CN111969207A

CN111969207A - Negative electrode adhesive and lithium ion secondary battery containing same

Info

Publication number: CN111969207A
Application number: CN202010860560.XA
Authority: CN
Inventors: 严涛; 翟传鑫; 张小海; 徐子福; 张明慧
Original assignee: Amprius Wuxi Co ltd
Current assignee: Amprius Wuxi Co ltd
Priority date: 2020-08-25
Filing date: 2020-08-25
Publication date: 2020-11-20
Anticipated expiration: 2040-08-25
Also published as: CN111969207B

Abstract

The invention discloses a negative electrode binder and a lithium ion secondary battery comprising the same. Compared with the traditional negative electrode adhesive, the functional monomer and functional ions are introduced into the adhesive, so that the structure is crosslinked, the branched chains are rich, the adhesive strength is greatly improved, and the rebound of a pole piece in the charging/discharging process is inhibited; on the other hand, due to the introduction of functional ions and graphene quantum dots, the diffusion resistance of lithium ions is reduced, and the ionic conductivity is improved; in addition, the functional monomer graphene quantum dots have a certain emulsification effect, and the dosage of an emulsifier can be reduced, so that the risk of generating bubbles in the homogenization process is controlled; meanwhile, the lithium ion secondary battery containing the adhesive has small expansion in the battery cycle process, excellent low-temperature performance and very excellent dynamic performance.

Description

Negative electrode adhesive and lithium ion secondary battery containing same

Technical Field

The invention relates to the technical field of lithium ion secondary batteries, in particular to a negative electrode adhesive and a lithium ion secondary battery comprising the same.

Background

Lithium ion batteries have high energy density and are widely used in consumer electronics and other fields. The adhesive in the lithium ion battery is used as a key material, the adhesion function among the current collector, the active material and the active material is played in the electrode, and the electrochemical performance of the battery is directly influenced by the quality of the adhesion effect. Particularly, in the case of a high-silicon negative electrode, the large volume expansion and contraction of the silicon material during charge and discharge cycles have extremely high requirements on the elasticity and viscosity of the adhesive, and the adhesive with excellent performance can obtain high adhesive strength on one hand, and can elastically hold the active material on the other hand, thereby greatly inhibiting the physical rebound of the electrode during charge and discharge. At present, binders SBR and PAA are mainly used for a negative electrode, wherein the SBR has good flexibility, but the binding effect is general, the PAA has good binding effect, but is brittle and poor in flexibility, and the ionic conductivity of the SBR and the PAA is extremely low, so that the dynamic performance of the electrode is influenced to a certain extent.

In order to improve the binding effect and ionic conductivity of the adhesive, the improvement can be designed by increasing molecular chains and introducing oxygen-containing functional groups, however, for PAA, the increase of molecular weight can obviously enhance the binding, but also increases the brittleness, and the increase of the oxygen-containing functional groups also improves the ionic conductivity to a certain extent. In order to complement the advantages, how to blend and compound the modified PAA and the SBR to realize the maximum functionalization of the adhesive is one of the effective directions for developing the high-efficiency adhesive in the future.

Disclosure of Invention

The invention aims to improve the adhesive force of a negative electrode, inhibit the expansion of the electrode in the charge and discharge process and improve the electrode dynamic performance by inventing a functional modified adhesive component, and particularly has obvious effect on a high-silicon negative electrode system.

Another object of the present invention is to provide a lithium ion secondary battery comprising the negative electrode binder.

The negative electrode binder PAA has strong binding effect, but has large brittleness, poor dynamic performance and difficult single use. At present, the improvement idea mainly focuses on improving the PAA dynamic performance, increasing the molecular weight or introducing functional groups or functional ions, improving the bonding and ionic conductivity, and realizes advantage complementation by compounding flexible SBR or other flexible adhesives and balancing and coordinating. The graphene quantum dots have special quantum effects, and the edges of the graphene quantum dots are provided with a large number of oxygen-containing functional groups; particularly, after the graphene quantum dots are functionalized, more abundant specific groups can be introduced, and the functional effect is realized. In addition, another effective way to improve the ionic conductivity of PAA is to introduce functional ions, and a large amount of literature work also proves that introducing functional ions such as lithium ions into adhesives such as PAA, CMC, polyacrylonitrile and the like can greatly improve the dynamic performance of the adhesives, and the lithium ions have smaller weight and homology in lithium ion batteries, so that lower electrochemical impedance is realized.

The invention discloses a negative electrode adhesive, which contains a substance A and has the following structural formula:

wherein R1 is a functional group or a functional monomer, and R2 is a functional ion.

Also comprises styrene butadiene rubber, an emulsifier and water.

R1 is an amino acid group that does not contain a carboxyl moiety, said amino acid group being at least one of alanine, glycine, serine, aspartic acid, valine, proline groups; or R1 is a monomer after amino acid functionalization, and the monomer is one of a carbon quantum dot and a graphene quantum dot.

R2 is one of functional lithium ion, sodium ion and potassium ion.

The A substance accounts for 30-100% of the mass of the negative electrode adhesive, the styrene butadiene rubber accounts for 20-90% of the mass of the negative electrode adhesive, and the emulsifier accounts for 0-10% of the mass of the negative electrode adhesive.

The solid content is 5-50%, and the viscosity at room temperature is 500-.

The lithium ion secondary battery comprises the negative electrode adhesive, and the battery comprises a negative electrode plate, a positive electrode plate, electrolyte, a dispersing agent and a diaphragm.

The negative plate active material is a graphite active material or a silicon active material, wherein the active mass ratio of the silicon active material is not less than 2%, and the dispersant is one or two of sodium carboxymethylcellulose or lithium carboxymethylcellulose; the positive active substance is one or two of lithium cobaltate or nickel cobalt lithium manganate ternary materials; the diaphragm is a ceramic coating diaphragm; the electrolyte contains an FEC additive.

The silicon-based active material is silicon, silicon oxide or pre-lithiated silicon oxide.

The proportion of the negative pole adhesive in the battery mass is 1.0-3.5%.

The adhesive and the lithium ion secondary battery comprising the same disclosed by the invention have the advantages that:

firstly, functional monomers are introduced into the adhesive, so that branched chains are rich, the structure is crosslinked, the adhesive strength is greatly improved, and the pole piece is prevented from rebounding in the charging/discharging process;

functional ions are introduced into the functional monomer by the adhesive, so that the diffusion resistance of lithium ions is reduced, and the ionic conductivity is improved;

functional monomer amino acid functionalized graphene quantum dots have a certain emulsification effect, and the using amount of an emulsifier can be reduced, so that the risk of bubbles generated in the homogenization process is controlled;

and a lithium ion secondary battery comprising the binder exhibits very excellent dynamic performance during charge and discharge.

Drawings

Fig. 1 is a graph of the peel strength of the negative electrode comprising the binder prepared in example 1 and a conventional binder PAA electrode after lamination.

Fig. 2 is a graph of the pole piece rebound rate of the negative electrode containing the binder prepared in example 1 and a conventional binder PAA electrode in the charge and discharge process.

Fig. 3 is a graph showing the normal temperature cycle performance of the lithium ion secondary battery comprising the binder prepared in example 1 and a conventional binder lithium ion secondary battery.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The present embodiment only exemplifies a winding type flexible package battery, but is also applicable to a lamination type battery, and is also applicable to batteries with other cases and structures, such as a square steel case, a cylindrical battery, and the like.

Description of typical cell manufacture:

preparing a positive pole piece: adding a positive electrode active material Lithium Cobaltate (LCO) and a binder polyvinylidene fluoride (PVDF) conductive agent Super-P into N-methylpyrrolidone (NMP) according to the required weight ratio of 96:2:2, stirring and homogenizing to prepare positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector on two sides, and drying, compacting, cutting, manufacturing a sheet and welding a tab to obtain the positive electrode sheet.

Preparing a negative pole piece: adding artificial graphite (or containing silicon, silicon alloy, silicon-carbon composite and silicon oxide) serving as a negative electrode active material, an adhesive and a dispersing agent into deionized water according to a required weight ratio, stirring and homogenizing to prepare negative electrode slurry; coating the two sides of the negative electrode slurry on a negative electrode current collector, and drying, compacting, slitting, sheet-making and welding a tab to obtain a negative electrode sheet.

Preparing a lithium ion battery: assembling the negative pole piece and the positive pole piece prepared by the process with a diaphragm to prepare a battery core, filling the battery core into an outer package, injecting electrolyte into the outer package, sealing, pre-charging, and forming to prepare the lithium ion secondary battery.

The lithium ion battery manufactured this time has a capacity of 2Ah, a charge voltage of 4.45V and a discharge cut-off voltage of 3.0V.

Synthesis method

The method for synthesizing the substance A comprises the following specific steps:

1) mixing a carbon source precursor citric acid and a functional reagent amino acid according to a certain proportion, stirring and dissolving in deionized water, directly carrying out high-temperature and high-pressure water thermal cracking in a thermal reaction kettle to obtain functional amino acid graphene quantum dots, filtering, and then carrying out vacuum drying;

2) dispersing functionalized amino acid graphene quantum dots in an alcohol-water mixed solution with a certain concentration, adding a small amount of dilute nitric acid, heating by microwave until reflux, continuously injecting ethylene gas into the liquid by using a conduit, stirring for reacting for several hours, fully reacting, then cooling and filtering, adding a certain amount of lithium hydroxide solution, and stirring for completely reacting;

3) filtering, washing and drying the mixture obtained in the step 2) to obtain a substance A.

Example 1

A negative pole adhesive contains 60% of substance A, 35% of SBR and 5% of emulsifier, the solid content is 38%, and the viscosity is 6000 mPa.s; and then uniformly mixing 1.7% of the adhesive, 90% of artificial graphite, 7% of silicon monoxide, 0.5% of SP and 0.8% of CMC, homogenizing, coating on the surface of a copper foil current collector, drying and rolling to prepare a negative electrode. Then, carrying out lamination assembly and tab welding on the positive pole piece and the diaphragm prepared by the process to prepare a battery cell, putting the battery cell into an aluminum-plastic film outer package, injecting electrolyte, fully soaking, forming, degassing and packaging to prepare the lithium ion secondary battery;

for comparison, 1.7% of adhesive (conventional 70% of PAA + 25% of SBR + 5% of emulsifier), 90% of artificial graphite, 7% of silicon monoxide, 0.5% of SP and 0.8% of CMC are uniformly mixed, the mixture is coated on the surface of a copper foil current collector after being homogenized, a negative electrode is manufactured after drying and rolling, and a lithium ion secondary battery is assembled by adopting positive electrode plates and diaphragms in the same batch;

FIG. 1 shows the peel strength of the negative electrode comprising the binder prepared in example 1 and a conventional binder PAA electrode after rolling; it can be obviously seen that the peel strength of the cathode electrode made of the adhesive is 1.7 times higher than that of the conventional adhesive PAA electrode after rolling, and the excellent adhesion effect is shown, so that the electrode can be ensured not to fall off powder in the assembling process, the through rate is improved, and the stability of the whole electrode in the circulating process is easier to support due to the large peel strength.

Fig. 2 shows the rebound rate of the electrode sheet of the negative electrode containing the binder prepared in example 1 and the conventional binder PAA electrode in the charge and discharge process at normal temperature. After 100 cycles of charging and discharging, the full-electricity disassembly of the battery shows that the rebound rate of the thickness of the negative electrode containing the adhesive is only 3.5 percent, which is lower than that of the conventional adhesive PAA electrode; even after 300 cycles, the rebound rate is still kept at 6.8%, and after 500 cycles of 400 and 500 cycles, the rebound tendency is obviously reduced, and excellent bonding stability is shown.

Fig. 3 is a graph showing cycle performance of the lithium ion secondary battery comprising the binder prepared in example 1 and a conventional binder lithium ion secondary battery. It can be clearly seen that the lithium ion secondary battery prepared in example 1 shows excellent cycle performance, and particularly after 100 cycles, the lithium ion secondary battery is clearly distinguished from the lithium ion secondary battery with a conventional PAA electrode, which indicates that the PAA functionalization can effectively improve the adhesion performance of the negative electrode.

Table 1 shows the rate and low-temperature discharge performance curves of the battery of the negative electrode comprising the binder prepared in example 1 and the battery comprising the conventional binder PAA electrode,

it can be seen that the battery containing the negative electrode of the binder is obviously superior to the battery containing the conventional binder PAA electrode in terms of rate discharge performance or low-temperature discharge performance, and the binder has excellent dynamic performance mainly due to the improvement of the ionic conductivity.

Example 2

A negative pole adhesive contains 70% of substance A, 25% of SBR and 5% of emulsifier, the solid content is 30%, and the viscosity is 7000 mPa.s; and then uniformly mixing 1.7% of adhesive, 90% of artificial graphite, 7% of silicon monoxide, 0.5% of SP and 0.8% of CMC, homogenizing, coating on the surface of a copper foil current collector, drying and rolling to prepare a negative electrode, and correspondingly preparing the lithium ion secondary battery by adopting the positive electrodes and the diaphragms in the same batch.

Example 3

A negative pole adhesive contains 80% of substance A, 15% of SBR and 5% of emulsifier, the solid content is 25%, and the viscosity is 8000 mPa.s; and then uniformly mixing 1.7% of adhesive, 90% of artificial graphite, 7% of silicon monoxide, 0.5% of SP and 0.8% of CMC, homogenizing, coating on the surface of a copper foil current collector, drying and rolling to prepare a negative electrode, and correspondingly preparing the lithium ion secondary battery by adopting the positive electrodes and the diaphragms in the same batch.

Example 4

A negative pole adhesive comprises 90% of substance A, 5% of SBR and 5% of emulsifier, the solid content is 10%, and the viscosity is 8800mPa & s; and then uniformly mixing 1.7% of adhesive, 90% of artificial graphite, 7% of silicon monoxide, 0.5% of SP and 0.8% of CMC, homogenizing, coating on the surface of a copper foil current collector, drying and rolling to prepare a negative electrode, and correspondingly preparing the lithium ion secondary battery by adopting the positive electrodes and the diaphragms in the same batch.

Example 5

A negative pole adhesive contains 50% of substance A, 45% of SBR and 5% of emulsifier, the solid content is 40%, and the viscosity is 5000 mPa.s; and then uniformly mixing 1.7% of adhesive, 90% of artificial graphite, 7% of silicon monoxide, 0.5% of SP and 0.8% of CMC, homogenizing, coating on the surface of a copper foil current collector, drying and rolling to prepare a negative electrode, and correspondingly preparing the lithium ion secondary battery by adopting the positive electrodes and the diaphragms in the same batch.

Example 6

A negative pole adhesive contains 60% of substance A, 35% of SBR and 5% of emulsifier, the solid content is 38%, and the viscosity is 6000 mPa.s; and then uniformly mixing 2.0% of adhesive, 88% of artificial graphite, 9% of silicon monoxide, 0.5% of SP and 0.5% of CMC, homogenizing, coating on the surface of a copper foil current collector, drying and rolling to prepare a negative electrode, and correspondingly preparing the lithium ion secondary battery by adopting the positive electrodes and the diaphragms in the same batch.

Example 7

A negative pole adhesive contains 60% of substance A, 35% of SBR and 5% of emulsifier, the solid content is 38%, and the viscosity is 6000 mPa.s; and then uniformly mixing 2.0% of adhesive, 85% of artificial graphite, 12% of silicon monoxide, 0.5% of SP and 0.5% of CMC, homogenizing, coating on the surface of a copper foil current collector, drying and rolling to prepare a negative electrode, and correspondingly preparing the lithium ion secondary battery by adopting the positive electrodes and the diaphragms in the same batch.

Comparative examples and examples illustrate that:

and (3) analyzing an experimental result:

compared with comparative examples of batteries, examples 1 to 5 of batteries show that the peel strength of the negative electrode using the binder is superior to that of a conventional PAA electrode, and the negative electrode is obviously inhibited from rebounding in the process of charging and discharging at normal temperature, and has excellent elastic expansion strength. The negative electrodes of the batteries of examples 6 to 7 are added with the higher content of the silicon oxide material, and the negative electrode prepared by the adhesive has higher peel strength and obvious rebound inhibition effect on the silicon oxide material, which shows that the adhesive has beneficial effect on graphite or silicon materials.

The above description is only a preferred embodiment of the present invention, and should not be taken as limiting the invention in any way, and any person skilled in the art can make any simple modification, equivalent replacement, and improvement on the above embodiment without departing from the technical spirit of the present invention, and still fall within the protection scope of the technical solution of the present invention.

Claims

1. A negative electrode binder characterized in that: contains A substance with the following structural formula:

2. The negative electrode binder as claimed in claim 1, wherein: also comprises styrene butadiene rubber, an emulsifier and water.

3. The negative electrode binder as claimed in claim 1, wherein: r1 is an amino acid group that does not contain a carboxyl moiety, said amino acid group being at least one of alanine, glycine, serine, aspartic acid, valine, proline groups; or R1 is a monomer after amino acid functionalization, and the monomer is one of a carbon quantum dot and a graphene quantum dot.

4. The negative electrode binder as claimed in claim 1, wherein: r2 is one of functional lithium ion, sodium ion and potassium ion.

5. The negative electrode binder as claimed in claim 1, wherein: the A substance accounts for 30-100% of the mass of the negative electrode adhesive, the styrene butadiene rubber accounts for 20-90% of the mass of the negative electrode adhesive, and the emulsifier accounts for 0-10% of the mass of the negative electrode adhesive.

6. The negative electrode binder as claimed in claim 1, wherein: the solid content is 5-50%, and the viscosity at room temperature is 500-.

7. A lithium ion secondary battery characterized in that: a negative electrode binder according to any one of claims 1 to 6, wherein the battery comprises a negative electrode sheet, a positive electrode sheet, an electrolyte, a dispersant and a separator.

8. A lithium ion secondary battery according to claim 7, characterized in that: the negative plate active material is a graphite active material or a silicon active material, wherein the active mass ratio of the silicon active material is not less than 2%, and the dispersant is one or two of sodium carboxymethylcellulose or lithium carboxymethylcellulose; the positive active substance is one or two of lithium cobaltate or nickel cobalt lithium manganate ternary materials; the diaphragm is a ceramic coating diaphragm; the electrolyte contains an FEC additive.

9. A lithium ion secondary battery according to claim 8, characterized in that: the silicon-based active material is silicon, silicon oxide or pre-lithiated silicon oxide.

10. A lithium ion secondary battery according to claim 7, characterized in that: the proportion of the negative pole adhesive in the battery mass is 1.0-3.5%.