CN115602942B

CN115602942B - Negative pole piece, secondary battery and electric equipment

Info

Publication number: CN115602942B
Application number: CN202211587815.5A
Authority: CN
Inventors: 从广涛; 罗赛凡; 彭婉婷
Original assignee: Shenzhen University
Current assignee: Shenzhen University
Priority date: 2022-12-12
Filing date: 2022-12-12
Publication date: 2023-04-07
Anticipated expiration: 2042-12-12
Also published as: CN115602942A

Abstract

The invention discloses a negative pole piece, a secondary battery and electric equipment, wherein the negative pole piece comprises a negative pole current collector and a negative pole active layer arranged on at least one side of the negative pole current collector, the negative pole active layer comprises a conductive agent, a binder and a comb-shaped polymer, and the structural formula of the comb-shaped polymer is shown as a formula I:

formula I; wherein n is more than or equal to 10000; r is selected from substituted or unsubstituted naphthyl, substituted or unsubstituted biphenyl, substituted or unsubstituted anthryl or substituted or unsubstituted phenanthryl. The negative pole piece prepared by the comb-shaped polymer shown in the structure of the formula I, the conductive agent and the binder has high coulombic efficiency, circulation stability and energy density.

Description

Negative pole piece, secondary battery and electric equipment

Technical Field

The invention relates to the technical field of energy storage, in particular to a negative pole piece, a secondary battery and electric equipment.

Background

The energy storage technology is the core technology for determining national energy safety and sustainable development strategy. The current traditional lithium ion battery energy storage technology faces the severe problems of limited material reserves, high price, serious pollution, limited energy density improvement and the like. The current optimization of lithium ion batteries is mainly focused on improving the voltage and the capacity of the batteries. However, the actual lithium storage capacity of the transition metal layered compound anode and the graphite cathode of the traditional lithium ion battery is very close to a theoretical value, and what can be done at present is to optimize the electrode structure and modify the components of the battery, so that the promotion space is limited. Many researchers believe that improvements to lithium ion batteries can still increase the energy density by up to 30%. The main metal elements used by the lithium ion battery comprise lithium, cobalt, nickel and copper, but the limited resources and uneven distribution of reserves lead to overhigh cost of lithium ion energy storage, and the large-scale application of the lithium ion battery in the fields of large-scale energy storage and electric automobiles is limited to a great extent. Meanwhile, the mining and processing processes of the transition metal cause serious environmental pollution. All these challenges make the development of next generation electrode materials with high energy density, inexpensive, and environmentally friendly, increasingly urgent. The specific research and development plan released by the new energy industry and technology integrated development organization (NEDO) of the Japanese national research institution is as follows: 300 Wh/kg in 2025, 400 Wh/kg in 2030 and 500 Wh/kg in 2035. The united center for energy storage research (JCESR) sponsored by the united states department of energy (DOE) issued a "5-5-5" program, and from 2013, a battery with energy density increased to 5 times and price decreased to 1/5 was developed within 5 years.

Organic materials are the popular choice for the next generation of energy storage technology because of the advantages of abundant resources, low cost, safety, little pollution and the like. The currently reported organic electrodes are mainly classified into seven types: conjugated hydrocarbons, conjugated amines, conjugated thioethers, organosulfides, thioethers, nitroxyl radicals and conjugated carbonyl groups. The redox potential of most reported organic molecules is mostly distributed between 1.5-3.5V vs Li/Li ⁺ The lithium ion battery is generally used as a positive electrode material of the battery, and a matched negative electrode is still traditional graphite or metallic lithium. Although the combination avoids the use of a transition metal anode and reduces the cost of the battery, lithium dendrites generated by long-time circulation of the graphite cathode or lithium metal finally cause short circuit of the battery, thereby bringing great potential safety hazards to the operation of the battery. Therefore, the organic negative electrode material with high energy density and low oxidation-reduction potential is developed to replace the graphite negative electrode suffering from the following problems, and has a very high industrial application prospect.

In order to develop an organic negative electrode material with a low oxidation-reduction potential, researchers have screened many organic molecules, and aromatic hydrocarbons (such as naphthalene, biphenyl, phenanthrene and the like) represent another potential organic negative electrode material, but the aromatic hydrocarbons and aromatic radicals are relatively easy to dissolve in common organic solvents and are commonly used as negative electrodes of flow batteries. However, the specific capacity of the liquid-state negative electrode is far lower than that of a solid-state electrode of a lithium ion battery, so that the liquid-state negative electrode is difficult to apply to an energy storage system with high energy density.

Disclosure of Invention

The present invention is directed to solving at least one of the problems of the prior art. Therefore, the invention provides a negative pole piece in the first aspect, which can effectively improve the coulombic efficiency, the cycling stability and the energy density.

The second aspect of the invention also provides a secondary battery.

The third aspect of the invention also provides an electric device.

According to the negative electrode plate of the embodiment of the first aspect of the present invention, the negative electrode plate includes a negative electrode current collector and a negative electrode active layer disposed on at least one side of the negative electrode current collector, the negative electrode active layer includes a conductive agent, a binder and a comb-shaped polymer, and a structural formula of the comb-shaped polymer is as shown in formula i:

formula I;

wherein n is more than or equal to 10000;

r is selected from substituted or unsubstituted naphthyl, substituted or unsubstituted biphenyl, substituted or unsubstituted anthryl or substituted or unsubstituted phenanthryl.

The negative pole piece provided by the embodiment of the invention at least has the following beneficial effects:

the negative pole piece prepared by the comb-shaped polymer shown in the structure of the formula I, the conductive agent and the binder has higher coulombic efficiency, capacity retention rate and energy density. This is because the comb polymer has a large molecular weight and a greatly reduced solubility in an electrolyte solution, and the anion radicals generated by reduction mainly exist in a solid phase form, and thus there is almost no shuttle effect.

According to some embodiments of the invention, R is selected from naphthyl, biphenyl, anthracenyl or phenanthrenyl.

According to some embodiments of the invention, the comb polymer is one of the following structural formulae:

。

according to some embodiments of the invention, the comb polymer has a number average molecular weight ≧ 10000.

According to some embodiments of the invention, the method of preparing the comb polymer comprises the steps of:

under the conditions of inert atmosphere, toluene, n-butyl lithium and n-hexane, vinyl aromatic compound monomers are added for polymerization reaction, and polymerization inhibitor is added for stopping the polymerization reaction, so that the comb-shaped polymer is obtained.

According to some embodiments of the invention, the comb polymer accounts for 80% -99% of the total mass of the negative active layer.

According to some embodiments of the invention, the conductive agent comprises at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and carbon fiber.

According to some embodiments of the invention, the binder comprises at least one of styrene butadiene rubber or polyvinylidene fluoride.

According to some embodiments of the present invention, the negative active layer comprises the following components in percentage by mass, calculated as the total mass of the negative active layer:

80% -99% of comb-type polymer;

0.05 to 15 percent of conductive agent;

0.05 to 15 percent of binder.

According to some embodiments of the present application, the method for preparing the negative electrode sheet comprises the following steps:

s1, stirring the comb-shaped polymer, the conductive agent and the first binder to obtain a negative active layer

And S2, coating the upper surface and the lower surface of the negative current collector by adopting a double-layer coating method, drying, rolling and cutting to obtain the negative pole piece.

According to a second aspect embodiment of the present invention, there is provided a secondary battery, which comprises a positive electrode sheet, an electrolyte, a separator and the negative electrode sheet as described above.

According to some embodiments of the invention, the separator is interposed between the positive electrode sheet and the negative electrode sheet, and the electrolyte is filled between the positive electrode sheet and the negative electrode sheet and infiltrates the separator.

According to some embodiments of the invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. For example, the positive electrode current collector includes two opposite surfaces in a thickness direction thereof, and the positive electrode active material layer is stacked on either or both of the two surfaces of the positive electrode current collector.

According to some embodiments of the present invention, the positive electrode sheet includes a positive active material, which may be selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, olivine-structured lithium phosphate, and the like, but the present application is not limited to these materials, and other conventionally known materials that may be used as a positive active material of a lithium ion battery may also be used. These positive electrode active materials may be used alone or in combination of two or more. Preferably, the positive active material may be selected from LiCoO ₂ 、LiNiO ₂ 、LiMnO ₂ 、LiMn ₂ O ₄ 、LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM111)、LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (NCM523)、LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (NCM622)、LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811)、LiNi _0.85 Co _0.15 Al _0.05 O ₂ 、LiFePO ₄ 、LiMnPO ₄ One or more of them.

According to some embodiments of the present application, the positive electrode active material layer may further include a conductive agent to improve conductive performance of the positive electrode. The type of the conductive agent is not particularly limited, and can be selected according to actual requirements. As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphite, graphene, or carbon nanofibers.

According to some embodiments of the present application, the positive electrode active material layer may further include a binder to firmly bind the positive electrode active material and the optional conductive agent to the positive electrode current collector. The application does not specifically limit the type of the binder, and the binder can be selected according to actual requirements. As an example, the binder may be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyvinyl alcohol (PVA), ethylene-vinyl acetate copolymer (EVA), styrene Butadiene Rubber (SBR), carboxymethyl cellulose (CMC), sodium Alginate (SA), polymethacrylic acid (PMA), or carboxymethyl chitosan (CMCs).

According to some embodiments of the present application, the positive current collector employs a conductive carbon sheet, a metal foil, a carbon-coated metal foil, a porous metal plate or a composite current collector, wherein the conductive carbon material of the conductive carbon sheet may be one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphite, graphene or carbon nanofibers, and the metal materials of the metal foil, the carbon-coated metal foil and the porous metal plate may be independently selected from at least one of copper, aluminum, nickel and stainless steel. The composite current collector can be a composite current collector formed by compounding a metal foil and a polymer base film.

According to some embodiments of the present application, the separator may be any material suitable for a separator of a secondary battery in the art, for example, including but not limited to at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fiber.

According to some embodiments of the present application, the electrolyte solution includes an organic solvent and an electrolyte sodium salt. For example, the organic solvent includes one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, methyl acetate, ethyl propionate, fluoroethylene carbonate, diethyl ether, diglyme, triglyme, tetraglyme, and methyl tert-butyl ether; the electrolyte sodium salt comprises one or more of sodium hexafluorophosphate, sodium bifluorosulfonyl imide, sodium bistrifluoromethanesulfonyl imide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, sodium perchlorate and sodium chloride.

An embodiment of a third aspect of the present application provides an electric device including the secondary battery described above.

According to some embodiments of the application, the electric equipment comprises a mobile phone, a computer, a wearable device, a mobile power supply, an electric vehicle, an energy storage device and the like.

Definitions and general terms

As used herein, "substituted or unsubstituted" means that the group may or may not be further substituted with one or more groups selected from: alkyl, alkenyl, alkynyl, aryl, halogen, haloalkyl, haloalkenyl, haloalkynyl, haloaryl, hydroxy, alkoxy, alkenyloxy, aryloxy, benzyloxy, haloalkoxy, haloalkenyloxy, haloaryloxy, nitro, nitroalkyl, nitroalkenyl, nitroalkynyl, nitroaryl, nitroheterocyclyl, amino, alkylamino, dialkylamino, alkenylamino, alkynylamino, arylamino, diarylamino, phenylamino, diphenylamino, benzylamino, dibenzylamino, hydrazino, acyl, acylamino, diamido, acyloxy, heterocyclyl, heterocyclyloxy, heterocyclylamino, haloheterocyclyl, carboxy ester, carboxy, carboxamide, mercapto, alkylthio, benzylthio, acylthio, and phosphorus-containing groups.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a NMR spectrum of a comb polymer prepared in example 1;

FIG. 2 is a charge and discharge test chart of the negative electrode tab prepared in example 1;

fig. 3 is a charge and discharge test chart of the negative electrode tab prepared in comparative example 1.

Detailed Description

The following are specific examples of the present invention, and the technical solutions of the present invention will be further described with reference to the examples, but the present invention is not limited to the examples.

The reagents, methods and equipment adopted by the invention are conventional in the technical field if no special description is given.

Example 1

Embodiment 1 provides a negative pole piece, and negative pole piece includes the negative current collector and sets up the negative active layer in negative current collector one side, and the negative active layer includes conductive agent, binder and comb type polymer, and the structural formula of comb type polymer is shown as formula I:

formula I

The preparation method of the comb polymer comprises the following steps:

1. a50 mL Schlenk bottle was flushed with dry nitrogen at room temperature, 5mL of toluene were added, and a solution of n-BuLi in n-hexane (1.25M) 0.2 mL was added under nitrogen.

2. After stirring for 10 minutes, 5mL (0.65M) toluene solution of 2-vinylnaphthalene was added and 3 h was polymerized with stirring under nitrogen. An excess of methanol (20 mL) was added to terminate the polymerization and white poly (2-vinylnaphthalene) (formula I) was precipitated.

3. The precipitated precipitate was filtered and dissolved again in 10mL of toluene and stirred until the precipitate was completely dissolved. An excess of methanol (20 mL) was added to precipitate poly (2-vinylnaphthalene). This purification process was repeated 1-3 times.

4. The dried and ground precipitate was placed in a glove box for future use.

The poly (2-vinylnaphthalene) thus prepared was subjected to a nuclear magnetic resonance hydrogen spectroscopy test, and as a result, as shown in FIG. 1, a peak (Hb) in the range of 5 to 8ppm was attributed to hydrogen on the aromatic ring of the naphthyl group, and a peak (Ha) in the range of 0 to 2ppm was attributed to methylene hydrogen on the alkyl chain.

The preparation method of the negative pole piece comprises the following steps:

s1, dissolving a binder polyvinylidene fluoride (PVDF) in N-methyl pyrrolidone, and preparing uniform slurry with ground conductive carbon black and poly (2-vinyl naphthalene). The mass percentages of PVDF, conductive carbon black and poly (2-vinyl naphthalene) are 10%, 10% and 80%, respectively.

S2, uniformly coating the slurry on a copper foil by using a coating machine, airing in a fume hood at normal temperature, and completely drying in a blast drying oven at 60 ℃.

And S3, cutting the dried electrode into a circle with the diameter of 14 mm by using an edge cutter, and placing the electrode in a drying box for later use.

Example 2

Embodiment 2 provides a negative pole piece, and negative pole piece includes the negative current collector and sets up the negative active layer in negative current collector one side, and the negative active layer includes conductive agent, binder and comb type polymer, and the structural formula of comb type polymer is shown as formula I:

formula I

The preparation method of the comb polymer comprises the following steps:

1. a50 mL Schlenk bottle was purged with dry nitrogen at room temperature, 5mL of toluene was added, and n-BuLi in n-hexane (1.25M) 0.2 mL was added under nitrogen.

2. After stirring for 10 minutes, 5mL (0.65M) of 4-vinylbiphenyl was added and 3 h was polymerized under stirring under nitrogen. An excess of methanol (20 mL) was added to terminate the polymerization and white poly (4-vinylbiphenyl) (formula I) was precipitated.

4. The dried and ground precipitate was placed in a glove box for future use.

s1, dissolving a binder polyvinylidene fluoride (PVDF) in N-methyl pyrrolidone, and preparing uniform slurry with ground conductive carbon black and poly (4-vinyl biphenyl). The mass percentages of PVDF, conductive carbon black and poly (4-vinyl biphenyl) are 10%, 10% and 80%, respectively.

S3, cutting the dried electrode into a circle with the diameter of 14 mm by using an edge cutter, and placing the circle in a drying box for later use.

Example 3

Embodiment 3 provides a negative pole piece, and negative pole piece includes the negative current collector and sets up the negative active layer in negative current collector one side, and the negative active layer includes conductive agent, binder and comb type polymer, and the structural formula of comb type polymer is shown as formula I:

formula I

The preparation method of the comb polymer comprises the following steps:

2. After stirring for 10 minutes, 5mL (0.65M) which is a toluene solution of 2-vinylanthracene was added, and 3 h was polymerized with stirring under nitrogen. An excess of methanol (20 mL) was added to terminate the polymerization reaction and to precipitate white poly (2-vinylanthracene) (formula I).

4. The dried and ground precipitate was placed in a glove box for future use.

s1, dissolving a binder polyvinylidene fluoride (PVDF) in N-methyl pyrrolidone, and preparing a uniform slurry with ground conductive carbon black and poly (2-vinyl anthracene). The mass percentages of PVDF, conductive carbon black and poly (2-vinyl anthracene) are 10%, 10% and 80%, respectively.

Comparative example 1

The comparative example 1 provides a negative pole piece, the negative pole piece includes the negative current collector and sets up the negative active layer on one side of the negative current collector, the negative active layer includes conductive agent, binder and 2-vinylnaphthalene, the structural formula of 2-vinylnaphthalene is shown as follows:

the preparation method and the content of the negative pole piece are the same as those of the embodiment 1.

Performance detection

Preparation of secondary battery:

(1) A diaphragm: a polypropylene film;

(2) Preparing a positive pole piece:

lithium iron phosphate (LiFePO) as positive electrode active material ₄ ) Mixing acetylene black serving as a conductive agent and PVDF serving as a binder according to a mass ratio of 96; and uniformly coating the positive electrode slurry on a positive electrode current collector aluminum foil, airing at room temperature, transferring to an oven for continuous drying, and then performing cold pressing and slitting to obtain the positive electrode piece.

(3) Preparing an electrolyte:

ethylene Carbonate (EC), ethyl Methyl Carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1 ₆ Dissolving in the mixed organic solvent to prepare electrolyte with the concentration of 0.5 mol/L.

Winding the negative electrode plate, the positive electrode plate and the diaphragm prepared in the embodiment 1~3 and the comparative example 1 to obtain a winding core, packaging the winding core to obtain a dry cell, baking the dry cell, injecting liquid, forming, secondary sealing and sorting to obtain a secondary battery, and finally testing the electrochemical workstation for the secondary battery.

And (3) electrochemical performance testing:

coulombic efficiency: the test voltage range is 2.0-3.8V. The testing steps and conditions are 1 and 2 hours of rest; 2. charging to a voltage of more than or equal to 3.8V at 0.2C; 3. discharging at 0.5 deg.C to voltage not more than 2.0V; 4. and (3) performing charge and discharge cycles for 100 times at a multiplying power of 0.5C, obtaining the coulombic efficiency of each cycle, and calculating the average coulombic efficiency of 100 cycles, wherein the test results are shown in Table 1.

Capacity retention ratio: the test voltage range is 2.0-3.8V. The testing steps and conditions are 1 and 2 hours of rest; 2. charging to a voltage of more than or equal to 3.8V at 0.2C; 3. discharging at 0.5 deg.C to voltage not more than 2.0V; 4. the charge and discharge were cycled 100 times at a rate of 0.5C, and the ratio of the discharge capacity at the 100 th cycle to the first discharge capacity was taken as the capacity retention rate.

Energy density: the energy density is calculated only by considering the mass of the positive and negative electrode active materials, and the voltage and the capacity respectively adopt the average discharge voltage and the average capacity of the first 100 cycles. The data are recorded in Table 1.

TABLE 1 data for example 1~3 and comparative example 1

	Coulomb efficiency%	Capacity retention ratio%	Energy Density (Wh/kg)
				Example 1	97.6	91.3	221.9
Example 2	98.8	90.6	208.7
				Example 3	97.5	94.6	232.4
Comparative example 1	83.2	40.4	143.6

Fig. 2 is a half-cell charge test chart of the negative electrode tab prepared in example 1, and from fig. 2, the coulombic efficiency in the first discharge is not high because SEI is generated during the first discharge. The cyclic coulombic efficiency is improved to and stabilized above 95%, and the generated SEI is very stable, and the dissolution and shuttling effects of the electrode material are effectively inhibited basically.

Fig. 3 is a half-cell charge and discharge test chart of the negative electrode tab prepared in comparative example 1, and it can be seen from fig. 3 that the SEI is also generated during the first discharge, but the generated SEI is not stable due to the greater solubility of ethylnaphthalene. The voltage in the first charging process can not reach the charging cut-off voltage, which indicates that the dissolution of the ethyl naphthalene micromolecules causes serious shuttle effect, and the coulombic efficiency is greatly reduced.

While the present invention has been described in detail with reference to the embodiments thereof, the present invention is not limited to the embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art.

Claims

1. The negative pole piece is characterized by comprising a negative pole current collector and a negative pole active layer arranged on at least one side of the negative pole current collector, wherein the negative pole active layer comprises a conductive agent, a binder and a comb-shaped polymer, and the comb-shaped polymer is an active substance; the structural formula of the comb polymer is shown as the formula I:

formula I;

wherein n is more than or equal to 10000;

r is selected from naphthyl, biphenyl, anthryl or phenanthryl.

2. The negative electrode plate as claimed in claim 1, wherein the comb polymer is one of the following structural formulas:

。

3. the negative electrode plate as claimed in claim 1, wherein the comb-shaped polymer has a number average molecular weight of 10000 or more.

4. The negative electrode plate as claimed in claim 1, wherein the comb-shaped polymer accounts for 80-99% of the total mass of the negative electrode active layer.

5. The negative electrode sheet according to claim 1, wherein the conductive agent comprises at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and carbon fiber.

6. The negative electrode tab of claim 1, wherein the binder comprises at least one of styrene butadiene rubber or polyvinylidene fluoride.

7. The negative electrode sheet according to claim 1, wherein the negative electrode active layer comprises the following components in percentage by mass, based on the total mass of the negative electrode active layer:

80% -99% of comb-type polymer;

0.05 to 15 percent of conductive agent;

0.05 to 15 percent of binder.

8. A secondary battery comprising a positive electrode sheet, an electrolyte, a separator and the negative electrode sheet defined in any one of claims 1~7.

9. An electric device comprising the secondary battery according to claim 8.