CN115863797A - Lithium supplement agent suitable for high-voltage positive electrode and preparation method and application thereof - Google Patents

Abstract

The invention relates to a lithium supplement agent suitable for a high-voltage positive electrode, and a preparation method and application thereof, wherein the lithium supplement agent is Li modified by reduced graphene oxide _4+x Si _1‑x Fe _x O ₄ And x is more than or equal to 0.5 and more than or equal to 0.01. The invention can not only supplement the capacity loss of the lithium ion battery in the initial cycle, but also supplement the irreversible capacity loss in the long-term cycle, improve the available capacity of the battery after multiple cycles and greatly prolong the service life of the battery; the lithium supplement additives of the present invention can be applied to high voltage layered positive electrodes, such as LiNi _x Co _y Mn _z O ₂ (x + y + z = 1) positive electrode, and the battery assembled by the positive electrode material has higher energy than other positive electrode materialsThe density, the practicality is stronger, and commercial value is higher. The steps executed by the invention are simple and easy to implement, are safe and pollution-free, have low equipment and post-treatment cost, are adapted to the current battery production process, are suitable for large-scale amplification and can be quickly put into use.

Description

Lithium supplement agent suitable for high-voltage positive electrode and preparation method and application thereof

Technical Field

The invention belongs to the field of lithium ion batteries, and relates to a lithium supplement agent suitable for a high-voltage positive electrode, and a preparation method and application thereof.

Background

In the modern times, energy shortage and greenhouse effect have become major crises facing mankind. In the face of crisis, it is imperative to replace fossil energy with clean renewable energy, but renewable energy cannot be continuously and stably output, and in order to solve this problem, it is necessary to develop a high-performance energy storage system, such as a lithium ion battery system, which is attracting attention. Since the sony corporation applied the lithium ion battery to the mobile phone in 1991, the lithium ion battery rapidly occupies the market of the battery of the electronic product, and the development of the electric automobile further widens the corresponding market nowadays.

However, the current lithium cobaltate-graphite (LiCoO) ₂ The energy density of the (LCO) -Gr) lithium ion battery system is close to the limit, the requirements of power batteries and electronic product batteries on the energy density are continuously improved, and the battery system using higher specific energy is imperative. The most promising high energy density battery system for commercial applications today is the high voltage positive-composite negative electrode system, such as LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM 811) a positive electrode-SiO/C + graphite composite negative electrode system, wherein the system uses an NCM811 positive electrode (LCO positive electrode is 170 mAh/g) with the reversible capacity of about 200mAh/g and a SiO/C + graphite composite negative electrode (wherein the reversible capacity of the SiO/C negative electrode is about 1400mAh/g, the Gr negative electrode is about 360mAh/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 is continuously disturbed by the irreversible loss of the battery capacity in the use process, the composite negative electrode consumes a large amount of active lithium to generate SEI in the first cycle, and the composite negative electrode in the subsequent cycleThe SiO/C also can generate the conditions of particle fragmentation, side reaction with electrolyte and the like, so that the battery capacity is continuously reduced in the circulating process, the energy density and the service life of the battery are reduced, and the use of power supply equipment is influenced.

Prelithiation technique for irreversible loss of Li in a battery ⁺ Provides extra Li supplement and has wide prospect, including anode lithium supplement, cathode lithium supplement and diaphragm lithium supplement. The positive pole lithium supplement agent is a positive pole lithium supplement mode, and means that a certain high-capacity lithium-rich material is used, lithium is released on the positive pole side in the first cycle, and the lithium loss of the first cycle of the battery is supplemented. However, the pre-lithiation technique, including the positive electrode lithium supplement, has a disadvantage in that Li supplementation is only possible for capacity loss in the initial cycle, and Li loss in the long-term cycle cannot be supplemented. In view of this, CN113540591B discloses a method for lithium supplement of positive electrode, which increases the charging voltage of battery in a plurality of times during long-term circulation to supplement lithium for a plurality of times, wherein the lithium supplement agent used is a conventional lithium supplement agent, such as Li ₂ NiO ₂ 、Li ₅ FeO ₄ 、Li ₂ CuO ₂ 、Li ₆ CoO ₄ 、Li ₃ N、Li ₂ S, and the like; however, the capacity of these lithium replenishing agents is concentrated near the plateau, and when lithium is replenished during the circulation, the voltage gradually rises and exceeds the voltage plateau of the lithium replenishing agent, so that the capacity that the lithium replenishing agent can exert during the circulation is very small, and the capacity that can be replenished to the battery is also very small, for example, li ₅ FeO ₄ The charging platform has nearly full play of charging capacity when the charging platform is charged to 4.1V at 3.6V and 3.9V, and the charging platform has no charging capacity when the voltage is increased to be more than 4.1V during lithium supplement in circulation, so that the voltage is increased meaninglessly. Most importantly, the positive electrode lithium supplement agent in the patent method cannot be used for a high-voltage high-specific-capacity positive electrode material such as an NCM811 positive electrode, because the NCM811 generally needs to be charged to 4.2V to exert the capacity of 200mAh/g, and the capacity of the lithium supplement agent is fully exerted at this moment, so that the voltage cannot be increased in subsequent cycles to supplement lithium continuously; in order to implement the strategy of voltage boosting and step-by-step lithium supplement, in example 10 of the patent, the charge cut-off voltage of the non-lithium supplement cycle of the NCM811 battery is limited to 3.8V, and at this time, the NCM811 only exerts a capacity of about 100mAh/g and is only of a normal capacityThe method is a method for using the material of GmbH 26911and the method for using the ball completely loses the meaning of using the material of high pressure and high specific capacity. In summary, the lithium supplementing method in this patent is only suitable for low-voltage lithium iron phosphate (LiFePO) ₄ ) Batteries, even not suitable for current LCO batteries, let alone high specific energy battery systems using NCM811 positive electrodes.

Li ₄ SiO ₄ Is a matrix material of a lithium ion conductor and is widely researched CO ₂ Trapping materials, the prior art has been much studied. In order to increase the applicability, some high valence ions are doped, such as boron (B), aluminum (Al), vanadium (V), iron (Fe). At present, al-doped Li has also been reported ₄ SiO ₄ As lithium-supplementing agents, for example, patent CN 112467122A reports the use of metal-doped Li ₄ Si _1-y X _y O ₄ The material is used as a lithium supplement agent, however, the lithium removal potential of the material is high, the material needs to be charged to 4.6V and charged at constant voltage to exert the capacity, and almost all the capacity needs to be charged to more than 4.4V to exert the capacity. The charging curve determines that the lithium supplement agent can only play all capacities once and cannot play a lithium supplement effect in the first circle and the cycle.

In conclusion, a lithium supplement compound which can supplement lithium for many times in the first cycle and the long-term cycle and can be applied to a high-voltage layered positive electrode and a matched lithium supplement method are very valuable.

Disclosure of Invention

In order to supplement active lithium lost in the first cycle and the circulation for a battery system using a high-voltage positive electrode material of a lithium ion battery, such as a high-nickel NCM ternary positive electrode material, and improve the service life and the energy density of the battery system, the invention particularly provides a lithium supplement agent suitable for a high-voltage layered positive electrode and an application method thereof, and the lithium supplement agent is reduced graphene oxide (rGO) modified Li _4+x Si _{1- x} Fe _x O ₄ (rGO@Li _4+x Si _1-x Fe _x O ₄ )，0.5≥x≥0.01。

Further, 0.3. Gtoreq.x.gtoreq.0.05, more preferably, 0.15. Gtoreq.x.gtoreq.0.10.

The inventors found that the ratio of Fe to SiThe influence of the value on the lithium supplement agent is relatively large, and the optimal lithium supplement effect can be achieved within a specific range. If the Fe content is too high, li will remain in the final product ₅ FeO ₄ Phase, and Li ₅ FeO ₄ After the treatment of the invention, the material has no capacity, thus leading to the reduction of the whole capacity of the material; if the amount of Fe to be added is too small, the Fe element does not exert a doping effect, and part of Li ₄ SiO ₄ Decomposition into Li in ball milling ₂ SiO ₃ Therefore, the ratio of Fe to Si needs to be chosen carefully.

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

Furthermore, in an XRD spectrum of the lithium supplement agent of the high-voltage positive electrode, the diffraction peak width is greatly widened. This is because the crystallite size of the material decreases after ball milling. The so-called crystallite size, not the size of the material particles: for a typical polycrystalline material, the grains of each material are not completely crystallized, each internal atom is not perfectly arranged according to the arrangement rule of crystals, the inside of each material contains a plurality of tiny crystal regions, the arrangement of the internal atoms of each crystal region is relatively regular, and a region with poor crystallinity and disordered atomic arrangement is arranged between the internal atoms of each crystal region. When the size of the microcrystal is reduced, lithium ions in the material can be extracted from a crystalline region at a shorter distance and then conducted to the outer side of the particle from an amorphous region; after doping, the lithium ion conductivity of the material in the amorphous region is increased, and lithium ions are more easily conducted to the outside, so that the strategies of doping and reducing the crystallite size are complementary, the polarization of the material can be simultaneously reduced, and the delithiation potential of the material is further reduced. The present material is advanced compared to the material in CN 112467122A in that: the lithium supplement provided by CN 112467122A has a charging capacity of more than 4V, and the capacity is 100mAh/g at 4.5V; the material of the present invention has a much lower delithiation potential than the former, for example, rGO @ Li in preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ The capacity was developed at 3.3V, 435mAh/g at 4.2V and 615mAh/g at 4.6V, because of which the material could develop capacity step by voltage controlAnd (5) supplementing lithium in the first circle and the cycle. If this strategy is applied to the lithium supplement provided in CN 112467122A, the capacity of the material to be charged to 4.2V is too low to function in the first cycle and the cycle. This advantage is derived from the very reduction of crystallite size.

By fitting the diffraction peaks, the crystallite size of the material can be calculated from the width of the fitted peaks. The Width generally used is a Full Width at Half Maximum (FWHM), that is, the Width of a peak of a diffraction peak at Half of the total height (Y value at the peak), and is calculated according to the scherrer equation (equation 1) after conversion into a radian.

In the formula, D represents a crystallite size, K represents a scherrer constant (generally taken to be 0.89), γ represents a wavelength of X-rays used when X-ray diffraction is performed, and γ =1.54 angstroms when Cu ka light is generally used; β is the camber 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 is selected, and the physical meaning of the D value is the crystallite size in the normal direction of the crystal face corresponding to the diffraction peak. The peaks selected for the calculation here are the crystal planes

The corresponding peak has the interplanar spacing of 0.316nm and the 2 theta value of 28.174 degrees in the standard spectrogram; the reason for this is that the number of neighboring peaks around it is small, and a clearer and more accurate result can be obtained by peak-to-peak fitting. The use of other peaks for analysis is entirely possible.

Further, the lithium supplement agent is on the crystal face

Is less than 20nm, preferably from 8 to 15nm, more preferably from 10 to 14nm. Converted to FWHM, it can be seen that the FWHM of the diffraction peak of 28.174 + -0.3 DEG in the XRD diffraction spectrum of the lithium supplement agent should be greater than 0.405 DEG and between 0.539 DEG and 1.013 deg.

Further, the carbon content of the lithium supplement agent is 0.5wt% to 25wt%, and more preferably, 5wt% to 15wt%.

The lithium supplement agent coated carbon contains rGO, the graphitization degree of the rGO is very high, the coated carbon containing the rGO is subjected to I calculated from a D band and a G band of a carbon peak on a Raman spectrum _D /I _G The value will be lower, wherein I _D Representing D band integrated intensity, I _G Representing the G-band integrated intensity. In the Raman spectrum of the lithium supplement agent of the high-voltage anode, I _D /I _G A value of 0.8 to 1.2 _D /I _G The lower value of (A) indicates that the degree of graphitization of the carbon coated on the surface of the lithium supplement material is higher. The coated carbon with higher graphitization degree has higher electronic conductivity compared with the carbon with lower graphitization degree, so that the polarization degree of the material can be better reduced, and the oxidation potential of the material is reduced. With Li _4.1 Si _0.9 Fe _0.1 O ₄ For example, the electron conductivity of the material, that of the material without carbon coating (e.g., li prepared in comparative preparation example 1) was measured _4.1 Si _0.9 Fe _0.1 O ₄ ) Is 1.24x10 ^-9 S/cm, and carbon-coated materials (rGO @ Li as prepared in preparation example 1) _4.1 Si _0.9 Fe _0.1 O ₄ ) The electron conductivity of (2) is 0.56S/cm, which is improved by eight orders of magnitude, therefore, the rGO coating can greatly improve the conductivity of the material.

Compared with the common additive, the lithium battery added with the lithium supplement agent has the advantages that the charging curve has a longer charging slope, the part with lower voltage of the slope can supplement irreversible capacity loss in the first cycle of the battery, and the part with higher voltage of the slope can supplement lithium for many times through voltage control in long-term cycle, so that the purposes of overcoming the lithium loss in the first cycle and the long-term cycle and prolonging the service life of the lithium battery are achieved.

The lithium supplement agent provided by the invention is particularly suitable for lithium supplement of high-voltage positive electrode materials in the first circle and the circulation process, so that the rGO @ Li prepared in the preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ For example, the charging ramp of the lithium supplement agent is from 3.3V to 4.7V, and the charging ramp is in such a long voltage intervalCapacity can be provided, and the policy requirement that the high-voltage anode material is supplied with lithium as required through voltage control is met: the high-voltage anode material can exert the characteristics of high voltage and high capacity only when charged to 4.2V, and the lithium supplement agent exerts the capacity of 440mAh/g after charged to 4.2V, so that the lithium supplement agent can be used for supplementing lithium for the first circle; when the battery is circulated between 2.8 and 4.2V, the lithium supplement agent can not continuously exert the charge capacity, and can not be inserted into lithium to provide the discharge capacity; when the battery capacity is reduced to the point that secondary lithium supplement is needed after the circulation for a period of time, the battery can be charged to 4.6V in a certain cycle for a short time, the capacity of 200mAh/g of the lithium supplement agent between 4.2 and 4.6V is released, and the lithium loss of the battery in the circulation is supplemented. This is an advantage unique to the lithium supplement of the present invention. Other lithium-supplementing agents do not have this advantage in comparison, for example Li ₅ FeO ₄ The charging capacity is exhausted when the battery is charged to 4.2V, and the voltage can not be increased in the subsequent circulation to continuously supplement lithium.

The high-voltage cathode material is a cathode material that has been put into practical use and needs to be charged to 4.2V or more (e.g., 4.3v,4.4v, 4.5v) to fully exert its own capacity, and is well known in the art, such as a ternary cathode material, an aluminum-doped ternary cathode material, and the like. Specific examples include, but are not limited to, NCM811, NCM622. Of course, the present invention is particularly advantageous when applied to battery systems using high voltage positive electrodes, and does not represent that the present invention can only be applied to high voltage positive electrode battery systems, but it is also possible to apply the present invention to other battery systems, such as lithium iron phosphate (LFP) positive electrode battery systems (e.g., example 8) or lithium vanadate (LiVO) ₃ ) Battery systems and the like are also fully contemplated and are intended to be within the scope of this patent.

The second purpose of the invention is to provide a preparation method of the lithium supplement agent, which comprises the following steps:

(T1) preparation of rGO composite crystalline Li _4+x Si _1-x Fe _x O ₄ A material;

(T2) reducing the crystallite size of the material by high-energy ball milling to obtain rGO @ Li with smaller crystallite size _4+x Si _1-x Fe _x O ₄ A material.

The step (T1) is one of the following methods a, B, C, and D:

the method A comprises the following steps: weighing a lithium source, a silicon source and an iron source according to a stoichiometric ratio, adding a graphene oxide solid, uniformly mixing, pre-sintering and calcining to obtain the graphene oxide solid;

the method B comprises the following steps: weighing a lithium source, a silicon source and an iron source according to a stoichiometric ratio, dispersing the lithium source, the silicon source and the iron source in a solvent, adding a graphene oxide dispersion liquid dispersed in the solvent, heating and drying the solvent to obtain a precipitate, grinding, and then pre-burning and calcining to obtain the graphene oxide nano-particles;

the method C comprises the following steps: weighing a lithium source, a silicon source, an iron source and a complexing agent according to a stoichiometric ratio, dispersing the lithium source, the silicon source, the iron source and the complexing agent in a solvent, dispersing the lithium source, the silicon source, the iron source and the complexing agent in graphene oxide dispersion liquid of the solvent to obtain sol, heating and drying the solvent to obtain xerogel, grinding, presintering and calcining to obtain the graphene oxide sol;

the method D comprises the following steps: weighing a lithium source, a silicon source and an iron source according to a stoichiometric ratio, dispersing in a solvent, adding a graphene oxide dispersion liquid dispersed in the solvent, carrying out high-pressure solvothermal reaction under a heating condition under the sealing of an autoclave, centrifuging, washing, drying, grinding, presintering and calcining to obtain the graphene oxide.

The method of step (T1) is conventional in the art and well known in the art. Examples thereof include a solid phase calcination method (the above-mentioned method A), a precipitation method (the above-mentioned method B), a sol-gel method (the above-mentioned method C), and a solvothermal synthesis method (the above-mentioned method D). According to the invention, a certain amount of graphene oxide is added during preparation, the graphene oxide generates rGO in the subsequent calcination process in the preparation process, and in the ball milling process of (T2), the hardness of the rGO is higher than that of Li serving as a main material _4+x Si _1-x Fe _x O ₄ Much lower and therefore coat the surface of the material.

Further, the lithium source, the silicon source and the iron source are used in amounts satisfying the requirement of Li _4+x Si _1-x Fe _x O ₄ Based on the equivalent ratio of (A), the lithium source needs to be slightly excessive, because there may be some volatilization during the calcination process to cause the loss of Li, and the lithium is excessive by 3-10%.

The lithium source, silicon source and iron source are well known in the art, for example, the lithium source is a lithium-containing solid compound, includingBut are not limited to, lithium carbonate (Li) ₂ CO ₃ ) Lithium hydroxide monohydrate (LiOH. H) ₂ O), lithium nitrate (LiNO) ₃ ) Lithium acetate (CH) ₃ COOLi), lithium oxide (Li) ₂ O) and the like; the silicon source includes but is not limited to SiO ₂ Powder, nano SiO ₂ Gas phase SiO ₂ Silicic acid (H) ₂ SiO ₃ ) Tetraethoxysilane (C) ₈ H ₂₀ O ₄ Si, TEOS), butyl orthosilicate (C) ₁₆ H ₃₆ O ₄ Si), diatomite, vermiculite, zeolite, SBA-15, waste silicon, biomass ash, fly ash, halloysite and the like; the iron source refers to iron oxide and various iron salts, including but not limited to iron oxalate (Fe) ₂ (C ₂ O ₄ ) ₃ ) Iron nitrate (Fe (NO) ₃ ) ₃ ) Basic iron acetate (Fe (C) ₂ H ₃ O ₂ ) ₂ OH), iron oxide (Fe) ₂ O ₃ ) Iron carbonate (Fe) ₂ (CO ₃ ) ₃ ) Iron hydroxide (Fe (OH) ₃ ) And the like.

The solvent in the present invention refers to a liquid that can disperse the selected lithium source, silicon source, iron source and graphene oxide, and includes, but is not limited to, one or more combinations of deionized water, ethanol, isopropanol, and the like, preferably deionized water.

The complexing agent used in method C of the present invention is an organic chelating agent capable of coordinating with metal ions, and includes citric acid (C) ₆ H ₈ O ₇ ) Ethylene glycol ((CH) ₂ OH) ₂ ) One or more combinations of micromolecular polydentate ligands, polyvinylpyrrolidone (PVP), polyacrylic acid (PAA) and other macromolecule polydentate ligands, preferably citric acid. In the case of method C, the molar ratio of citric acid to lithium source is between 1 and 4.

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

The presintering temperature is 300-500 ℃, and the presintering time is 2-10h; the calcining temperature is 650-1000 ℃, and the calcining time is 5-20h. The calcination is carried out under a protective atmosphere, such as under an argon atmosphere.

And (3) performing high-energy ball milling in the step (T2) for 5-40 h at the ball-to-material ratio of 500-800rpm and 10-80, and sieving with a sieve mesh of 400-2000 meshes.

The third purpose of the invention is to provide a lithium supplementing method of a lithium ion battery, which comprises the following steps:

(S1) assembling a lithium ion battery containing the novel lithium supplement agent;

further, in the step (S1), a lithium supplement agent rGO @ Li is added _4+x Si _1-x Fe _x O ₄ There are various ways to add to a lithium ion battery, including one of method X, method Y, and method Z:

method X: coating the slurry containing the lithium supplement agent on the anode side of the diaphragm;

preferably, in the method X, the lithium supplement agent and the adhesive are dispersed in the organic solvent for pulping, coated on the positive electrode side of the diaphragm, and the organic solvent is dried; the diaphragm is a polyolefin porous diaphragm, including but not limited to a single or multiple material combined diaphragm such as polypropylene (PP), polyethylene (PE) and the like, the thickness is controlled to be 8-50 μm, and the preferable thickness is 8-20 μm; also included in the slurry is a binder, which is well known in the art, including, but not limited to, one or more combinations of polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyethylene glycol (PEG), and the like; the organic solvent includes, but is not limited to, one or more combinations of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), N-Dimethylformamide (DMF), and the like. The coating thickness is 0.5-10 μm, preferably 1-5 μm after the slurry is dried.

Method Y: pulping the lithium supplement agent and the active positive electrode material together, and coating the pulp on a current collector to obtain a positive electrode piece;

preferably, in the method Y, the raw materials including the lithium supplement agent, the active positive electrode material, the conductive additive and the binder are mixed and pulped, and coated on the current collector to obtain the working electrode. The positive electrode material comprises a layerThe positive electrode material, the olivine-type positive electrode material and the corresponding doped and modified positive electrode material specifically include but are not limited to LiCoO ₂ 、LiFePO ₄ 、LiMn ₂ O ₄ 、LiNi _x Co _y Mn _z O ₂ (x+y+z＝1)、LiNi _x Co _y Al _z O ₂ (x+y+z＝1)、LiNiO ₂ 、LiVO ₂ 、LiCrO ₂ Etc., especially those of V _{Charging device} The high-voltage cathode material with 4.2V, such as ternary high-nickel layered cathode material, specifically comprises LiNi _x Co _y Mn _z O ₂ (x+y+z＝1)、LiNi _x Co _y Al _z O ₂ (x + y + z = 1), and wherein x ≧ 0.5, preferably x ≧ 0.7.

Preferably, the conductive additive includes, but is not limited to, one or more combinations of Super P, ketjen black, CMK-3, conductive carbon tube, graphene, and the like.

Method Z: and coating the slurry containing the lithium supplement agent on the prepared positive plate.

Preferably, in the method Z, the lithium supplement agent and the binder are dispersed in an organic solvent for pulping, and the pulp is coated on the surface of the coated positive pole piece. The lithium supplementing agent accounts for 1-20wt%, preferably 3-10wt% of the active positive electrode material.

In the method, if pulping is needed, the mass ratio of the lithium supplement agent to the binder is 80-95:5-20. The dosage of the solvent is that the solid content of the slurry obtained by pulping is 0.1-1 mg/mu L.

(S2) performing lithium ion battery cycle, firstly, at V _{Charging device} To V _Put When the battery capacity is reduced to 70-90% of the initial discharge capacity, the charging voltage is raised by 0.2-0.4V in the next cycle, if V before raising _{Charging device} When the voltage reaches above 4.6V, the voltage is not increased and the voltage is discharged to V _Put After which the battery continues at V _{First stage} To V _Put Until the capacity decays to less than 60% of the initial capacity, the cycle is stopped.

Further, in step (S2), V _{Charging device} And V _Put Respectively represent lithium ion batteriesCharge cutoff voltage and discharge cutoff voltage during cycling. V.v. of _{Charging device} And V _Put The value of (b) is known in the art and varies according to the material of the positive electrode. For example, when the anode material is LiFePO ₄ When, V _Put ＝2.5V，V _{Charging device} =3.8V; due to the characteristics of the material used in the present invention, it is more preferable to apply to high voltage ternary positive electrode materials, including but not limited to LiNi _0.8 Co _0.1 Mn _0.1 O ₂ 、LiNi _0.6 Co _0.2 Mn _0.2 O ₂ 、LiNi _0.5 Co _0.2 Mn _0.3 O ₂ Or LiNi ₀₈ Co _0.1 Al _0.1 O ₂ Etc., when V is _{Placing the} ＝2.8V，V _{Charging device} ＝4.2V。

The prior positive pole lithium supplement agent for the lithium battery is not specially designed for a high-voltage positive pole material, the charging capacity of the prior positive pole lithium supplement agent is concentrated near a platform, the platform voltage of most of the lithium supplement agents is lower and lower than the charge cut-off potential of a high-voltage positive pole, and when the voltage is charged to be higher than the platform in the first circle of charging, the lithium supplement agent releases all the capacity for lithium supplement, so the prior positive pole lithium supplement agent can only be used for the first circle of lithium supplement. However, the lithium ion battery also loses capacity in the cycle process, and the capacity of the battery is attenuated again and again along with the cycle, so that the energy density of the battery is reduced, and the service life of the battery is shortened. At this time, even when the battery capacity decays to a certain range of the initial capacity (typically 60-70%, which indicates that the battery capacity has not been sufficient), even if the charging voltage is further increased, since the capacity of the lithium supplement agent has been nearly fully exerted in the first turn, there is no active lithium left at a higher charging voltage for supplementing the battery capacity. The invention provides a lithium supplement agent rGO @ Li _4+x Si _1-x Fe _x O ₄ Because the charging curve is a 3.3-4.7V long slope, the charging capacity can be exerted more by increasing some potentials, after the capacity is attenuated, secondary lithium supplement can be carried out when the charging voltage is increased, the capacity of a high-voltage part of a lithium supplement agent is exerted, and the long cycle service life and the efficiency of the lithium battery of the high-voltage cathode material are further improved.

Compared with the prior art, the invention has the advantages that:

the invention can not only supplement the capacity loss of the lithium ion battery in the initial cycle, but also supplement the irreversible capacity loss in the long-term cycle, improve the available capacity of the battery after multiple cycles and greatly prolong the service life of the battery;

2, the lithium supplement additive of the present invention can be applied to a practical high-voltage layered positive electrode, such as LiNi _x Co _y Mn _z O ₂ (x + y + z = 1) positive electrode, compared with batteries assembled by other positive electrode materials, the positive electrode has higher energy density, stronger practicability and higher commercial value;

the steps executed by the invention are simple and easy to implement, not only are safe and pollution-free, but also have low cost of equipment and post-treatment, are adapted to the current battery production process, are suitable for large-scale amplification and can be quickly put into use;

4, the selected positive electrode lithium supplement agent Li _4+x Si _1-x Fe _x O ₄ Low cost and easy synthesis. The abundance of Si element in the crust reaches 25.7%, which is second only to oxygen; the abundance of Fe element in the crust reaches 4.75%, and ranking is the fourth; the silicon source and the iron source can be made of cheap materials, and the cost is reduced in large-scale production.

Drawings

FIG. 1 is rGO @ Li synthesized in preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ Li obtained by high-temperature sintering ₄ SiO ₄ And Li ₄ SiO ₄ X-ray diffraction (XRD) contrast pattern of XRD standard diffraction spectrum of (c).

In FIG. 2, a is rGO @ Li synthesized in preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ And Li obtained by high-temperature sintering ₄ SiO ₄ And Li ₄ SiO ₄ The XRD standard diffraction spectrum of the compound is in the range of 26-31 degrees, and an X-ray diffraction (XRD) contrast diagram is obtained after the background is deducted; b is Li obtained by high-temperature sintering ₄ SiO ₄ The XRD diffraction spectrum is obtained by peak-splitting fitting within the range of 26-31 degrees; c is rGO @ Li synthesized in preparation example 1 _4+x Si _1-x Fe _x O ₄ The XRD diffraction spectrum of the compound is obtained by peak-splitting fitting in the range of 26-31 degrees.

FIG. 3 is rGO @ Li synthesized in preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ Scanning Electron Microscope (SEM) images of (a).

FIG. 4 is rGO @ Li synthesized in preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ High Resolution Transmission Electron Microscope (HRTEM) images.

FIG. 5 is rGO @ Li synthesized in preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ A raman spectrum of (a).

FIG. 6 is rGO @ Li synthesized in preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ Thermogravimetric spectrum of (a).

FIG. 7 is rGO @ Li synthesized in preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ First turn charge and discharge curves in half cells.

FIG. 8 is rGO @ Li synthesized in preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ Preparation example 2 synthetic rGO @ Li _4.25 Si _0.75 Fe _0.25 O ₄ Preparation example 3 synthetic rGO @ Li _4.02 Si _0.98 Fe _0.02 O ₄ And Li ₄ SiO ₄ XRD comparison of standard samples.

FIG. 9 is a graph showing the first-turn charge-discharge curves of the products of preparations 1 to 3 and comparative preparations 1 to 2.

Detailed Description

The present invention will be further described with reference to specific examples, but the present invention is not limited to the specific examples.

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

Preparation example 1

(T1) Synthesis of rGO @ Li _4.1 Si _0.9 Fe _0.1 O ₄ : weighing CH ₃ COOLi powder 28.409g (430.5 mmol), feCl ₃ ·6H ₂ O (10 mmol) powder 2.703g, citric acidPowder 13.129g (68.3 mmol) was added to 500mL of deionized water; subsequently weighing the gas phase SiO ₂ Adding 5.407g (90 mmol) of powder into the solution, stirring and dispersing to form sol, finally weighing 240g of graphene oxide aqueous dispersion with the mass fraction of 1wt%, adding the sol, and dispersing graphene oxide by using an ultrasonic crusher for 30min to obtain viscous black sol. Heating the sol in water bath at 80 ℃, evaporating deionized water to dryness to form gel, heating and drying the gel at 150 ℃ for 24 hours to obtain dry gel, scraping and grinding the dry gel into powder; the xerogel powder is pre-calcined for 3 hours at 300 ℃ and then calcined for 12 hours at 900 ℃ in Ar atmosphere, and the heating rate is 5 ℃/min.

(T2) carrying out high-energy ball milling on the calcined product for 10h under the conditions of 600rpm and a ball-to-material ratio of 10, screening powder obtained by ball milling by using a 2000-mesh screen, and taking the powder which can pass through the screen as a positive electrode lithium supplement agent.

FIG. 1 shows the positive electrode lithium-supplementing agent rGO @ Li obtained in preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ Crystalline Li ₄ SiO ₄ And Li ₄ SiO ₄ XRD comparison of standard samples. It can be seen that rGO @ Li synthesized in preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ In the XRD spectrum of (1), all XRD peaks are greatly broadened.

In FIG. 2, a is rGO @ Li synthesized in preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ Li obtained by high-temperature sintering ₄ SiO ₄ And Li ₄ SiO ₄ The XRD standard diffraction spectrum of the compound is in the range of 26-31 degrees, and an X-ray diffraction (XRD) contrast diagram is obtained after the background is deducted; for Li obtained by high temperature sintering in figure a ₄ SiO ₄ The XRD diffraction spectrum of the compound is subjected to peak-splitting fitting in the range of 26-31 degrees to obtain a graph b, wherein the FWHM value of a 28.099-degree peak after fitting is 0.1373; FIG. a rGO @ Li synthesized in preparation example 1 _4+x Si _1-x Fe _x O ₄ The XRD diffraction spectrum of (1) is subjected to peak-splitting fitting in the range of 26-31 degrees to obtain a graph c, wherein the FWHM value of a 28.049-degree peak after fitting is 0.6089. Li obtained by high-temperature sintering and calculated by the Sherle formula ₄ SiO ₄ On the crystal face

Crystallite size in the normal direction 59.1nm; while the rGO @ Li synthesized in preparation example 1 _4+x Si _1-x Fe _x O ₄ On the plane->

The crystallite size in the normal direction was 13.3nm.

FIG. 3 shows the rGO @ Li lithium-supplementing agent obtained in preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ Scanning Electron Microscope (SEM) images of (a). It can be seen that the particle size of the material is between 0.5 and 5 μm.

FIG. 4 shows rGO @ Li, a lithium supplementing agent obtained in preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ High Resolution Transmission Electron Microscope (HRTEM) images. As can be observed from the figure, the particle surface has a carbon coating layer between 2 and 10 nm; the inside of the particle is provided with a crystallization area, the lattice stripe interval of the area is 0.316nm, and the interval corresponds to a crystal face

Meanwhile, the length of the region in the normal direction of the lattice fringes is 13.5nm, which is close to the calculated 13.3nm, and the calculation of the crystallite size in the particle is correct.

FIG. 5 preparation example 1 synthesized rGO @ Li _4.1 Si _0.9 Fe _0.1 O ₄ A raman spectrum of (a). Can see that _D /I _G The value is 1.14, which indicates that the obtained lithium supplement agent has a high graphitization degree.

FIG. 6 is rGO @ Li synthesized in preparation example 1 _4.1 Si _0.9 Fe _0.1 O ₄ The thermogravimetric spectrum of the test method has the test conditions of 40-1000 ℃ and the heating rate of 5 ℃/min. From the figure it can be seen that rGO @ Li _4.1 Si _0.9 Fe _0.1 O ₄ Has a carbon content of 12.7wt%.

FIG. 7 shows the new Li-supplementing agent rGO @ Li prepared in preparation example 1 _4+x Si _1-x Fe _x O ₄ The first circle of charge-discharge curve in the half cell has a voltage interval of 2.5-4.7V and is in a constant current modeAnd (4) charging and discharging, wherein the multiplying power is 0.02C, and a constant-voltage charging section is not added. When the material is charged to 4.7V, the specific capacity of the material is 669.5mAh/g; in practical application, the material exerts 435mAh/g of capacity when the first circle is charged to 4.2V, and exerts 190mAh/g of capacity at 4.2-4.6V.

Preparation example 2

The other conditions were the same as in preparation example 1 except that CH was adjusted in step (T1) ₃ COOLi powder, gas phase SiO ₂ Powder and FeCl ₃ In such an amount that Li: si: fe =4.46:0.75:0.25. obtaining the Li modified by the graphene oxide _4.25 Si _0.75 Fe _0.25 O ₄ As the lithium supplement agent of the invention. XRD of the obtained product was measured, and as shown in FIG. 8, li was found to be present ₅ FeO ₄ Shown as orange stars. The charge capacity of the material is also reduced accordingly, as shown in fig. 9, the first turn charge capacity is 307.6mAh/g.

Preparation example 3

The other conditions were the same as in preparation example 1 except that CH was adjusted in step (T1) ₃ COOLi powder, gas phase SiO ₂ Powder and FeCl ₃ In such an amount that Li: si: fe =4.22:0.98:0.02. obtaining the Li modified by the graphene oxide _4.05 Si _0.95 Fe _0.05 O ₄ As the lithium supplement agent of the invention. XRD of the obtained product was measured, and as shown in FIG. 8, li was found to be present ₂ SiO ₃ Shown as blue stars. Due to the fact that the Fe doping amount is too small, the charging capacity of the material is reduced, and as shown in figure 9, the charging capacity of the first circle is only 186.3mAh/g.

FIG. 8 shows Li as a lithium-supplementing agent for positive electrode obtained in production example 1 _4.1 Si _0.9 Fe _0.1 O ₄ Preparation of Li obtained in example 2 _4.25 Si _0.75 Fe _0.25 O ₄ Preparation of Li obtained in example 3 _4.02 Si _0.98 Fe _0.02 O ₄ And Li ₄ SiO ₄ XRD comparison of standard samples. In the figure, li obtained in preparation example 2 is marked with a star symbol _4.25 Si _0.75 Fe _0.25 O ₄ Middle Li ₅ FeO ₄ The hetero-phase peak of (1) is marked by a star mark with Li obtained in preparation example 3 _4.02 Si _0.98 Fe _0.02 O ₄ Middle Li ₂ SiO ₃ The hetero-phase peak of (1).

Comparative preparation example 1

The other conditions were the same as in preparation example 1 except that in step (T1), no graphene oxide and citric acid were added to obtain carbon-uncoated Li _4.1 Si _0.9 Fe _0.1 O ₄ . Without the carbon coating, the electronic conductivity of the material is greatly reduced to only 1.24x10 ^-9 S/cm, which is an integral drop of 8 orders of magnitude compared to the electron conductivity of the material of example 1 of 0.56S/cm; the performance of the material is reflected in that the charge capacity of the material in the first circle is greatly reduced, as shown in fig. 9, the purple curve represents the charge-discharge curve of the product in the first circle, and the charge capacity of the first circle is only 184.9mAh/g.

Comparative preparation example 2

The other conditions were the same as in preparation example 1 except that step (T2) was not carried out. Without the step (T2), the doped solid phase reaction can not occur, and the first circle charging capacity of the doped solid phase reaction is greatly reduced, as shown in FIG. 9, the blue color curve represents the first circle charging and discharging curve of the product of the present example, and the first circle charging capacity of the product is only 162.5mAh/g.

FIG. 9 shows the positive electrode lithium-supplementing agent rGO @ Li obtained in production example 1 _4.1 Si _0.9 Fe _0.1 O ₄ Preparation example 2 the obtained positive electrode lithium supplement agent rGO @ Li _4.25 Si _0.75 Fe _0.25 O ₄ Preparation example 3 the obtained positive electrode lithium supplement agent rGO @ Li _4.02 Si _0.98 Fe _0.02 O ₄ Comparative preparation example 1 Li without rGO recombination _4.1 Si _0.9 Fe _0.1 O ₄ rGO @ Li obtained in production example 3 without performing the step (T2) _4.1 Si _0.9 Fe _0.1 O ₄ The first circle of charge-discharge curves of (1) are compared with the figure. It can be seen that either too much or too little iron doping, or no rGO modification, or step (T2) omission, leads to a significant reduction in the first-turn charge capacity of the material.

Example 1

(S1) 240mg of the lithium supplement agent prepared in preparation example 1 was taken, 30mg of Super P was added,PVDF (polyvinylidene fluoride) 30mg, NMP (N-methyl pyrrolidone) 800 mu L is added, the mixture is uniformly mixed into slurry, the slurry is uniformly coated on a Celgard polypropylene diaphragm in the thickness of 10 mu m, the drying is carried out for 3 hours at the temperature of 60 ℃, and then the diaphragm is placed in a vacuum oven for overnight at the temperature of 60 ℃ to obtain the positive electrode lithium-supplementing diaphragm. The prepared lithium-supplemented separator was cut into phi =16mm discs. LiNi as active positive electrode material _0.8 Co _0.1 Mn _0.1 O ₂ Super P and polyvinylidene fluoride (PVDF) binder in a mass ratio of 80:10:10, mixing the mixture to prepare slurry, uniformly coating the slurry on an aluminum foil current collector, and cutting the slurry into a wafer with phi =10mm to obtain a working electrode; mixing graphite serving as a negative electrode material, siO/C (from Jiangxi Yi gold, product number HL-1400), super P and a polyacrylate adhesive in a mass ratio of 68:12:10:10, mixing the mixture to prepare slurry, uniformly coating the slurry on a copper foil current collector, and cutting the slurry into a wafer with phi =10mm to obtain a counter electrode; 1mol/L ternary electrolyte (1M LiPF) ₆ EC/DEC/DMC (volume ratio 1. The assembled battery will be subjected to a charge and discharge test on a LAND charge and discharge tester.

(S2) long cycle testing: in the first three cycles, the battery was charged and discharged at 0.1C rate of the battery, with a charge cut-off voltage of 4.2V and a discharge cut-off voltage of 2.8V. From the 4 th turn, the cell was cycled at a 1C rate in the range of 2.8-4.2V. When the current is circulated to the 363 th circle, the discharge capacity of the battery is reduced to be less than 70 percent of the initial discharge capacity; at the 364 th circle, the battery was charged to 4.6V at 0.1C rate of the positive active material and then discharged to 2.8V at 1C rate, and the battery discharge capacity was restored to 80% of the initial discharge capacity. From the 365 th turn, the cell was cycled at a rate of 1C in the range of 2.8-4.2V. When the cell discharge capacity dropped below 60% of the initial discharge capacity, the cycle was terminated.

Example 2

(S1) preparing an active positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ The lithium supplement agent obtained in preparation example 1, super P and polyvinylidene fluoride (PVDF) binder in a mass ratio of 72:8:10:10, mixing the materials to prepare slurry, uniformly coating the slurry on an aluminum foil current collector to obtain a lithium-supplementing positive pole piece, and cutting the lithium-supplementing positive pole piece into a wafer with phi =10mm to be used as a working electrode; preparing a negative electrode material graphite, siO/C, super P and a polyacrylate adhesive in a mass ratio of 68:12:10:10, mixing the mixture to prepare slurry, uniformly coating the slurry on a copper foil current collector, and cutting the slurry into a wafer with phi =10mm to obtain a counter electrode; 1mol/L ternary electrolyte (1M LiPF) ₆ EC/DEC/DMC (volume ratio 1.

(S2) long cycle testing: in the first three cycles, the battery was charged and discharged at 0.1C rate, with a charge cut-off voltage of 4.2V and a discharge cut-off voltage of 2.8V. From the 4 th cycle, the cell was cycled at a rate of 1C in the range of 2.8 to 4.2V. When the discharge capacity of the battery is cycled to the 305 th circle, the discharge capacity of the battery is reduced to below 70 percent of the initial discharge capacity; at the 306 th circle, the battery was charged to 4.6V at 0.1C rate of the positive active material, and then discharged to 2.8V at 1C rate, and the battery discharge capacity was restored to 80% of the initial discharge capacity. From the 307 th turn, the cell was cycled at a rate of 1C in the range of 2.8-4.2V. When the cell discharge capacity dropped below 60% of the initial discharge capacity, the cycle was terminated.

Example 3

(S1) preparing a positive pole piece: liNi as active positive electrode material _0.8 Co _0.1 Mn _0.1 O ₂ Super P and polyvinylidene fluoride (PVDF) binder in a mass ratio of 80:10:10, mixing the materials to prepare slurry, uniformly coating the slurry on an aluminum foil current collector, and cutting the slurry into wafers with phi =10mm to obtain a positive pole piece for later use; adding Super P30mg and PVDF 30mg into 270mg of the positive electrode lithium supplement agent obtained in the preparation example 1, adding 800 mu L of NMP, uniformly mixing to obtain slurry, coating the slurry on a positive electrode plate with the thickness of 10 mu m, and cutting the positive electrode plate into a wafer with phi =10mm to be used as a working electrode; preparing a negative electrode material graphite, siO/C, super P and a polyacrylate adhesive in a mass ratio of 68:12:10:10 mixing to obtain slurry, uniformly coating on copper foil current collector, and cutting into final productA wafer with phi =10mm, obtaining a counter electrode; 1mol/L ternary electrolyte (1M LiPF) ₆ EC/DEC/DMC (volume ratio 1.

(S2) long cycle testing: in the first three cycles, the battery was charged and discharged at 0.1C rate, with a charge cut-off voltage of 4.2V and a discharge cut-off voltage of 2.8V. From the 4 th turn, the cell was cycled at a rate of 1C in the range of 2.8 to 4.2V. When the discharge capacity of the battery is circulated to the 281 th circle, the discharge capacity of the battery is reduced to below 70 percent of the initial discharge capacity; and at the 282 th circle, the battery is cycled at the rate of 1C of the positive active material, the battery is charged to 4.6V and discharged to 2.8V, and the discharge capacity of the battery is recovered to 80 percent of the initial discharge capacity. From the 283 th turn, the battery was cycled at a rate of 1C in the range of 2.8 to 4.2V. The cycle was terminated when the cell discharge capacity dropped to 60% of the initial discharge capacity.

Example 4

(S1) the other conditions are the same, except that carbon-coated SiO is used as the negative electrode when the battery is assembled.

(S2) long cycle testing: in the first three cycles, the battery was charged and discharged at 0.1C rate of the battery, with a charge cut-off voltage of 4.2V and a discharge cut-off voltage of 2.8V. From the 4 th turn, the cell was cycled at a rate of 1C in the range of 2.8 to 4.3V. When the discharge capacity of the battery is reduced to below 70 percent of the initial discharge capacity after the cycle reaches the 167 th circle; at the 168 th circle, the battery was charged to 4.6V at 0.1C rate of the positive active material, and then discharged to 2.8V at 1C rate, and the battery discharge capacity was restored to 80% of the initial discharge capacity. From the 169 th cycle, the battery was cycled at a rate of 1C in the range of 2.8 to 4.2V. When the cell discharge capacity dropped below 60% of the initial discharge capacity, the cycle was terminated.

Example 5

(S1) the other conditions were the same except that LiNi was used as the positive electrode in assembling the battery _0.5 Co _0.2 Mn _0.3 O ₂ ，

(S2) long cycle testing: in the first cycle, the battery was charged and discharged at 0.1C rate, with a charge cut-off voltage of 4.2V and a discharge cut-off voltage of 2.8V. From the 2 nd cycle, the cell was cycled at a rate of 1C in the range of 2.8 to 4.2V. When the discharge capacity of the battery is cycled to 368 th circle, the discharge capacity of the battery is reduced to be less than 60 percent of the initial discharge capacity; at the 369 th circle, the battery was charged to 4.6V at 0.1C rate of the positive active material, and then discharged to 2.8V at 1C rate, and the battery discharge capacity was recovered to 82% of the initial discharge capacity. From the 370 th turn, the cell was cycled at a rate of 1C in the range of 2.8 to 4.2V. When the cell discharge capacity dropped below 60% of the initial discharge capacity, the cycle was terminated.

Example 6

(S1) the other conditions were the same except that LiNi was used as the positive electrode in assembling the battery _0.8 Co _0.15 Al _0.5 O ₂ ，

(S2) long cycle testing: in the first three cycles, the battery was charged and discharged at 0.1C rate, with a charge cut-off voltage of 4.2V and a discharge cut-off voltage of 2.8V. From the 4 th cycle, the cell was cycled at a rate of 1C in the range of 2.8 to 4.2V. When the discharge capacity of the battery is cycled to the 243 rd circle, the discharge capacity of the battery is reduced to below 70 percent of the initial discharge capacity; at circle 244, the cell was charged to 4.6V at 0.1C rate of the positive active material and then discharged to 2.8V at 1C rate, and the cell discharge capacity was restored to 80% of the initial discharge capacity. From the 245 th turn, the cell was cycled at a rate of 1C in the range of 2.8 to 4.2V. When the cell discharge capacity dropped below 60% of the initial discharge capacity, the cycle was terminated.

Example 7

(S1) the other conditions were the same except that LiCoO was used for the positive electrode when assembling the battery ₂ The negative electrode uses graphite as an active material.

(S2) long cycle testing: in the first three cycles, the battery was charged and discharged at 0.1C rate, with a charge cut-off voltage of 4.2V and a discharge cut-off voltage of 2.8V. From the 4 th turn, the cell was cycled at a rate of 1C in the range of 2.8 to 4.2V. When the discharge capacity of the battery is cycled to 597 th circles, the discharge capacity of the battery is reduced to below 70 percent of the initial discharge capacity; at the 598 th circle, the battery is charged to 4.6V at the rate of 0.1C of the positive active material, and then discharged to 2.8V at the rate of 1C, and the discharge capacity of the battery is recovered to 84 percent of the initial discharge capacity. From the 599 th round, the cell was cycled at a rate of 1C in the range of 2.8 to 4.2V. When the cell discharge capacity dropped below 60% of the initial discharge capacity, the cycle was terminated.

Example 8

(S1) the other conditions are the same, except that LiFePO is used as the positive electrode when the battery is assembled ₄ The negative electrode uses graphite as an active material.

(S2) long cycle testing: in the first three cycles, the battery was charged and discharged at 0.1C rate, with a charge cut-off voltage of 3.8V and a discharge cut-off voltage of 2.8V. From the 4 th cycle, the cell was cycled at a rate of 1C in the range of 2.8 to 3.8V. When the discharge capacity of the battery is circulated to the 755 th circle, the discharge capacity of the battery is reduced to below 70 percent of the initial discharge capacity; at the 756 th circle, the battery was charged to 4.2V at 0.1C rate of the positive active material, and then discharged to 2.8V at 1C rate, and the battery discharge capacity was recovered to 83% of the initial discharge capacity. From the 757 th turn, the battery was cycled at a rate of 1C in the range of 2.8 to 3.8V. When the discharge capacity of the battery is cycled to 1059 th circle, the discharge capacity of the battery is reduced to below 70 percent of the initial discharge capacity; at circle 1060, the cell was charged to 4.6V at 0.1C rate of the positive active material and then discharged to 2.8V at 1C rate, and the cell discharge capacity was restored to 83% of the initial discharge capacity. From the 1061 st turn, the battery was cycled at a rate of 1C in the range of 2.8 to 3.8V. When the cell discharge capacity dropped below 60% of the initial discharge capacity, the cycle was terminated.

Example 9

The other conditions were the same, except that the lithium replenishing agent prepared in preparation example 2 was used when the positive electrode lithium replenishing separator was prepared.

Example 10

The other conditions were the same, except that the lithium replenishing agent prepared in preparation example 3 was used when the positive electrode lithium replenishing separator was prepared.

Comparative example 1:

(S1) the other conditions were the same except that a commercial Celgard polypropylene separator was used as a battery separator when assembling the battery.

(S2) long cycle testing: in the first three cycles, the battery was charged and discharged at a rate of 0.1C, charged to 4.2V, and then discharged to 2.8V. From the 4 th cycle, the battery was cycled at a rate of 1C, with a charge cut-off voltage of 4.2V and a discharge cut-off voltage of 2.8V.

The charging and discharging results are as follows: after the 362 th cycle, the discharge capacity was reduced to 60% of the first cycle discharge capacity, and the cycle was stopped.

Comparative example 2:

the other conditions were the same except that the lithium replenishing agent prepared in comparative example preparation example 1 was used.

Comparative example 3:

the other conditions were the same except that the lithium supplement agent prepared in comparative example preparation example 2 was used.

TABLE 1 comparison of results of various examples

According to the embodiment, the Li modified by the graphene oxide serving as the novel multi-platform positive electrode lithium supplement agent of the lithium ion battery provided by the invention _4+x Si _1-x Fe _x O ₄ The method for supplementing lithium according to needs has a good effect of relieving irreversible attenuation of battery capacity, can supplement the lithium ion loss of the battery in the first cycle and also can supplement the capacity loss of the battery in the cycle, can be applied to a battery system applying a high-voltage ternary positive electrode, greatly relieves the capacity reduction trend of the high-specific-energy battery, and prolongs the service life of the battery.

The invention can be popularized to various systems of lithium batteries, including but not limited to battery systems obtained by mutually combining various anode and cathode materials: wherein the positive electrode material includes but is not limited to LiCoO ₂ 、LiFePO ₄ 、LiMn ₂ O ₄ 、LiNi _x Co _y Mn _z O ₂ (x+y+z＝1)、LiNi _x Co _y Al _z O ₂ (x+y+z＝1)、LiNiO ₂ 、LiVO ₂ 、LiVO ₃ The invention fills the blank in the aspect of high-voltage layered positive electrode; the negative electrode material includes, but is not limited to, graphite, si, siO/C, and a composite negative electrode obtained by compounding three materials in any form and any proportion, a carbon negative electrode other than graphite such as hard carbon, an alloy negative electrode other than Si such as Sn, and Fe ₂ O ₃ Isoconversion type negative electrode, li ₄ Ti ₅ O ₁₂ A negative electrode, and the like.

In conclusion, the lithium-supplementing lithium-ion battery can supplement lithium for multiple times in the first cycle and the long-term cycle, can be applied to a high-voltage layered anode, has a very high value, is simple in implementation method and low in cost, realizes efficient lithium supplementation on the anode side to relieve capacity attenuation of the lithium-ion battery, is safe and pollution-free, is adaptive to the existing battery production system, and has a very high application prospect.

Claims (10)

1. The lithium supplement agent suitable for supplementing lithium to the high-voltage anode as required is characterized by being Li modified by reduced graphene oxide _4+x Si _1-x Fe _x O ₄ ，0.5≥x≥0.01。

2. The lithium supplement agent suitable for the high-voltage positive electrode according to claim 1, wherein x is 0.3 ≥ x ≥ 0.05; preferably, 0.15 ≧ x ≧ 0.10.

3. The lithium supplement suitable for a high-voltage positive electrode according to claim 1, wherein the particle size of the lithium supplement is 0.1-50 μm, preferably 0.5-5 μm.

4. The lithium supplement agent applicable to the high-voltage positive electrode according to claim 1, wherein the lithium supplement agent is in a crystal plane

Is less than 20nm in the normal direction; preferably 8-15nm.

5. Adapted for use in accordance with claim 1The lithium supplement agent for the high-voltage positive electrode is characterized in that the carbon content of the lithium supplement agent is 0.5-25 wt%, more preferably 5-15 wt%, and further in that I in a Raman spectrum of the lithium supplement agent for the high-voltage positive electrode is I _D /I _G The value is 0.8 to 1.2 _D Representing D band integrated intensity, I _G Representing the G-band integrated intensity.

6. The method for preparing the lithium supplementing agent according to any one of claims 1 to 5, which comprises the following steps:

(T1) preparation of rGO composite crystalline Li _4+x Si _1-x Fe _x O ₄ A material;

(T2) reducing the crystallite size of the material by high-energy ball milling to obtain rGO @ Li with smaller crystallite size _4+x Si _1-x Fe _x O ₄ A material;

the step (T1) is one of the following methods a, B, C, and D:

the method A comprises the following steps: weighing a lithium source, a silicon source and an iron source according to a stoichiometric ratio, adding a graphene oxide solid, uniformly mixing, pre-sintering and calcining to obtain the graphene oxide solid;

the method B comprises the following steps: weighing a lithium source, a silicon source and an iron source according to a stoichiometric ratio, dispersing the lithium source, the silicon source and the iron source in a solvent, adding a graphene oxide dispersion liquid dispersed in the solvent, heating and drying the solvent to obtain a precipitate, grinding, and then pre-burning and calcining to obtain the graphene oxide nano-particles;

the method C comprises the following steps: weighing a lithium source, a silicon source, an iron source and a complexing agent according to a stoichiometric ratio, dispersing the lithium source, the silicon source, the iron source and the complexing agent in a solvent, dispersing the lithium source, the silicon source, the iron source and the complexing agent in graphene oxide dispersion liquid of the solvent to obtain sol, heating and drying the solvent to obtain xerogel, grinding, presintering and calcining to obtain the graphene oxide sol;

the method D comprises the following steps: weighing a lithium source, a silicon source and an iron source according to a stoichiometric ratio, respectively adding the lithium source, the silicon source and the iron source into a solvent, adding graphene oxide dispersion liquid dispersed in the solvent, carrying out high-pressure solvothermal reaction under heating conditions under sealing of an autoclave, centrifuging, washing, drying, grinding, presintering and calcining to obtain the graphene oxide.

7. The method according to claim 6, wherein the reaction mixture is heated to a temperature in the reaction mixtureThe lithium source is a lithium-containing solid compound, including but not limited to lithium carbonate (Li) ₂ CO ₃ ) Lithium hydroxide monohydrate (LiOH. H) ₂ O), lithium nitrate (LiNO) ₃ ) Lithium acetate (CH) ₃ COOLi), lithium oxide (Li) ₂ O) and the like; the silicon source comprises SiO ₂ Powder, nano SiO ₂ Gas phase SiO ₂ Silicic acid (H) ₂ SiO ₃ ) Tetraethoxysilane (C) ₈ H ₂₀ O ₄ Si, TEOS), butyl orthosilicate (C) ₁₆ H ₃₆ O ₄ Si), diatomite, vermiculite, zeolite, SBA-15, waste silicon, biomass ash, fly ash, halloysite and the like; the iron source refers to iron oxide and various iron salts, including but not limited to iron oxalate (Fe) ₂ (C ₂ O ₄ ) ₃ ) Iron nitrate (Fe (NO) ₃ ) ₃ ) Basic iron acetate (Fe (C)) ₂ H ₃ O ₂ ) ₂ OH), iron oxide (Fe) ₂ O ₃ ) Iron carbonate (Fe) ₂ (CO ₃ ) ₃ ) Iron hydroxide (Fe (OH) ₃ ) One or more combinations of the above; the complexing agent refers to an organic chelating agent capable of coordinating with metal ions, and comprises citric acid (C) ₆ H ₈ O ₇ ) Ethylene glycol ((CH) ₂ OH) ₂ ) One or more combinations of micromolecular polydentate ligands, polyvinylpyrrolidone (PVP), polyacrylic acid (PAA) and other macromolecular polydentate ligands; the solvent-dispersed graphene oxide refers to a mixture liquid formed by uniformly dispersing graphene oxide in a solvent without agglomeration, wherein the mass fraction of the graphene oxide in the dispersion liquid is between 0.5 and 5wt percent.

8. The preparation method according to claim 6, wherein the high energy ball milling in step (T2) is performed at 500-800rpm and a ball-to-material ratio of 10-80.

9. A lithium supplementing method of a lithium ion battery is characterized by comprising the following steps:

(S1) assembling a lithium ion battery comprising the lithium supplement agent according to any one of claims 1 to 5 or the lithium supplement agent prepared by the preparation method according to any one of claims 6 to 8;

(S2) performing lithium ion battery cycle, firstly, at V _{Charging device} To V _Put When the battery capacity is reduced to 70-90% of the initial discharge capacity, the charging voltage is raised by 0.2-0.4V in the next cycle, if V before raising _{Charging (CN)} When the voltage reaches above 4.6V, the voltage is not increased any more, and the voltage is discharged to V _Put After which the battery continues at V _{First stage} To V _Put Until the capacity decayed to below 60% of the initial capacity, the cycle was stopped.

10. The method of claim 9, wherein the step (S1) of adding a lithium replenishing agent to the lithium ion battery comprises one of method X, method Y, and method Z:

method X: coating the slurry containing the lithium supplement agent on the anode side of the diaphragm;

preferably, in the method X, the lithium supplement agent and the adhesive are dispersed in the organic solvent for pulping, coated on the positive electrode side of the diaphragm, and the organic solvent is dried; the diaphragm is a polyolefin porous diaphragm, comprises a single or multiple material combined diaphragm of polypropylene (PP), polyethylene (PE) and the like, and has the thickness controlled within 8-50 mu m, preferably 8-20 mu m; the slurry also comprises a binder, wherein the binder comprises one or more of polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyethylene glycol (PEG) and the like; the organic solvent includes but is not limited to one or more of N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), N-Dimethylformamide (DMF), and the like; the coating thickness is that after the slurry is dried, the thickness of the coating layer is between 0.5 and 10 mu m, preferably between 1 and 5 mu m;

method Y: pulping the lithium supplement agent and the active positive electrode material together, and coating the pulp on a current collector to obtain a positive electrode piece;

preferably, in the method Y, the raw materials including the lithium supplement agent, the active positive electrode material, the conductive additive and the binder are mixed and pulped, and coated on the current collector to obtain the working electrode. The positive electrode material comprises a layered positive electrodeMaterial, olivine-type positive electrode material and corresponding doped and modified positive electrode material, including LiCoO ₂ 、LiFePO ₄ 、LiMn ₂ O ₄ 、LiNi _x Co _y Mn _z O ₂ (x+y+z＝1)、LiNi _x Co _y Al _z O ₂ (x+y+z＝1)、LiNiO ₂ 、LiVO ₂ 、LiVO ₃ One or more combinations of the above; the conductive additive comprises one or more of Super P, ketjen black, CMK-3, a conductive carbon tube, graphene and the like;

method Z: coating the slurry containing the lithium supplement agent on the prepared anode plate;

preferably, in the method Z, the lithium supplement agent and the binder are dispersed in an organic solvent for pulping, and the pulp is coated on the surface of the coated positive pole piece. The lithium supplementing agent accounts for 1-20wt%, preferably 3-10wt% of the active positive electrode material.

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