CN113540571A

CN113540571A - Lithium ion battery preparation method and lithium ion battery

Info

Publication number: CN113540571A
Application number: CN202010316168.9A
Authority: CN
Inventors: 朱阳阳; 代康伟; 盛军; 赖兴强; 张鹏; 尹壮
Original assignee: Beijing Electric Vehicle Co Ltd
Current assignee: Beijing Electric Vehicle Co Ltd
Priority date: 2020-04-21
Filing date: 2020-04-21
Publication date: 2021-10-22

Abstract

The invention provides a lithium ion battery and a preparation method thereof, and relates to the technical field of batteries. The preparation method for preparing the lithium ion battery comprises the following steps: acquiring different conductivities of different active materials under a preset compaction density and types of batteries required to be prepared; selecting a first active material, a binder and a conductive agent to prepare a pole piece according to the different conductivities and the types of the batteries to be prepared; obtaining target porosity and target conductivity under a preset compaction density according to the pole piece; and preparing the battery according to the target porosity, the target conductivity and the type of the battery required to be prepared. Aiming at the defects of the current battery design, the lithium ion battery preparation method provided by the embodiment of the invention obtains reasonable designs which accord with different types of batteries by optimizing electrode compaction density and conductivity parameters according to the battery demand type, avoids the defect of long development period and improves the research and development efficiency.

Description

Lithium ion battery preparation method and lithium ion battery

Technical Field

The invention relates to the technical field of batteries, in particular to a lithium ion battery and a preparation method thereof.

Background

With the continuous development of new energy industry, power and energy storage batteries develop rapidly, with the development of positive electrode materials such as lithium iron phosphate, ternary (NCM, NCA) materials, lithium cobaltate, lithium manganate and the like and negative electrode materials such as natural graphite, artificial graphite, silicon carbon and the like, the technical route of the battery presents selection diversity and is continuously updated, and different application scenes have different requirements on the cycle capacity, the rate capability, the energy density and the like of the battery, such as the energy storage battery emphasizes the cycle performance, and the power battery emphasizes the energy density and the rate capability and the like. Thus, the design of the cell varies for different application scenarios, different electrochemical systems. The unreasonable battery design may cause the battery to be over-designed to cause waste, and the unreasonable design may also cause the battery to have poor cycle life, thereby causing potential safety hazards and other problems. Therefore, more efficient and rational battery design is needed to meet the diverse application requirements of batteries.

At present, lithium ion batteries of the same electrochemical system (the same type of anode and cathode materials) have basically the same preparation process, but have great differences in the design rate performance, energy density, cycle life and the like of different batteries. The main ideas of the current battery design optimization are as follows: the same anode and cathode materials can meet the use requirements through the previous data experience and formula fine adjustment design; for the design of new systems and new materials, a finished product battery is prepared by searching from the beginning, mixing slurry, coating, laminating or winding through orthogonal experiments, and then the battery design is optimized through electric performance and other performance tests and continuous experiments, so that the development period of the new battery is too long, and a large amount of resources are wasted.

Disclosure of Invention

The embodiment of the invention provides a lithium ion battery and a preparation method thereof, and aims to solve the problem that the development cycle of the existing battery is too long.

In order to solve the technical problems, the invention adopts the following technical scheme:

the embodiment of the invention provides a preparation method of a lithium ion battery, which comprises the following steps:

acquiring different conductivities of different active materials under a preset compaction density and types of batteries required to be prepared;

selecting a first active material, a binder and a conductive agent to prepare a pole piece according to the different conductivities and the types of the batteries to be prepared;

obtaining target porosity and target conductivity under a preset compaction density according to the pole piece;

and preparing the battery according to the target porosity, the target conductivity and the type of the battery required to be prepared.

Further, the obtaining different electrical conductivities of different active materials at preset compaction densities comprises:

selecting one active material from different active materials, stirring and mixing the active material with a binder and a conductive agent according to a preset proportion, and drying the mixed material to obtain a solid mixed material;

acquiring the conductivity under a preset compaction density according to the solid mixed material;

and after the conductivity of the different active materials under the preset compaction density is obtained, another active material in the different active materials is reselected, and the conductivity of the different active materials under the preset compaction density is obtained until the total conductivity of the different active materials under the preset compaction density is obtained.

Further, the obtaining of the electrical conductivity at a preset compaction density from the solid mixed material comprises:

grinding the dried solid mixed material for a preset time to obtain a powder;

wherein the compacted density is the mass of the powder/volume of the powder.

Further, the preset ratio includes:

93-97% of active material, 2-4% of binder and 1-4% of conductive agent.

Further, the types of the batteries required to be prepared comprise:

a power cell having an electrical conductivity greater than a first value and an energy density value greater than a second value; alternatively, the first and second electrodes may be,

an energy type battery, the energy type battery being a battery having a compaction density higher than a third value.

Further, the step of selecting a first active material, a binder and a conductive agent to prepare the pole piece according to the different conductivities and the types of the batteries to be prepared comprises the following steps:

and preparing the first active material, the binder and the conductive agent into a pole piece through the processes of mixing and coating.

Further, the obtaining of the target porosity and the target conductivity at the preset compaction density according to the pole piece includes:

according to the pole piece, obtaining a processing pole piece under a preset compaction density through rolling;

and analyzing according to the processing pole piece to obtain the target porosity under the preset compaction density, and obtaining the target conductivity through the preset compaction density.

Further, the preparing the battery according to the target porosity, the target conductivity and the type of the prepared battery, which is required, comprises:

analyzing the energy density and the power density of the pole piece according to the target porosity and the target conductivity;

acquiring electrode design parameters according to the energy density and the power density;

preparing a small soft package battery according to the electrode design parameters, and testing the electrical property and the cycle performance of the small soft package battery;

a battery was prepared according to the electrical and cycling properties.

The embodiment of the invention also provides a lithium ion battery which is prepared by adopting the preparation method of the lithium ion battery.

The invention has the beneficial effects that:

aiming at the defects of the current battery design, the preparation method of the lithium ion battery provided by the embodiment of the invention comprehensively considers factors such as energy density, power density, cycle life and the like according to the battery demand type, obtains reasonable designs conforming to different types of batteries by analyzing the conductivity and porosity of materials and electrodes and optimizing the electrode compaction density and conductivity parameters, and verifies and optimizes by preparing a soft package battery. According to the embodiment of the invention, the procedures of preparing the finished battery by multiple times of mixing, coating, laminating or winding in the formula design stage, testing the electrochemical performance and the like are omitted, and the soft package battery test is carried out only when verification is needed. The method can avoid the defects of long overall development period and high cost caused by material iteration or system change, and improve the research and development efficiency.

Drawings

Fig. 1 is a schematic flow chart of a method for manufacturing a lithium ion battery according to an embodiment of the present invention;

fig. 2 is a schematic diagram illustrating the cycle number of the lithium ion battery manufacturing method according to the embodiment of the present invention.

Detailed Description

In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments. In the following description, specific details such as specific configurations and components are provided only to help the full understanding of the embodiments of the present invention. Thus, it will be apparent to those skilled in the art that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

It should be appreciated that reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

In various embodiments of the present invention, it should be understood that the sequence numbers of the following processes do not mean the execution sequence, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.

The invention provides a preparation method of a lithium ion battery and the lithium ion battery, aiming at the problems of complex design steps and long manufacturing period of the conventional battery.

As shown in fig. 1, a method for preparing a lithium ion battery provided in an alternative embodiment of the present invention includes:

step 100, acquiring different conductivities of different active materials under a preset compaction density and types of batteries to be prepared;

200, selecting a first active material, a binder and a conductive agent to prepare a pole piece according to the different conductivities and the types of the batteries to be prepared;

step 300, acquiring a target porosity and a target conductivity under a preset compaction density according to the pole piece;

and 400, preparing the battery according to the target porosity, the target conductivity and the type of the battery required to be prepared.

In this embodiment, the lithium ion battery preparation method provided by the embodiment of the present invention, aiming at the defects of the current battery design, comprehensively considers factors such as energy density, power density, cycle life, and the like according to the battery demand type, obtains reasonable designs conforming to different types of batteries by analyzing the conductivity and porosity of materials and electrodes, optimizing electrode compaction density and conductivity parameters, and verifies and optimizes by preparing a soft package battery.

In an embodiment of the present invention, the step 100 includes:

110, selecting one active material from different active materials, stirring and mixing the active material with a binder and a conductive agent according to a preset proportion, and drying the mixed material to obtain a solid mixed material;

in this embodiment, one of the different active materials, a binder and a conductive agent are added into a small stirring tank according to a predetermined ratio, a certain amount of solvent is added, and the mixture is uniformly mixed by a small high-speed stirrer, wherein the solvent is generally N-methylpyrrolidone (NMP) as a positive electrode and deionized water as a negative electrode. Specifically, the preset proportion includes: 93-97% of active material, 2-4% of binder and 1-4% of conductive agent. Further, the uniformly mixed slurry was sufficiently dried by a forced air oven, and after the solvent was completely volatilized, the dried solid was sufficiently ground to a powder shape using a mortar for 30 min.

Step 120, acquiring the conductivity under a preset compaction density according to the solid mixed material;

further, grinding the dried solid mixed material for a preset time to obtain a powder;

wherein the compacted density is the mass of the powder/volume of the powder.

It should be noted that, a certain mass of ground powder is weighed according to the solid mixed material, the conductivity of the powder under the preset compaction density is obtained, that is, the conductivity of the powder under different compaction densities is measured by setting different compaction densities through a powder conductivity tester; presetting compaction densities as different compaction densities; the compaction density is the powder mass/powder volume, and the powder mass and the pole piece area are fixed during the compaction test, so the compaction density can be controlled by adjusting the height of the powder.

Step 130, after the conductivity at the preset compaction density is obtained, another active material in different active materials is reselected, and another conductivity at the preset compaction density is obtained until all conductivities of the different active materials at the preset compaction density are obtained.

This example compares the overall conductivity of different active materials at a preset compaction density until an active material meeting design requirements is selected. The method specifically comprises the steps of mixing selected active materials, a conductive agent and a binding agent according to different formulas, uniformly mixing the active materials, the conductive agent and the binding agent through a small high-speed stirrer, and testing the compacted densities of the different formulas and the conductivities of the different compacted densities through drying and grinding procedures.

In an embodiment of the present invention, the step 100 of obtaining the type of the battery to be prepared includes:

It should be noted that this example initially screened several designs suitable for different battery applications based on the compaction densities of different formulations and conductivity data for different compaction densities. Wherein the power type battery needs to have the conductivity higher than a first value and the energy density value higher than a second value, and the compaction density is higher than a third value on the premise that the energy type battery has long cycle life; and the first value, the second value and the third value are standard values which accord with the design battery.

Optionally, the step 200 includes:

and preparing the first active material, the binder and the conductive agent into a pole piece through the processes of mixing and coating. Here, the first active material is an active material preferably selected from different active materials; specifically, a small amount of pole pieces are prepared through the procedures of slurry mixing and coating by a small-sized stirrer.

Optionally, the step 300 includes:

The method includes the steps of obtaining a processing pole piece under preset compaction densities (different compaction densities) through rolling, analyzing the processing pole piece by using a full-automatic aperture analyzer, testing target porosity of the pole piece with different compaction densities, and obtaining target conductivity through the preset compaction densities.

In an embodiment of the present invention, the step 400 includes:

a battery was prepared according to the electrical and cycling properties.

In the embodiment, a curve graph is prepared according to the obtained target porosity and the target conductivity, energy density and power density are comprehensively considered according to the obtained conductivity curve and the porosity data and the type of the prepared battery, the compaction density and conductivity parameters of the electrode are optimized, the small soft package battery is prepared according to the optimized electrode design parameters, the small soft package battery is prepared according to the electrode design parameters, the electrical performance and the cycle performance of the small soft package battery are tested, and the battery design is continuously verified and optimized until the optimal design meeting the type of the prepared battery is obtained.

The above method is illustrated by an alternative embodiment.

For example, a power type lithium ion battery is designed according to requirements. Taking a lithium iron phosphate battery as an example, on the premise of keeping a battery cathode unchanged, the anode formula and the porosity of a pole piece are optimally designed.

The first step is as follows: selection of power type positive electrode material (active material). According to market research, three samples of the positive electrode materials (active materials) in the field of power batteries are selected preliminarily, namely a first sample, a second sample and a third sample, and the proper positive electrode materials (active materials) are selected by representing the intrinsic conductivity of raw materials. Since the positive electrode material powder was easily broken after being compacted, 3% of a binder (HSV900), i.e., a positive electrode material (active material): binder 97: 3. adding a positive electrode material (active material) and a binder into a stirring tank according to a ratio, adding a solvent, uniformly mixing by using a high-speed stirrer, drying by using a blast oven, fully grinding into powder by using a mortar, and testing the intrinsic conductivity of the material by using a conductivity meter, wherein the specific data are as shown in the following table 1:

TABLE 1 conductivity of different compacted densities, different samples

As can be seen from table 1, the second sample of the three samples has high conductivity, the polarization of the battery is small during high-rate charge and discharge, and the output power of the battery is higher under the same rate and system-on-chip, which best meets the design of a high-power battery, so that the material of the second sample is selected for further formula optimization and design of the porosity of a pole piece.

The second step is that: and optimizing the formula design of the high-power battery. In order to achieve high power cell design while ensuring high energy density of the cell, the current positive electrode material (active material) ratio is generally not less than 93%, while the fixed binder content is 3%. Therefore, the ratio of the positive electrode material (active material) and the conductive agent was formulated as shown in the following tables 2(1) and 2 (2). Adding a positive electrode material (active material), a conductive agent and a binder into a small stirring tank according to the proportion in tables 2(1) and 2(2), adding a certain amount of solvent, uniformly mixing by using a small high-speed stirrer, drying by using a forced air oven, fully grinding into powder by using a mortar, and testing the conductivity of the material by using a conductivity meter. The specific data are shown in the following tables 2(1) and 2 (2):

TABLE 2(1) conductivity at different conductive agent ratios, different compacted densities

TABLE 2(2) conductivity at different conductive agent ratios, different compacted densities

As can be seen from tables 2(1) and 2(2), the powder has higher and higher conductivity as the proportion of the conductive agent increases. However, when the proportion of the conductive agent exceeds 2%, the conductivity of the powder increases and slows, and when the proportion of the conductive agent exceeds 3%, the conductivity is basically not changed. The conductive agent addition ratio was determined to be 3% in consideration of both energy density requirements and cost.

The third step: and analyzing and designing the porosity of the optimized pole piece at different compaction densities. Mixing the positive electrode material (active material), the conductive agent and the binder according to a ratio of 94:3:3, and performing slurry mixing, coating and drying processes by using a small high-speed stirrer to prepare a small amount of pole pieces. Adjusting the compaction density of the pole piece through a roller press, analyzing the rolled pole piece through a full-automatic aperture analyzer, and testing the porosity of the pole piece with different compaction densities. Specific different compacted densities versus porosity can be shown by table 3:

TABLE 3 Effect of different compaction densities on porosity, gram Capacity and Capacity Retention

The purpose of the 500 cycles test in table 3 above is that the battery life begins to decay after normal heavy discharge of the lithium battery, typically 500 cycles.

In an alternative embodiment, data of normal discharge of the lithium ion battery at different compaction densities and different cycle times are obtained, and the data are analyzed to obtain fig. 2, where fig. 2 shows the influence of different compaction densities and different cycle times on the battery life, and the data are further analyzed from fig. 2 to obtain: under different compaction densities, the capacity retention rate after 500 cycles shows a tendency of increasing and then decreasing with the increase of the compaction density, and the cycle performance (service life) of the battery is influenced by too low or too high compaction density.

Specifically, table 4 shows data on the effect of different compaction densities and different cycle times on battery life, table 4 only shows part of the process data, not all data for 500 cycles are shown, and further data for 500 cycles are shown in fig. 2, where the cycle times are integers.

TABLE 4 Effect of different compaction Density, different cycle number on Battery Life

In a specific embodiment, a small pouch cell was prepared according to the above procedure: and (4) verifying and optimizing the design through the electrical property test of the soft package battery. And mixing the positive electrode material (active material), the conductive agent and the binder according to a ratio of 94:3:3, coating, rolling and laminating to prepare the small flexible package battery.

As can be seen from table 3, as the compaction density increases, the porosity gradually decreases, the gram capacity exertion and the 500cycle capacity retention rate of the material both show the tendency of increasing and then decreasing, when the compaction density is 2.3g/cm3, the capacity retention rate of the battery after 500 cycles is 98.6%, and when the compaction density is too low or too high, the cycle performance of the battery is reduced, because: on one hand, the porosity of the pole piece is reduced along with the increase of the compaction density, so that the full contact of material particles is facilitated, the contact internal resistance is reduced, the polarization of the battery is reduced, and the material capacity exertion and the cycle performance are facilitated; on the other hand, the too high compaction density causes the porosity of the pole piece to be too low, the poor electrolyte infiltration and liquid retention effects are poor, the electrolyte is difficult to permeate into the pole piece, and the material capacity exertion and the cycle performance are poor.

Therefore, by integrating the data of conductivity, compaction density, porosity and the like, the optimal design of the battery is determined through gram capacity exertion and cycle performance. For the design requirement, the second sample is selected in the final design, the proportion of the positive electrode material (active material), the conductive agent and the binder is 94:3:3, the compaction density is 2.3g/cm3, and the energy density and the power density of the designed battery are both optimized to the maximum extent. The method and the thought can be adopted in the design of energy type, long service life, low cost, extreme climate and other types of batteries, the research and development cost can be effectively reduced, the battery development period can be shortened, and the product development efficiency can be improved.

In summary, according to the preparation method of the lithium ion battery provided by the embodiment of the invention, for the defects of the current battery design, according to the type of the battery demand, the factors such as energy density, power density, cycle life and the like are comprehensively considered, the reasonable design conforming to different types of batteries is obtained by analyzing the conductivity and porosity of the material and the electrode, optimizing the electrode compaction density and conductivity parameters, and the verification and optimization are carried out by preparing the soft package battery.

According to the embodiment of the invention, the procedures of preparing the finished battery by multiple times of mixing, coating, laminating or winding in the formula design stage, testing the electrochemical performance and the like are omitted, and the soft package battery test is carried out only when verification is needed. The method can avoid the defects of long overall development period and high cost caused by material iteration or system change, and improve the research and development efficiency.

While the preferred embodiments of the present invention have been described, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.

Claims

1. A preparation method of a lithium ion battery is characterized by comprising the following steps:

2. The method for preparing a lithium ion battery according to claim 1, wherein the obtaining different electrical conductivities of different active materials at preset compaction densities comprises:

3. The method for preparing a lithium ion battery according to claim 2, wherein the obtaining of the conductivity at the preset compaction density according to the solid mixed material comprises:

grinding the dried solid mixed material for a preset time to obtain a powder;

wherein the compacted density is the mass of the powder/volume of the powder.

4. The method according to claim 2, wherein the predetermined ratio comprises:

93-97% of active material, 2-4% of binder and 1-4% of conductive agent.

5. The method for preparing the lithium ion battery according to claim 1, wherein the type of the battery to be prepared comprises:

6. The method for preparing the lithium ion battery according to claim 1, wherein the step of selecting the first active material, the binder and the conductive agent to prepare the pole piece according to the different conductivities and the types of the batteries to be prepared comprises the following steps:

7. The method for preparing the lithium ion battery according to claim 1, wherein the obtaining of the target porosity and the target conductivity at the preset compaction density according to the pole piece comprises:

8. The method of claim 7, wherein the preparing a battery according to the target porosity, the target conductivity and the type of battery required to be prepared comprises:

a battery was prepared according to the electrical and cycling properties.

9. A lithium ion battery prepared by the method of any one of claims 1 to 8.