Application of dilithium ferrocene, secondary battery and manufacturing method of secondary battery

Abstract

The invention discloses application of dilithium-substituted ferrocene, a secondary battery and a manufacturing method of the secondary battery. The application of the dilithium-substituted ferrocene comprises the steps that the dilithium-substituted ferrocene serves as a lithium supplement agent, and the dilithium-substituted ferrocene is dissolved in electrolyte. Compared with a solid lithium supplement agent in the prior art, the lithium supplement mode does not generate gas; moreover, the dilithium-substituted ferrocene is not slurried together with the positive electrode active material, the influence of the dilithium-substituted ferrocene on the processability of the positive electrode slurry does not need to be considered, and the proportion of the positive electrode active material is not occupied, so that the cracking and pulverization of the pole piece are not caused; and moreover, the product obtained after the lithium supplement reaction can be dissolved in the electrolyte, and no side reaction is generated.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to an application of dilithium ferrocene, a secondary battery and a manufacturing method thereof. Background Art

[0002] During the first charging process of lithium-ion batteries, a large amount of solid electrolyte interface film will be produced on the surface of the negative electrode of the battery, which consumes the limited lithium ions and electrolyte in the battery, causing irreversible capacity loss, reducing the energy density of lithium-ion secondary batteries, and limiting the application of lithium-ion batteries. In the prior art, the first irreversible capacity loss of lithium batteries can be effectively compensated by adding positive electrode lithium supplements to the positive electrode materials. However, most of the existing lithium supplement materials have problems such as large gas production, poor processability, easy side reactions between decomposition products and electrolytes, squeezing the proportion of positive electrode materials, and easy to cause cracking and powdering of pole pieces. Summary of the invention

[0003] The purpose of the present invention is to provide an application of dilithium ferrocene, a secondary battery and a method for manufacturing the same, so as to solve the problem that the existing lithium supplementation method generates gas and produces side reactions with the electrolyte.

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

[0005] In a first aspect, the present invention provides an application of dilithium ferrocene, wherein the dilithium ferrocene is used as a lithium supplement and is dissolved in an electrolyte.

[0006] The present invention provides a liquid lithium supplement and applies the lithium supplement to the positive electrode lithium supplement scenario. Compared with the solid lithium supplement in the prior art, the lithium supplement does not generate gas. Moreover, the lithium supplement is not slurried together with the positive electrode active material, so there is no need to consider the effect of the lithium supplement on the processability of the positive electrode slurry, and it does not occupy the proportion of the positive electrode active material, so it will not cause the electrode sheet to crack and pulverize. Moreover, the product after the lithium supplement reaction is soluble in the electrolyte, and no side reaction will occur.

[0007] In one embodiment, a solid lithium supplement material is also soaked in the electrolyte, and the dilithium ferrocene is mixed with the lithium supplement material.

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

[0009] In one embodiment, the chemical formula of the lithium supplement 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,0<z<7。

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

[0011] In a second aspect, the present invention provides a method for preparing a lithium supplement, comprising the following steps: adding n-butyl lithium and an initiator to a n-hexane solution of ferrocene, washing and drying after sufficient reaction to obtain dilithium ferrocene; and dissolving the dilithium ferrocene in an electrolyte.

[0012] In a third aspect, the present invention 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 includes a positive electrode active material, and the amount of the dilithium ferrocene added in the secondary battery satisfies the 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 coulomb efficiency of the secondary battery, and a is the correction coefficient, 0.95≤a≤1.05.

[0014] In a fourth aspect, the present invention provides a method for manufacturing 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; forming the assembled battery, and after the 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: the assembled battery is charged to 3.7V at a rate of 0.02C, and then discharged to 2.5V at a rate of 0.02C. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 is a flow chart of the preparation of a lithium supplement according to an embodiment;

[0018] Figure 2 The present invention is a flow chart of a secondary battery preparation process according to an embodiment. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used in the present invention includes any and all combinations of one or more of the related listed items.

[0021] Some embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0022] The invention provides an application method of dilithium ferrocene as a lithium supplement agent. The dilithium ferrocene is dissolved in an electrolyte.

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

[0024] After the positive electrode active material forms the SEI film, due to the loss of some lithium ions in the positive electrode active material, some Li vacancies exist in the bulk of the positive electrode active material; dilithium ferrocene is a strong nucleophilic reagent, and after being added to the battery, due to the higher potential of the positive electrode, it is easy to combine with the positive electrode; and because the potential of dilithium ferrocene itself is relatively low, the small potential difference between it and the positive electrode active material acts as a driving force to enable the lithium ions in dilithium ferrocene to enter the Li vacancies, compensating for the lithium ions lost in the positive electrode active material, and achieving the lithium replenishment effect. Taking lithium iron phosphate positive electrode as an example, dilithium ferrocene reacts with lithium iron phosphate after delithiation as follows:

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

[0026] From the above reaction equation, it can be seen that the lithium ions in the dilithium ferrocene are added to the lithium vacancies formed by lithium iron phosphate, and the ferrocene that has lost its lithium ions is separated from the positive electrode and dissolved in the electrolyte due to its solubility. Therefore, the ferrocene after lithium removal will not affect the positive or negative electrode.

[0027] It should be noted that the lithium supplement provided by the present invention is different from the conventional solid lithium supplement in the prior art. In order to achieve positive electrode lithium supplement, the conventional solid lithium supplement needs to be mixed with the positive electrode active material to form a slurry when making the positive electrode, and then the positive electrode sheet is made by a coating process. The dilithium ferrocene provided by the present invention 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 can be injected into the battery through the liquid injection and liquid supply process after the battery is packaged. Therefore, the lithium supplement is not only present on the positive electrode, but can be filled in the battery (including the positive electrode and the negative electrode), and migrate to the positive electrode under the action of the potential difference to supplement lithium.

[0028] It should be noted that dilithium ferrocene is a strong nucleophile and tends to combine with substances with high potential in secondary batteries, so it will flow to the positive terminal under the action of potential; and because there is a lithium vacancy after the positive electrode loses Li, and the redox potential of dilithium ferrocene is about 3.2v (vs Li / Li + ), compared to LiFePO4 (3.4V vs Li / Li + ) There is a small potential difference. Under the dual effects of lithium vacancies and potential difference, the lithium in the dilithium-substituted ferrocene is removed and embedded in the lithium vacancy of the positive electrode to achieve lithium replenishment. The potential of the ferrocene that loses lithium ions becomes higher, decouples from the positive electrode, and dissolves in the solvent.

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

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

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

[0032] From the above solid lithium supplement process, it can be seen that the existing solid lithium supplement will release gas during the lithium supplement process, and there will be residues after the lithium supplement is completed. Both the released gas and the residual impurities will affect the use of secondary batteries. On the other hand, the lithium supplement of dilithium ferrocene will not only not release gas, but also can be dissolved in the electrolyte after lithium supplement due to its excellent solubility.

[0033] It can be understood that due to the difference in morphology and addition process, the lithium supplement provided by the present invention can overcome the various shortcomings of existing solid lithium supplements, including: 1) the preparation process is simple. Compared with the solid lithium supplement, the lithium supplement only needs to dissolve the prepared dilithium ferrocene in the corresponding volume, without considering the post-processing and compounding process; 2) convenient storage and not easy to deteriorate. The existing solid lithium supplement is sensitive to water vapor, so both the preparation link and the storage link need to consider water avoidance, such as setting a coating layer, etc.; 3) the impact on the positive electrode after lithium supplementation is small. After the existing lithium supplement is consumed during discharge, pit defects will be formed in the positive electrode, resulting in poor structural stability in the positive electrode, and the residue of the lithium supplement after discharge has poor solubility in the electrolyte, which will also affect the electrochemical performance of the battery. The lithium supplement is liquid and does not participate in the production process of the positive electrode. It will not cause defects in the positive electrode after lithium supplementation, and can be dissolved in the electrolyte again after lithium supplementation.

[0034] Furthermore, the lithium supplement of dilithium ferrocene provided by the present invention is also different from the additive for regenerating waste positive electrode active materials in the prior art. In the prior art, in order to recycle the waste lithium iron phosphate positive electrode in the waste battery, the waste lithium iron phosphate is mixed with dilithium ferrocene. However, the application scenarios of the two are different. Dilithium ferrocene is used as a lithium supplement in the environment of secondary battery lithium supplementation, while dilithium ferrocene is used as a regeneration additive in the environment of positive electrode active material recovery. The lithium replenisher provided by the present invention is different from and has advantages over the lithium replenisher provided by the present invention in that: 1) the regeneration reaction can only be carried out after the waste positive electrode is dismantled and recycled, while the lithium replenishment process of the present invention is completed in the battery, and the purpose of the present invention is not to recycle the waste positive electrode, but to replenish lithium for the new battery; 2) the waste positive electrode has many dead lithium sites and poor reaction activity due to long-term circulation, and the positive electrode structure is damaged, resulting in low reaction rate and efficiency, so the efficiency of waste positive electrode recycling is very low, while the present invention is for the new positive electrode after formation, the lost Li sites are easier to be deintercalated / intercalated, and the structure is intact and not damaged, the reaction activity is high, and the reaction rate and lithium replenishment efficiency are high.

[0035] The present invention provides a liquid lithium supplement agent and applies the lithium supplement agent in the scenario of supplementing lithium to the positive electrode. Compared with the solid lithium supplement agent in the prior art, this lithium supplement method does not generate gas; moreover, the lithium supplement agent is not slurried with the positive electrode active material, so there is no need to consider the influence of the lithium supplement agent on the processability of the positive electrode slurry, nor does it occupy the proportion of the positive electrode active material, so it will not cause cracking and pulverization of the electrode sheet; furthermore, the product after the lithium supplement reaction is soluble in the electrolyte and no side reaction will occur.

[0036] In one embodiment, the concentration A of dilithioferrocene in the electrolyte satisfies: 0 mol / L < A ≤ 1 mol / L. Optionally, the concentration A of dilithioferrocene in the lithium supplement 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 one embodiment, a solid lithium supplement material is also immersed in the electrolyte, and dilithioferrocene is mixed with the lithium supplement material. The chemical formula of the lithium supplement material includes Li x M y O z , where M is at least one element among Fe, Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, V, Mo, Sn, etc., 1 ≤ x ≤ 8, 0 < y, 0 < z < 7. In a specific embodiment, the lithium supplement 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, when using the Li5FeO4 material in combination, due to different application links, it is possible to accurately judge how many active Li ions are released by Li5FeO4 when dilithioferrocene is applied, so that verification design can be carried out for both dilithioferrocene and Li5FeO4; in addition, since there are still some problems of possible gas generation in Li5FeO4 that need to be solved, then using a small amount of Li5FeO4 as the coating layer of dilithioferrocene to isolate the electrolyte can achieve high-capacity and stable lithium supplementation, and greatly reduce the usage amount of Li5FeO4, and can also effectively achieve the purpose of both increasing the lithium supplementation capacity and reducing gas generation; at the same time, it enables dilithioferrocene to act after contacting the electrolyte during formation, and can be used directly when reassembling the battery, without the need to inject it after formation.

[0038] In one embodiment, the molar ratio of the lithium replenishing material and dilithium ferrocene is 1:(2.9-3.1). It should be explained that in the secondary battery, the lithium replenishing material and dilithium ferrocene are mixed according to the molar ratio of lithium of 1:(2.9-3.1). Optionally, the molar ratio of the lithium replenishing material and 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. Meeting the above mass ratio of dilithium ferrocene and lithium replenishing material can ensure that dilithium ferrocene and lithium replenishing material stably replenish lithium to the positive electrode, and can also minimize the generation of gas in the secondary battery.

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

[0040] Because the role of the lithium supplement provided by the present invention is different from that of the electrolyte. The electrolyte provides an ion conduction channel for the battery or capacitor to ensure that the chemical reaction occurring during the operation of the device is reversible, while the dilithium ferrocene lithium supplement is used to supplement lithium, and the electrolyte in the secondary battery is to provide a dissolving environment for the dilithium ferrocene. In addition, the use order of the dilithium ferrocene lithium supplement provided by the present invention is different from that of the electrolyte. The dilithium ferrocene lithium supplement does not need to be mixed with the electrolyte. After the electrolyte is injected into the battery, the battery needs to be formed before the dilithium ferrocene lithium supplement is injected.

[0041] In one embodiment, the present invention also provides a method for preparing a lithium supplement, please refer to Figure 1 , including the following steps:

[0042] Step S10, adding n-butyl lithium and an initiator to a n-hexane solution of ferrocene, washing and drying after sufficient reaction to obtain dilithioferrocene.

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

[0044] Specifically, in step S10, the molar ratio of ferrocene to lithium ions in n-butyllithium is 1: 2. The initiator may be tetramethylethylenediamine, and the amount of the initiator added is the same as the amount of ferrocene added.

[0045] Optionally, in step S20, ferrocene and n-butyllithium will generate an orange-red precipitate after sufficient reaction. The orange-red precipitate is centrifuged out, washed with n-hexane solution for multiple times, and dried to obtain dilithioferrocene.

[0046] In one embodiment, the present invention further provides a secondary battery, comprising a plastic film, a positive electrode, a negative electrode, an electrolyte and a lithium supplement, wherein the positive electrode, the negative electrode, the electrolyte and the lithium supplement are all encapsulated in the plastic film.

[0047] Optionally, the positive electrode includes a current collector and a positive electrode active material layer disposed on the current collector, and the positive electrode active material layer includes components such as positive electrode active material, conductive agent, and binder. The negative electrode includes a current collector and a negative electrode active material layer disposed on the current collector, and the negative electrode active material layer includes components such as negative electrode active material, conductive agent, and binder. The present invention does not specifically limit these materials, and appropriate materials can be selected according to actual application requirements.

[0048] Optionally, the positive electrode active material can be a phosphate positive electrode active material or a ternary positive electrode active material. In a specific embodiment, the positive electrode active material includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium fluorovanadium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

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

[0050] Optionally, the electrolyte may be an electrolyte solution, in which case the secondary battery further includes a diaphragm disposed between the positive electrode plate and the negative electrode plate; or, the electrolyte may be a solid electrolyte, in which case the secondary battery does not include a diaphragm but is replaced by a solid electrolyte.

[0051] In one embodiment, the amount of lithium supplement added to the secondary battery satisfies the relationship: M1 = M2 × (1-ICE) × a, where M1 is the molar amount of dilithium ferrocene in the secondary battery, M2 is the molar amount of the positive electrode active material, ICE is the first cycle coulomb efficiency of the secondary battery, and 0.95≤a≤1.05. a is a correction factor, which is used to correct the error caused by the difference in active materials caused by the slight thickness difference on the electrode and the slight unevenness that may exist in the dilithium ferrocene solution.

[0052] In one embodiment, the present invention also provides a method for manufacturing a secondary battery, please refer to Figure 2 , including the following steps:

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

[0054] Step S200, forming the assembled battery, and after the formation, injecting dilithium ferrocene 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 an electrolyte to obtain an assembled battery, which specifically includes: stacking the positive electrode, the separator, and the negative electrode in order in a dry environment, and then welding the positive electrode ear and the negative electrode ear to obtain a battery cell, packaging the battery cell in an aluminum-plastic film of a fixed size, and then injecting the 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 the formation, dilithium ferrocene is injected into the assembled battery, specifically including: charging the assembled battery to 3.7V at a rate of 0.02C, and then discharging it to 2.5V at a rate of 0.02C, adding a lithium replenisher from a reserved injection hole after the discharge is completed, and the lithium replenishment process can be completed after standing.

[0057] It is understandable that in the method for making a secondary battery provided by the present invention, the order of adding the lithium supplement agent is different from that of the electrolyte. The lithium supplement agent needs to be injected into the battery pack after the electrolyte is added and the secondary battery is filled. No additional charging and discharging conditions are required. During the static stage, the Li ions lost by the positive electrode active material during the filling can be compensated by reaction, thereby playing a role in lithium supplementation. Therefore, the lithium supplement agent provided by the present invention is not equivalent to the electrolyte and the electrolyte additive. The electrolyte and the electrolyte additive need to be added before the formation to complete the formation process.

[0058] The technical solution of the present invention is described in detail below through specific embodiments.

[0059] Example 1

[0060] This embodiment provides a secondary battery. The secondary battery includes a positive electrode, a negative electrode, an electrolyte and a lithium supplement. The lithium supplement includes dilithium ferrocene and propylene carbonate, and the solubility of dilithium ferrocene in 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 (ferrocene to lithium ion molar ratio = 1:2) is added to a n-hexane solution of ferrocene, and an equal amount of tetramethylethylenediamine as an initiator is added to the ferrocene, and the solution is then allowed 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) dissolving the dilithioferrocene in step 2) in propylene carbonate to prepare a 0.5 mol / L solution, thereby obtaining a lithium supplement.

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

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

[0067] Step 5) Preparation of negative electrode: The negative electrode active material (graphite), conductive agent (acetylene black), binder (styrene butadiene rubber), and thickener (sodium carboxymethyl cellulose) are mixed in a mass ratio of graphite: acetylene black: styrene butadiene rubber: sodium carboxymethyl cellulose = 95:2:2:1, deionized water is added, and the mixture is stirred thoroughly to form a uniform negative electrode slurry, which is evenly coated on an 8-micron thick copper foil, and then dried to obtain a negative electrode sheet.

[0068] Step 6) Assemble the battery: stack the positive electrode sheet, separator, and negative electrode sheet in order in a dry environment, then weld the positive and negative electrode tabs to obtain a battery cell, and encapsulate the battery cell in an aluminum-plastic film of a fixed size, followed by electrolyte injection and packaging. Leave an injection hole on the edge of the assembled battery. The composition of the electrolyte includes 1M LiPF6 and EC (ethylene carbonate): DEC (diethyl carbonate): DMC (dimethyl carbonate) = 1:1:1.

[0069] Step 7) formation and injection of lithium replenisher: the assembled battery 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 replenisher is added from the reserved injection hole (the added molar amount M1 = M2 × (1-ICE) × a, wherein M1 is the molar amount of dilithium ferrocene in the lithium replenisher, M2 is the molar amount of the positive electrode active material, ICE is the first cycle coulomb efficiency, and a = 1).

[0070] Step 8) After standing for 30 minutes, the lithium replenishment process is completed.

[0071] Example 2

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

[0073] Example 3

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

[0075] Example 4

[0076] The difference between 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 embodiment provides a secondary battery, which includes a positive electrode, a negative electrode and an electrolyte.

[0079] The difference between Comparative Example 1 and Example 1 is that no lithium supplement agent is added, that is, the preparation steps 1) to 3) of the lithium supplement agent are not performed, and the process of adding the lithium supplement agent in step 7) is not performed in the secondary battery manufacturing method.

[0080] Comparative Example 2

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

[0082] The difference between Comparative Example 1 and Example 1 is that the lithium supplement agent is added before the formation.

[0083] Comparative Example 3

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

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

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

[0087] The parameters of the secondary batteries provided by Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 1:

[0088] Table 1 Secondary battery parameters provided by the examples and comparative examples

[0089] a concentration Joining 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 (twice the volume) 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 charging process was carried out at a rate of 0.1C, with a cut-off voltage of 4.3V; constant voltage charging was carried out at a cut-off voltage of 4.3V; after the charging process was completed, the battery was allowed to stand for 10 minutes and then discharged at a rate of 0.1C, with a cut-off voltage of 2.5V; and the first cycle efficiency = (discharge specific capacity / charge specific capacity)*100%.

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

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

[0094]

[0095] From the test results of Examples 1 to 4 and Comparative Example 1 in Table 2, it can be seen that by adding dilithium ferrocene as a lithium supplement to the secondary battery, the first cycle charge and discharge capacity of the secondary battery after lithium supplementation is significantly improved compared to the secondary battery without adding the dilithium ferrocene lithium supplement. Therefore, it is shown that dilithium ferrocene can be used as a lithium supplement to supplement lithium to the secondary battery.

[0096] It can be seen from the test results of Examples 1 to 4 and Comparative Example 2 in Table 2 that the timing of adding dilithium ferrocene to the secondary battery needs to be after the secondary battery is formed. If dilithium ferrocene is added before formation, redox reaction occurs in the first cycle of charge and discharge, and the lithium supplementation effect cannot be achieved.

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

[0098] From the test results of Examples 1 to 3 in Table 2, it can be seen that the lithium replenishment capacity is positively correlated with the content of dilithium ferrocene added. Moreover, when the amount of dilithium ferrocene added (solid content) is the same, the proportion of the electrolyte has a small effect on the lithium replenishment capacity.

[0099] In the description of the embodiments of the present invention, it should be noted that the orientation or positional relationship of terms such as "center", "up", "down", "left", "right", "vertical", "horizontal", "inside" and "outside" are based on the orientation or positional relationship described in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0100] What is disclosed above is only a preferred embodiment of the present invention, and it certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. An application of dilithium ferrocene, characterized in that: The dilithium ferrocene is used as a lithium supplement and is dissolved in an electrolyte.

2. The use of dilithium ferrocene according to claim 1, characterized in that: Solid lithium supplement material is also soaked in the electrolyte, and the dilithium ferrocene is mixed with the lithium supplement material.

3. The use of dilithioferrocene according to claim 2, characterized in that: The molar ratio of the lithium supplement material to the dilithium ferrocene is 1:(2.9-3.1).

4. The use of dilithioferrocene according to claim 3, characterized in that: The chemical formula of the lithium supplement 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, 1≤x≤8, 0 <y,0<z<7。 5. The use of dilithioferrocene according to claim 1, characterized in that: The electrolyte includes one or more of propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and methylpropyl carbonate.

6. A method for preparing dilithium ferrocene as a lithium supplement, characterized in that: The steps include: n-Butyl lithium and an initiator are added to a n-hexane solution of ferrocene, and after sufficient reaction, the solution is washed and dried to obtain dilithioferrocene; The dilithium ferrocene is dissolved in an electrolyte.

7. A secondary battery, characterized in that: The invention comprises a positive electrode, a negative electrode, an electrolyte and dilithium ferrocene. The positive electrode and the negative electrode are both immersed in the electrolyte. The dilithium ferrocene is dissolved in the electrolyte. The dilithium ferrocene is used to provide lithium ions to the positive electrode.

8. The secondary battery according to claim 7, characterized in that: The positive electrode includes a positive electrode active material, and the amount of the dilithium ferrocene added in the secondary battery satisfies the 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 coulomb efficiency of the secondary battery, and a is the correction coefficient, 0.95≤a≤1.

05.

9. A method for manufacturing a secondary battery, characterized in that: The steps include: Fixing the positive electrode and the negative electrode in a container containing an electrolyte to obtain an assembled battery; The assembled battery is subjected to chemical formation, and after the chemical formation, dilithium ferrocene is injected into the assembled battery to obtain the secondary battery.

10. The method for manufacturing a secondary battery according to claim 9, characterized in that: The formation environment of the assembled battery is as follows: the assembled battery is charged to 3.7V at a rate of 0.02C, and then discharged to 2.5V at a rate of 0.02C.

Images