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GB/T 42260-2022: Electrochemical performance test of lithium iron phosphate -- Test method for cycle life
GB/T 42260-2022
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.160
CCS H 21
GB/T 42260-2022
Electrochemical performance test of lithium iron phosphate
- Test method for cycle life
ISSUED ON: DECEMBER 30, 2022
IMPLEMENTED ON: APRIL 01, 2023
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Terms and definitions ... 4
4 Test conditions ... 4
5 Reagents and materials ... 4
6 Instruments and equipment ... 5
7 Test steps ... 7
8 Data recording and cycle life test ... 16
9 Allowable difference ... 17
10 Test report ... 17
Electrochemical performance test of lithium iron phosphate
- Test method for cycle life
1 Scope
This document describes the test method for cycle life of lithium iron phosphate, i.e.,
the cathode material for lithium-ion batteries.
This document applies to the test using the winding method for cycle life of lithium
iron phosphate, i.e., the cathode material for lithium-ion batteries.
2 Normative references
The following referenced documents are indispensable for the application of this
document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
GB/T 6682 Water for analytical laboratory use - Specification and test methods
GB/T 18287 General specification of lithium-ion cells and batteries for mobile
phone
3 Terms and definitions
There are no terms or definitions to be defined in this document.
4 Test conditions
Unless otherwise specified, each test step should be carried out at a relative humidity
not greater than 40.0 % and an ambient temperature of 20 ℃ ~ 30 ℃. The rolling
process should be carried out at a relative humidity not greater than 30.0 % and an
ambient temperature not greater than 30 °C.
5 Reagents and materials
5.1 Lithium iron phosphate: the particle size characteristic value (D50) is 0.5 μm ~ 8.0
μm, and the specific surface area is 6 m2/g ~ 30 m2/g.
5.2 Conductive agent: conductive carbon material.
5.3 Polyvinylidene fluoride (PVDF): battery grade, the weight average molecular
weight is not less than 5 × 105, and the moisture (mass fraction) is not greater than
0.10 %.
5.4 N-methylpyrrolidone (NMP): battery grade, the purity is not less than 99.9 %, and
the moisture (mass fraction) is not greater than 0.02 %.
5.5 Aluminum foil: the thickness is 8 μm ~ 20 μm.
5.6 Positive electrode tab (positive terminal): made of aluminum, with tab glue.
5.7 Lithium-ion battery separator: polyolefin porous membrane, the porosity is 35.0 %
~ 60.0 %, the air permeability is 100 s/100 mL ~ 500 s/100 mL, the average pore size
is not greater than 1.0 μm, and the thickness is 9.0 μm ~ 25.0 μm.
5.8 Graphite: D50 is 10.0 μm ~ 22.0 μm, the initial discharge specific capacity is not less
than 340.0 mA • h/g, and the initial charge-discharge efficiency is not less than 90.0 %.
5.9 Sodium carboxymethyl cellulose (CMC): the main content (mass fraction) is not
less than 99.5 %, and the relative molecular mass is 6.5 × 106.
5.10 Styrene-butadiene rubber emulsion (SBR): water-soluble binder, special for
lithium batteries, the solid content is 35 % ~ 52 %, the viscosity is 80 mPa • s ~ 400
mPa • s, and the pH is 6.0 ~ 7.0.
5.11 Deionized water: GB/T 6682, not less than grade three.
5.12 Copper foil: the thickness is 5 μm ~ 12 μm.
5.13 Negative electrode tab (negative terminal): made of nickel, with tab glue.
5.14 Aluminum plastic film: special for lithium batteries, and the thickness is 110 μm
~ 160 μm.
5.15 Polyimide tape.
5.16 Lithium-ion battery electrolyte: lithium-ion battery electrolyte composed of
lithium hexafluorophosphate (LiPF6) and mixed carbonate-based organic solvents
[ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC),
etc.], the moisture is not greater than 0.002 %, the free acid (HF) is not greater than
0.005 %, and the conductivity (25 ℃) is not less than 7.0 mS/cm.
5.17 Nitrogen (or argon): the purity (volume fraction) is not less than 99.99 %.
6 Instruments and equipment
6.1 Balance: the accuracy is 0.01 g.
7 Test steps
7.1 Preprocessing
7.1.1 Place lithium iron phosphate (5.1) and conductive agent (5.2) into a vacuum oven
(6.3); during drying, vacuum or circulate in a nitrogen (or argon) (5.17) atmosphere;
bake at a temperature of 100 ℃ ~ 150 ℃ for 2 h ~ 20 h to dry; cool to room temperature
and place in a desiccator (6.4).
7.1.2 Place PVDF (5.3) into a vacuum oven (6.3); during drying, vacuum or circulate
in a nitrogen (or argon) (5.17) atmosphere; bake at a temperature of 70 ℃ ~ 90 ℃ for
4 h ~ 6 h to dry; cool to room temperature and place in a desiccator (6.4).
7.2 Preparation of positive electrode sheets
7.2.1 Weighing
Calculate the lithium iron phosphate, conductive agent, and PVDF pretreated in 7.1
according to the mass fractions of 90 % ~ 97 %, 1 % ~ 5 %, and 2 % ~ 5 % respectively,
and weigh them with a balance (6.1). Calculate the amount of NMP (5.4) according to
the design requirements of solid content (mass fraction) of 40 % ~ 65 %, and weigh
with a balance (6.1).
7.2.2 Pulping
The cathode pulping process is as follows:
a) Add the weighed NMP into the mixing tank of a dispersing mixer (6.5); gradually
add the weighed PVDF; disperse and stir until completely dissolved; to prepare a
transparent glue;
b) Add the weighed conductive agent to the above transparent glue; vacuum,
disperse and stir evenly;
c) Gradually add the weighed lithium iron phosphate in portions; vacuum, disperse
and stir evenly;
d) Add another NMP according to the designed solid content (mass fraction), to
control the slurry viscosity at 4000 mPa • s ~ 8000 mPa • s; vacuum, disperse and
stir evenly; complete the pulping process.
NOTE: The solid content in this document is the ratio of the mass of the cathode active material
lithium iron phosphate, conductive agent, and PVDF to the mass of the cathode slurry.
7.2.3 Coating
digital thickness gauge (6.11) to measure the mass (mc) and thickness (dc) of the positive
electrode sheet, respectively.
Use a punching machine (6.10) to punch out an aluminum foil substrate with an area of
Sc, and use an electronic balance (6.2) and a desktop digital thickness gauge (6.11) to
measure the mass (mAl) and thickness (dAl) of the aluminum foil substrate, respectively.
The compacted density of the positive electrode sheet (ρc) is calculated according to
formula (1):
where:
ρc - the compacted density of the positive electrode sheet, in grams per cubic
centimeter (g/cm3);
mc - the mass of the positive electrode sheet, in grams (g);
mAl - the mass of the aluminum foil substrate, in grams (g);
Sc - the area of the positive electrode sheet, in square centimeters (cm2);
Dc - the thickness of the positive electrode sheet, in centimeters (cm);
dAl - the thickness of the aluminum foil substrate, in centimeters (cm).
Design according to the compacted density of 2.1 g/cm3 ~ 2.7 g/cm3, calculate the
theoretical thickness of the positive electrode sheet, use a roller machine (6.12) to roll
the positive electrode sheet after the secondary baking in 7.2.3 to the target thickness,
and operate according to the following steps:
a) Use an edge trimming machine (6.7) to trim the edges of the positive elect...