reversible capacity of the Gr negative electrode is about 360 mAh / g, and the specific capacity of the composite negative electrode is determined by the addition ratio of the two). However, the high-specific-energy battery system will continue to be plagued by the problem of irreversible loss of battery capacity during use. In the first cycle, the composite negative electrode will consume a large amount of active lithium to generate SEI, and in the subsequent cycles, the SiO / C in the composite negative electrode will also undergo particle fragmentation, side reactions with electrolyte, etc., resulting in continuous decline of the battery capacity during the cycle process, reducing the energy density and service life of the battery, and affecting the use of power supply equipment.

[0004] Pre-lithiation technology is a method for supplementing Li +Additional Li supplement has broad prospects, including positive electrode lithium supplement, negative electrode pre-lithiation, and separator lithium supplement. Positive electrode lithium supplement agent is a positive electrode lithium supplement method, which uses a certain high-capacity lithium-rich material to release the contained lithium on the positive electrode side in the first cycle to supplement the lithium loss in the first cycle of the battery. However, the pre-lithiation technology, including the positive electrode lithium supplement agent, has the disadvantage that it can only supplement Li for the capacity loss in the initial cycle, but cannot supplement Li for the loss in long-term cycling. In view of this, CN113540591B discloses a positive electrode lithium supplement method, which increases the battery charging voltage in long-term cycling in stages to supplement lithium multiple times, and the lithium supplement agent used is a conventional lithium supplement agent, such as Li2NiO2, Li5FeO4, Li2CuO2, Li6CoO4, Li3N, Li2S, etc.; however, the capacity of these lithium supplement agents is concentrated near the platform, and when the lithium supplement agent is supplemented in the cycle, the voltage is gradually increased to exceed the voltage platform of the lithium supplement agent, so the capacity that can be developed by the lithium supplement agent in the cycle is very small, and the capacity that can be supplemented to the battery is also very small. For example, the charging platform of Li5FeO4 is at 3.6, 3.9V, and when charged to 4.1V, the charging capacity is almost fully developed, and when the voltage is increased to more than 4.1V during the lithium supplement in the cycle, there will be no charging capacity, and the increase in voltage is meaningless. Most importantly, the positive electrode lithium supplement agent in the patent method cannot be used for high-voltage high-specific-capacity positive electrode materials such as NCM811 positive electrodes, because NCM811 generally needs to be charged to 4.2V to develop its own capacity of ~200mAh / g, and at this time the capacity of the above-mentioned lithium supplement agent has already been fully developed, and it is impossible to increase the voltage to continue lithium supplement in the subsequent cycle; in order to implement the voltage increase and step-by-step lithium supplement strategy, the patent limits the charging cut-off voltage of the NCM811 battery to 3.8V in the non-lithium supplement cycle in Example 10, at which time the NCM811 develops a capacity of only about 100mAh / g, which is only half of the normal capacity, completely losing the significance of using this high-voltage high-specific-capacity material, and is a practice of buying a pearl and throwing away a bowl. In summary, the lithium supplement method in the patent is only applicable to low-voltage lithium iron phosphate (LiFePO4) batteries, and is not even applicable to the current LCO battery, let alone high-energy battery systems using NCM811 positive electrodes.

[0005] Li4SiO4 is a lithium ion conductor matrix material and a widely studied CO2 capture material, and there are many studies in the prior art. In order to increase its applicability, some high-valence ion doping is carried out, such as boron (B), aluminum (Al), vanadium (V), and iron (Fe). At present, there are also reports that Al-doped Li4SiO4 is used as a lithium supplement agent, for example, patent CN112467122A reports the use of metal-doped Li4Si 1-y X yO4 material as a lithium supplement, however, the delithiation potential of the material is high, and the capacity can be developed only by charging to 4.6V and constant voltage charging, and almost all the capacity can be developed only by charging to 4.4V or above. The charging curve determines that the lithium supplement can only develop all the capacity at one time, and cannot play a lithium supplement effect in the first cycle and cycle.

[0006] In summary, a lithium supplement compound and a matching lithium supplement method that can supplement lithium multiple times in the first cycle and long-term cycle and can be applied to high-voltage layered positive electrodes are very valuable. SUMMARY

[0007] In order to supplement the active lithium lost in the first cycle and cycle for the battery system using high-voltage positive electrode material of lithium ion battery, such as high-nickel NCM ternary positive electrode material, and improve the service life and energy density, the present application particularly proposes a lithium supplement agent suitable for high-voltage layered positive electrodes and its application method, which is Li 4+x Si 1- x Fe x O4(rGO@Li 4+x Si 1-x Fe x O4), 0.5≥x≥0.01.

[0008] Further, 0.3≥x≥0.05, more preferably, 0.15≥x≥0.10.

[0009] The inventors found that the ratio of Fe and Si has a greater impact on the lithium supplement agent, and the best lithium supplement effect can be achieved within a specific range. If too much Fe is added, Li5FeO4 phase will be left in the final product, and Li5FeO4 has no capacity after the treatment of the present application, which will lead to the overall capacity of the material to decrease; and if too little Fe is added, the Fe element will not have a doping effect, and part of Li4SiO4 will be decomposed into Li2SiO3 in the ball milling, so the ratio of Fe and Si needs to be carefully selected.

[0010] Further, the particle size of the lithium supplement agent is 0.1-50μm, preferably 0.5-5μm.

[0011] Further, the XRD spectrum of the high-voltage positive electrode lithium supplement agent has a greatly broadened diffraction peak. This is because the crystallite size of the material decreases after ball milling. The so-called crystallite size is not the size of the material particles: for a typical polycrystalline material, each material particle is not completely crystalline, and each internal atom is not perfectly arranged according to the rules of crystal arrangement, and it contains many small crystal regions inside. The atoms inside the crystal region are arranged relatively regularly, and the area between them is not well crystallized and the atoms are arranged randomly. When the crystallite size decreases, lithium ions inside the material can escape from the crystal region at a shorter distance, and then conduct to the outside of the particle from the amorphous region. After doping, the lithium ion conductivity of the material in the amorphous region increases, making it easier to conduct lithium ions to the outside. Therefore, the strategies of doping and reducing the crystallite size are complementary and can work together to reduce the polarization of the material and further reduce the delithiation potential of the material. The advantage of the material over the material in CN 112467122 A lies in this: the lithium supplement agent provided in CN 112467122 A starts to have a charge capacity above 4V, and the capacity is only ~100mAh / g at 4.5V; the delithiation potential of the material in the present application is much lower than that of the former, for example, the rGO@Li 4.1 Si 0.9 Fe 0.1 O4 in Preparation Example 1 starts to develop capacity at 3.3V, the capacity is 435mAh / g at 4.2V, and the capacity is 615mAh / g at 4.6V. Therefore, this material can be used to control the voltage step by step to develop capacity in the first cycle and in the cycle. If this strategy is applied to the lithium supplement agent provided in CN 112467122 A, the material develops too low capacity when charged to 4.2V, and cannot function in the first cycle and in the cycle. This advantage comes from reducing the crystallite size.

[0012] By fitting the diffraction peak, the crystallite size of the material can be calculated from the width of the fitted peak. The width commonly used is the full width at half maximum (FWHM), that is, the width of the peak at half the total height (the Y value at the peak). After conversion to radians, it is calculated according to the Scherrer formula (Formula 1).

[0013]

[0014] In the formula, D represents the crystallite size, K represents the Scherrer constant (generally taken as 0.89), γ represents the wavelength of the X-rays used in X-ray diffraction, generally γ = 1.54 angstroms when Cu Kα light is used; β is the radian value of the FWHM, and θ is the diffraction angle corresponding to the peak used. When the Scherrer formula is used for calculation, a diffraction peak needs to be selected, and the physical meaning of the D value is the crystallite size in the normal direction of the crystal plane corresponding to the diffraction peak. The peak used for calculation here is the peak corresponding to the crystal plane with a crystal plane spacing of 0.316 nm and a 2θ value of 28.174° in the standard spectrum; the reason for selecting it is that there are few peaks adjacent to it, and the peak fitting can obtain a relatively clear and accurate result. It is completely possible to use other peaks for analysis.

[0015] Further, the microcrystalline size of the lithium supplementing agent in the normal direction of the crystal plane is less than 20 nm, preferably 8-15 nm, and more preferably 10-14 nm. When converted to FWHM, it can be known that the FWHM of the peak at 28.174±0.3° in the XRD diffraction spectrum of the lithium supplementing agent should be greater than 0.405°, and between 0.539° and 1.013°.

[0016] Further, the carbon content of the lithium supplementing agent is 0.5wt%-25wt%, and more preferably between 5wt% and 15wt%.

[0017] The coated carbon of the lithium supplementing agent contains rGO, and the graphitization degree of the rGO is very high. The I D / I G value calculated from the D band and the G band of the carbon peak in the Raman spectrum of the coated carbon containing rGO is relatively low, where I D represents the integral intensity of the D band, and I G represents the integral intensity of the G band. In the Raman spectrum of the lithium supplementing agent of the high-voltage positive electrode, the I D / I G value is 0.8-1.2, and the I D / I G value is relatively low, indicating that the graphitization degree of the carbon coated on the surface of the lithium supplementing agent material is relatively high. The electronic conductivity of the coated carbon with a relatively high graphitization degree is higher than that of the carbon with a relatively low graphitization degree, and can better reduce the polarization degree of the material and lower the oxidation potential of the material. Taking Li 4.1 Si 0.9 Fe 0.1 O4 as an example, the electronic conductivity of the material is measured, and the electronic conductivity of the material without carbon coating (such as Li 4.1 Si 0.9 Fe 0.1 O4 prepared in Comparative Preparation Example 1) is 1.24x10 -9S / cm, while the carbon-coated material (such as rGO@Li 4.1 Si 0.9 Fe 0.1 O4) is 0.56 S / cm, which is eight orders of magnitude higher, thus it can be seen that the rGO coating can greatly improve the conductivity of the material.

[0018] Compared with the ordinary additive, the lithium battery added with the lithium supplementing agent of the application has a longer charging curve with a lower voltage, which can supplement the irreversible capacity loss in the first cycle of the battery, and the higher voltage part of the slope can supplement lithium multiple times through voltage control in long-term cycling, so as to overcome the lithium loss in the first cycle and long-term cycling, and prolong the service life of the lithium ion battery.

[0019] The lithium supplementing agent provided by the application is particularly suitable for supplementing lithium for high-voltage positive electrode materials in the first cycle and the cycling process, and the rGO@Li 4.1 Si 0.9 Fe 0.1 O4 as an example, the charging slope of the lithium supplementing agent is from 3.3 V to 4.7 V, and the capacity can be provided in such a long voltage interval, which meets the demand of the strategy of supplementing lithium on demand through voltage control of the high-voltage positive electrode material: the high-voltage positive electrode material can only be charged to 4.2 V to exhibit the characteristics of high voltage and high capacity, and the lithium supplementing agent exhibits a capacity of ~ 440 mAh / g after being charged to 4.2 V, which can be used for supplementing lithium in the first cycle; when the battery is cycled between 2.8 V and 4.2 V, the lithium supplementing agent will not continue to exhibit charging capacity, nor will it embed lithium to provide discharging capacity; when the battery capacity decreases to the point where it needs to be supplemented with lithium for the second time after a period of cycling, the battery can be temporarily charged to 4.6 V in a certain cycle to release the capacity of ~ 200 mAh / g of the lithium supplementing agent between 4.2 V and 4.6 V, which can supplement the lithium loss of the battery in the cycling process. This is the unique advantage of the lithium supplementing agent of the application. In comparison, other lithium supplementing agents do not have this advantage, for example, Li5FeO4, which has exhausted its charging capacity when charged to 4.2 V, and cannot continue to supplement lithium in subsequent cycles by increasing the voltage.

[0020] The high-voltage positive electrode material refers to a positive electrode material that has been practically used and needs to be charged to above 4.2V (such as 4.3V, 4.4V, 4.5V) to fully play its own capacity, which is well known in the art, such as ternary positive electrode material, aluminum-doped ternary positive electrode material, etc. Specific examples include but are not limited to NCM811, NCM622. Of course, the present application has special advantages when applied to battery systems using high-voltage positive electrodes, and does not mean that the present application can only be applied to high-voltage positive electrode battery systems. The present application can also be applied to battery systems other than this, such as lithium iron phosphate (LFP) positive electrode battery systems (such as Example 8) or lithium vanadate (LiVO3) battery systems, etc. are also completely possible, and should be included in the scope of protection of the present patent.

[0021] A second object of the present application is to provide a preparation method of the above-mentioned lithium supplement, comprising the following steps:

[0022] (T1) preparing rGO-composite crystalline Li 4+x Si 1-x Fe x O4 material;

[0023] (T2) reducing the microcrystalline size of the material by high-energy ball milling to obtain an rGO@Li 4+x Si 1-x Fe x O4 material with smaller microcrystalline size.

[0024] Step (T1) is one of the following methods A, method B, method C, method D:

[0025] Method A: take lithium source, silicon source, iron source according to stoichiometric ratio, and add graphene oxide solid, mix uniformly, then pre-burn and calcine to obtain;

[0026] Method B: take lithium source, silicon source, iron source according to stoichiometric ratio, disperse in solvent, and add graphene oxide dispersion in solvent, heat and dry the solvent to obtain a precipitate, grind and then pre-burn and calcine to obtain;

[0027] Method C: take lithium source, silicon source, iron source, and complexing agent according to stoichiometric ratio, disperse in solvent, and disperse in graphene oxide dispersion in solvent to obtain sol, heat and dry the solvent to obtain xerogel, grind, pre-burn and calcine to obtain;

[0028] Method D: take lithium source, silicon source, iron source according to stoichiometric ratio, disperse in solvent, and add graphene oxide dispersion in solvent, perform high-pressure reaction under heating in a high-pressure kettle, centrifuge, wash, dry, grind, pre-burn and calcine to obtain.

[0029] The method of step (T1) is conventional in the art and well known in the art. For example, solid state calcination (method A), precipitation (method B), sol-gel (method C), and solvothermal synthesis (method D). The present application is to add a certain amount of graphene oxide during preparation, which generates rGO in the subsequent calcination process. During the ball milling process of (T2), the hardness of rGO is much lower than that of Li 4+x Si 1-x Fe x O4, so it will be coated on the surface of the material.

[0030] Further, the amount of lithium source, silicon source, and iron source is based on the equivalent ratio of Li 4+x Si 1-x Fe x O4, the lithium source needs to be slightly excessive, because there may be some volatilization during calcination, causing loss of Li, and generally the lithium is excessive by 3% to 10%.

[0031] The lithium source, silicon source, and iron source are well known in the art. For example, the lithium source is a solid-state compound containing lithium, including but not limited to lithium carbonate (Li2CO3), lithium hydroxide monohydrate (LiOH·H2O), lithium nitrate (LiNO3), lithium acetate (CH3COOLi), lithium oxide (Li2O), etc. in one or more combinations; the silicon source includes but is not limited to SiO2 powder, nano-SiO2, fumed SiO2, silicic acid (H2SiO3), tetraethyl orthosilicate (C8H 20 O4Si, TEOS), tetra-n-butyl orthosilicate (C 16 H 36 O4Si), diatomite, vermiculite, zeolite, SBA-15, waste silicon, biomass ash, fly ash, halloysite, etc. in one or more combinations; the iron source refers to iron oxide and various iron salts, including but not limited to iron oxalate (Fe2(C2O4)3), iron nitrate (Fe(NO3)3), basic iron acetate (Fe(C2H3O2)2OH), iron oxide (Fe2O3), iron carbonate (Fe2(CO3)3), iron hydroxide (Fe(OH)3), etc. in one or more combinations.

[0032] The solvent in the present application refers to a liquid that can disperse the selected lithium source, silicon source, iron source, and graphene oxide, including but not limited to deionized water, ethanol, isopropanol, etc. in one or more combinations, preferably deionized water.

[0033] The complexing agent in Method C in the present invention refers to an organic chelating agent that can coordinate with metal ions, including one or more combinations of small molecule multidentate ligands such as citric acid (C6H8O7), ethylene glycol ((CH2OH)2), and high molecular weight multidentate ligands such as polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), and the like, with citric acid being preferred. In using Method C, the molar ratio of citric acid to lithium source is between 1:4 and 10.

[0034] The solvent-dispersed graphene oxide in the present invention refers to a mixture liquid formed by uniformly dispersing graphene oxide in a solvent without agglomeration, with the mass fraction of graphene oxide in the dispersion being between 0.5 and 5 wt%. The input mass of graphene oxide is 5-10% of the mass of the lithium source.

[0035] The pre-burning temperature is between 300 and 500°C, and the pre-burning time is between 2 and 10 hours; the calcination temperature is between 650 and 1000°C, and the calcination time is between 5 and 20 hours. The calcination is carried out in a protective atmosphere, such as an argon atmosphere.

[0036] The high-energy ball milling in step (T2) is carried out at 500-800 rpm and a ball-to-material ratio of 10-80:1 for 5-40 hours, and the sieving is carried out using a sieve mesh size of 400-2000 mesh.

[0037] The third object of the present invention is to provide a method for supplementing lithium in lithium ion batteries, comprising the following steps:

[0038] (S1) Assembling a lithium ion battery containing the above-mentioned new lithium supplementing agent;

[0039] Further, in step (S1), the lithium supplementing agent rGO@Li 4+x Si 1-x Fe x There are various ways to add SiO4 to lithium ion batteries, including one of Method X, Method Y, and Method Z:

[0040] Method X: Coating a slurry containing the lithium supplementing agent on the positive electrode of the separator;

[0041] Preferably, in method X, the lithium supplement and binder are dispersed in an organic solvent to form a slurry, which is then coated onto the positive electrode side of the separator, and the organic solvent is dried. The separator is a polyolefin porous separator, including but not limited to single or multiple material combinations such as polypropylene (PP) and polyethylene (PE), with a thickness controlled at 8-50 μm, preferably 8-20 μm. The slurry also includes a binder, which is well known in the art and includes but is not limited to one or more combinations of polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), and polyethylene glycol (PEG). The organic solvent includes but is not limited to one or more combinations of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and N,N-dimethylformamide (DMF). The coating thickness is such that after the slurry is dried, the coating layer thickness is between 0.5-10 μm, preferably 1-5 μm.

[0042] Method Y: The lithium supplement and the active positive electrode material are slurried together and coated onto the current collector to obtain the positive electrode sheet;

[0043] Preferably, in method Y, raw materials including lithium supplementer, active positive electrode material, conductive additive, and binder are mixed to form a slurry, which is then coated onto a current collector to obtain the working electrode. The positive electrode material includes layered positive electrode materials, olivine-type positive electrode materials, and corresponding doped and modified positive electrode materials, specifically including but not limited to LiCoO2, LiFePO4, LiMn2O4, and LiNi. x Co y Mn z O2(x+y+z=1), LiNi x Co y Al z One or more combinations of O2(x+y+z=1), LiNiO2, LiVO2, LiCrO2, etc., especially those V 充 High-voltage cathode materials for 4.2V, such as ternary high-nickel layered cathode materials, specifically including LiNi. x Co y Mn z O2(x+y+z=1), LiNi x Co y Al z O2(x+y+z=1), where x≥0.5, preferably x≥0.7.

[0044] Preferably, the conductive additive includes, but is not limited to, one or more combinations of Super P, Ketjen Black, CMK-3, conductive carbon nanotubes, graphene, etc.

[0045] Method Z: Coat the prepared positive electrode sheet with a slurry containing lithium replenishing agent.

[0046] Preferably, in method Z, the lithium supplement and the binder are dispersed in an organic solvent to form a slurry, which is coated on the surface of the already coated positive electrode sheet. The lithium supplement accounts for 1-20wt% of the active positive electrode material, preferably 3-10wt%.

[0047] In the above method, if a slurry is needed, the mass ratio of the lithium supplement and the binder is 80-95:5-20. The amount of solvent is such that the solid content of the slurry obtained by slurring is 0.1-1mg / μL.

[0048] (S2) cycle the lithium ion battery, first in the voltage range of V 充 to V 放 , when the battery capacity decreases to 70-90% of the initial discharge capacity, in the next cycle the charging voltage is increased by 0.2-0.4V, if the V 充 before the increase is less than 4.6V, then no increase, discharge to V 放 , after which the battery continues to cycle in the voltage range of V 初 to V 放 , until the capacity decays to less than 60% of the initial capacity, stop cycling.

[0049] Further, in step (S2), V 充 and V 放 respectively represent the charging cut-off voltage and the discharging cut-off voltage during the cycling of the lithium ion battery. The values of V 充 and V 放 are different for different positive electrode materials, and are well known in the art. For example, when the positive electrode material is LiFePO4, V 放 =2.5V, V 充 =3.8V; while for the materials used in the present application, it is more recommended to be applied to high-voltage ternary positive electrode materials, including but not limited to one or more combinations of LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2 or LiNi 08 Co 0.1 Al 0.1 O2, etc., in which case V 放 =2.8V, V 充 =4.2V.

[0050] The positive electrode lithium supplementing agent for the lithium battery in the prior art is not designed specially for high-voltage positive electrode materials, and the charging capacity thereof is concentrated near the platform, while the platform voltage of most lithium supplementing agents is low, lower than the charging cut-off potential of the high-voltage positive electrode, and when the voltage is higher than the platform in the first charging, the lithium supplementing agent releases all the capacity for lithium supplementing, and therefore can only be used for the first cycle lithium supplementing. However, the lithium ion battery also loses capacity during the cycle process, and with the cycle process, the capacity of the battery is repeatedly attenuated, and the energy density of the battery is also reduced, reducing the service life of the battery. At this time, even when the capacity of the battery is attenuated to a certain range of the initial capacity (generally 60-70%, at this time, it indicates that the capacity of the battery cannot meet the demand), even if the charging voltage is increased, since the capacity of the lithium supplementing agent is almost fully exerted in the first cycle, there is no active lithium left for supplementing the capacity of the battery at a higher charging voltage. The lithium supplementing agent rGO@Li 4+x Si 1-x Fe x O4, since the charging curve thereof is a long slope of 3.3-4.7V, the charging capacity thereof can be exerted more by increasing some potential, and after the capacity is attenuated, the second lithium supplementing can be performed when the charging voltage is increased, the capacity of the high-voltage part of the lithium supplementing agent is exerted, and the long cycle service life and efficiency of the lithium battery of the high-voltage positive electrode material are improved.

[0051] Compared with the prior art, the advantages of the present application are that:

[0052] 1. The present application can not only supplement the capacity loss of the lithium ion battery in the initial cycle, but also supplement the long-term cycle irreversible capacity loss, improve the available capacity of the battery after multiple cycles, and greatly prolong the service life of the battery;

[0053] 2. The lithium supplementing agent additive of the present application can be applied to practical high-voltage layered positive electrodes, such as LiNi x Co y Mn z O2(x+y+z=1) positive electrode, and the battery assembled by the positive electrode has higher energy density, stronger practicability and higher commercial value than other positive electrode materials;

[0054] 3. The steps of the present application are simple and easy to implement, safe, pollution-free, low in equipment and post-processing cost, and suitable for large-scale expansion and rapid use;

[0055] 4. The positive electrode lithium supplementing agent Li 4+x Si 1-x Fe xO4 is low in cost and easy to synthesize. The abundance of Si element in the earth's crust reaches 25.7%, second only to oxygen; and the abundance of Fe element in the earth's crust reaches 4.75%, ranking fourth; the silicon source and iron source used can adopt very cheap materials, thereby reducing the cost in large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 is an rGO@Li 4.1 Si 0.9 Fe 0.1 O4 synthesized in Preparation Example 1, the X-ray diffraction (XRD) comparison diagram of Li4SiO4 obtained by high-temperature sintering and the XRD standard diffraction spectrum of Li4SiO4.

[0057] Figure 2 is an rGO@Li 4.1 Si 0.9 Fe 0.1 O4 synthesized in Preparation Example 1, the X-ray diffraction (XRD) comparison diagram in the range of 26-31° after background subtraction of the XRD standard diffraction spectrum of Li4SiO4 and Li4SiO4 obtained by high-temperature sintering; b is the spectrum obtained by peak fitting in the range of 26-31° of the XRD diffraction spectrum of Li4SiO4 obtained by high-temperature sintering; c is the XRD diffraction spectrum in the range of 26-31° of rGO@Li 4+x Si 1-x Fe x O4 synthesized in Preparation Example 1.

[0058] Figure 3 is a scanning electron microscope (SEM) image of rGO@Li 4.1 Si 0.9 Fe 0.1 O4 synthesized in Preparation Example 1.

[0059] Figure 4 is a high-resolution transmission electron microscope (HRTEM) image of rGO@Li 4.1 Si 0.9 Fe 0.1 O4 synthesized in Preparation Example 1.

[0060] Figure 5 is a Raman spectrum of rGO@Li 4.1 Si 0.9 Fe 0.1 O4 synthesized in Preparation Example 1.

[0061] Figure 6 is a thermogravimetric spectrum of rGO@Li 4.1 Si 0.9 Fe 0.1 O4 synthesized in Preparation Example 1.

[0062] Figure 7 is rGO@Li 4.1 Si 0.9 Fe 0.1 O4in half-cell.

[0063] Figure 8 is rGO@Li 4.1 Si 0.9 Fe 0.1 O4, rGO@Li 4.25 Si 0.75 Fe 0.25 O4, rGO@Li 4.02 Si 0.98 Fe 0.02 O4, and Li4SiO4standard sample.

[0064] Figure 9 is rGO@Li DETAILED DESCRIPTION

[0065] The application will be further described below in connection with specific embodiments, but is not limited to the specific embodiments.

[0066] The experimental methods described in the following examples are conventional methods, unless otherwise specified; the reagents and materials described are commercially available, unless otherwise specified.

[0067] Preparation Example 1

[0068] (T1) Synthesis of rGO@Li 4.1 Si 0.9 Fe 0.1 O4: CH3COOLi powder 28.409 g (430.5 mmol), FeCl3·6H2O (10 mmol) powder 2.703 g, citric acid powder 13.129 g (68.3 mmol) were weighed and added to 500 mL of deionized water; then gas-phase SiO2 powder 5.407 g (90 mmol) was weighed and added to the solution and stirred to disperse to form a sol, and finally 240 g of graphene oxide aqueous dispersion with a mass fraction of 1 wt% was weighed and added to the sol, and an ultrasonic crusher was used to ultrasonically disperse the graphene oxide for 30 min to obtain a viscous black sol. The sol was heated in a water bath at 80°C, and the deionized water was evaporated to form a gel, and the gel was heated and dried at 150°C for 24 h to obtain a dry gel, which was scraped off and ground into powder; the dry gel powder was pre-calcined at 300°C for 3 h and then calcined at 900°C for 12 h under an Ar atmosphere, and the heating rate was 5°C / min.

[0069] (T2) The calcined product was high-energy ball-milled at 600 rpm with a ball-to-material ratio of 10:1 for 10 h. The powder obtained by ball-milling was sieved using a 2000-mesh sieve, and the powder that passed through the sieve was used as the positive electrode lithium supplement.

[0070] Figure 1 is the XRD pattern of the positive electrode lithium supplement rGO@Li 4.1 Si 0.9 Fe 0.1 O4, the crystalline Li4SiO4, and the XRD standard sample of Li4SiO4. It can be seen that all the XRD peaks in the XRD pattern of the rGO@Li 4.1 Si 0.9 Fe 0.1 O4 synthesized in Preparation Example 1 are greatly broadened.

[0071] Figure 2 , wherein a is the XRD pattern of the rGO@Li 4.1 Si 0.9 Fe 0.1 O4 synthesized in Preparation Example 1, the Li4SiO4 obtained by high-temperature sintering, and the XRD standard diffraction spectrum of Li4SiO4 in the range of 26-31° after background subtraction; the XRD diffraction spectrum of the Li4SiO4 obtained by high-temperature sintering in a in the range of 26-31° is subjected to peak fitting to obtain b, wherein the FWHM value of the 28.099° peak after fitting is 0.1373; the XRD diffraction spectrum of the rGO@Li 4+x Si 1-x Fe x O4 synthesized in Preparation Example 1 in a in the range of 26-31° is subjected to peak fitting to obtain c, wherein the FWHM value of the 28.049° peak after fitting is 0.6089. Calculation by the Scherrer formula shows that the crystallite size of the Li4SiO4 obtained by high-temperature sintering in the direction normal to the crystal face is 59.1 nm; and the crystallite size of the rGO@Li 4+x Si 1-x Fe x O4 synthesized in Preparation Example 1 in the direction normal to the crystal face is 13.3 nm.

[0072] Figure 3 is the scanning electron microscope (SEM) image of the lithium supplement rGO@Li 4.1 Si 0.9 Fe 0.1 O4 obtained in Preparation Example 1. It can be seen that the particle size of the material is 0.5-5 μm.

[0073] Figure 4rGO@Li 4.1 Si 0.9 Fe 0.1 O4. It can be observed from the figure that the particle surface has a carbon coating layer between 2-10 nm; the particle interior has a crystalline region, and the lattice fringe spacing of the region is 0.316 nm, corresponding to the crystal face At the same time, the length of the region in the normal direction of the lattice fringe is 13.5 nm, which is close to the calculated value of 13.3 nm, also indicating that the calculation of the crystallite size in the particle interior is correct.

[0074] Figure 5 rGO@Li 4.1 Si 0.9 Fe 0.1 O4 synthesized in Preparation Example 1. It can be seen that the I D / I G value is 1.14, indicating that the obtained lithium supplement has a high degree of graphitization.

[0075] Figure 6 rGO@Li 4.1 Si 0.9 Fe 0.1 O4 synthesized in Preparation Example 1. It can be seen that the I 4.1 / I 0.9 value of rGO@Li 0.1 O4 is 12.7wt%.

[0076] Figure 7 rGO@Li 4+x Si 1-x Fe x O4 prepared in Preparation Example 1 in a half-cell, the voltage interval is 2.5-4.7 V, and the charging and discharging is in a constant current mode, the rate is 0.02C, and no constant voltage charging section is added. When charged to 4.7 V, the specific capacity of the material is 669.5 mAh / g; in actual application, the material delivers a capacity of ~435 mAh / g when charged to 4.2 V in the first cycle, and a capacity of ~190 mAh / g when charged to 4.2-4.6 V.

[0077] Preparation Example 2

[0078] The other conditions are the same as those in Preparation Example 1, except that in step (T1), the amounts of CH3COOLi powder, gaseous SiO2 powder and FeCl3 are adjusted so that Li:Si:Fe = 4.46:0.75:0.25. The obtained graphene oxide modified Li 4.25 Si 0.75Fe 0.25 O4 as the lithium supplement of the present application. The XRD of the product obtained is shown in Fig. 2, from which the impurity peak of Li5FeO4, as indicated by the orange star, can be found. The charge capacity of the material is also decreased, as shown in Fig. 3, the first cycle charge capacity is 307.6 mAh / g. Figure 8 Figure 9

[0079] Preparation Example 3

[0080] The other conditions are the same as those in Preparation Example 1, except that in step (T1), the amounts of CH3COOLi powder, gas-phase SiO2 powder and FeCl3 are adjusted so that Li:Si:Fe = 4.22:0.98:0.02. The graphene oxide-modified Li 4.05 Si 0.95 Fe 0.05 O4 as the lithium supplement of the present application. The XRD of the product obtained is shown in Fig. 2, from which the impurity peak of Li5FeO4, as indicated by the orange star, can be found. The charge capacity of the material is also decreased, as shown in Fig. 3, the first cycle charge capacity is 307.6 mAh / g. Figure 8 Figure 9

[0081] Figure 8 is the XRD comparison chart of the Li 4.1 Si 0.9 Fe 0.1 O4 obtained in Preparation Example 1, the Li 4.25 Si 0.75 Fe 0.25 O4 obtained in Preparation Example 2, the Li 4.02 Si 0.98 Fe 0.02 O4 obtained in Preparation Example 3, and a Li4SiO4 standard sample. In the chart, the impurity peak of Li5FeO4 in the Li 4.25 Si 0.75 Fe 0.25 O4 obtained in Preparation Example 2 is indicated by the star, and the impurity peak of Li2SiO3 in the Li 4.02 Si 0.98 Fe 0.02 O4 obtained in Preparation Example 3 is indicated by the star.

[0082] Comparative Preparation Example 1

[0083] The other conditions are the same as those in Preparation Example 1, except that in step (T1), no graphene oxide and citric acid are added, obtaining Li 4.1 Si 0.9 Fe 0.1 O4 without carbon coating. In the absence of carbon coating, the electronic conductivity of the material is greatly decreased, only 1.24 x 10​​​​-9 S / cm, which is 0.56 S / cm, a decrease of 8 orders of magnitude in electronic conductivity compared to the material of Example 1; the reaction on the performance of the material is that the first cycle charge capacity of the material is greatly reduced, as shown in the figure, the purple curve represents the first cycle charge-discharge curve of the product of this example, and the first cycle charge capacity is only 184.9 mAh / g. Figure 9

[0084] Comparative Preparation Example 2

[0085] The other conditions are the same as those of Preparation Example 1, and the difference is that step (T2) is not performed. Without performing step (T2), the doping solid-phase reaction cannot occur, and the first cycle charge capacity is greatly reduced, as shown in the figure, the blue curve represents the first cycle charge-discharge curve of the product of this example, and the first cycle charge capacity is only 162.5 mAh / g. Figure 9

[0086] Figure 9 is the positive electrode lithium supplement rGO@Li 4.1 Si 0.9 Fe 0.1 O4, the positive electrode lithium supplement rGO@Li 4.25 Si 0.75 Fe 0.25 O4of Preparation Example 2, the positive electrode lithium supplement rGO@Li 4.02 Si 0.98 Fe 0.02 O4of Preparation Example 3, the Li 4.1 Si 0.9 Fe 0.1 O4without rGO composite of Comparative Preparation Example 1, and the rGO@Li 4.1 Si 0.9 Fe 0.1 O4of Preparation Example 3 without step (T2). It can be seen that whether the amount of iron doping is too much or too little, or rGO is not used for modification, or step (T2) is omitted, the first cycle charge capacity of the material is greatly reduced.

[0087] Example 1

[0088] (S1) Take 240 mg of the lithium supplement prepared in Preparation Example 1, add 30 mg of Super P and 30 mg of PVDF, and then add 800 μL of NMP, uniformly mix into a slurry, uniformly coat on a Celgard polypropylene separator at a thickness of 10 μm, dry at 60°C for 3 h, and then place in a vacuum oven at 60°C overnight to obtain a positive electrode lithium supplement separator. The prepared lithium supplement separator is punched into a Φ = 16 mm round sheet. An active positive electrode material LiNi 0.8 Co 0.1 Mn​​0.1 O2, Super P and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 80:10:10 to form a slurry, which was uniformly coated on an aluminum foil current collector, punched into a Φ = 10 mm round sheet to obtain a working electrode; the negative material graphite, SiO / C (from Jiangxi Yijin, product number HL-1400), Super P and polyacrylate binder were mixed in a mass ratio of 68:12:10:10 to form a slurry, which was uniformly coated on a copper foil current collector, punched into a Φ = 10 mm round sheet to obtain a counter electrode; 1 mol / L ternary electrolyte (1M LiPF6 EC / DEC / DMC (volume ratio 1:1:1)) was used as the electrolyte, and the obtained lithium supplementing diaphragm round sheet was used as the diaphragm to assemble a 2032 type button cell in a glove box, wherein the side coated with the novel lithium supplementing agent was in contact with the positive electrode, and the mass ratio of the active positive electrode material to the novel lithium supplementing agent was about 10:1. The assembled battery will be subjected to charge and discharge test on a LAND charge and discharge tester.

[0089] (S2) Long cycle test: In the first three cycles, the battery was charged and discharged at a rate of 0.1C of the battery, the charge cut-off voltage was 4.2V, and the discharge cut-off voltage was 2.8V. From the 4th cycle, the battery was cycled at a rate of 1C in the range of 2.8-4.2V. When the battery discharge capacity decreased to less than 70% of the initial discharge capacity at the 363rd cycle, the battery was charged at a rate of 0.1C of the positive active material to 4.6V and then discharged at a rate of 1C to 2.8V at the 364th cycle, and the battery discharge capacity recovered to 80% of the initial discharge capacity. From the 365th cycle, the battery was cycled at a rate of 1C in the range of 2.8-4.2V. When the battery discharge capacity decreased to less than 60% of the initial discharge capacity, the cycle was terminated.

[0090] Example 2

[0091] (S1) The active positive electrode material LiNi 0.8 Co 0.1 Mn 0.1O2. The lithium replenishing agent, Super P and polyvinylidene fluoride (PVDF) binder obtained in Example 1 were mixed in a mass ratio of 72:8:10:10 to form a slurry, which was uniformly coated onto an aluminum foil current collector to obtain a lithium replenishing positive electrode sheet. The slurry was cut and punched into a disc with a diameter of 10 mm to serve as the working electrode. The negative electrode material, graphite, SiO / C, Super P and polyacrylate binder were mixed in a mass ratio of 68:12:10:10 to form a slurry, which was uniformly coated onto a copper foil current collector. The disc was cut and punched into a disc with a diameter of 10 mm to obtain the counter electrode. A 1 mol / L ternary electrolyte (1 M LiPF6 EC / DEC / DMC (volume ratio 1:1:1)) was used as the electrolyte, and polypropylene (purchased from Celgard, USA) cut into discs with a diameter of 16 mm was used as the separator. The 2032 coin cell was assembled in a glove box, and the assembled battery was tested for charge and discharge on a LAND charge and discharge tester.

[0092] (S2) Long Cycle Test: In the first three cycles, the battery is charged and discharged at a rate of 0.1C, with a charging cut-off voltage of 4.2V and a discharging cut-off voltage of 2.8V. From the fourth cycle onwards, the battery is cycled at a rate of 1C within the range of 2.8V to 4.2V. By the 305th cycle, the battery discharge capacity has dropped to below 70% of the initial discharge capacity. In the 306th cycle, the battery is charged to 4.6V at a rate of 0.1C with the positive electrode active material, and then discharged to 2.8V at a rate of 1C, restoring the battery discharge capacity to 80% of the initial discharge capacity. From the 307th cycle onwards, the battery is cycled at a rate of 1C within the range of 2.8V to 4.2V. The cycle is terminated when the battery discharge capacity drops to below 60% of the initial discharge capacity.

[0093] Example 3

[0094] (S1) Preparation of the positive electrode sheet: The active positive electrode material LiNi... 0.8 Co 0.1 Mn 0.1O2, Super P and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 80:10:10 to form a slurry, which was uniformly coated on an aluminum foil current collector, punched into a Φ = 10 mm round sheet, and obtained as a positive electrode sheet for standby; 270 mg of the positive electrode lithium supplement obtained in Preparation Example 1, 30 mg of Super P, and 30 mg of PVDF were added, and 800 μL of NMP was further added to uniformly mix into a slurry, which was coated on the positive electrode sheet at a thickness of 10 μm, punched into a Φ = 10 mm round sheet, and used as a working electrode; a negative electrode material graphite, SiO / C, Super P, and a polyacrylate binder were mixed in a mass ratio of 68:12:10:10 to form a slurry, which was uniformly coated on a copper foil current collector, punched into a Φ = 10 mm round sheet, and obtained as a counter electrode; 1 mol / L ternary electrolyte (1M LiPF6 EC / DEC / DMC (volume ratio 1:1:1)) was used as an electrolyte, and a Φ = 16 mm round sheet of polypropylene (purchased from Celgard, USA) was used as a separator, and a 2032 type button cell was assembled in a glove box, and the assembled cell was subjected to charge and discharge tests on a LAND charge and discharge tester.

[0095] (S2) Long cycle test: in the first three cycles, the battery was charged and discharged at a rate of 0.1C of the battery, the charge cut-off voltage was 4.2V, and the discharge cut-off voltage was 2.8V. From the 4th cycle, the battery was cycled at a rate of 1C in the range of 2.8-4.2V. When the battery discharge capacity decreased to less than 70% of the initial discharge capacity at the 281st cycle, the battery was cycled at a rate of 1C of the positive electrode active material at the 282nd cycle, charged to 4.6V, and discharged to 2.8V, and the battery discharge capacity recovered to 80% of the initial discharge capacity. From the 283rd cycle, the battery was cycled at a rate of 1C in the range of 2.8-4.2V. When the battery discharge capacity decreased to 60% of the initial discharge capacity, the cycle was terminated.

[0096] Example 4

[0097] (S1) The other conditions were the same, except that when the battery was assembled, the negative electrode used carbon-coated SiO.

[0098] (S2) Long cycle test: In the first three cycles, the battery was charged and discharged at 0.1C rate of the battery, the charge cut-off voltage was 4.2V, and the discharge cut-off voltage was 2.8V. From the 4th cycle, the battery was cycled at 1C rate in the range of 2.8-4.3V. When the battery discharge capacity dropped to below 70% of the initial discharge capacity at the 167th cycle, the battery was charged at 0.1C rate of the positive active material to 4.6V and then discharged at 1C rate to 2.8V at the 168th cycle, and the battery discharge capacity recovered to 80% of the initial discharge capacity. From the 169th cycle, the battery was cycled at 1C rate in the range of 2.8-4.2V. The cycle was terminated when the battery discharge capacity dropped to below 60% of the initial discharge capacity.

[0099] Example 5

[0100] (S1) The other conditions were the same except that when assembling the battery, the positive electrode used LiNi 0.5 Co 0.2 Mn 0.3 O2,

[0101] (S2) Long cycle test: In the first cycle, the battery was charged and discharged at 0.1C rate of the battery, the charge cut-off voltage was 4.2V, and the discharge cut-off voltage was 2.8V. From the 2nd cycle, the battery was cycled at 1C rate in the range of 2.8-4.2V. When the battery discharge capacity dropped to below 60% of the initial discharge capacity at the 368th cycle, the battery was charged at 0.1C rate of the positive active material to 4.6V and then discharged at 1C rate to 2.8V at the 369th cycle, and the battery discharge capacity recovered to 82% of the initial discharge capacity. From the 370th cycle, the battery was cycled at 1C rate in the range of 2.8-4.2V. The cycle was terminated when the battery discharge capacity dropped to below 60% of the initial discharge capacity.

[0102] Example 6

[0103] (S1) The other conditions were the same except that when assembling the battery, the positive electrode used LiNi 0.8 Co 0.15 Al 0.5 O2,

[0104] (S2) Long cycle test: In the first three cycles, the battery was charged and discharged at 0.1C rate of the battery, the charge cut-off voltage was 4.2V, and the discharge cut-off voltage was 2.8V. From the 4th cycle, the battery was cycled at 1C rate in the range of 2.8-4.2V. When the battery discharge capacity decreased to less than 70% of the initial discharge capacity at the 243rd cycle, the battery was charged at 0.1C rate of the positive active material to 4.6V and then discharged at 1C rate to 2.8V at the 244th cycle, and the battery discharge capacity recovered to 80% of the initial discharge capacity. From the 245th cycle, the battery was cycled at 1C rate in the range of 2.8-4.2V. The cycle was terminated when the battery discharge capacity decreased to less than 60% of the initial discharge capacity.

[0105] Example 7

[0106] (S1) The other conditions were the same except that LiCoO2was used as the positive active material and graphite was used as the negative active material when assembling the battery.

[0107] (S2) Long cycle test: In the first three cycles, the battery was charged and discharged at 0.1C rate of the battery, the charge cut-off voltage was 4.2V, and the discharge cut-off voltage was 2.8V. From the 4th cycle, the battery was cycled at 1C rate in the range of 2.8-4.2V. When the battery discharge capacity decreased to less than 70% of the initial discharge capacity at the 597th cycle, the battery was charged at 0.1C rate of the positive active material to 4.6V and then discharged at 1C rate to 2.8V at the 598th cycle, and the battery discharge capacity recovered to 84% of the initial discharge capacity. From the 599th cycle, the battery was cycled at 1C rate in the range of 2.8-4.2V. The cycle was terminated when the battery discharge capacity decreased to less than 60% of the initial discharge capacity.

[0108] Example 8

[0109] (S1) The other conditions were the same except that LiFePO4was used as the positive active material and graphite was used as the negative active material when assembling the battery.

[0110] (S2) Long cycle test: In the first three cycles, the battery was charged and discharged at 0.1C rate of the battery, the charge cut-off voltage was 3.8V, and the discharge cut-off voltage was 2.8V. From the 4th cycle, the battery was cycled at 1C rate in the range of 2.8-3.8V. When the battery discharge capacity dropped to less than 70% of the initial discharge capacity at the 755th cycle, the battery was charged at 0.1C rate of the positive active material to 4.2V and then discharged at 1C rate to 2.8V at the 756th cycle, the battery discharge capacity recovered to 83% of the initial discharge capacity. From the 757th cycle, the battery was cycled at 1C rate in the range of 2.8-3.8V. When the battery discharge capacity dropped to less than 70% of the initial discharge capacity at the 1059th cycle, the battery was charged at 0.1C rate of the positive active material to 4.6V and then discharged at 1C rate to 2.8V at the 1060th cycle, the battery discharge capacity recovered to 83% of the initial discharge capacity. From the 1061th cycle, the battery was cycled at 1C rate in the range of 2.8-3.8V. The cycle was terminated when the battery discharge capacity dropped to less than 60% of the initial discharge capacity.

[0111] Example 9

[0112] Other conditions were the same except that the lithium supplementing agent prepared in Preparation Example 2 was used when preparing the positive electrode lithium supplementing separator.

[0113] Example 10

[0114] Other conditions were the same except that the lithium supplementing agent prepared in Preparation Example 3 was used when preparing the positive electrode lithium supplementing separator.

[0115] Comparative Example 1:

[0116] (S1) Other conditions were the same except that when assembling the battery, the battery separator used was a commercial Celgard polypropylene separator.

[0117] (S2) Long cycle test: In the first three cycles, the battery was charged and discharged at 0.1C rate of the battery, the charge cut-off voltage was 3.8V, and the discharge cut-off voltage was 2.8V. From the 4th cycle, the battery was cycled at 1C rate in the range of 2.8-3.8V. When the battery discharge capacity dropped to less than 70% of the initial discharge capacity at the 755th cycle, the battery was charged at 0.1C rate of the positive active material to 4.2V and then discharged at 1C rate to 2.8V at the 756th cycle, the battery discharge capacity recovered to 83% of the initial discharge capacity. From the 757th cycle, the battery was cycled at 1C rate in the range of 2.8-3.8V. When the battery discharge capacity dropped to less than 70% of the initial discharge capacity at the 1059th cycle, the battery was charged at 0.1C rate of the positive active material to 4.6V and then discharged at 1C rate to 2.8V at the 1060th cycle, the battery discharge capacity recovered to 83% of the initial discharge capacity. From the 1061th cycle, the battery was cycled at 1C rate in the range of 2.8-3.8V. The cycle was terminated when the battery discharge capacity dropped to less than 60% of the initial discharge capacity.

[0118] The charge-discharge results were that after the 362nd cycle, the discharge capacity dropped to 60% of the first cycle discharge capacity, and the cycle was stopped.

[0119] Comparative Example 2:

[0120] Other conditions were the same except that the lithium supplementing agent prepared in Comparative Preparation Example 1 was used.

[0121] Comparative Example 3:

[0122] All other conditions were the same, except that the lithium supplement prepared in Comparative Example 2 was used.

[0123] Table 1 Comparison of Results from Different Embodiments

[0124]

[0125] As can be seen from the above embodiments, the novel lithium-ion battery multi-platform cathode lithium replenishment agent graphene oxide-modified Li provided by the present invention... 4+x Si 1-x Fe x O4 combined with on-demand lithium replenishment has a good effect on mitigating irreversible battery capacity degradation. It not only replenishes the lithium-ion loss in the first cycle, but also replenishes the capacity loss in the cycle. It can be applied to battery systems using high-voltage ternary cathodes, which greatly slows down the capacity decline trend of high-energy-density batteries and extends battery life.

[0126] This invention can be extended to various lithium battery systems, including but not limited to battery systems obtained by combining various positive and negative electrode materials: wherein the positive electrode materials include, but are not limited to, LiCoO2, LiFePO4, LiMn2O4, and LiNi. x Co y Mn z O2(x+y+z=1), LiNi x Co y Al z This invention fills a gap in high-voltage layered positive electrodes by using one or more mixtures of O2 (x+y+z=1), LiNiO2, LiVO2, and LiVO3. The negative electrode materials include, but are not limited to, graphite, Si, SiO / C, and composite negative electrodes obtained by combining these three materials in any form and proportion, as well as carbon-based negative electrodes other than graphite such as hard carbon, alloy-based negative electrodes other than Si such as Sn, conversion-based negative electrodes such as Fe2O3, and Li4Ti5O3. 12 One or more of the negative electrode, etc.

[0127] In summary, this invention can replenish lithium multiple times during the first cycle and long-term cycle and can be applied to high-voltage layered cathodes, which is very valuable. The implementation method is simple and low-cost. It achieves efficient lithium replenishment on the cathode side to alleviate the capacity decay of lithium-ion batteries, and is safe and pollution-free. It is compatible with existing battery production systems and has high application prospects.

Claims

1. A lithium ion battery lithium supplementing method, characterized in that, The method comprises the following steps: (S1) Assemble a lithium-ion battery containing a lithium replenishing agent; the lithium replenishing agent is Li-ion battery modified with reduced graphene oxide. 4+a Si 1- a Fe a O4, 0.5 ≥ a ≥ 0.01; the lithium supplement agent is on the crystal plane ( The crystallite size in the normal direction is less than 20 nm; the cathode material of the lithium-ion battery is the ternary cathode material LiNi. x Co y Mn z O2, x+y+z=1; (S2) Perform lithium-ion battery cycling, first cycle in the voltage range of V 充 to V 放 , when the battery capacity decreases to 70-90% of the initial discharge capacity, in the next cycle the charge cut-off voltage is increased by 0.2-0.4V based on the charge cut-off voltage of the previous cycle or the last increase, if the charge cut-off voltage before the increase reaches 4.6V or above, no longer increase, discharge to V 放 , then the battery continues to cycle in the voltage range of V 充 to V 放 , until the capacity decays to below 60% of the initial capacity, stop cycling; V 放 = 2.8V, V 充 = 4.2V.

2. The lithium supplementing method according to claim 1, wherein 0.3≥a≥0.05。 3. The lithium supplementing method according to claim 1, wherein 0.15≥a≥0.10。 4. The lithium supplementing method according to claim 1, wherein The particle size of the lithium supplement agent is 0.1-50 μm.

5. The lithium supplementing method according to claim 1, wherein The particle size of the lithium supplement agent is 0.5-5 μm.

6. The lithium supplementing method according to claim 1, wherein The lithium supplement agent is on the crystal plane ( The crystallite size in the normal direction is 8-15 nm.

7. The lithium supplementing method according to claim 1, wherein The carbon content of the lithium supplement agent is 0.5wt%-25wt%.

8. The lithium supplementing method according to claim 1, wherein The carbon content of the lithium supplement agent is 5wt%-15wt%.

9. The lithium supplementing method according to claim 1, wherein The Raman spectrum of the lithium supplementing agent has I D / I G The value is 0.8-1.2, I D I represents the integral intensity of the carbon peak D band in the Raman spectrum, I G I represents the integral intensity of the carbon peak G band in the Raman spectrum.

10. The lithium supplementing method according to claim 1, wherein The lithium supplement agent is prepared by a preparation method comprising the following steps: (T1) preparing rGO-composite crystalline Li 4+a Si 1-a Fe a O4 materials; (T2) reducing the crystallite size of the material by high-energy ball milling, to obtain rGO@Li 4+a Si 1-a Fe a O4 material; Step (T1) is one of the following methods A, B, C and D: Method A: lithium source, silicon source and iron source are weighed according to the stoichiometric ratio, and graphene oxide solid is added, mixed uniformly, pre-burned and calcined to obtain the lithium supplement agent; Method B: lithium source, silicon source and iron source are weighed according to the stoichiometric ratio, dispersed in a solvent, and graphene oxide dispersion liquid dispersed in the solvent is added, the precipitate is obtained by heating and drying the solvent, and then grinding, pre-burning and calcining are performed to obtain the lithium supplement agent; Method C: lithium source, silicon source, iron source and complexing agent are weighed according to the stoichiometric ratio, dispersed in a solvent, and graphene oxide dispersion liquid dispersed in the solvent is added to obtain a sol, the dry gel is obtained by heating and drying the solvent, and then grinding, pre-burning and calcining are performed to obtain the lithium supplement agent; Method D: lithium source, silicon source and iron source are weighed according to the stoichiometric ratio, dispersed in a solvent, and graphene oxide dispersion liquid dispersed in the solvent is added, and the solvothermal reaction is carried out under heating in a sealed kettle, and then centrifugation, washing, drying, grinding, pre-burning and calcining are performed to obtain the lithium supplement agent.

11. The lithium supplementing method according to claim 10, wherein The lithium source is a lithium-containing solid compound, including one or a combination of lithium carbonate, lithium hydroxide monohydrate, lithium nitrate, lithium acetate and lithium oxide; the silicon source includes one or a combination of SiO2 powder, silicic acid, tetraethyl orthosilicate, tetra-n-butyl orthosilicate, diatomite, vermiculite, zeolite, SBA-15, waste silicon, biomass ash, fly ash and halloysite; the iron source includes one or a combination of iron oxalate, iron nitrate, basic iron acetate, iron oxide, iron carbonate and iron hydroxide; the complexing agent is an organic chelating agent for coordinating with metal ions; the solvent-dispersed graphene oxide refers to a mixture liquid in which graphene oxide is uniformly dispersed in a solvent without agglomeration, and the mass fraction of graphene oxide in the dispersion liquid is between 0.5wt% and 5wt%.

12. The lithium supplementing method according to claim 11, wherein The complexing agent includes one or a combination of citric acid, ethylene glycol, polyvinylpyrrolidone and polyacrylic acid.

13. The lithium supplementing method according to claim 10, wherein In step (T2), the high-energy ball milling is carried out at 500-800 rpm and a ball-to-material ratio of 10-80:1 for 5-40 h, and then sieving is performed with a mesh size of 400-2000.

14. The lithium supplementing method according to claim 1, wherein In step (S1), the method for adding the lithium supplement agent in the lithium ion battery includes one of method X, method Y and method Z: Method X: the slurry containing the lithium supplement agent is coated on the separator positive electrode; Method Y: the lithium supplement agent and the active positive electrode material are slurried together, and then coated on the current collector to obtain a positive electrode sheet; Method Z: the slurry containing the lithium supplement agent is coated on the prepared positive electrode sheet.

15. The lithium supplementing method according to claim 14, wherein In Method X, the lithium supplement agent and the binder are dispersed in an organic solvent to form a slurry, which is coated on the positive side of the separator and the organic solvent is dried; the separator is a polyolefin porous separator with a thickness of 8-50 μm; the slurry further comprises a binder, one or a combination of polyvinylidene fluoride, polyacrylonitrile, and polyethylene glycol; the organic solvent comprises one or a combination of N-methylpyrrolidone, dimethyl sulfoxide, and N,N-dimethylformamide; the thickness of the coating layer is between 0.5-10 μm after the slurry is dried.

16. The lithium supplementing method according to claim 15, wherein The polyolefin porous separator comprises polypropylene or polyethylene.

17. The lithium supplementing method according to claim 15, wherein The polyolefin porous separator has a thickness of 8-20 μm.

18. The lithium supplementing method according to claim 15, wherein The thickness of the coating layer is between 1-5 μm.

19. The lithium supplementing method according to claim 14, wherein In the method Y, the raw materials including the lithium supplement, the active positive electrode material, the conductive additive and the binder are mixed to form a slurry, which is coated on the current collector to obtain the working electrode; the positive electrode material includes the layered positive electrode material, the olivine positive electrode material and the corresponding doped modified positive electrode material, including LiCoO2, LiFePO4, LiMn2O4, LiNi x Co y Mn z O2, LiNi x Co y Al z O2, wherein x+y+z=1, LiNiO2, LiVO2, LiVO3 in one or more combinations; the conductive additive includes one and more combinations of Super P, Ketjen black, CMK-3, conductive carbon tube, graphene.

20. The lithium supplementing method according to claim 14, wherein In Method Z, the lithium supplement agent and the binder are dispersed in an organic solvent to form a slurry, which is coated on the surface of the positive electrode sheet that has been coated, and the lithium supplement agent accounts for 1-20 wt% of the active positive electrode material.

21. The lithium supplementing method according to claim 20, wherein The lithium supplement agent accounts for 3-10 wt% of the active positive electrode material.

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