Use of dilithioferrocene, secondary battery and method of manufacturing the same

Abstract

The application of dilithioferrocene, a secondary battery and a manufacturing method thereof. The application of dilithioferrocene includes that the dilithioferrocene is used as a lithium supplement agent, and the dilithioferrocene is dissolved in an electrolyte. Compared with a solid lithium supplement agent in the prior art, the lithium supplement method does not produce gas; and the dilithioferrocene is not mixed with a positive active material to form a slurry, and the influence of the dilithioferrocene on the processability of the positive slurry does not need to be considered, and the proportion of the positive active material is not occupied, so that the positive plate is not cracked and powdered; and the product after the lithium supplement reaction is soluble in the electrolyte, and no side reaction is produced.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of secondary batteries, in particular to application of dilithioferrocene, a secondary battery and a manufacturing method thereof. BACKGROUND

[0002] During the first charging process of a lithium ion battery, a large amount of solid electrolyte interface film is generated on the surface of the negative electrode of the battery, the limited lithium ions and electrolyte in the battery are consumed, irreversible capacity loss is caused, the energy density of the lithium ion secondary battery is reduced, and the application of the lithium ion battery is limited. In the prior art, by adding a positive electrode lithium supplement to the positive electrode material, the first irreversible capacity loss of the lithium battery can be effectively compensated. However, most of the existing lithium supplement materials have problems such as large gas production, poor processability, decomposition products and electrolyte easy to produce side reactions, occupation of the proportion of the positive electrode material and easy to cause the cracking and pulverization of the pole piece. SUMMARY

[0003] The purpose of the application is to provide application of dilithioferrocene, a secondary battery and a manufacturing method thereof, to solve the problems that the existing lithium supplement method produces gas and produces side reactions with electrolyte.

[0004] To achieve the purpose of the application, the application provides the following technical solutions:

[0005] In a first aspect, the application provides application of dilithioferrocene, the dilithioferrocene is used as a lithium supplement, and the dilithioferrocene is dissolved in electrolyte.

[0006] The application provides a liquid lithium supplement and applies the lithium supplement in the scene of positive electrode lithium supplement. Compared with the solid lithium supplement in the prior art, the lithium supplement method does not produce gas. Moreover, the lithium supplement is not mixed with the positive electrode active material to form a paste, the influence of the lithium supplement on the processability of the positive electrode paste does not need to be considered, the proportion of the positive electrode active material is not occupied, and therefore the cracking and pulverization of the pole piece will not be caused. Moreover, the product after the lithium supplement reaction is soluble in the electrolyte, and no side reaction is caused.

[0007] In an embodiment, the electrolyte is also soaked with a solid lithium supplement material, and the dilithioferrocene is mixed with the lithium supplement material.

[0008] In an embodiment, the molar ratio of the lithium supplement material to the dilithioferrocene is 1:(2.9-3.1).

[0009] In an embodiment, the chemical formula of the lithium supplement material includes Li x M y O zwherein M is at least one element selected from Fe, Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, V, Mo, Sn, and the like, 1≤x≤8, 0<y, and 0<z<7.

[0010] In one embodiment, the electrolyte comprises one or more of propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl propyl carbonate.

[0011] In a second aspect, the present application provides a preparation method of a lithium supplement agent, comprising the following steps: adding n-butyllithium and an initiator into a n-hexane solution of ferrocene, and obtaining dilithium ferrocene after sufficient reaction, washing and drying; and dissolving the dilithium ferrocene in an electrolyte.

[0012] In a third aspect, the present application provides a secondary battery, comprising a positive electrode, a negative electrode, an electrolyte, and dilithium ferrocene, wherein the positive electrode and the negative electrode are both immersed in the electrolyte, the dilithium ferrocene is dissolved in the electrolyte, and the dilithium ferrocene is used to provide lithium ions to the positive electrode.

[0013] In one embodiment, the positive electrode comprises a positive electrode active material, and the amount of the dilithium ferrocene added in the secondary battery satisfies the following relationship: M1=M2×(1-ICE)×a, wherein M1 is the molar amount of the dilithium ferrocene in the secondary battery, M2 is the molar amount of the positive electrode active material, ICE is the first cycle coulombic efficiency of the secondary battery, a is a correction coefficient, and 0.95≤a≤1.05.

[0014] In a fourth aspect, the present application provides a preparation method of a secondary battery, comprising the following steps: fixing a positive electrode and a negative electrode in a container containing an electrolyte to obtain an assembled battery; performing formation on the assembled battery, and after formation, injecting dilithium ferrocene into the assembled battery to obtain the secondary battery.

[0015] In one embodiment, the formation environment of the assembled battery is as follows: after charging the assembled battery at a 0.02C rate to 3.7V, discharging the assembled battery at a 0.02C rate to 2.5V. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort based on these drawings.

[0017] Figure 1 It is a preparation flowchart of the lithium supplement agent in one embodiment.

[0018] Figure 2 A flow chart of preparation of the secondary battery is one embodiment. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be clearly and completely described in connection with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The use of the terms "and / or" includes a combination of one or more of the associated listed items.

[0021] Some embodiments of the present application will be described in detail below with reference to the accompanying drawings. The following embodiments and features in the embodiments can be combined with each other without conflict.

[0022] The present application provides a method for using dilithioferrocene as a lithium supplement agent. The dilithioferrocene is dissolved in an electrolyte.

[0023] Specifically, the dilithioferrocene is the main lithium supplement agent in the secondary battery, which can provide a large amount of lithium ions. The electrolyte is the main body of the dilithioferrocene, and the dilithioferrocene can be dissolved in the electrolyte. The electrolyte can be an organic electrolyte.

[0024] After the SEI film is formed on the positive active material, part of the lithium ions is lost, and there are Li vacancies in the bulk phase of the positive active material. The dilithioferrocene is a strong nucleophile. After the dilithioferrocene is added to the battery, it is easy to combine with the positive electrode due to the high potential of the positive electrode. In addition, due to the low potential of the dilithioferrocene itself, the small potential difference between the dilithioferrocene and the positive active material serves as a power to make the lithium ions in the dilithioferrocene enter the Li vacancies, compensate for the lost lithium ions in the positive active material, and achieve the effect of supplementing lithium. Taking a lithium iron phosphate positive electrode as an example, the dilithioferrocene and the delithiated lithium iron phosphate react as follows:

[0025] Fe(C5H4)2Li2+Li 1-x FePO4→Fe(C5H5)2+LiFePO4

[0026] As can be seen from the above reaction equation, the lithium ion in the dilithium ferrocene is supplemented into the lithium vacancy formed by the lithium iron phosphate, and the ferrocene with the lithium ion removed is dissolved in the electrolyte again due to the solubility and is separated from the positive electrode. Therefore, the ferrocene after lithium removal does not affect the positive electrode or the negative electrode.

[0027] It should be noted that the dilithium ferrocene provided by the present application as a lithium supplement agent is different from the conventional solid-state lithium supplement agent in the prior art. In order to realize the lithium supplement of the positive electrode, the conventional solid-state lithium supplement agent needs to be mixed with the positive electrode active material to form a slurry during the preparation of the positive electrode, and then the positive electrode sheet is prepared by a coating process. The dilithium ferrocene provided by the present application can be dissolved in the electrolyte to form a liquid state, and does not need to be mixed with the positive electrode active material to form a slurry. The lithium supplement agent can be injected into the inside of the battery through the liquid injection process after the battery is packaged, so the lithium supplement agent does not exist only on the positive electrode, but can be filled in the inside of the battery (including the positive electrode and the negative electrode), and can migrate to the positive electrode under the action of the potential difference to supplement lithium.

[0028] It should be noted that the dilithium ferrocene is a very strong nucleophile, and tends to combine with substances with high potential in the secondary battery, so it will flow to the positive electrode end under the action of the potential; and since the positive electrode loses Li and has lithium vacancies, and the redox potential of the dilithium ferrocene is about 3.2v(vs Li / Li + ), there is a small potential difference compared with LiFePO4(3.4V vs Li / Li + ), under the double action of the lithium vacancy and the potential difference, the lithium in the dilithium ferrocene is removed and embedded into the lithium vacancy of the positive electrode to supplement lithium, and the potential of the ferrocene losing lithium becomes high, and the ferrocene is separated from the positive electrode and dissolved in the solvent.

[0029] Compared with the conventional solid-state lithium supplement agent (taking Li5FeO4 as an example), the lithium supplement process of the solid-state lithium supplement agent includes the following two stages:

[0030] Stage I: Li5FeO4→Li3FeO 3.5 +0.25O2+2Li + +2e -

[0031] Stage II: Li3FeO 3.5 →LiFeO2+0.75O2+2Li + +2e -

[0032] From the above lithium supplement process of the solid-state lithium supplement agent, it can be seen that the existing solid-state lithium supplement agent will release gas during the lithium supplement process, and will also have residues after the lithium supplement is completed. Both the release of gas and the residues will affect the use of the secondary battery. In contrast, the lithium supplement agent of the lithium dicyclopentadienyl ferrous salt will not release gas, and due to its excellent solubility, it can also be dissolved in the electrolyte after lithium supplement.

[0033] It can be understood that due to the difference in form and adding process, the lithium supplement agent provided by the present application can overcome the various shortcomings of the existing solid-state lithium supplement agent, including: 1) simple preparation process, compared with the solid-state lithium supplement agent, the lithium supplement agent only needs to dissolve the prepared lithium dicyclopentadienyl ferrous salt in the corresponding volume, without considering the post-processing and compounding process; 2) convenient to store, not easy to deteriorate, the existing solid-state lithium supplement agent is sensitive to water vapor, so whether it is in the preparation link or the storage link, it needs to consider avoiding water, such as setting a coating layer; 3) little effect on the positive electrode after lithium supplement, the existing lithium supplement agent will form a pit defect in the positive electrode after discharge consumption, which will cause the structure stability of the positive electrode to be poor, and the solubility of the residue of the lithium supplement agent in the electrolyte after discharge will also affect the electrochemical performance of the battery, while the lithium supplement agent is in liquid state and does not participate in the preparation process of the positive electrode, and will not cause defects in the positive electrode after lithium supplement, and can be dissolved in the electrolyte after lithium supplement.

[0034] Further, the lithium dicyclopentadienyl ferrous salt lithium supplement agent provided by the present application is also different from the additive for regenerating waste positive active material in the prior art. In the prior art, waste lithium iron phosphate positive electrode is mixed with lithium dicyclopentadienyl ferrous salt in order to recover the waste lithium iron phosphate positive electrode from waste battery. However, the application scenarios of the two are different. The lithium dicyclopentadienyl ferrous salt as a lithium supplement agent is applied in the environment of lithium supplement of the secondary battery, while the lithium dicyclopentadienyl ferrous salt as a regenerating additive is applied in the environment of positive active material recovery. And the difference and advantage of the lithium supplement agent provided by the present application are: 1) the regeneration reaction needs to be carried out after the waste positive electrode is recovered, while the lithium supplement process of the present application is completed in the battery, and the purpose of the present application is not to recover the waste positive electrode, but to supplement lithium for the new battery; 2) the waste positive electrode has many dead lithium sites due to long-term cycling, poor reaction activity, and damaged positive electrode structure, resulting in low reaction rate and efficiency, so the recovery efficiency of the waste positive electrode is very low, while the new positive electrode after formation has high reaction activity, high reaction rate and high lithium supplement efficiency.

[0035] Compared with the solid-state lithium supplementing agent in the prior art, the lithium supplementing agent is liquid, and the lithium supplementing method does not produce gas. The lithium supplementing agent is not mixed with the positive active material to form a slurry, and the influence of the lithium supplementing agent on the processability of the positive slurry does not need to be considered, and the proportion of the positive active material is not occupied, so that the positive plate is not cracked and pulverized. The product after the lithium supplementing reaction is soluble in the electrolyte, and no side reaction occurs.

[0036] In an embodiment, the concentration A of dilithium ferrocene in the electrolyte satisfies: 0 mol / L < A < 1 mol / L. Optionally, the concentration A of dilithium ferrocene in the lithium supplementing agent can be 0.001 mol / L, 0.005 mol / L, 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L.

[0037] In an embodiment, the electrolyte also has a solid lithium supplementing material soaked therein, and the dilithium ferrocene is mixed with the lithium supplementing material. The chemical formula of the lithium supplementing material includes Li x M y O z , wherein M is at least one element selected from Fe, Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, V, Mo, Sn, etc., 1 < x < 8, 0 < y, and 0 < z < 7. In specific embodiments, the lithium supplementing material can be at least one of Li5FeO4, Li6MnO4, Li6CoO4, Li6ZnO4, Li2NiO2, Li2CuO2, Li2CoO2, Li2MnO2, Li2Ni 0.5 Mn 1.5 O4, Li2Ni d Cu (1-d) O2 (0 < d < 1), etc. For example, Li5FeO4 material is used in combination. Because the application links are different, the amount of active Li ions released by Li5FeO4 can be accurately judged when the dilithium ferrocene is applied, so that the dilithium ferrocene and Li5FeO4 can be designed for verification. In addition, because there are some problems of Li5FeO4 that need to be solved, such as gas production, a small amount of Li5FeO4 is used to coat the dilithium ferrocene to isolate the electrolyte, so that high-capacity stable lithium supplementing can be achieved, the use amount of Li5FeO4 is greatly reduced, and the purpose of increasing the lithium supplementing capacity and reducing the gas production can be effectively achieved. At the same time, the dilithium ferrocene is in contact with the electrolyte after formation to work, and can be used directly when the battery is reassembled, without the need for injection after formation.

[0038] In one embodiment, the molar ratio of the lithium supplement material and the dilithium ferrocene is 1:(2.9-3.1). It is to be explained that in the secondary battery, the lithium supplement material and the dilithium ferrocene are mixed according to the molar ratio of lithium of 1:(2.9-3.1). Alternatively, the molar ratio of the lithium supplement material and the dilithium ferrocene can be 1:2.9, 1:2.92, 1:2.94, 1:2.96, 1:2.98, 1:3, 1:3.02, 1:3.04, 1:3.06, 1:3.08, 1:3.1. The mass ratio of the above dilithium ferrocene and lithium supplement material can ensure that the dilithium ferrocene and the lithium supplement material stably supplement lithium to the positive electrode, and can also reduce the generation of gas in the secondary battery as much as possible.

[0039] In one embodiment, the electrolyte comprises one or more of propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl propyl carbonate.

[0040] Because the role of the lithium supplement agent provided by the present application is different from that of the electrolyte, the electrolyte provides an ion conduction channel for the battery or the capacitor, and ensures that the chemical reaction occurring in the working process of the device is reversible, while the dilithium ferrocene lithium supplement agent is used for lithium supplement, and the electrolyte in the secondary battery is used to provide a dissolution environment for the dilithium ferrocene. In addition, the use sequence of the dilithium ferrocene lithium supplement agent provided by the present application is different from that of the electrolyte. The dilithium ferrocene lithium supplement agent does not need to be mixed with the electrolyte, and after the electrolyte is injected into the battery, the battery needs to be formed and then the dilithium ferrocene lithium supplement agent is injected.

[0041] In one embodiment, the present application also provides a preparation method of the lithium supplement agent, please refer to Figure 1 , comprising the following steps:

[0042] Step S10, adding n-butyllithium and an initiator into the n-hexane solution of ferrocene, and after sufficient reaction, washing and drying to obtain dilithium ferrocene.

[0043] Step S20, dissolving the dilithium ferrocene in the electrolyte.

[0044] Specifically, in step S10, the molar ratio of ferrocene to lithium ions in n-butyllithium is 1:2. The initiator can be tetramethyl ethylenediamine, and the addition amount of the initiator is the same as that of ferrocene.

[0045] Alternatively, in step S20, orange-red precipitate is generated after the ferrocene and n-butyllithium are sufficiently reacted, the orange-red precipitate is centrifuged out, washed with n-hexane solution for multiple times, and dried to obtain dilithium ferrocene.

[0046] In one embodiment, the present application also provides a secondary battery, which comprises a plastic film, a positive electrode, a negative electrode, an electrolyte and a lithium supplement agent, and the positive electrode, the negative electrode, the electrolyte and the lithium supplement agent are all encapsulated in the plastic film.

[0047] Optionally, the positive electrode comprises a current collector and a positive active material layer disposed on the current collector, and the positive active material layer comprises positive active material, conductive agent, binder and the like. The negative electrode comprises a current collector and a negative active material layer disposed on the current collector, and the negative active material layer comprises negative active material, conductive agent, binder and the like. The present application does not make specific limitations on these materials, and suitable materials can be selected according to actual application requirements.

[0048] Optionally, the positive active material can be phosphate positive active material or ternary positive active material. In specific embodiments, the positive active material comprises one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, fluorinated lithium vanadium phosphate, lithium titanate, lithium nickel cobalt manganate and lithium nickel cobalt aluminate.

[0049] Optionally, the positive current collector comprises but is not limited to any one of copper foil and aluminum foil. The conductive agent comprises one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nanotube, and the content of the conductive agent in the positive active layer is 3wt%-5wt%. The types of the binder comprise one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, butadiene rubber, hydroxypropyl methyl cellulose, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivatives, and the content of the binder in the positive active layer is 2wt%-4wt%.

[0050] Optionally, the electrolyte can be electrolyte solution, so that the secondary battery further comprises a separator disposed between the positive electrode sheet and the negative electrode sheet; or the electrolyte can be solid-state electrolyte, so that the secondary battery does not have a separator, which is replaced by the solid-state electrolyte.

[0051] In one embodiment, the added amount of the lithium supplement agent in the secondary battery satisfies the relationship: M1=M2×(1-ICE)×a, wherein M1 is the molar amount of dilithium ferrocene in the secondary battery, M2 is the molar amount of the positive active material, ICE is the first cycle coulombic efficiency of the secondary battery, and 0.95≤a≤1.05. a is a correction factor used to correct the errors caused by the small thickness difference existing on the electrode sheet and the possible small unevenness in the dilithium ferrocene solution.

[0052] In one embodiment, the present application also provides a manufacturing method of a secondary battery, which comprises the following steps: Figure 2

[0053] ​Step S100, fixing the positive electrode and the negative electrode in a container containing electrolyte to obtain an assembled battery.

[0054] Step S200, forming the assembled battery, and after formation, injecting dilithium dicyclopentadiene into the assembled battery to obtain a secondary battery.

[0055] Optionally, in step S100, the positive electrode and the negative electrode are fixed in a container containing electrolyte to obtain an assembled battery, specifically comprising: stacking the positive electrode, the separator and the negative electrode in sequence in a dry environment, then welding the positive electrode lug and the negative electrode lug to obtain an electric core, packaging the electric core in a fixed size of aluminum plastic film, and then injecting electrolyte to obtain an assembled battery, leaving an injection hole at the edge of the assembled battery.

[0056] Optionally, in step S200, the assembled battery is formed, and after formation, dilithium dicyclopentadiene is injected into the assembled battery, specifically comprising: charging the assembled battery at 0.02C rate to 3.7V, then discharging at 0.02C rate to 2.5V, after completing the discharge, adding a lithium supplement from the reserved injection hole, and after standing, the lithium supplement process is completed.

[0057] It can be understood that in the method for manufacturing the secondary battery provided by the application, the addition sequence of the lithium supplement and the electrolyte is different, the lithium supplement needs to be injected into the battery pack after the electrolyte is added and the secondary battery is formed and tested, and under the condition that no additional charging and discharging is required, the Li ions lost by the positive active material during formation and testing can be compensated through reaction during the standing stage, thereby playing a lithium supplement role. Therefore, the lithium supplement provided by the application is not equivalent to the electrolyte and the electrolyte additive, and the electrolyte and the electrolyte additive need to be added before formation to complete the formation process.

[0058] The technical solutions of the application will be described in detail through specific embodiments.

[0059] Example 1

[0060] The embodiment provides a secondary battery. The secondary battery comprises a positive electrode, a negative electrode, an electrolyte and a lithium supplement. The lithium supplement comprises dilithium dicyclopentadiene and propylene carbonate, and the solubility of the dilithium dicyclopentadiene in the propylene carbonate is 0.5 mol / L.

[0061] The preparation method of the lithium supplement comprises the following steps:

[0062] Step 1) In a dry and inert atmosphere, n-butyllithium (molar ratio of ferrocene to lithium ion = 1:2) is added to a ferrocene solution in n-hexane, and an equal amount of tetramethyl ethylenediamine as an initiator is added, and then the solution is left to stand for 24 hours.

[0063] Step 2) The orange-red precipitate generated in step 1) is centrifuged out and washed with n-hexane solution for multiple times to obtain dilithioferrocene.

[0064] Step 3) Dilithioferrocene in step 2) is dissolved in propylene carbonate to form a 0.5 mol / L solution, which is the lithium supplement agent.

[0065] The method for manufacturing the secondary battery comprises the following steps:

[0066] Step 4) Preparation of the positive electrode: the positive electrode active material (lithium iron phosphate), the conductive agent (acetylene black) and the binder (polytetrafluoroethylene) are mixed according to the mass ratio of lithium iron phosphate: acetylene black: polytetrafluoroethylene = 95:2.5:2.5, N-methylpyrrolidone is added, and the mixture is fully stirred and uniformly coated on a 15-micron-thick aluminum foil to form a uniform positive electrode slurry. After drying, the positive electrode sheet is obtained.

[0067] Step 5) Preparation of the negative electrode: the negative electrode active material (graphite), the conductive agent (acetylene black), the binder (styrene-butadiene rubber) and the thickening agent (sodium carboxymethyl cellulose) are mixed according to the mass ratio of graphite: acetylene black: styrene-butadiene rubber: sodium carboxymethyl cellulose = 95:2:2:1, deionized water is added, and the mixture is fully stirred and uniformly coated on an 8-micron-thick copper foil to form a uniform negative electrode slurry. After drying, the negative electrode sheet is obtained.

[0068] Step 6) Assembly of the battery: the positive electrode sheet, the separator and the negative electrode sheet are sequentially stacked in a dry environment, and then the positive and negative electrode tabs are welded to obtain the battery cell. The battery cell is packaged in an aluminum-plastic film of a fixed size, and then electrolyte injection packaging is performed. The battery has an injection hole at the edge, and the electrolyte comprises 1M LiPF6 and EC (ethylene carbonate):DEC (diethyl carbonate):DMC (dimethyl carbonate) = 1:1:1.

[0069] Step 7) Formation and injection of the lithium supplement agent: the battery assembled in step 6) is charged at a rate of 0.02C to 3.7V, and then discharged at a rate of 0.02C to 2.5V. After the discharge is completed, the lithium supplement agent is added from the reserved injection hole (the molar amount M1 of dilithioferrocene in the lithium supplement agent is M2 x (1-ICE) x a, where M1 is the molar amount of dilithioferrocene in the lithium supplement agent, M2 is the molar amount of the positive electrode active material, ICE is the first-cycle coulombic efficiency, and a = 1).

[0070] Step 8) The lithium supplement process is completed after standing for 30 minutes.

[0071] Example 2

[0072] The difference between this example 2 and example 1 is that a is 1.05.

[0073] Example 3

[0074] The difference between this example 3 and example 1 is that a is 0.95.

[0075] Example 4

[0076] The difference between this example 4 and example 1 is that the concentration of dilithioferrocene in propylene carbonate is 0.5 mol / L.

[0077] Comparative Example 1

[0078] This example provides a secondary battery. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte.

[0079] The difference between this comparative example 1 and example 1 is that no lithium supplement is added, i.e. no preparation steps 1) - step 3) of the lithium supplement are performed, and in the method of manufacturing the secondary battery, the process of adding the lithium supplement in step 7) is not performed.

[0080] Comparative Example 2

[0081] This example provides a secondary battery. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte.

[0082] The difference between this comparative example 1 and example 1 is that the lithium supplement is added before formation.

[0083] Comparative Example 3

[0084] This example provides a secondary battery. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a lithium supplement (LFO).

[0085] The difference between this comparative example 2 and example 1 is that no lithium supplement is added, but a solid lithium supplement is added to the positive electrode. That is, no preparation steps 1) - step 3) of the lithium supplement are performed, and in the method of manufacturing the secondary battery, the process of adding the lithium supplement in step 7) is not performed.

[0086] In the method of manufacturing the secondary battery, step 4) positive electrode preparation: the positive electrode active material (lithium iron phosphate), the lithium supplement (LFO), the conductive agent (acetylene black), and the binder (polytetrafluoroethylene) are mixed according to the mass ratio lithium iron phosphate: LFO: acetylene black: polytetrafluoroethylene = 92:3:2.5:2.5, N-methylpyrrolidone is added, and the mixture is fully stirred and mixed to form a uniform positive electrode slurry and uniformly coated on a 15-micron-thick aluminum foil. After drying, a positive electrode sheet is obtained.

[0087] The parameters of the secondary batteries provided by examples 1-4 and comparative examples 1-3 are shown in Table 1:

[0088] Table 1 Parameters of secondary batteries provided by examples and comparative examples

[0089] a Concentration Addition stage Example 1 1 1 After formation Example 2 0.95 1 After formation Example 3 1.05 1 After formation Example 4 1 0.5 (two volumes) After formation Comparative Example 1 0 0 / Comparative Example 2 1 1 Before formation Comparative Example 3 0 0 /

[0090] The above secondary battery was subjected to electrochemical performance test, and the test conditions were as follows:

[0091] The rate charging was performed at 0.1C, the cutoff voltage was 4.3V; the constant voltage charging was performed at 4.3V; after the end of the charging process, 10 minutes of rest was performed, the rate discharging was performed at 0.1C, the cutoff voltage was 2.5V; and the first cycle efficiency = (discharge specific capacity / charge specific capacity)*100%.

[0092] The test results of the above secondary battery are shown in Table 2 as follows:

[0093] Table 2. Test results of examples and comparative examples

[0094]

[0095] As can be seen from the test results of Example 1-Example 4 and Comparative Example 1 in Table 2, by adding dilithium ferrocene as a lithium supplement into the secondary battery, the first cycle charge-discharge capacity of the secondary battery after lithium supplement is significantly improved compared with the secondary battery without adding dilithium ferrocene lithium supplement. Therefore, it is proved that dilithium ferrocene can be used as a lithium supplement for lithium supplement of the secondary battery.

[0096] As can be seen from the test results of Example 1-Example 4 and Comparative Example 2 in Table 2, the timing of adding dilithium ferrocene into the secondary battery needs to be after formation of the secondary battery. If dilithium ferrocene is added before formation, redox reaction occurs in the first cycle charge-discharge, and the lithium supplement function is not achieved.

[0097] As can be seen from the test results of Example 1-Example 4 and Comparative Example 3 in Table 2, compared with the solid-state lithium supplement method in the prior art, the secondary battery provided by the present application which is added with dilithium ferrocene not only can achieve the same lithium supplement effect, but also can avoid the gas production phenomenon in the battery.

[0098] As can be seen from the test results of Example 1-Example 3 in Table 2, the lithium supplement capacity is positively correlated with the content of added dilithium ferrocene. And in the case of consistent amount of dilithium ferrocene (solid content), the proportion of electrolyte has little effect on the lithium supplement capacity.

[0099] In the description of the embodiments of the present application, it should be noted that the orientation or positional relationship of the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like is based on the orientation or positional relationship described in the drawings, and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0100] The above disclosed is only a preferred embodiment of the present application, of course, cannot be limited by this, the person skilled in the art can understand that the all or part of the processes of the above-mentioned embodiment are realized, and the equivalent changes made according to the claims of the present application still belong to the scope covered by the present application.

Claims

1. A secondary battery characterized by comprising: The secondary battery comprises a positive electrode, a negative electrode, an electrolyte and dilithium ferrocene, the positive electrode and the negative electrode are both soaked in the electrolyte, the dilithium ferrocene is used as a lithium supplement agent, the dilithium ferrocene is dissolved in the electrolyte, and the dilithium ferrocene is used to provide lithium ions to the positive electrode. The positive electrode comprises a positive electrode active material, and an adding amount of the dilithium ferrocene in the secondary battery satisfies a relationship: M1=M2×(1-ICE)×a, wherein M1 is a molar amount of the dilithium ferrocene in the secondary battery, M2 is a molar amount of the positive electrode active material, ICE is a first circle coulombic efficiency of the secondary battery, a is a correction coefficient, and 0.95≤a≤1.

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2. The secondary battery according to claim 1, characterized by The electrolyte further soaks a solid lithium supplement material, and the dilithium ferrocene is mixed with the lithium supplement material.

3. The secondary battery according to claim 2, characterized by A molar ratio of the lithium supplement material to the dilithium ferrocene is 1: (2.9-3.1).

4. The secondary battery according to claim 3, characterized by The chemical formula of the lithium supplementing material includes Li x M y O z , wherein M is at least one element of Fe, Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, V, Mo, Sn, 1≤x≤8, 0<y, 0<z<7.

5. The secondary battery according to claim 1, characterized by The electrolyte comprises one or more of propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate and methyl propyl carbonate.

6. The secondary battery according to claim 1, characterized by A preparation method of the dilithium ferrocene as the lithium supplement agent comprises the following steps: n-butyllithium and an initiator are added into a n-hexane solution of ferrocene, and the dilithium ferrocene is obtained by washing and drying after sufficient reaction; The dilithium ferrocene is dissolved in the electrolyte.

7. A method for manufacturing a secondary battery, characterized by The preparation method is used for preparing the secondary battery according to any one of claims 1-6, and comprises the following steps: The positive electrode and the negative electrode are fixed in a container containing the electrolyte to obtain an assembled battery; The assembled battery is subjected to formation, and the dilithium ferrocene is injected into the assembled battery after formation to obtain the secondary battery.

8. The method of producing a secondary battery according to claim 7, wherein The formation environment of the assembled battery is that the assembled battery is charged at a 0.02C rate to 3.7V, and then discharged at a 0.02C rate to 2.5V.

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