CN109659493B

CN109659493B - Low-porosity negative electrode containing solid electrolyte and lithium battery applying negative electrode

Info

Publication number: CN109659493B
Application number: CN201811604753.8A
Authority: CN
Inventors: 赵春荣; 张立; 弓胜民; 朱秀龙; 阚素荣; 赵尚骞; 孙浩博
Original assignee: China Automotive Battery Research Institute Co Ltd
Current assignee: China Automotive Battery Research Institute Co Ltd
Priority date: 2018-12-26
Filing date: 2018-12-26
Publication date: 2021-03-23
Anticipated expiration: 2038-12-26
Also published as: CN109659493A

Abstract

The present invention provides a low porosity negative electrode comprising a solid state electrolyte, comprising: the negative electrode active material, the solid electrolyte, the conductive agent and the adhesive are prepared by the following steps: dividing the negative active material and the solid electrolyte into at least 3 grades according to the granularity, and mixing according to a certain proportion to realize the granularity grading; mixing the material obtained by the grain size distribution with a conductive agent, an adhesive and an organic solvent according to a certain proportion, uniformly stirring, smearing and drying; and pressurizing the dried pole piece at normal temperature, and pressing into a usable electrode. According to the invention, the solid electrolyte is added into the negative pole piece, participates in the negative pole material grading, the low-porosity electrode is prepared by cold pressing, and the lithium ion channel is provided for the low-porosity negative pole, so that the energy density of the lithium battery can be improved, and the using amount of the electrolyte is reduced.

Description

Low-porosity negative electrode containing solid electrolyte and lithium battery applying negative electrode

Technical Field

The invention belongs to the technical field of lithium batteries, and particularly relates to a negative electrode containing a solid electrolyte and low porosity and a lithium battery applying the negative electrode.

Background

With the rapid development of applications such as electric vehicles and new energy power generation, the development of advanced energy storage technology has become an urgent need, and among the energy storage technologies, lithium ion batteries are considered as one of the most potential energy storage technologies. In the lithium ion battery commonly used in the current market, the electrolyte is made of an organic electrolyte material, so that the problems of leakage, flammability, explosiveness and the like can be caused, and the lithium ion battery has potential safety hazards in the use process. In recent years, with the rapid expansion of the size of electric vehicles, battery safety has been increasingly emphasized. In view of the safety problem, development of a solid electrolyte that can replace the conventional lithium separator and electrolyte of a battery has become one of the most effective solutions.

Solid-state lithium-ion electrolytes also have a plurality of defects at present, which are mainly shown as follows: lithium ion conductivity is lower than that of liquid electrolyte, and interfacial resistance between solid electrolyte and electrode material is very large, which limits the application of all-solid lithium batteries. At present, the inorganic electrolyte filler reinforced polymer matrix composite Solid electrolyte effectively improves the lithium ion conductivity of the Solid electrolyte and improves the interface resistance between the Solid electrolyte and an electrode material (Nature, 1998, 394, 456; Solid State Ionics, 2009, 180, 1267; Nano Energy, 2016, 28, 447), but still cannot meet the requirement of the commercial development of the Solid lithium ion battery.

Patent document No. CN1050946A discloses a nanostructured quasi-solid electrolyte for lithium ion batteries or lithium sulfur batteries, and a preparation method and application thereof, wherein the solid electrolyte layer is a macroscopic solid electrolyte material formed by adsorbing an ion conductive agent by an inorganic-organic hybrid framework material, wherein the inorganic-organic hybrid framework material only has the function of adsorbing ions, and has no lithium ion transmission performance, and only the adsorbed ion conductive agent has the function of transmitting lithium ions, and the quasi-solid electrolyte replaces the electrolyte and the diaphragm in the lithium ion batteries. Patent document No. CN 10107645013 a discloses a composite quasi-solid electrolyte membrane including a solid electrolyte, a liquid electrolyte solution containing a lithium salt, inorganic nanoparticles, and a binder, and a method for preparing the same. Patent document CN 108365260 a discloses a quasi-solid electrolyte, which comprises a polymer, a ceramic electrolyte, a lithium salt and an ionic liquid, and is used for a metal lithium battery, a lithium air battery and a lithium sulfur battery.

Although the composite quasi-electrolyte in the above patent has higher conductivity, the problem of interfacial stability between the electrolyte and the electrode still exists, and in the current Solid battery research, there are methods for processing the electrode mainly using various sputtering and deposition means to make thin film electrode (Journal of electrochemical society, 1996,143(10): 3203-3213; Solid State ionic nics.2000,135(3-4): 41-42; functional material 2008,39(1):91-94) or method for coating electrode active material using PEO-based polymer electrolyte (Advanced Energy materials, 2017, 1701437; angel w.chem.int.ed.2016,55,1-5), but both of them have their own disadvantages: the former has limited energy density, which limits the application range of the thin film battery; the latter has low room temperature conductivity and poor electrochemical and chemical stability. In order to reduce the impedance of the composite electrode, the energy density of the battery is improved.

The invention designs and manufactures the active material/solid electrolyte/conductive material composite solid electrode with the porosity of less than 20 percent; the electrode was applied to a lithium ion battery, which was prepared to include a negative electrode (porosity less than 20%)/separator/positive electrode with a solid electrolyte and a small amount of electrolyte.

In the conventional electrode, as the compaction density is increased, ion channels in the electrode sheet are reduced, so that the capacity of an active material is exerted, and the power characteristic of the battery is deteriorated. The solid electrolyte is added into the electrode material, and the smooth ion transmission channel can be still constructed under the condition that the addition amount of the electrolyte is reduced under the condition that the electrode is in a high compaction density state. In addition, the solid electrode is not suitable for sintering process in order to realize continuous industrial production and improve battery yield. On the premise, the invention refers to the modern cement paste preparation method, and uses a cold pressing-grading mode to prepare the cathode containing the solid electrolyte; the lithium battery is prepared by adopting a preparation method of a conventional lithium battery.

According to the close packing model, the gaps formed by the large particles in close arrangement are filled with the medium particles, and the gaps formed by the large and medium particles are filled with the small particles (as shown in the figure I), and the packing density can be greatly improved by sequential graded filling. However, this case is only applicable to the theoretical pendulum-ball-like filling, and is not applicable to the actual particle filling. In actual operation, large particles, medium particles, and small particles including very small particles are not strictly distributed according to the mathematically optimal arrangement, so the level difference between the particles at each level should be increased, and the amount of small particles is much higher than the amount used in the close packing model. The method is researched in modern cement slurry preparation in a large amount, and the Lepeng et al conclude that the average particle size ratio of different component particles of a multi-component system is at least 4 times more than that of the particles, so that a good compact packing effect can be obtained (oil drilling and production process, 2017, Vol.39No. 3.307-312); the Zhoushi et al also note that the amount of finer particles should be sufficient to fill the voids formed by the closely packed particles. Increasing the amount of coarse fraction appropriately increases the bulk density of the mixture to near closest packing, but when the fraction is greater than 3, it is of little practical significance (oil drilling technology. 2007.Vol.35No. 4.46-49.). When the solid electrode is prepared, because the granularity of the used material is smaller, the interparticle action is stronger, and a compact electrode with the porosity within 20 percent is more difficult to prepare, the invention combines the battery homogenate and tabletting technologies on the basis of the cement paste preparation process, and more carefully provides the cold pressing-grading gradation method process.

Compared with the electrode in the current lithium ion battery, the invention obviously improves the active material loading under the condition of approximate coating thickness; the porosity of the electrode is obviously reduced; the electrode can play a role in transferring ions and electrons; the usage amount of the liquid electrolyte in the lithium battery is greatly reduced.

Disclosure of Invention

The invention aims to develop a negative pole piece containing solid electrolyte and having low porosity and high energy density and a lithium battery applying the negative pole by adding the solid electrolyte into the negative pole piece, participating in negative pole material grading, preparing a low porosity electrode by cold pressing, and providing a lithium ion channel for a low porosity negative pole, improving the energy density of the lithium battery, reducing the using amount of the electrolyte.

In order to achieve the purpose, the invention provides the following technical scheme:

a low porosity negative electrode comprising a solid state electrolyte, comprising: the negative electrode comprises a negative electrode active material, a solid electrolyte, a conductive agent and a binder, wherein the amount of the solid electrolyte is not more than 30wt% of the total amount, the particle size of the negative electrode active material and the solid electrolyte is at least divided into 3 grades, and the porosity is between 10% and 20%.

A method of making a low porosity negative electrode comprising a solid state electrolyte includes: dividing the negative active material and the solid electrolyte into at least 3 grades according to the granularity, and mixing according to a certain proportion to realize the granularity grading; mixing the material obtained by the grain size distribution with a conductive agent, an adhesive and an organic solvent according to a certain proportion, uniformly stirring, smearing and drying; and pressurizing the dried pole piece, and pressing into a usable electrode.

Preferably, in a low porosity anode comprising a solid state electrolyte, the solid state electrolyte comprises: at least 1 of polymer solid electrolyte and inorganic solid electrolyte.

Preferably, in a low porosity anode comprising a solid state electrolyte, the anode active material comprises: one or more of a silicon-based negative electrode material, a carbon negative electrode material, a silicon-oxygen-carbon-based negative electrode material, a lithium titanate negative electrode material, a tin-based negative electrode material, a lithium-containing transition metal oxide negative electrode material and an alloy negative electrode material.

Preferably, in a solid electrolyte-containing, low porosity anode, the carbon anode material comprises: one or more of conductive carbon black, carbon nano tubes, graphene oxide, reduced graphene oxide and the like. Preferably, the conductive carbon black is one or more of Super-P, KB and XC 72.

Preferably, in the negative electrode containing the solid electrolyte and low porosity, when the grade 3 is matched, the particle sizes of large, medium and small particles are respectively D50 (0.4-20 μm) and D50 (0.1-5 μm) D50 (0.02-1 μm), and the particle size ratio of two adjacent grades is more than or equal to 4.

Preferably, in a low porosity negative electrode comprising a solid electrolyte, when the grade 3 is matched, the volume of the large particles is more than 60% of the total volume, and the volume of the small particles is more than 5% of the total volume.

Preferably, in the negative electrode containing the solid electrolyte and low porosity, when the grade 4 is matched, the particle sizes of large, medium, small and extremely small particles are respectively D50 (1.5-32 μm), D50 (0.3-8 μm), D50 (0.08-2 μm) and D50 (0.02-0.5 μm), and the particle size ratio of two adjacent grades is more than or equal to 4.

Preferably, in a negative electrode containing a solid electrolyte and having a low porosity, when the grade 4 is matched, the volume of the large particles is more than 50% of the total volume, and the volume of the very small particles is more than 3% of the total volume.

Preferably, in the negative electrode containing the solid electrolyte and low porosity, the dispersion and mixing of the powder are carried out in a liquid, and the liquid is N-methyl pyrrolidone, propylene carbonate, tetrahydrofuran and butyl butyrate.

Preferably, in a low-porosity negative electrode comprising a solid electrolyte, the content of the binder does not exceed 10wt% of the total amount of each material, and the solid content of the mixed slurry is between 30% and 65 wt%.

Preferably, in a low porosity negative electrode comprising a solid state electrolyte, the well dispersed slurry is knife coated on a current collector comprising: aluminum foil, copper foil, stainless steel foil.

Preferably, in a method for preparing a low-porosity negative electrode comprising a solid electrolyte, the tabletting may be performed at normal temperature by using a roller or a hydraulic pressure.

A lithium battery is formed by placing the solid electrolyte, the low-porosity negative electrode, the electrically compatible positive electrode, the interlayer between the positive electrode and the negative electrode and the electrolyte in a container.

Preferably, the amount of the electrolyte is 1.0-3 times of the total pore volume in the negative electrode, the positive electrode and the interlayer between the positive electrode and the negative electrode.

The invention has the beneficial effects that: the electrode prepared by adding the solid electrolyte into the negative pole piece has low porosity, is beneficial to reducing the electrode impedance, improves the energy density of the battery and simultaneously reduces the using amount of the electrolyte; the solid electrolyte participates in the graded gradation of the cathode material, reduces the porosity of the electrode, increases the ion transmission channel of the electrode with low porosity and improves the ion transmission capability of the electrode.

Drawings

FIG. 1: distribution of pore diameters of SiC + LLZTO negative electrodes with different porosities (18%, 30%)

FIG. 2 a: first-time charge and discharge curve of soft package battery assembled by SiC + LLZTO negative electrode with porosity of 18% and NCM523 positive electrode

FIG. 2 b: first-time charge and discharge curve of soft package battery assembled by SiC + LLZTO negative electrode with porosity of 30% and NCM523 positive electrode

FIG. 3: cycle performance curve of soft package battery assembled by SiC + LLZTO negative electrode and NCM523 positive electrode with different porosities (18%, 30%)

Detailed Description

The invention will be further described with reference to the figures and examples. The description is intended to be illustrative of the invention and is not to be construed as limiting the invention.

Example 1

A method of making a low porosity negative electrode comprising a solid state electrolyte, the method comprising:

(1) silicon-carbon composite material of D50(15.9 μm), silicon-carbon composite material of D50(2.5 μm) and solid electrolyte LLZTO powder of D50(500nm) were selected, and the ratio of the particles in large particles: and (3) medium particle: small particles 7: 2: 1 (actual volume ratio), carrying out 3-grade grading, checking the true density of each component, calculating the mass ratio, and weighing the powder material with the total weight of 190 g.

(2) Mixing 56g of N-methyl pyrrolidone, 100g of 6% PVDF glue solution, 1.5g of SP conductive agent and 190g of weighed powder material, homogenizing by using a homogenizer, dispersing at 1000 rpm/min for 5min, 5000 rpm/min for 5min and 7000 rpm for 5min, repeating for 4 times, cooling the slurry, testing the viscosity of the slurry to be 3600 Pa.s and the fineness of the slurry to be 35 mu m, then coating the two sides of the slurry on a copper foil on a coating machine, and testing the surface density of an electrode to be 8.1mg/cm²。

(3) Cutting the electrode into pole pieces with the width of 60mm and the length of 210mm, rolling on a roller press, adjusting the distance between rollers of the roller press, rolling 3 times for each pole piece, respectively obtaining the pole pieces with the porosity of 18% and 30% by setting different roller distances (the pore volumes of the pole pieces are respectively 18%: 0.046mL/g and 30%: 0.12mL/g), cutting the pole pieces into required sizes, drying and weighing.

Example 2

A lithium ion battery is formed by placing the cathode containing solid electrolyte and low porosity, the anode compatible with electricity, a separator and electrolyte into a container, and the method comprises the following steps:

(1) according to the steps (2) and (3) in example 1, a positive electrode sheet of NCM523 was prepared, and according to a P/N ratio of 1.15, the surface density of the positive electrode sheet was prepared to be 26.1mg/cm²And after rolling, obtaining the pole piece with the porosity of 30% and the single-side coated positive pole, cutting the pole piece into the required size, drying and weighing.

(2) The cut positive pole piece, the cut negative pole piece and the diaphragm with the thickness of 32 mu m are adopted for lamination, then the positive pole piece and the negative pole piece are welded with a tab, finally, the battery is packaged in an aluminum plastic film, a port is reserved above the aluminum plastic film for injection, and the amount of electrolyte is 2 times of the total pore volume of the positive pole piece, the negative pole piece and the diaphragm.

(3) And packaging the battery after liquid injection, standing for 24h, and then carrying out vacuum packaging to obtain the soft package battery with the negative porosity of 18% and 30%.

(4) And (4) testing the soft package battery, namely adopting a method of controlling the capacity by charging for the first time and then selecting a cut-off voltage for charging and discharging.

(5) And (3) testing the soft package battery, wherein the first charge capacity is the theoretical capacity of the silicon-carbon cathode, the voltage at the moment is set as a charge cut-off voltage, the discharge cut-off voltage is 2.8V, and the discharge multiplying power is 0.1C, 0.3C, 0.5C and 1C.

The pore size distribution of the electrode with the porosity of 18 percent and 30 percent is shown in figure 1, the pore size of the electrode with the porosity of 18 percent is intensively distributed at 0.7 mu m and is narrow, the pore size of the electrode with the porosity of 30 percent is intensively distributed at 1.8 mu m and is wide; the pore volume of the pole piece is respectively 18%: 0.046mL/g, 30%: the amount of the electrolyte in the pole piece with the porosity of 30 percent is 0.12mL/g and is 2.6 times of that in the pole piece with the porosity of 18 percent.

The first discharge capacity of the soft package battery assembled by the electrode with the negative electrode porosity of 18% is very close to the first discharge capacity of the soft package battery assembled by the electrode with the negative electrode porosity of 30%, and the rate capability and the cycle performance are better, so that the LLZTO plays a role in conducting lithium ions in the low-porosity electrode.

The present invention is capable of other embodiments and its several details are capable of modifications in various obvious respects, all without departing from the invention and its spirit, and all such modifications and changes are deemed to be within the scope of the appended claims.

Claims

1. A lithium battery formed by placing a container containing a solid state electrolyte, a low porosity negative electrode and an electrically compatible positive electrode, a separator between the positive and negative electrodes, and an electrolyte, the low porosity negative electrode comprising: the negative electrode comprises a negative electrode active material, a solid electrolyte, a conductive agent and a binder, wherein the amount of the solid electrolyte is not more than 30wt% of the total amount, the particle size of the negative electrode active material and the solid electrolyte is at least divided into 3 grades, and the porosity is between 10% and 20%; the amount of the electrolyte is 1.0-3 times of the total pore volume in the negative electrode, the positive electrode and the interlayer between the positive electrode and the negative electrode.

2. A lithium battery as claimed in claim 1, characterized in that: the solid electrolyte includes: at least one of a polymer solid electrolyte and an inorganic solid electrolyte.

3. A lithium battery as claimed in claim 1, characterized in that: the negative active material includes: one or more of a silicon-based negative electrode material, a carbon negative electrode material, a silicon-oxygen-carbon-based negative electrode material, a lithium titanate negative electrode material, a tin-based negative electrode material, a lithium-containing transition metal oxide negative electrode material and an alloy negative electrode material.

4. A lithium battery as claimed in claim 3, characterized in that: the carbon negative electrode material comprises one or more of conductive carbon black, carbon nano tubes, graphene oxide and reduced graphene oxide.

5. A lithium battery as claimed in claim 4, characterized in that: the conductive carbon black is one or more of Super-P, KB and XC 72.

6. A lithium battery as claimed in claim 1, characterized in that: when the grain size is distributed in 3 grades, the grain size ranges of the large, medium and small grains are respectively 0.4-20 μm, 0.1-5 μm and 0.02-1 μm, the grain size ratio of two adjacent grades is more than or equal to 4, and the grain size is D50 value.

7. A lithium battery as claimed in claim 6, characterized in that: when the grade 3 is matched, the volume of the large particles accounts for more than 60 percent of the total volume, and the volume of the small particles accounts for more than 5 percent of the total volume.

8. A lithium battery as claimed in claim 1, characterized in that: when the grain size is in 4-level distribution, the grain size ranges of large, medium, small and very small grains are respectively 1.5-32 μm, 0.3-8 μm, 0.08-2 μm and 0.02-0.5 μm, the grain size ratio of two adjacent levels is more than or equal to 4, and the grain size is D50 value.

9. A lithium battery as claimed in claim 8, characterized in that: when the grain size is 4-level, the volume of the large grains is more than 50% of the total volume, and the volume of the small grains is more than 3% of the total volume.

10. A lithium battery as claimed in claim 1, characterized in that: the powder is dispersed and mixed in liquid, and the liquid is N-methyl pyrrolidone, propylene carbonate, tetrahydrofuran and butyl butyrate.

11. A lithium battery as claimed in claim 1, characterized in that: the content of the binder is not more than 10wt% of the total amount of each material, and the solid content of the mixed slurry is between 30 and 65 wt%.

12. A lithium battery as claimed in claim 1, characterized in that: the thick liquids after the abundant dispersion blade coating is on the mass flow body, the mass flow body includes: aluminum foil, copper foil, stainless steel foil.

13. A lithium battery as claimed in any one of claims 1 to 12, characterized in that: a method of making a low porosity negative electrode comprising a solid state electrolyte includes: dividing the negative active material and the solid electrolyte into at least 3 grades according to the granularity, and mixing according to a certain proportion to realize the granularity grading; mixing the material obtained by the grain size distribution with a conductive agent, an adhesive and an organic solvent according to a certain proportion, uniformly stirring, smearing and drying; and pressurizing the dried pole piece, and pressing into a usable electrode.

14. A lithium battery as claimed in claim 13, characterized in that: the pole piece is pressurized by rolling or hydraulic pressure, and tabletting is carried out at normal temperature.