CN-121995240-A - Method for evaluating structural stability of lithium iron phosphate electrode based on button cell pressure effect and application thereof

CN121995240ACN 121995240 ACN121995240 ACN 121995240ACN-121995240-A

Abstract

The invention discloses a method for evaluating structural stability of a lithium iron phosphate electrode based on a button cell pressure effect and application thereof, wherein a to-be-tested sample is assembled into two groups of button cells with different internal pressures, charge and discharge tests are respectively carried out, discharge specific capacity under 1C multiplying power and 3.2V voltage platform duty ratio are recorded and calculated, absolute values of differences of average values of the two groups of button cells |Δ1C| and |Δr 3.2V | are calculated, and structural stability of the lithium iron phosphate electrode is evaluated based on the absolute values of the differences of the average values of the two groups of button cells |Δ1C| and |Δr 3.2V |. The method has the advantages that in the button cell tests with different internal pressures and different types, particularly in the case of 1C and above multiplying power, the obvious difference exists in the electrical performance is closely related to the particle morphology (particularly the content of large-size framework particles) of the material, the stability of the electrode material when the electrode material is pressed can be represented, the concept of a pressure sensitivity coefficient is provided and verified, the process adaptability of the material in mass production is effectively predicted, and a new optimization direction is indicated for material research.

Inventors

AN JIANHONG
SHI YINGFEI
SHI YI
JIANG JINYAN
Lou Xunnan
LI YULONG
SHI JUNFENG

Assignees

锂源(深圳)科学研究有限公司
常州锂源新能源科技有限公司
锂源(亚太)新能源科技有限公司

Dates

Publication Date: 20260508
Application Date: 20260210

Claims (10)

1. A method for evaluating structural stability of a lithium iron phosphate electrode based on button cell pressure effect, comprising the steps of: Assembling lithium iron phosphate samples to be tested into two groups of button cells with different internal pressures, respectively performing charge and discharge tests, and recording the discharge specific capacity under 1C multiplying power and the 3.2V voltage platform duty ratio; Respectively calculating the average value of the specific capacity of the performance discharge of each group of button cells under the 1C multiplying power and the duty ratio of a 3.2V voltage platform; The absolute value of the difference between the average value of the discharge specific capacity of the two groups of button cells under the 1C rate performance and the 3.2V voltage platform duty ratio is calculated as follows: |Δ1C|=|1C 1 -1C 2 |; |Δr 3.2v |=|r 3.2V1 -r 3.2V2 |; evaluating the structural stability of the lithium iron phosphate electrode based on |Δ1c| and |Δr 3.2V |; Wherein, the average value of the discharge specific capacity of the first group of button cells under the 1C multiplying power performance and the 3.2V voltage platform ratio is 1C 1 and r 3.2V1 , and the average value of the discharge specific capacity of the second group of button cells under the 1C multiplying power performance and the 3.2V voltage platform ratio is 1C 2 and r 3.2V2 .
2. The method for evaluating structural stability of a lithium iron phosphate electrode based on a button cell pressure effect according to claim 1, the two groups of button cells with different internal pressures are selected from 2016 button cells and 2430 button cells or 2016 button cells and 2032 button cells.
3. The method for evaluating structural stability of a lithium iron phosphate electrode based on a coin cell pressure effect of claim 1, wherein the lithium iron phosphate electrode material is determined to be insensitive to pressure if |Δ1c| is 3mAH/g or less and |Δr 3.2V | is 3% or less.
4. The method for evaluating the structural stability of a lithium iron phosphate electrode based on the pressure effect of a button cell according to claim 3, wherein the lithium iron phosphate electrode structure is determined based on |Δ1c| and |Δr 3.2V | and the powder resistivity, and is of an intrinsic electron conductivity type if |Δ1c| is 3mAH/g or less and |Δr 3.2V | is 3% or less and the powder resistivity is 10 Ω -cm or less, and is of a physical skeleton type if |Δ1c| is 3mAH/g or less and |Δr 3.2V | is 3% or less and the powder resistivity is 10 Ω -cm or more.
5. The method for evaluating the structural stability of a lithium iron phosphate electrode based on the pressure effect of a button cell according to claim 1, wherein at least 5 button cells of the same model are assembled.
6. The method of assessing the structural stability of a lithium iron phosphate electrode based on the pressure effect of a button cell of claim 5 wherein the assembled plurality of button cells require at least 3 hours of rest prior to testing.
7. The method for evaluating structural stability of a lithium iron phosphate electrode based on a button cell pressure effect according to claim 6, wherein the assembled plurality of button cells are subjected to a charge-discharge test at 25±0.5 ℃.
8. The method for evaluating the structural stability of a lithium iron phosphate electrode based on the pressure effect of a button cell according to claim 1, wherein the ratio of active material to conductive agent to binder in the plurality of button cells is 90:5:5.
9. The method for evaluating structural stability of a lithium iron phosphate electrode based on a button cell pressure effect according to claim 1, wherein the button cell is assembled in an argon glove box, the counter electrode is a metal lithium sheet, the assembling sequence of the battery is positive electrode shell, 1-2 drops of electrolyte, positive electrode sheet, 4-5 drops of electrolyte, diaphragm, 1-2 drops of electrolyte, lithium sheet, nickel screen, negative electrode shell, and the battery is sealed by an electric sealing machine under the pressure of 600-700kg for 3-5s.
10. Use of the method for evaluating structural stability of lithium iron phosphate electrode based on button cell pressure effect according to claim 1 in research of performance of lithium iron phosphate positive electrode material.

Description

Method for evaluating structural stability of lithium iron phosphate electrode based on button cell pressure effect and application thereof Technical Field The invention relates to a method for testing the performance of a lithium iron phosphate electrode material, in particular to a method for evaluating the structural stability of a lithium iron phosphate electrode based on a button cell pressure effect and application thereof. Background Lithium iron phosphate (LiFePO 4) has become an important positive electrode material in the fields of power batteries and energy storage batteries because of the advantages of high safety, long cycle life, relatively low cost and the like. However, its low intrinsic electron conductivity and slow lithium ion diffusion rate limit its high rate performance. In order to improve its performance, button cells are standard tools for assessing its electrochemical performance in material development and quality control. At present, the materials meeting the preliminary screening conditions are primarily screened according to conventional indexes such as powder resistivity of the materials, buckling performance under a single test condition and the like in the industry, and the materials are further processed into full electricity for processing performance and electrical performance evaluation. The laboratory generally uses button cell battery cases with 2430 (diameter 24mm, height 3.0 mm) or 2016 (diameter 20mm, height 1.6 mm) specifications for testing, and concerns the absolute performance (such as gram capacity and multiplying power performance) of materials under a single testing condition, however, the performance of button cell batteries with different specifications is different, but the testing results of the button cell battery cases with different specifications are currently generally regarded as equivalent or normal measuring errors. In addition, in the conductivity test of materials, the intrinsic electronic conductivity (powder resistivity) of the materials is generally focused, however, after the powder materials are made into batteries, the electrical performance is not only affected by the powder resistivity of the materials, but also affected by the battery structure, and the electric performance of the batteries is affected by the fact that the electric carrier concentration and mobility are required to be affected by the larger internal pressure. Therefore, only the powder resistivity of the material is focused on and does not fully represent the performance of the electrode material in the practical application environment. How to analyze the performance of the material as early and comprehensively as possible, how to evaluate the stability of the material in a battery electrode conductive network, how to evaluate the sensitivity of the material to the internal pressure of the battery and whether the rate performance is influenced by the internal pressure of the battery, thereby providing prospective guidance for the design and production of the material, and being the target pursued by research personnel. Disclosure of Invention Aiming at different lithium iron phosphate positive electrode materials, in the button cell test with different internal pressures, particularly, the electric performance (such as discharge specific capacity and voltage platform duty ratio) under the 1C and above multiplying power is obviously different, the amplitude of the difference is different from sample to sample, in order to fully research the material performance information contained in the difference, rather than stand alone or attribute the data to experimental errors, the performance of the lithium iron phosphate positive electrode material is evaluated as early as possible and comprehensively, so that whether the material is sensitive to pressure in practical cell application or not is predicted, whether a conductive network is stable or not is predicted, the advantages and disadvantages of the material are effectively distinguished, the basis is provided for the selection of the material, the performance of the positive electrode material is fully exerted, and the method for evaluating the structural stability of the lithium iron phosphate electrode based on the pressure effect of the button cell is provided. The technical scheme is that the method for evaluating the structural stability of the lithium iron phosphate electrode based on the button cell pressure effect comprises the following steps: Assembling lithium iron phosphate samples to be tested into two groups of button cells with different internal pressures, respectively performing charge and discharge tests, and recording the discharge specific capacity under 1C multiplying power and the 3.2V voltage platform duty ratio; Respectively calculating the average value of the specific capacity of the performance discharge of each group of button cells under the 1C multiplying power and the duty ratio of a 3.2V v