CN107808978B - A kind of liquid active lithium supplement, its preparation method and use - Google Patents

Abstract

The invention provides a liquid active lithium supplement for supplementing active lithium in a lithium ion battery, which is a solution or suspension and comprises a lithium sulfide and a solvent; wherein the solvent is capable of dissolving or partially dissolving the sulfide of lithium without a chemical reaction between the two; and/or the solvent does not physically and/or chemically react with the electrolyte of the lithium ion battery; and/or the solvent is selected from the electrolyte of the lithium ion battery. The invention also provides a method for supplementing active lithium in the lithium ion battery and the lithium ion battery. The liquid active lithium supplement provided by the invention is simple to prepare, convenient to use, high in safety and low in cost. The liquid active lithium replenisher provided by the invention has good compatibility with various anode materials, cathode materials and electrolytes of lithium ion batteries, and can be used for preparing various lithium ion batteries, so that the reversible charge-discharge capacity and the subsequent cycle stability of the full battery are improved.

Description

A kind of liquid active lithium supplement, its preparation method and use

technical field

The invention belongs to the field of lithium ion batteries. Specifically, the present invention relates to a liquid active lithium supplement based on lithium sulfide, and the present invention also relates to a preparation method of the active lithium supplement and use thereof.

Background technique

Due to the advantages of high discharge voltage, high energy density and long cycle life, lithium-ion batteries have been widely used in various small portable electronic devices, such as notebook computers, mobile phones and cameras, etc. Favored by high-tech fields, such as aerospace satellites, electric vehicles and military, these applications require lithium-ion batteries with better capacity and cycle life.

It is known to those skilled in the art that a solid electrolyte film (SEI film) is formed on the surface of the negative electrode material of the lithium ion battery when the lithium ion battery performs the first charge-discharge cycle. The lithium ions of the active lithium in the positive electrode and the lithium ions in the electrolyte cannot be completely extracted after being inserted into the negative electrode material. Further, the current commercial electrolytes are ethylene carbonate (EC), dimethyl carbonate (DMC), and vinylene carbonate. Ester (VC) and other carbonate electrolytes, so the main components of the SEI film are LiF, Li ₂ CO ₃ and alkyl ester lithium, etc., and the lithium ions in these products mainly come from the active lithium in the positive electrode, these situations are unavoidable It will lead to capacity decay and cycle efficiency reduction of lithium-ion batteries, especially after the first charge-discharge cycle, the cycle efficiency decrease is more obvious.

In order to supplement the loss of active lithium caused by the formation of the SEI film during the first charging process and the subsequent long-cycle irreversible capacity loss, it is necessary to supplement the active lithium in the lithium-ion battery, and some methods of supplementing lithium have been reported in the existing patent literature.

The Chinese Patent Publication No. CN1290209C discloses a method for replenishing lithium in the negative electrode. After forming a slurry of metal lithium, negative electrode material and non-aqueous liquid, scrape coating on the current collector, and then form a pole piece through subsequent processes. Although this method can also supplement the consumed active lithium, due to the very high activity of metal lithium, it is easy to react with oxygen, water vapor and nitrogen in the air, so the whole process needs to be carried out under completely anhydrous conditions, and the process is cumbersome. This greatly increases the production cost, and because lithium powder is easy to float in the air, there is a great safety hazard.

In the patent application with the application number CN201310070202.9, it is proposed to directly incorporate lithium supplements containing lithium compounds into the positive electrode material or directly coat the surface of the positive electrode. During the charging process of the first charge-discharge cycle, these lithium supplements will It is decomposed to provide active lithium, although it supplements active lithium to a certain extent, but due to the electronic insulating properties of lithium sulfide, its electrochemical activity is smaller when its particles are larger, and it cannot be fully charged during the first charge-discharge cycle. Therefore, the first charge-discharge cycle is active only when the lithium sulfide is dispersed into small particles, but the method of preparing small particles of lithium sulfide in advance, such as high-energy ball milling, is more complicated, which will It greatly increases the cost, and the small particles of lithium have high sulfide activity, which will quickly react with water vapor in the air and deteriorate, making it difficult to store.

The patent application with the application number of CN 201210350770.X discloses a method of "wet lithium replenishment", in which organic lithium is sprayed or dripped on the surface of the positive electrode, so that the lithium in the organic lithium is reduced and embedded in the positive electrode sheet . But this invention has some problems, such as the n-butyllithium, tert-butyllithium, etc. used are highly flammable and explosive dangerous goods, and the safety is not higher than that of lithium powder; although the organic lithium sprayed on the surface of the positive electrode is partially The organolithium is reduced and intercalated into the cathode, but there is still a lot of residue, which in turn reduces the capacity further.

Therefore, there is currently a need for a reagent and method for replenishing active lithium in lithium-ion batteries to reduce the capacity fading of lithium-ion batteries during charging and discharging and to improve their cycle efficiency.

SUMMARY OF THE INVENTION

In order to make up for the deficiencies of the prior art, the present invention provides a liquid active lithium supplement for supplementing active lithium in a lithium ion battery. The active lithium supplement provided by the present invention is a lithium sulfide that is dissolved or partially dissolved in a solvent. Therefore, the liquid active lithium supplement provided by the present invention can directly prepare small particles of lithium sulfide and can be uniform with carbon composite, and since the lithium sulfide is dispersed in the solvent, it is easier to preserve. The present invention also provides a method of using the liquid active lithium supplement. Therefore, the preparation method of the liquid active lithium supplement provided by the present invention is simple, low in cost, suitable for mass production, and can be widely used in industrial production.

In one aspect, the present invention provides a liquid active lithium supplement for supplementing active lithium in a lithium ion battery, the liquid active lithium supplement is a solution or suspension, including lithium sulfide and a solvent;

wherein the solvent is capable of dissolving or partially dissolving the lithium sulfide without a chemical reaction between the two; and/or

The solvent does not physically and/or chemically react with the electrolyte of the lithium-ion battery; and/or

The solvent is selected from the electrolyte of the lithium ion battery.

Preferably, the lithium sulfide is selected from one or more of lithium sulfide, lithium persulfide, and lithium polysulfide. More preferably, the lithium sulfide is lithium sulfide.

Preferably, the lithium sulfide can be synthesized in advance, or can be formed by mixing lithium sulfide and sulfur into the above-mentioned solvent at a molar ratio of Li:S of 2:1-8.

Preferably, the molar concentration of lithium ions in the liquid active lithium supplement is 0.01mol/L-5mol/L, more preferably 0.01mol/L-0.5mol/L, most preferably 0.01mol/L-0.25 mol/L.

Preferably, the solvent is selected from one or more organic solvents that can dissolve lithium sulfide; more preferably, the solvent is selected from methanol, ethanol, tetraethylene glycol dimethyl ether (TEGDME) and diethylene glycol One or more of methyl ether (DME).

Preferably, the liquid active lithium supplement also includes optional conductive additives and/or optional binders;

Preferably, the conductive additive is selected from one or more of carbon black conductive agent, conductive carbon tube, graphene or graphene oxide; more preferably, the carbon black conductive agent is selected from acetylene black, Super P, One or more of Super S, 350G, carbon fiber (VGCF), carbon nanotubes (CNTs), Ketjen black (Ketjen black EC 300J, Ketjen black EC 600JD, Carbon ECP or Carbon ECP600JD); preferably, the The mass of the conductive additive in the liquid active lithium supplement is 0-50% of the mass of the lithium sulfide; preferably 5-20%; more preferably 5-10%. Preferably, the binder is selected from polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC) , one or more of copolymers of styrene and butadiene (SBR). Preferably, the mass of the binder in the liquid active lithium supplement is 0-20% of the mass of the lithium sulfide; preferably 2-10%; more preferably 2-5%.

Preferably, the electrolyte is selected from one or more of liquid electrolytes, solid electrolytes, semi-solid electrolytes and polymer electrolytes.

On the other hand, the present invention provides a method for preparing the above-mentioned liquid active lithium supplement, the method comprising the following steps:

The lithium sulfide, optional conductive additive, and optional binder are added to the solvent and mixed to obtain a liquid active lithium extender.

Preferably, the addition is a one-time addition or a step-by-step addition.

In another aspect, the present invention provides a method for replenishing active lithium in a lithium ion battery, the method comprising adding the above-mentioned liquid active lithium replenisher to a positive electrode material slurry of the lithium ion battery and/or incorporating to the positive electrode of the lithium ion battery and/or added to the electrolyte of the lithium ion battery.

Preferably, when the solvent does not physically and/or chemically react with the active lithium extender, the active lithium extender is added to the positive electrode material slurry and/or incorporated into the positive electrode;

Preferably, the liquid active lithium extender is incorporated into the positive electrode by means of coating, dipping and/or spraying. Preferably, the mass percentage of the active lithium supplement in the positive electrode or positive electrode material is 0.1-20%, preferably 2-10%, more preferably 2-5%.

Preferably, the liquid active lithium extender is added to the electrolyte of the lithium ion battery when the solvent does not physically and/or chemically react with the electrolyte of the lithium ion battery. Preferably, the liquid active lithium extender is added to the electrolyte of the lithium ion battery when the solvent is selected from the electrolyte of the lithium ion battery.

In yet another aspect, the present invention also provides a lithium ion battery, the lithium ion battery includes the liquid active lithium supplement of the present invention.

In another aspect, the present invention also provides a method for preparing a lithium ion battery, the method comprising using the above-mentioned liquid active lithium supplement to prepare a lithium battery, and/or using the above method to prepare a lithium battery.

The inventors of the present invention found that when the active lithium supplement is added to the battery system in the form of a solution, it is fully decomposed during the first charge-discharge cycle, releasing lithium ions to be embedded or deposited in the negative electrode or alloyed with the negative electrode, making up for the negative electrode. The metal lithium lost during the formation of the SEI film and subsequent cycles releases excess active lithium, and the lithium consumed during the formation of the negative SEI film is supplemented. Therefore, the inventors of the present invention use one or several solvents to dissolve or partially dissolve the active lithium. Lithium supplements obtain liquid active lithium supplements, which are then added to the battery system, so that the first charge-discharge capacity and long-term cycle stability of lithium-ion batteries have been significantly improved. Therefore, the lithium ion secondary battery of the present invention can significantly improve the energy density and service life.

Based on this, the liquid active lithium supplement provided by the present invention is simple in preparation, convenient in use, high in safety and low in cost. Further, the liquid active lithium supplement provided by the present invention has good compatibility with various positive electrode materials, negative electrode materials and electrolytes of lithium ion batteries, and can be used to prepare various lithium ion batteries, thereby improving the reversible charge and discharge capacity of the full battery. Subsequent cycle stability.

Description of drawings

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein:

Fig. 1 is the cyclic voltammetry curve of the lithium ion battery (half cell) composed of the positive electrode plate D1 and the lithium plate according to the present invention;

Fig. 2 is the cyclic voltammetry curve of the lithium ion battery (half cell) composed of the positive electrode plate D3 and the lithium plate according to the present invention;

Fig. 3 is the first-week charge-discharge curve comparison diagram of the full battery F1 and F3 according to the present invention;

Fig. 4 is the first-week charge-discharge curve comparison diagram of the full battery F1 and H1 according to the present invention;

Detailed ways

The present invention will be further described in detail below in conjunction with specific embodiments, and the given examples are only for illustrating the invention, rather than for limiting the scope of the present invention.

Example 1 Preparation of liquid active lithium supplement

This example prepares a liquid active lithium supplement according to the following steps, the operation being carried out at room temperature:

1. Take 0.16g lithium sulfide (Li ₂ S), 0.02g Super P and 0.02g PVP, put them in 20ml methanol, ultrasonicate for 10h, stir for 10h and evenly mix to obtain a liquid active lithium supplement. Lithium supplements are noted as A1.

2. Take 0.16g lithium sulfide (Li ₂ S), 0.02g Super P and 0.02g PVP, put them in 20ml ethanol, ultrasonicate for 10h, stir for 10h and evenly mix to obtain a liquid active lithium supplement. Lithium supplements are noted as A2.

3. Take 0.16g lithium sulfide (Li ₂ S), 0.02g Super P and 0.02g PVP, place them in 20ml TEGDME, ultrasonicate for 10h, and stir for 10h to mix evenly to obtain a liquid active lithium supplement. Lithium supplements are noted as A3.

4. Take 0.16g lithium sulfide (Li ₂ S), 0.02g Super P and 0.02g PVP, place them in 20ml DME, ultrasonicate for 10h, and stir for 10h to mix evenly to obtain a liquid active lithium supplement. Lithium supplements are noted as A4.

5. Take 0.08g lithium sulfide (Li ₂ S), 0.09g Super P and 0.04g PVP, put them in 20ml methanol, ultrasonicate for 10h, stir for 10h and evenly mix to obtain a liquid active lithium supplement. Lithium supplements are noted as A5.

6. Take 0.08g lithium sulfide (Li ₂ S), 0.09g Super P and 0.04g PVP, put them in 20ml ethanol, ultrasonicate for 10h, and stir for 10h to mix evenly to obtain a liquid active lithium supplement. Lithium supplements are noted as A6.

7. Take 0.08g lithium sulfide (Li ₂ S), 0.09g Super P and 0.04g PVP, place them in 20ml TEGDME, ultrasonicate for 10h, and stir for 10h to mix evenly to obtain a liquid active lithium supplement. Lithium supplements are noted as A7.

8. Take 0.08g lithium sulfide (Li ₂ S), 0.09g Super P and 0.04g PVP, place them in 20ml DME, ultrasonicate for 10h, and stir for 10h to mix evenly to obtain a liquid active lithium supplement. Lithium supplements are noted as A8.

9. Take 0.18g lithium sulfide (Li ₂ S) and 0.02g PVP, place them in 20ml methanol, ultrasonicate for 10h, stir for 10h and mix evenly to obtain a liquid active lithium supplement, which is recorded as A9.

10. Take 0.18g lithium sulfide (Li ₂ S) and 0.02g PVP, put them in 20ml ethanol, ultrasonicate for 10h, stir for 10h and evenly mix to obtain a liquid active lithium supplement, which is recorded as A10.

11. Take 0.18g lithium sulfide (Li ₂ S) and 0.02g PVP, put them in 20ml TEGDME, ultrasonicate for 10h, and stir for 10h to evenly mix to obtain a liquid active lithium supplement, which is recorded as A11.

12. Take 0.18g lithium sulfide (Li ₂ S) and 0.02g PVP, place them in 20ml DME, ultrasonicate for 10h, and stir for 10h to evenly mix to obtain a liquid active lithium supplement, which is recorded as A12.

13. Take 0.18g lithium sulfide (Li ₂ S) and 0.02g Super P, put them in 20ml methanol, ultrasonicate for 10h, and stir for 10h to mix evenly to obtain a liquid active lithium supplement. The liquid active lithium supplement is recorded as for A13.

14. Take 0.18g of lithium sulfide (Li ₂ S) and 0.02g of Super P, put them in 20ml of ethanol, ultrasonicate for 10h, and stir for 10h to evenly mix to obtain a liquid active lithium supplement. The liquid active lithium supplement is recorded as for A14.

15. Take 0.18g lithium sulfide (Li ₂ S) and 0.02g Super P, put them in 20ml TEGDME, ultrasonicate for 10h, and stir for 10h to evenly mix to obtain a liquid active lithium supplement. The liquid active lithium supplement is recorded as for A15.

16. Take 0.18g lithium sulfide (Li ₂ S) and 0.02g Super P, place them in 20ml DME, ultrasonicate for 10h, and stir for 10h to mix evenly to obtain a liquid active lithium supplement. The liquid active lithium supplement is recorded as for A16.

Example 2 Preparation of liquid active lithium supplement

This example prepares a liquid active lithium supplement according to the following steps, the operation being carried out at room temperature:

1. Take 0.0115g lithium sulfide (Li ₂ S) and 0.056g sulfur (S), place them in tetraethylene glycol dimethyl ether (TEGDME), stir for 6h and evenly mix to obtain a liquid active lithium supplement. The liquid active lithium supplement is denoted as B1.

2. Take 0.0115g lithium sulfide (Li ₂ S) and 0.056g sulfur (S), place them in dimethyl ether (DME), stir for 6h and mix them evenly to obtain a liquid active lithium supplement, the liquid active lithium supplement The agent is denoted as B2.

3. Take 0.0115g lithium sulfide (Li ₂ S) and 0.048g sulfur (S), place them in tetraethylene glycol dimethyl ether (TEGDME), stir for 6h and evenly mix to obtain a liquid active lithium supplement. The liquid active lithium supplement is denoted as B3.

4. Take 0.0115g lithium sulfide (Li ₂ S) and 0.048g sulfur (S), place them in dimethyl ether (DME), stir for 6h and mix them evenly to obtain a liquid active lithium supplement. The agent is denoted as B4.

5. Take 0.0115g lithium sulfide (Li ₂ S) and 0.032g sulfur (S), place them in tetraethylene glycol dimethyl ether (TEGDME), stir for 6h and evenly mix to obtain a liquid active lithium supplement. The liquid active lithium supplement is denoted as B5.

6. Take 0.0115g lithium sulfide (Li ₂ S) and 0.032g sulfur (S), place them in dimethyl ether (DME), stir for 6h and mix them evenly, to obtain a liquid active lithium supplement, the liquid active lithium supplement The agent is denoted as B6.

7. Take 0.0115g lithium sulfide (Li ₂ S) and 0.024g sulfur (S), place them in tetraethylene glycol dimethyl ether (TEGDME), stir for 6h and evenly mix to obtain a liquid active lithium supplement. The liquid active lithium supplement is denoted as B7.

8. Take 0.0115g lithium sulfide (Li ₂ S) and 0.024g sulfur (S), put them in dimethyl ether (DME), stir for 6h and mix them evenly, to obtain a liquid active lithium supplement, the liquid active lithium supplement The agent is recorded as B8.

9. Take 0.0115g lithium sulfide (Li ₂ S), put it in tetraethylene glycol dimethyl ether (TEGDME), stir for 6h and evenly mix to obtain a liquid active lithium supplement, which is recorded as B9.

10. Take 0.0115g of lithium sulfide (Li ₂ S), put it in dimethyl ether (DME), stir for 6h and evenly mix to obtain a liquid active lithium supplement, which is denoted as B10.

Example 3 Comparative example

This example was formulated for use as a comparative active lithium supplement according to the following procedure, performed at room temperature:

Take 0.16g lithium sulfide (Li ₂ S), 0.02g Super P and 0.02g PVP and mix them uniformly in NMP to obtain an active lithium supplement, which is denoted as C1.

Take 0.08g lithium sulfide (Li ₂ S), 0.09g Super P and 0.04g PVP and mix them uniformly in NMP to obtain an active lithium supplement, which is denoted as C2.

Take 0.18g lithium sulfide (Li ₂ S) and 0.02g PVP and mix them uniformly in NMP to obtain an active lithium supplement, which is denoted as C3.

Take 0.18g lithium sulfide (Li ₂ S) and 0.02g Super P and mix them uniformly in NMP to obtain an active lithium supplement, which is denoted as C4.

Example 4 Performance Test

The solutions A1 to A16 prepared in Example 1 were assembled into coin cells according to the following steps.

4.1 Preparation of positive electrode and negative electrode

的圆片，置于真空烘箱中以120℃烘6h，自然冷却后，取出，置于手套箱中用作正极极片，记为D1。LiFePO ₄ is used as positive active material, carbon black is used as conductive additive, and carboxymethyl cellulose (CMC), copolymer of styrene and butadiene (SBR) is used as binder, and the mass ratio is 90:7:1 :2 Mix well in water to prepare a uniform positive electrode slurry. The uniform positive electrode slurry was uniformly coated on the aluminum foil current collector with a thickness of 15 μm, dried at 55 °C to form a pole piece with a thickness of 100 μm, and placed under a roller press for rolling (pressure about 1MPa×1.5cm2) , cut the pole piece to a diameter of

The discs were placed in a vacuum oven at 120 °C for 6 h, and after natural cooling, they were taken out and placed in a glove box to be used as a positive pole piece, denoted as D1.

的圆片，置于真空烘箱中以120℃烘6h，自然冷却后，取出置于手套箱中用作负极极片。Graphite was used as the negative electrode active material, carbon black was used as a conductive additive, and carboxymethyl cellulose (CMC), a copolymer of styrene and butadiene (SBR) was used as a binder, and the mass ratio was 93:2:2: 3 Mix evenly in water to prepare a uniform negative electrode slurry. The uniform negative electrode slurry was evenly coated on the copper foil current collector with a thickness of 8 μm, and dried at 55 °C to form pole pieces with a thickness of 50 μm and 59 μm. 1.5cm2), cut the pole piece to a diameter of

The wafers were placed in a vacuum oven at 120 °C for 6 h, and after natural cooling, they were taken out and placed in a glove box to be used as negative pole pieces.

的正极圆片上。在120℃下烘10h，自然冷却后，用作正极，记做D2-D17。取与A1、A5、A9和A13对应的活性锂补充剂同样质量的C1～C4涂覆与

的正极圆片上。在120℃下烘10h，自然冷却后，用作正极，记做E1～E4In a glove box filled with an inert atmosphere, take 50 μl of A1~A4, 80 μl A5~A8 and 50 μl A9~A16 solution dropwise to

on the positive disc. Bake at 120°C for 10h, and after natural cooling, it is used as a positive electrode, denoted as D2-D17. Take C1~C4 of the same quality as the active lithium supplements corresponding to A1, A5, A9 and A13 to coat with

on the positive disc. Bake at 120℃ for 10h, after natural cooling, use as positive electrode, denoted as E1~E4

4.2 Assembling the lithium-ion secondary battery

In a glove box filled with an inert atmosphere, a three-layer film of PP/PE/PP (purchased from Celegard, USA) was used as a separator between the positive electrode and the negative electrode, and 1M LiPF6 was added dropwise to dissolve in EC/DMC (1:1, Volume ratio) non-aqueous electrolyte (purchased from BASF, Germany), the 50 μm graphite negative electrode plate prepared in 4.1 was used as the negative electrode of the battery, and the D1 prepared in step 4.1 was used as the positive electrode. Do F1. The 59 μm graphite negative electrode plate prepared in step 4.1 was used as the negative electrode of the battery, and the D2-D17 prepared in step 4.1 was used as the positive electrode to assemble a CR2032 button battery and denoted as F2~F17. The 59 μm graphite negative electrode plate prepared in step 4.1 was used as the negative electrode of the battery, and the E1 to E4 prepared in step 4.1 were used as the positive electrode to assemble a button battery with model CR2032 and recorded as G1 to G4.

In a glove box filled with an inert atmosphere, a three-layer film of PP/PE/PP (purchased from Celegard, USA) was used as a separator between the positive electrode and the negative electrode, and 1M LiPF6 was added dropwise to dissolve in EC/DMC (1:1, volume ratio) non-aqueous electrolyte (purchased from BASF, Germany), and then 30 μl of B1-B10 solution was added to the electrolyte. The 59 μm graphite negative electrode plate prepared in step ① was used as the negative electrode of the battery, and the D1 prepared in step ① was used as the positive electrode to assemble a button battery with model number CR2032 and record it as H1~H10.

After the prepared button batteries F1-F17, G1-G4 and H1-H10 were allowed to stand at room temperature for 24 hours, the battery charge and discharge tester (purchased from Wuhan Landian Electronics Co., Ltd.) was used to test the batteries. The coin-type battery prepared above was subjected to a charge-discharge cycle test. Firstly, the specific capacity of LiFePO4 was calculated as 160mAhg ^-1 , cycled at a rate of 0.05C for 1 week, and then continued to cycle at a rate of 0.2C for 100 cycles. The charge-discharge voltage range of the control battery was 2.5V-3.6V. The preparation parameters and results are shown in Tables 1 and 2.

result

From the cyclic voltammetry curve in Figure 1, the redox peak of lithium iron phosphate is shown, while in Figure 2, it can be clearly seen that there is an oxidation peak around 2.6V, which shows that the lithium supplement is charged at 2.6 V during the first week of charging. Decomposition begins near V.

Figure 3 shows the comparison of the first-week charge-discharge curves of lithium-ion batteries F1 and F3. It can be seen that lithium-ion battery F3 has a lower potential capacity than F1, and its first-week charge capacity reaches 174.8mAhg ^{- 1} , the excess capacity contribution comes from the decomposition of lithium sulfide, and the discharge capacity of Example F3 in the first week is as high as 146.6mAhg-1, which is 15.5mAhg-1 more than the 131.1mAhg-1 of F1, indicating that Lithium sulfide can decompose and release lithium ions during the first charge, which compensates for the loss of lithium ions when the SEI film is formed on the surface of the negative electrode, and compensates for the loss of lithium ions in the positive electrode material and electrolyte, thereby significantly improving the reversibility of lithium ion batteries in the first cycle. discharge capacity.

Figure 4 shows the comparison of the first-week charge-discharge curves of lithium-ion batteries F1 and H2, from which it can be seen that lithium-ion battery H2 has a lower potential capacity than F1, and its first-week charge capacity reaches 162.1mAhg ^-1 , this excess capacity contribution comes from the decomposition of lithium sulfide, and the discharge capacity of H2 in the first week is as high as 139mAhg-1, which is about 10mAhg-1 more than that of F1, which is only 131.1mAhg-1, indicating that Lithium sulfide can decompose and release lithium ions during the first charge, which compensates for the loss of lithium ions when the SEI film is formed on the surface of the negative electrode, and compensates for the loss of lithium ions in the positive electrode material and electrolyte, thereby significantly improving the performance of lithium ion batteries. Cycle reversible discharge capacity.

Table 1 compares the 100-cycle capacity retention rates of lithium-ion batteries F1-F17 and G1-G4 with different parameters. It can be seen that the long-cycle stability of batteries containing lithium sulfide supplements has been significantly improved, indicating that lithium sulfide The active lithium generated by the decomposition also continuously compensates for the active lithium lost during the electrochemical cycling of the lithium-ion battery in subsequent cycles. However, the capacity retention rate and first-week capacity of lithium-ion batteries G1-G4 are much smaller than those of lithium-ion batteries F2-F17, indicating that when a solvent that does not dissolve lithium sulfide is used, its activity is low and cannot be fully exerted. The loss of active lithium cannot be fully replenished.

Table 2 compares the 100-cycle capacity retention rates of lithium-ion batteries F1, H1-H10 with different parameters. It can be seen that the reversible capacity and long-term cycle stability of lithium-ion batteries containing liquid active lithium supplements are extremely good. The large increase indicates that the active lithium generated by the decomposition of lithium sulfide also continuously compensates for the active lithium lost during the electrochemical cycle of the lithium-ion battery in the subsequent cycles. In general, the reversible capacity and long cycle stability of the lithium ion battery can be significantly improved with the method for supplementing lithium provided by the present invention.

Table 1 shows the variation trend of the discharge capacity of lithium-ion batteries F1-F17 and G1-G4 with different parameters with the number of cycles

Table 2 shows the variation trend of the discharge capacity of lithium-ion batteries F1, H1-H15 with different parameters with the number of cycles.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features thereof can be equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention. scope.

Claims (27)

1. A liquid active lithium supplement for supplementing active lithium in a lithium ion battery, the liquid active lithium supplement is a solution or a suspension, including a lithium sulfide and a solvent; wherein the solvent is capable of dissolving or partially dissolving the lithium sulfide without a chemical reaction between the two; and/or The solvent does not physically and/or chemically react with the electrolyte of the lithium-ion battery; and/or The solvent is selected from the electrolyte of the lithium ion battery; Wherein, the sulfide of the lithium is selected from one or more of lithium sulfide, lithium persulfide, and lithium polysulfide; The solvent is selected from tetraethylene glycol dimethyl ether and/or dimethyl ether. 2. The liquid active lithium replenisher of claim 1, wherein the lithium sulfide is lithium sulfide. 3 . The liquid active lithium supplement according to claim 1 , wherein the molar concentration of lithium ions in the liquid active lithium supplement is 0.01 mol/L-5 mol/L. 4 . 4 . The liquid active lithium supplement according to claim 1 , wherein the molar concentration of lithium ions in the liquid active lithium supplement is 0.01 mol/L-0.5 mol/L. 5 . 5 . The liquid active lithium supplement according to claim 1 , wherein the molar concentration of lithium ions in the liquid active lithium supplement is 0.01 mol/L-0.25 mol/L. 6 . 6. The liquid active lithium extender according to any one of claims 1-5, wherein the liquid active lithium extender further comprises optional conductive additives and/or optional binders. 7. The liquid active lithium supplement according to claim 6, wherein the conductive additive is selected from one or more of carbon black conductive agent, graphene or graphene oxide. 8. The liquid active lithium supplement according to claim 7, wherein the carbon black conductive agent is selected from one or more of acetylene black, SuperP, 350G, carbon fiber, carbon nanotube, and Ketjen black. 9 . The liquid active lithium supplement according to claim 6 , wherein the mass of the conductive additive in the liquid active lithium supplement is 0-50% of the mass of the lithium sulfide. 10 . 10 . The liquid active lithium supplement according to claim 6 , wherein the mass of the conductive additive in the liquid active lithium supplement is 5% to 20% of the mass of the lithium sulfide. 11 . 11 . The liquid active lithium supplement according to claim 6 , wherein the mass of the conductive additive in the liquid active lithium supplement is 5% to 10% of the mass of the lithium sulfide. 12 . 12. The liquid active lithium supplement of claim 6, wherein the binder is selected from the group consisting of polyvinylpyrrolidone, polyvinylidene fluoride, polyethylene oxide, polytetrafluoroethylene, carboxymethyl cellulose, One or more of the copolymers of styrene and butadiene. 13 . The liquid active lithium supplement of claim 6 , wherein the mass of the binder in the liquid active lithium supplement is 0-20% of the mass of the lithium sulfide. 14 . 14 . The liquid active lithium supplement according to claim 6 , wherein the mass of the binder in the liquid active lithium supplement is 2% to 10% of the mass of the lithium sulfide. 15 . 15 . The liquid active lithium supplement according to claim 6 , wherein the mass of the binder in the liquid active lithium supplement is 2% to 5% of the mass of the lithium sulfide. 16 . 16. The liquid active lithium replenisher of claim 1, wherein the electrolyte is selected from one or more of liquid electrolytes, solid electrolytes, semi-solid electrolytes, and polymer electrolytes. 17. The preparation method of the liquid active lithium supplement according to any one of claims 1-16, the method comprising the steps of: The lithium sulfide, optional conductive additive, and optional binder are added to the solvent and mixed to obtain the liquid active lithium extender. 18. The method of claim 17, wherein the adding is a one-time addition or a stepwise addition. 19. A method of replenishing active lithium in a lithium ion battery, the method comprising adding the liquid active lithium replenisher of any one of claims 1-16 to a positive electrode material slurry of the lithium ion battery and/or incorporated into the positive electrode of the lithium ion battery and/or added to the electrolyte of the lithium ion battery. 20. The method of claim 19, wherein when the solvent does not react physically and/or chemically with the active lithium extender, the liquid active lithium extender is added to the positive electrode material slurry to neutralize/ or incorporated into the positive electrode. 21. The method of claim 20, wherein the liquid active lithium extender is incorporated into the positive electrode using coating, dipping and/or spraying. 22 . The method of claim 19 , wherein the liquid active lithium extender accounts for 0.1-20% by mass of the positive electrode or positive electrode material. 23 . 23. The method of claim 19, wherein the mass percentage of the liquid active lithium extender in the positive electrode or positive electrode material is 2% to 10%. 24. The method of claim 19, wherein the mass percentage of the liquid active lithium extender in the positive electrode or positive electrode material is 2-5%. 25. The method of claim 19, wherein the liquid active lithium extender is added to the lithium ion battery when the solvent does not physically and/or chemically react with the electrolyte of the lithium ion battery in the electrolyte. 26. The method of claim 19, wherein the liquid active lithium extender is added to the electrolyte of the lithium ion battery when the solvent is selected from the electrolyte of the lithium ion battery. 27. A lithium ion battery comprising the liquid active lithium replenisher of any one of claims 1-16.

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