WO2016201941A1

WO2016201941A1 - Lithium ion battery with long cycle performance

Info

Publication number: WO2016201941A1
Application number: PCT/CN2015/098496
Authority: WO
Inventors: 田东
Original assignee: 田东
Priority date: 2015-06-13
Filing date: 2015-12-23
Publication date: 2016-12-22
Also published as: CN104993135A

Abstract

A lithium ion battery with a long cycle performance. The present invention relates to the field of batteries. A material system of the lithium ion battery takes lithium iron phosphate with a stable cycle performance as a cathode, lithium titanate with an excellent cycle performance as an anode and graphene with a high conductivity performance as a conductive additive. A cathode and anode material system with the excellent cycle performance is adopted, the areal density and compaction density of a cathode pole piece and an anode pole piece are optimized and controlled, and the cycle performance of the battery is greatly improved. The graphene with the high conductivity performance is adopted as a conductive agent additive, such that the defect of reduction of an active material proportion of a cathode to an anode due to the fact that a large number of conventional conductive agents need to be added when they are adopted is avoided, and the volume energy density of the battery is further improved. An electrolyte containing a PC solvent is adopted, and the high freezing point and high conductivity of the PC solvent are utilized, such that the problem of battery heat dissipation under the large current charge-discharge conditions is effectively buffered, and the cycle stability of the battery is further guaranteed. A preparation process for the lithium ion battery is simple, and a manufactured lithium battery is excellent in performance.

Description

Lithium ion battery with long cycle performance

Technical field

The invention relates to a lithium ion battery with long cycle performance, belonging to the field of lithium ion batteries.

Background technique

Since Sony Corporation of Japan took the lead in developing and commercializing lithium-ion batteries in 1990, lithium-ion batteries have developed rapidly. Today, lithium-ion batteries have been widely used in various fields of civil and military applications. With the continuous advancement of technology, people have put forward more and higher requirements for the performance of batteries: the miniaturization and personalized development of electronic devices require batteries with smaller volume and higher specific energy output; aerospace energy requirements The battery has a cycle life, better low temperature charge and discharge performance and higher safety performance; electric vehicles require batteries with high capacity, low cost, high stability and safety performance.

The negative electrode material of the lithium ion battery includes a carbon material, an intermetallic compound, a tin-based compound, and the like. At present, the commercial lithium ion battery anode material is made of graphite-based carbon material, has low lithium insertion/deintercalation potential, suitable reversible capacity, rich resources, and low price, and is an ideal anode material for lithium ion batteries. The graphite material has a low discharge and discharge platform, and has a high lithium insertion capacity. The lithium intercalation capacity of the lithium intercalation compound LiC6 is 372 mAh/g, and the first charge and discharge efficiency is high. It has been found through research that graphite forms a SEI film during the first cycle by reacting with the electrolyte. This film allows lithium ions to pass freely and prevents solvated lithium ions from entering, thus forming this layer of SEI film on the graphite surface. It is possible to prevent the graphite electrode from being further corroded by the electrolyte and maintaining good cycle performance.

The positive electrode material of a lithium ion battery is generally an excessive metal oxide such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , and LiNi _x Co _y Mn _(1-xy) O ₂ , and the like, and a phosphate of an excessive metal. Among them, the LiCoO ₂ electrode with layered structure has good performance, and is a cathode material widely used in commercial lithium ion batteries on the market, but it also has disadvantages such as high price and large pollution; LiMn ₂ O _{4 with} spinel structure is cheap and pollution-free. It has been regarded as the material of choice for replacing LiCoO ₂ and has been extensively studied. However, due to its low capacity and severe capacity degradation at high temperatures, its application range is still limited. Compared with LiCoO ₂ with similar structure, LiNiO _{2 It} has the advantages of high capacity, high power and moderate price, but it also has difficulties in synthesis and poor thermal stability, and its practical process has been slow. However, as the performance of doped multi-element oxides (such as LiNi _x Co _y Mn _(1-xy) O _{2 ,} etc.) is improved and improved, the application of lithium ion batteries is extended to electric vehicles (EV, HEV), Industrial large battery fields such as energy storage power stations and military applications are becoming research hotspots.

Whether it is a positive or negative active material, conductive agents are indispensable as a lithium battery. The purpose of the component is to form an effective conductive network in the active material. For the composite of the active material and the conductive agent (hereinafter referred to as "composite electrode"), in order to form a conductive network, the amount of the conductive agent must be added to and exceeds a certain amount. When the amount exceeds this amount, the conductive agent particles can be filled with full activity. The gap between the particles of the material, and the effective contact between the conductive agents, the conductivity of the composite electrode is fundamentally improved. The former lithium-ion battery conductive agent is mainly Super-P and KS series. Both of these products are imported from abroad. The former is a nano-scale carbon black product, which has a small particle size and a large specific surface area. It also has good electrical conductivity, but because of its small particle size and large specific surface area, it is difficult to disperse, and then it is micron-sized conductive graphite, which is easy to disperse, but its conductivity is worse than Super-P. Therefore, in the actual use process, both are added at the same time, and the complement is insufficient. The graphite thin structure is unique, with good electrical conductivity, thermal conductivity, stability and a large specific surface area. As a conductive agent for lithium ion batteries, it can greatly improve the energy density of the battery, and at the same time increase the rate of charge and discharge of the material to meet the requirements of the power battery.

The improvement of the performance of lithium-ion batteries is mainly due to the improvement of the performance of each material and the cooperation of various components. Therefore, by selecting a suitable material system, lithium-ion batteries with different performance characteristics can be prepared for different needs.

Summary of the invention

In view of the deficiencies in the conventional lithium ion battery in terms of low cycle performance, it is an object of the present invention to provide a lithium ion battery having long cycle performance and a method of preparing the same.

In order to achieve the above object, the invention provides a lithium ion battery with long cycle performance, the material system is lithium iron phosphate with stable cycle performance as positive electrode, lithium titanate with excellent cycle performance as negative electrode, and high conductivity. Graphene is a conductive additive.

The lithium iron phosphate positive electrode material has a specific capacity of 145 to 160 mAh/g, a first efficiency of 92.5 to 94.5%, a double-sided surface density of 15 to 30 mg/cm ² , and a positive electrode compaction density of 1.9 to 2.3 g/cm ³ .

The lithium titanate negative electrode material has a gram specific capacity of 150 to 165 mAh/g, a first efficiency of 93 to 95.5%, a negative electrode compaction density of 1.3 to 1.6 g/cm ³ , and a negative electrode sheet surface density corresponding to a positive electrode active material excess ratio. It is 3% to 10%.

Preferably, the positive electrode tab is prepared by first preparing 2 to 5 wt% of a binder-polyvinylidene fluoride (PVDF) and 80 to 120 wt% of a solvent-methylpyrrolidone (NMP), and then adding 1 to 3 wt%. The graphene conductive agent is well dispersed, and finally 80 to 95.5 wt% of active material lithium iron phosphate is added, mixed into a slurry, the viscosity is adjusted, and a pole piece is coated on an aluminum foil of 0.010 to 0.016 mm, and a positive electrode piece is obtained by rolling and slitting. And the double-sided density of the positive electrode is 20 to 30 mg/cm ² , and the compact density is 2.0 to 2.3 g/cm ³ .

Preferably, the negative electrode tab is prepared by disposing 1 to 2 wt% thickener sodium carboxymethylcellulose (CMC) and deionized water into a glue solution, and dispersing 0.5 to 2 wt% of graphene conductive agent, and then dispersing. Add 93.8 to 98% by weight of active material lithium titanate, and finally add 2 to 4.4% by weight of binder-styrene-butadiene rubber (SBR), mix into slurry, adjust viscosity, and coat the electrode on 0.08-0.010mm copper foil. The sheet has a negative compaction density of 1.4 to 1.6 g/cm ³ .

Preferably, the separator is separated between the positive electrode and the negative electrode, and the separator is 0.012 to 0.025 mm.

Preferably, the electrolyte is 1 mol/L of LiPF6/EC+DMC+PC (v/v=1:1:1), and a PC solvent having a high freezing point is additionally added.

When graphite is used as a negative electrode material, a solid electrolyte membrane (SEI film) is formed on the surface during the first charge and discharge process. The solid electrolyte membrane is formed by reacting an electrolyte, a negative electrode material and lithium ions, and irreversibly consuming lithium ions, which is a major factor in forming irreversible capacity. Secondly, in the process of lithium ion intercalation, the electrolyte is easily co-incorporated with it. During the process, the electrolyte is reduced, and the generated gas product causes the graphite sheet to peel off. Especially in the electrolyte containing PC, the graphite sheet peeling off will form a new interface, resulting in further SEI formation, thereby causing a decrease in battery cycle performance. Limits the use of graphite materials in power battery materials.

Compared with graphite carbon materials, lithium titanate has many advantages. Among them, the deintercalation of lithium ions in lithium titanate is reversible, and the crystal form of lithium ions does not occur during the process of inserting or extracting lithium titanate. Change, volume change is less than 1%, so it is called "zero strain material", which can avoid the structure damage caused by the back and forth expansion of the electrode material in the charge and discharge cycle, thereby improving the cycle performance and service life of the electrode, reducing the cycle The number of times increases to a large attenuation of the specific capacity, and has better cycle performance than the carbon negative electrode; according to the above, a high energy density lithium ion battery designed by the present invention, after the battery is assembled, is placed and formed. , aging, and can be divided. The beneficial effects and progress of the present invention are as follows:

1. Optimize and control the areal density and compaction density of the positive and negative pole pieces by using positive and negative material systems with excellent cycle characteristics, and greatly improve the cycle performance of the battery;

2. Using graphene with high conductivity as a conductive agent additive, avoiding the use of conventional conductive agents and requiring a large amount of addition to reduce the disadvantages of the ratio of positive and negative active materials, and further increasing the volumetric energy density of the battery;

3. Using electrolyte containing PC solvent, using the high freezing point and high electrical conductivity of PC solvent, effectively buffering the heat dissipation problem of the battery under the condition of large current charge and discharge, further ensuring the cycle stability of the battery.

DRAWINGS

Figure 1. Cycle diagram of a lithium ion battery prepared in Example 1.

detailed description

To facilitate an understanding of the invention, the invention is set forth below. It should be understood by those skilled in the art that the present invention is only to be construed as a

Example 1

A lithium ion battery having long cycle performance described in this embodiment uses lithium iron phosphate as a positive electrode active material, a lithium iron phosphate having a specific capacity of 149 mAh/g, a first efficiency of 93.2%, and a lithium titanate as a negative electrode material. The gram ratio is 160 mAh/g, and the first efficiency is 93.5%.

The positive electrode tab is prepared by first disposing the binder PVDF (3 wt%) and the solvent NMP (80 wt%) into a glue solution, dispersing 2 wt% of the graphene, and finally adding the active material lithium iron phosphate 95 wt%, mixing. The slurry was slurried, and the viscosity was adjusted. Then, a pole piece was coated on an aluminum foil of 0.016 mm, and the double-sided surface density was 30 mg/cm ² , and the positive electrode piece was obtained by rolling and cutting, and the compacted density was 2.0 g/cm ³ ;

The negative pole piece is prepared by disposing CMC 1.2wt% and deionized water into a glue solution, adding graphene 0.5% by weight to disperse, then adding active material lithium titanate 96.3wt%, and finally adding binder 2.0wt%. The mixture was mixed into a slurry to adjust the viscosity. The pole piece was coated on a copper foil of 0.010 mm, and the density of the negative electrode surface was calculated to correspond to the excess of the positive electrode active material capacity ratio of 5%, and the compactness of the negative electrode piece was 1.5 g/ Cm ³ ; The separator is separated by a separator between the positive electrode and the negative electrode, and the separator is a 0.02 mm three-layer PP separator, and the electrolyte is 1 mol/L of LiPF6/EC+DMC+PC (v/v=1:1:1).

By performing 1C charge and discharge performance test on the battery, the battery prepared by the present invention was subjected to a 3800-week cycle test, and the capacity retention rate was 81.91%, showing excellent cycle performance.

Example 2

A lithium ion battery having long cycle performance described in this embodiment uses lithium iron phosphate as a positive electrode active material, a lithium iron phosphate having a specific capacity of 155 mAh/g, a first efficiency of 94.5%, and a lithium titanate as a negative electrode material. The gram ratio is 162 mAh/g, and the first efficiency is 95.2%.

The positive electrode tab is prepared by first disposing the binder PVDF (2.5 wt%) and the solvent NMP (80 wt%) into a glue solution, dispersing 1.5 wt% of the graphene, and finally adding the active material lithium iron phosphate 96 wt%. , mixing into a slurry, adjusting the viscosity, and then coating a pole piece on a 0.016 mm aluminum foil, a double-sided surface density of 25 mg / cm ² , and rolling and slitting to obtain a positive electrode piece, compaction density of 2.2 g / cm ³ ;

The negative pole piece was prepared by disposing CMC 1.5wt% and deionized water into a glue solution, adding graphene 0.5% by weight to disperse, then adding active material lithium titanate 96.7wt%, and finally adding binder 1.8wt%. The mixture was mixed into a slurry to adjust the viscosity. The pole piece was coated on a copper foil of 0.010 mm, and the density of the negative electrode surface was calculated to correspond to the excess of the positive electrode active material capacity ratio of 6%, and the compact density of the negative electrode piece was 1.55 g/ Cm ³ ; The separator is separated by a separator between the positive electrode and the negative electrode, and the separator is a 0.02 mm three-layer PP separator, and the electrolyte is 1 mol/L of LiPF6/EC+DMC+PC (v/v=1:1:1).

By performing 1C charge and discharge performance test on the battery, the battery prepared by the present invention was subjected to a 1000-week cycle test, and the capacity retention rate was 97.70%, showing excellent cycle performance.

Example 3

A lithium ion battery having long cycle performance described in this embodiment uses lithium iron phosphate as a positive electrode active material, a lithium iron phosphate having a specific capacity of 160 mAh/g, a first efficiency of 94.3%, and a lithium titanate as a negative electrode material. The gram ratio is 165mAh/g, and the first efficiency is 95.5%.

The positive electrode tab is prepared by first disposing the binder PVDF (2.0 wt%) and the solvent NMP (80 wt%) into a glue solution, dispersing 1.0 wt% of the graphene, and finally adding the active material lithium iron phosphate 97 wt%. , mixing into a slurry, adjusting the viscosity, and then coating a pole piece on a 0.016 mm aluminum foil, the double-sided surface density of 20 mg / cm ² , and rolling and slitting to obtain a positive electrode piece, compaction density of 2.3 g / cm ³ ;

The negative electrode pole piece is prepared by disposing CMC 1.5wt% and deionized water into a glue solution, adding graphene 0.5% by weight to disperse, then adding active material lithium titanate 97wt%, and finally adding binder 1.5wt%, mixing. The slurry was formed into a slurry, and the viscosity was adjusted. The pole piece was coated on a copper foil of 0.010 mm, and the density of the negative electrode surface was calculated to correspond to the excess ratio of the positive electrode active material to 6%, and the compact density of the negative electrode piece was 1.60 g/cm. ³ ; The separator is separated by a separator between the positive electrode and the negative electrode, and the separator is a 0.02 mm three-layer PP separator, and the electrolyte is 1 mol/L LiPF6/EC+DMC+PC (v/v=1:1:1).

By performing 1C charge and discharge performance test on the battery, the battery prepared by the present invention was subjected to a 1000-week cycle test, and the capacity retention rate was 98.20%, showing excellent cycle performance.

The Applicant declares that the present invention illustrates the detailed process parameters and process flow of the present invention by the above embodiments, but the present invention is not limited to the above detailed process parameters and process flow, that is, does not mean that the present invention must rely on the above detailed process parameters and The process can only be implemented. It should be apparent to those skilled in the art that any modifications of the present invention, equivalent substitution of the various materials of the products of the present invention, addition of auxiliary components, selection of specific means, and the like, are all within the scope of the present invention.

Claims

A lithium ion battery with long cycle performance, characterized in that: the material system uses lithium iron phosphate with stable cycle performance as a positive electrode, lithium titanate with excellent cycle performance as a negative electrode, and graphene with high conductivity as a conductive additive; The lithium iron phosphate cathode material has a specific capacity of 145-160 mAh/g, a first efficiency of 92.5-94.5%, a double-sided density of 15-30 mg/cm 2 , and a positive compaction density of 1.9-2.3 g/cm 3 ; The lithium negative electrode material has a gram specific capacity of 150 to 165 mAh/g, a first efficiency of 93 to 95.5%, a negative electrode compaction density of 1.3 to 1.6 g/cm 3 , and a negative electrode sheet surface density corresponding to a positive electrode active material excess ratio of 3 %~10%.
The lithium ion battery with long cycle performance according to claim 1, wherein the positive electrode tab is made by first adding 2 to 5 wt% of a binder-polyvinylidene fluoride (PVDF) and 80 to 120 wt%. The solvent-methylpyrrolidone (NMP) is made into a glue, and then 1-3 wt% of graphene conductive agent is added to disperse, and finally 80-95.5% by weight of active material lithium iron phosphate is added, and the mixture is mixed into a slurry to adjust the viscosity at 0.010~ A pole piece was coated on an 0.016 mm aluminum foil, and a positive electrode piece was obtained by roll cutting; and the double-sided density of the positive electrode was 20 to 30 mg/cm 2 and the compact density was 2.0 to 2.3 g/cm 3 .
A lithium ion battery having long cycle performance according to claim 1, wherein the negative electrode tab is prepared by first adding 1 to 2 wt% thickener sodium carboxymethylcellulose (CMC) and deionization. The water is configured as a glue, and 0.5 to 2 wt% of graphene conductive agent is added to disperse, and then 93.8 to 98 wt% of active material lithium titanate is added, and finally 2 to 4.4 wt% of binder-styrene-butadiene rubber (SBR) is added and mixed. The slurry was adjusted in viscosity, and a pole piece was coated on a copper foil of 0.08 to 0.010 mm, and the compact density of the negative electrode was 1.4 to 1.6 g/cm 3 .
A lithium ion battery having long cycle performance according to claim 1, wherein a separator is separated between the positive electrode and the negative electrode, and the separator is 0.012 to 0.025 mm.
A lithium ion battery having long cycle performance according to claim 1, wherein the electrolyte is additionally added with 1 mol/L of LiPF6/EC+DMC+PC (v/v=1:1:1). A PC solvent with a high freezing point.