WO2018045940A1

WO2018045940A1 - Liquid active lithium supplement, preparation method therefor and use thereof

Info

Publication number: WO2018045940A1
Application number: PCT/CN2017/100487
Authority: WO
Inventors: 詹元杰; 黄学杰; 俞海龙
Original assignee: 中国科学院物理研究所
Priority date: 2016-09-08
Filing date: 2017-09-05
Publication date: 2018-03-15
Also published as: CN107808978B; CN107808978A

Abstract

Provided is a liquid active lithium supplement for supplementing a lithium ion battery with active lithium. The liquid active lithium supplement is a solution or a suspension, and comprises sulfides of lithium and a solvent. The solvent can dissolve or partially dissolve the sulfides of lithium; and/or the solvent does not physically and/or chemically react with electrolytes of the lithium ion battery; and/or the solvent is selected from the electrolytes of the lithium ion battery. Also provided are a method for supplementing a lithium ion battery with active lithium, and a lithium ion battery. The liquid active lithium supplement is simple to prepare and convenient to use, and has high safety and low costs. The liquid active lithium supplement has good compatibility with cathode materials, anode materials, and electrolytes of a lithium ion battery, and can be used for preparing lithium ion batteries, thereby improving the reversible charge and discharge capability and subsequent cyclic stability of all batteries.

Description

Liquid active lithium supplement, preparation method thereof and use thereof

The present application claims priority to the patent application filed on Sep. 8, 2016, entitled "A Liquid Active Lithium Replenisher, Its Preparation Method, and Its Use," the application number of which is incorporated herein by reference.

Technical field

The invention belongs to the field of lithium ion batteries. In particular, the present invention relates to a liquid active lithium extender based on a lithium-based sulfide, and to a process for the preparation of the active lithium extender and use thereof.

Background technique

Lithium-ion batteries are widely used in a variety of small portable electronic devices, such as notebook computers, mobile phones, and video cameras, due to their high discharge voltage, high energy density, and long cycle life. High-tech fields such as aerospace satellites, electric vehicles, and military applications require lithium-ion batteries with better capacity and cycle life.

It is known to those skilled in the art that when a lithium ion battery is subjected to a first charge and discharge cycle, a solid electrolyte film (SEI film) is formed on the surface of the negative electrode material of the lithium ion battery, and along with the cycle of the lithium ion battery, the source The lithium ion of the active lithium in the positive electrode and the lithium ion in the electrolyte cannot be completely removed after being embedded in the negative electrode material. Further, the commercially available electrolyte is ethylene carbonate (EC), dimethyl carbonate (DMC), vinylene carbonate. a carbonate-based electrolyte such as an ester (VC), and therefore the main components of the SEI film are LiF, Li ₂ CO _{3 ,} and alkyl ester lithium, and the lithium ions in these products are mainly derived from active lithium in the positive electrode, which is inevitable. This will result in a decrease in the capacity of the lithium ion battery and a decrease in the cycle efficiency, especially after the first charge and discharge cycle, the cycle efficiency is more pronounced.

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 for supplementing lithium have been reported in the prior patent documents.

The Chinese Patent Publication No. CN1290209C discloses a method for lithium-receiving a negative electrode. After forming a slurry of metal lithium, a negative electrode material and a non-aqueous liquid, it is scraped onto a current collector, and a pole piece is formed through a subsequent process. Although the method can also supplement the consumed active lithium, since the activity of the metal lithium is very high, 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. The production cost is greatly improved, and the lithium powder has a great safety hazard because it is easy to float in the air.

In the patent application No. CN201310070202.9, it is proposed to directly incorporate a lithium compound containing lithium compound into the positive electrode material or directly onto the surface of the positive electrode, and these lithium supplements will be charged during the charging process of the first charge and discharge cycle. Decomposition, providing active lithium, although it supplements the active lithium to a certain extent, due to the nature of lithium sulfide electronic insulation, the electrochemical activity is small when the particles are large, and cannot be completely charged during the first charge and discharge cycle. The active lithium is exerted, so the first charge and discharge cycle is active only when the lithium sulfide is dispersed into small particles, but the method of preparing small particles of lithium sulfide such as high energy ball milling in advance is complicated. The cost is greatly increased, and the lithium sulfide of the small particles has a high activity, and will quickly react with the water vapor in the air to deteriorate and is difficult to store.

In the patent application No. CN 201210350770.X, a method of "wet lithium supplementation" is disclosed. The organic lithium is sprayed or dropped onto the surface of the positive electrode, and the lithium in the organic lithium is reduced and embedded in the positive electrode sheet. . However, there are some problems in the invention. For example, the n-butyl lithium and t-butyl lithium used are high-flammable and explosive dangerous materials, and the safety is not higher than that of lithium powder; although the organic lithium sprayed on the surface of the positive electrode has a part. The organic lithium is reduced and embedded in the positive electrode, but there are still many residues, which in turn will further reduce the capacity.

Therefore, there is a need for a reagent and method for replenishing active lithium in a lithium ion battery to reduce the capacity decay of the lithium ion battery during charge and discharge and to increase its cycle efficiency.

Summary of the invention

In order to compensate for the deficiencies of the prior art, the present invention provides a liquid active lithium extender for supplementing active lithium in a lithium ion battery. The active lithium supplement provided by the present invention is a sulfide of lithium dissolved or partially dissolved in a solvent. Therefore, the liquid active lithium supplement provided by the present invention can directly prepare small-sized lithium sulfide and can be uniformly mixed with carbon. The composite, and because the lithium sulfide is dispersed in the solvent, is easier to store. The invention also provides a method of using the liquid active lithium supplement. Therefore, the liquid active lithium supplement provided by the invention is simple in preparation, low in cost and suitable for mass production, and can be widely applied to industrial production.

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

Wherein the solvent is capable of dissolving or partially dissolving the sulfide of the lithium; 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 sulfide of lithium is selected from one or more of lithium sulfide, lithium persulfide, and lithium polysulfide. More preferably, the sulfide of lithium is lithium sulfide.

Preferably, the sulfide of lithium may be synthesized in advance, or may be formed by mixing lithium sulfide and sulfur in a molar ratio of Li:S of 2:1 to 8 to the solvent as described above.

Preferably, the molar concentration of lithium ions in the liquid active lithium extender is from 0.01 mol/L to 5 mol/L, more preferably from 0.01 mol/L to 0.5 mol/L, most preferably from 0.01 mol/L to 0.25. Mol/L.

Preferably, no chemical reaction occurs between the solvent and the sulfide of the lithium. Preferably, the solvent is selected from one or more of organic solvents capable of dissolving lithium sulfide; more preferably, the solvent is selected from the group consisting of methanol, ethanol, tetraethylene glycol dimethyl ether (TEGDME) and two One or more of methyl ether (DME).

Preferably, the liquid active lithium supplement further comprises an optional conductive additive and/or an optional binder;

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

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

In another aspect, the present invention provides a method of preparing the above liquid active lithium extender, the method comprising the steps of:

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

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

In another aspect, the present invention provides a method of replenishing active lithium in a lithium ion battery, the method comprising adding the above liquid active lithium supplement 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 to the electrolyte of the lithium ion battery.

Preferably, when the solvent does not physically and/or chemically react with the active lithium supplement, the active lithium supplement 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 using coating, dip and/or spray coating. Preferably, the active lithium supplement accounts for a mass percentage of the positive or positive electrode material 0.1-20%, preferably 2% to 10%, more preferably 2 to 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, when the solvent is selected from the electrolyte of the lithium ion battery, the liquid active lithium supplement is added to the electrolyte of the lithium ion battery.

In still another aspect, the present invention also provides a lithium ion battery comprising the liquid active lithium extender of the present invention.

In another aspect, the present invention also provides a method of preparing a lithium ion battery, the method comprising preparing a lithium ion battery using the liquid active lithium supplement described above, and/or preparing a lithium ion battery using the above method.

The inventors of the present invention have found that the active lithium supplement is added to the battery system in the form of a solution, which is fully decomposed during the first charge and discharge cycle, releasing lithium ions embedded or deposited on the negative electrode or alloyed with the negative electrode to make up the negative electrode. The formation of the SEI film and the metal lithium lost during the subsequent cycle release excess active lithium, and the lithium consumed in the formation of the negative SEI film is replenished, and therefore, the inventors of the present invention use one or several solvents to dissolve or partially dissolve the activity. The lithium extender obtains a liquid active lithium supplement and then adds it to the battery system, so that the first charge and discharge capacity and long cycle stability of the lithium ion battery are significantly improved. Therefore, the lithium ion secondary battery of the present invention can significantly improve energy density and service life.

Based on this, the liquid active lithium supplement provided by the invention is simple to prepare, convenient to use, high in safety and low in cost. Further, the liquid active lithium supplement provided by the invention has good compatibility with various cathode materials, anode materials and electrolytes of the lithium ion battery, and can be used for preparing various lithium ion batteries, thereby improving the reversible charge and discharge capacity of the whole battery and Subsequent loop stability.

BRIEF DESCRIPTION OF THE DRAWINGS

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

1 is a cyclic voltammetry curve of a lithium ion battery (half battery) composed of a positive electrode tab D1 and a lithium sheet according to the present invention;

2 is a cyclic voltammetry curve of a lithium ion battery (half battery) composed of a positive electrode tab D3 and a lithium sheet according to the present invention;

3 is a comparison diagram of the first week charge and discharge curves of the full batteries F1 and F3 according to the present invention;

4 is a comparison diagram of the first week charge and discharge curves of the full batteries F1 and H1 according to the present invention;

The best way to implement the invention

The present invention is further described in detail with reference to the preferred embodiments thereof.

Example 1 Preparation of Liquid Active Lithium Replenisher

This example prepares a liquid active lithium extender according to the following procedure, which is carried out at room temperature:

1. Take 0.16g of lithium sulfide (Li ₂ S), 0.02g of Super P and 0.02g of PVP, put it in 20ml of methanol, sonicate for 10h, then stir for 10h and mix evenly to obtain liquid active lithium supplement. The lithium supplement is referred to as A1.

2. Take 0.16g of lithium sulfide (Li ₂ S), 0.02g of Super P and 0.02g of PVP, put it in 20ml of ethanol, sonicate for 10h, then stir for 10h and mix evenly to obtain liquid active lithium supplement. The lithium supplement is denoted as A2.

3. Take 0.16g of lithium sulfide (Li ₂ S), 0.02g of Super P and 0.02g of PVP, put it in 20ml TEGDME, sonicate for 10h, then stir for 10h and mix evenly to obtain liquid active lithium supplement, the liquid active lithium The supplement is recorded as A3.

4. Take 0.16g of lithium sulfide (Li ₂ S), 0.02g of Super P and 0.02g of PVP, place it in 20ml DME, sonicate for 10h, then stir for 10h and mix evenly to obtain liquid active lithium supplement. The lithium supplement is referred to as A4.

5. Take 0.08g of lithium sulfide (Li ₂ S), 0.09g of Super P and 0.04g of PVP, and place it in 20ml of methanol, sonicate for 10h, then stir for 10h and mix evenly to obtain liquid active lithium supplement. The lithium supplement is referred to as A5.

6. Take 0.08g of lithium sulfide (Li ₂ S), 0.09g of Super P and 0.04g of PVP, and place it in 20ml of ethanol, sonicate for 10h, then stir for 10h and mix evenly to obtain liquid active lithium supplement. The lithium supplement is referred to as A6.

7. Take 0.08g of lithium sulfide (Li ₂ S), 0.09g of Super P and 0.04g of PVP, and place it in 20ml of TEGDME, sonicate for 10h, then stir for 10h and mix evenly to obtain liquid active lithium supplement. The lithium supplement is referred to as A7.

8. Take 0.08g of lithium sulfide (Li ₂ S), 0.09g of Super P and 0.04g of PVP, and place it in 20ml of DME, sonicate for 10h, then stir for 10h and mix evenly to obtain liquid active lithium supplement. The lithium supplement is referred to as A8.

9. Take 0.18g of lithium sulfide (Li ₂ S) and 0.02g of PVP, put it in 20ml of methanol, sonicate for 10h, then stir for 10h and mix evenly to obtain liquid active lithium supplement. The liquid active lithium supplement is recorded as A9.

10. Take 0.18g of lithium sulfide (Li ₂ S) and 0.02g of PVP, put it in 20ml of ethanol, sonicate for 10h, then stir for 10h and mix evenly to obtain liquid active lithium supplement. The liquid active lithium supplement is recorded as A10.

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

12. Take 0.18g of lithium sulfide (Li ₂ S) and 0.02g of PVP, put it in 20ml DME, sonicate for 10h, then stir for 10h and mix evenly to obtain liquid active lithium supplement. The liquid active lithium supplement is recorded as A12.

13. Take 0.18g of lithium sulfide (Li ₂ S) and 0.02g of Super P, put it in 20ml of methanol, sonicate for 10h, then stir for 10h and mix evenly to obtain liquid active lithium supplement, the liquid active lithium supplement For A13.

14. Take 0.18g of lithium sulfide (Li ₂ S) and 0.02g of Super P, put it in 20ml of ethanol, sonicate for 10h, then stir for 10h and mix evenly to obtain liquid active lithium supplement, the liquid active lithium supplement For A14.

15. Take 0.18g of lithium sulfide (Li ₂ S) and 0.02g of Super P, put it in 20ml TEGDME, sonicate for 10h, then stir for 10h and mix evenly, then get liquid active lithium supplement, the liquid active lithium supplement For A15.

16. Take 0.18g of lithium sulfide (Li ₂ S) and 0.02g of Super P, put it in 20ml DME, sonicate for 10h, then stir for 10h and mix evenly to obtain liquid active lithium supplement, the liquid active lithium supplement For A16.

Example 2 Preparation of Liquid Active Lithium Replenisher

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

2. Take 0.0115g of lithium sulfide (Li ₂ S) and 0.056g of sulfur (S), put it in dimethyl ether (DME), stir evenly for 6h, then obtain liquid active lithium supplement, the liquid active lithium supplement The agent is recorded as B2.

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

4. Take 0.0115g of lithium sulfide (Li ₂ S) and 0.048g of sulfur (S), put it in dimethyl ether (DME), stir evenly for 6h, then obtain liquid active lithium supplement, the liquid active lithium supplement The agent is recorded as B4.

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

6. Take 0.0115g of lithium sulfide (Li ₂ S) and 0.032g of sulfur (S), put it in dimethyl ether (DME), stir evenly for 6h, then obtain liquid active lithium supplement, the liquid active lithium supplement The agent is recorded as B6.

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

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

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

10. Take 0.0115 g of lithium sulfide (Li ₂ S), place it in dimethyl ether (DME), and mix it evenly for 6 hours to obtain a liquid active lithium supplement. The liquid active lithium supplement 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, which was carried out at room temperature:

0.16 g of lithium sulfide (Li ₂ S), 0.02 g of Super P and 0.02 g of PVP were uniformly mixed in NMP to obtain an active lithium extender, which was designated as C1.

0.08 g of lithium sulfide (Li ₂ S), 0.09 g of Super P and 0.04 g of PVP were uniformly mixed in NMP to obtain an active lithium supplement, which was designated as C2.

0.18 g of lithium sulfide (Li ₂ S) and 0.02 g of PVP were uniformly mixed in NMP to obtain an active lithium supplement, which was designated as C3.

0.18 g of lithium sulfide (Li ₂ S) and 0.02 g of Super P were uniformly mixed in NMP to obtain an active lithium supplement, which was designated as C4.

Example 4 Performance Test

The solutions A1 to A16 prepared in Example 1 were assembled into a button cell in accordance with the following procedure.

4.1 Preparation of positive and negative pole pieces

LiFePO _{4 is} used as the positive electrode active material, carbon black is used as the conductive additive, and carboxymethyl cellulose (CMC), copolymer of styrene and butadiene (SBR) is used as the binder, and the mass ratio is 90:7:1. : 2 Mix well in water to prepare a uniform positive electrode slurry. A uniform positive electrode slurry was uniformly coated on an aluminum foil current collector having a thickness of 15 μm, and dried at 55 ° C to form a 100 μm thick pole piece, which was placed under a roll press (pressure was about 1 MPa × 1.5 cm 2 ). , cutting the pole piece into a diameter of

The 14 mm disc was placed in a vacuum oven and baked at 120 ° C for 6 h. After natural cooling, it was taken out and placed in a glove box for use as a positive electrode tab, denoted as D1.

Graphite was used as the negative electrode active material, carbon black was used as the conductive additive, and carboxymethyl cellulose (CMC), copolymer of styrene and butadiene (SBR) was used as the binder, and the mass ratio was 93:2:2: 3 Mix well in water to prepare a uniform negative electrode slurry. A uniform negative electrode slurry was uniformly coated on a copper foil current collector having a thickness of 8 μm, and dried at 55 ° C to form pole pieces of 50 μm and 59 μm thickness, which were placed under a roll press (pressure was about 1 MPa × 1.5cm2), cut the pole piece to a diameter of

A 15 mm wafer was placed in a vacuum oven and baked at 120 ° C for 6 h. After natural cooling, it was taken out and placed in a glove box for use as a negative electrode tab.

In a glove box filled with an inert atmosphere, take 50 μl of A1～A4, 80 μl of A5～A8 and 50 μl of A9～A16 solution to the solution.

14mm positive electrode disc. After baking at 120 ° C for 10 h, it was used as a positive electrode after being naturally cooled, and it was designated as D2-D17. The same quality C1 ~ C4 coating with the active lithium supplement corresponding to A1, A5, A9 and A13

14mm positive electrode disc. Bake at 120 ° C for 10 h, after natural cooling, used as a positive electrode, recorded as E1 ~ E4

4.2 Assembly of lithium ion secondary battery

In a glove box filled with an inert atmosphere, a three-layer film of PP/PE/PP was used as a separator (purchased from Celegard, USA) between the positive electrode and the negative electrode, and 1 M LiPF6 was added dropwise to dissolve in EC/DMC (1:1, A non-aqueous electrolyte (available from BASF Electrolyte Company, Germany), a 50 μm graphite negative electrode sheet prepared in 4.1 as a negative electrode of the battery, and a D1 prepared in the step 4.1 as a positive electrode, and a button battery of the molding number CR2032. Remember to be F1. The 59 μm graphite negative electrode sheet prepared in the step 4.1 was used as the negative electrode of the battery, and the D2-D17 prepared in the step 4.1 was used as the positive electrode, and the button type battery having the molding number CR2032 was assembled as F2 to F17. The 59 μm graphite negative electrode sheet prepared in the step 4.1 was used as the negative electrode of the battery, and E1 to E4 prepared in the step 4.1 were used as the positive electrode, and the button type battery having the molding number CR2032 was assembled as G1 to G4.

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

The prepared button batteries F1 to F17, G1 to G4 and H1 to H10 were allowed to stand at room temperature for 24 hours, and then a blue electric 11 battery charge and discharge tester (purchased from Wuhan Landian Electronics Co., Ltd.) was used. The button cell prepared above was subjected to a charge and discharge cycle test. First, the specific capacity of LiFePO4 was calculated to be 160 mAhg ^-1 , and it was cycled at a rate of 0.05 C for one week, and then continued to be cycled at a rate of 0.2 C for 100 weeks, wherein the charge and discharge voltage of the control battery was in the range of 2.5 V to 3.6 V. The preparation parameters and results are shown in Tables 1 and 2.

result

From the cyclic voltammetry curve of Figure 1, the redox peak of lithium iron phosphate is shown, while Figure 2 shows that an oxidation peak appears around 2.6V, indicating that the lithium supplement was charged during the first week of charging at 2.6. Decomposition begins near V.

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

Figure 4 shows the comparison of the first-period charge-discharge curves of lithium-ion batteries F1 and H2. It can be seen that lithium-ion battery H2 has a low potential compared to F1, and its first-cycle 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 139 mAhg-1, and the capacity of about 10 mAhg-1 is more than that of F1 only 131.1 mAhg-1. The lithium sulfide can be divided and explained during the first charge, which can compensate for the loss of lithium ions when forming the SEI film on the surface of the negative electrode, and compensate for the loss of lithium ions in the positive electrode material and the electrolyte, thereby significantly increasing the head of the lithium ion battery. Weekly reversible discharge capacity.

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

Table 2 compares the 100-percent capacity retention of lithium-ion batteries F1 and H1-H10 with different parameters. It can be seen that the reversible capacity and long-cycle stability of lithium-ion batteries containing liquid active lithium supplements have been extremely The large increase indicates that the active lithium produced by the decomposition of lithium sulfide continues to compensate for the loss of active lithium in the electrochemical cycle of the lithium ion battery in the subsequent cycle. In general, the lithium-recognition method provided by the present invention can significantly improve the reversible capacity and long cycle stability of a lithium ion battery.

Table 1 shows the variation 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 and H1 to H15 with different parameters with the number of cycles.

It should be noted that the above embodiments are merely illustrative of the technical solutions of the present invention, and are not intended to be limiting; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art will understand that The technical solutions described in the foregoing embodiments may be modified, or some or all of the technical features may be equivalently replaced; and the modifications or substitutions do not deviate from the technical solutions of the embodiments of the present invention. range.

Claims

A liquid active lithium supplement for replenishing active lithium in a lithium ion battery, the liquid active lithium supplement being a solution or a suspension, including a sulfide and a solvent of lithium;

Wherein the solvent is capable of dissolving or partially dissolving the sulfide of the lithium; 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 liquid active lithium supplement according to claim 1, wherein the sulfide of lithium is one or more selected from the group consisting of lithium sulfide, lithium persulfide, and lithium polysulfide;

Preferably, the sulfide of lithium is lithium sulfide;

Preferably, the molar concentration of the lithium ions is from 0.01 mol/L to 5 mol/L, more preferably from 0.01 mol/L to 0.5 mol/L, and most preferably from 0.01 mol/L to 0.25 mol/L.
The liquid active lithium extender according to claim 1 or 2, wherein a chemical reaction does not occur between the solvent and the sulfide of the lithium;

Preferably, the solvent is selected from one or more of organic solvents capable of dissolving lithium sulfide; more preferably, the solvent is selected from the group consisting of methanol, ethanol, tetraethylene glycol dimethyl ether and dimethyl ether. One or more.
The liquid active lithium supplement according to any one of claims 1 to 3, wherein the liquid active lithium supplement further comprises an optional conductive additive and/or an optional binder;

Preferably, the conductive additive is selected from one or more of a carbon black conductive agent, a conductive carbon tube, graphene and graphene oxide; more preferably, the carbon black conductive agent is selected from the group consisting of acetylene black, Super P, One or more of Super S, 350G, carbon fiber, carbon nanotube, and Ketchen Black;

Preferably, the ketjen black is selected from one or more of Ketjenblack EC300J, Ketjenblack EC600JD, Carbon ECP and Carbon ECP600JD;

Preferably, the mass of the conductive additive in the liquid active lithium extender is 0-50% of the mass of the sulfide of the lithium; preferably 5%-20%; more preferably 5%-10%; preferably The binder is selected from one or more of polyvinylpyrrolidone, polyvinylidene fluoride, polyethylene oxide, polytetrafluoroethylene, carboxymethyl cellulose, and a copolymer of styrene and butadiene. Preferably, the mass of the binder in the liquid active lithium extender is from 0 to 20% by mass of the sulfide of the lithium; preferably from 2% to 10%; more preferably from 2% to 5%.
The liquid active lithium extender according to any one of claims 1 to 4, wherein the electrolyte is selected from one or more of a liquid electrolyte, a solid electrolyte, a semi-solid electrolyte, and a polymer electrolyte.
A method of preparing a liquid active lithium extender according to any one of claims 1 to 5, the method comprising the steps of:

Adding a sulfide of lithium, an optional conductive additive, and an optional binder to a solvent to obtain the liquid active lithium supplement;

Preferably, the addition is a one-time addition or a step-wise addition.
A method of replenishing active lithium in a lithium ion battery, the method comprising adding the liquid active lithium supplement according to any one of claims 1 to 5 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.
The method of claim 7 wherein said liquid active lithium extender is added to and/or incorporated in the positive electrode material slurry when said solvent does not physically and/or chemically react with said reactive lithium extender Into the positive electrode;

Preferably, the liquid active lithium supplement is incorporated into the positive electrode using coating, dipping and/or spraying;

Preferably, the liquid active lithium supplement accounts for 0.1-20% by mass of the positive electrode or cathode material, preferably 2% to 10%, more preferably 2 to 5%;

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

Preferably, when the solvent is selected from the electrolyte of the lithium ion battery, the liquid active lithium supplement is added to the electrolyte of the lithium ion battery.
A lithium ion battery comprising the liquid active lithium extender of any one of claims 1 to 5.