Spherical Graphite Negative Electrode for Lithium Battery Swelling Control
Solution Overview
Problem
Lithium secondary batteries face challenges in achieving high electrode densities while maintaining excellent battery characteristics, such as charge-discharge efficiency, load characteristics, and minimizing swelling and gas generation, due to issues with graphite particle orientation, reactivity with electrolytes, and irreversible capacity.
Innovation Solution
A graphite powder with specific properties, including a tap density between 0.8 and 1.35 g/cm3, a BET specific surface area between 2.5 and 7.0 m2/g, and a Raman R value between 0.02 and 0.05, is used, and a method involving heat treatment of natural graphite at temperatures between 1600°C and 3200°C to produce a negative-electrode material that requires minimal pressing load and exhibits high discharge capacity and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If natural graphite is used to achieve high discharge capacity and low pressing load, then battery capacity increases and electrode formation becomes easier, but graphite particles orient parallel to current collector causing accelerated swelling and reduced battery capacity
Solution Approach 1:
The patent applies spheroidization treatment to convert flaky natural graphite particles into spherical particles. This curvature change prevents the flat particles from orienting parallel to the current collector during electrode formation, thereby suppressing graphite intercalation compound formation and electrode swelling while maintaining high discharge capacity
Solution Approach 2:
The patent changes the shape parameter of graphite particles from flaky to spherical through spheroidization treatment. This parameter change fundamentally alters the particle orientation behavior during electrode formation, resolving the contradiction between maintaining high capacity and controlling swelling
2Quantity of substance
If electrode density is increased to achieve higher battery capacity, then energy density improves, but irreversible capacity increases due to enhanced reaction with liquid electrolyte
Solution Approach 1:
The patent changes the surface area parameter by sphericalizing the graphite particles, which reduces the specific surface area compared to flaky particles. This parameter change decreases the reaction sites available for electrolyte interaction, thereby reducing irreversible capacity while allowing higher electrode density
Solution Approach 2:
The patent creates a simplified spherical particle morphology that replicates the essential function of graphite (lithium insertion/extraction) while eliminating the harmful orientation effect of flaky particles, enabling high density without excessive irreversible capacity
3Quantity of substance
If mechanical energy treatment is applied to produce roundish particles with isotropic crushed surfaces, then packing efficiency and capacity increase, but crystallinity decreases requiring additional heat treatment
Solution Approach 1:
The patent applies spheroidization treatment to create spherical particles with isotropic surfaces, achieving high packing efficiency while preserving the crystalline structure of natural graphite, eliminating the need for additional heat treatment to restore crystallinity
4Quantity of substance
If high electrode density is used to increase battery capacity, then energy density improves, but pore volume decreases reducing load characteristics
Solution Approach 1:
The patent uses spherical graphite particles that pack efficiently while maintaining inter-particle void spaces, preserving pore volume even at high electrode density, thereby maintaining good load characteristics alongside high capacity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables lithium secondary batteries to operate with a balance of excellent battery characteristics, including high charge-discharge efficiency, reduced swelling, and low gas generation, even at high electrode densities, while being produced efficiently and cost-effectively.
Implementation Method 1
heat-treated at a temperature of 1600° C. or higher and 3200° C. or lower
Data Source
AI summary
A negative-electrode material is provided that can be produced at a low cost and yields a lithium secondary battery with an excellent balance of various battery characteristics even when used in high electrode densities.It has a graphite powder with a tap density of 0.80 g/cm3 or higher and 1.35 g/cm3 or lower, an amount of surface functional groups, O/C value, of 0 or larger and 0.01 or smaller, a BET specific surface area of 2.5 m2/g or larger and 70 m2/g or smaller, a Raman R value of 0.02 or larger and 0.05 or smaller.