Composite Graphite Particle for High-Density Battery Negative Electrodes
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Solution Overview
Problem
Nonaqueous secondary batteries face challenges in achieving high energy density and excellent charge/discharge characteristics due to increased charge/discharge irreversible capacity and cycle deterioration when the active material layer on the negative electrode is highly densified.
Innovation Solution
A composite graphite particle is developed, comprising a spherical graphite particle and a graphitized binder, with specific structural and physical properties, including controlled diameter ratios, BET specific surface area, tap density, and pore volume, to enhance charge acceptance and cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the active material layer is highly densified to obtain high capacity, then the energy density is improved, but the charge/discharge irreversible capacity increases and cycle deterioration occurs
Solution Approach 1:
The patent uses a composite graphite particle consisting of flake graphite and spherical graphite components, where the spherical graphite acts as a binder and structural framework. This composite structure enables high densification of the active material layer while maintaining good cycle characteristics and charge acceptance, resolving the contradiction between energy density and reliability.
Solution Approach 2:
The patent controls specific parameters of the spherical graphite component including its content (0.1-10 mass%), particle size distribution (d50, d90, d10 ratios), and BET specific surface area (1.6-5.0 m2/g). By optimizing these parameters, the invention achieves both high energy density through densification and excellent cycle characteristics.
2Quantity of substance
If the active material layer is highly densified to obtain high capacity, then the energy density is improved, but the charge acceptance becomes insufficient
Solution Approach 1:
The composite graphite particle structure with spherical graphite component provides both high density for energy density and sufficient porosity for electrolyte penetration. This enables the electrode to achieve high capacity while maintaining good charge acceptance characteristics.
Solution Approach 2:
The spherical graphite component creates a porous network structure within the densified active material layer. This porous structure allows electrolyte to penetrate effectively, ensuring good charge acceptance even at high electrode densities.
3Ease of manufacture
If natural graphite is used as starting material, then the cost is reduced, but the charge/discharge irreversible capacity increases and cycle characteristics deteriorate
Solution Approach 1:
The patent combines flake graphite (from natural graphite) with spherical graphite component to create a composite structure. This composite approach maintains the cost advantage of natural graphite while the spherical component provides structural integrity and reduces irreversible capacity, improving cycle characteristics.
Solution Approach 2:
The introduction of spherical graphite component transforms the conventional flake graphite structure into a composite with spherical elements. This spheroidality improves particle packing, reduces void spaces, and enhances electrochemical performance while maintaining cost-effectiveness.
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 composite graphite particle enables a nonaqueous secondary battery with reduced initial charge/discharge irreversible capacity and improved high-capacity retention, maintaining excellent charge acceptance and cycle performance even at high electrode densities.
Implementation Method 1
a composite graphite particle (B) obtained by forming a composite of a spherical graphite particle (A) and a graphitized product of graphitizable binder
Implementation Method 2
graphitized product of graphitizable binder
Implementation Method 3
nonaqueous secondary battery having a high energy density and excellent large-current charge/discharge characteristics
Data Source
AI summary
To provide a nonaqueous secondary battery exhibiting a sufficiently small charge/discharge irreversible capacity in the initial cycle, exhibiting an excellent charge acceptance and excellent cycle characteristics, even when the negative electrode material-containing active material layer on a current collector is highly densified so as to obtain a high capacity. A composite graphite particle for nonaqueous secondary batteries, which is a composite graphite particle (B) obtained by forming a spherical graphite particle (A) and a graphitized product of graphitizable binder, wherein the spherical graphite particle (A) is a specific graphite particle or the composite graphite particle satisfies (a) and/or (b):(a) assuming that the cumulative 50% diameter (d50 size), 90% diameter (d90 size) and 10% diameter (d10 size) of the (A) by a laser diffraction method are D50(A), D90(A) and D10(A), respectively, and the cumulative 50% diameter (d50 size), 90% diameter (d90 size) and 10% diameter (d10 size) of the (B) by a laser diffraction method are D50(B), D90(B) and D10(B), respectively, the composite graphite particle satisfies all of (formula 1), (formula 2) and (formula 3):1.1≦D50(B)/D50(A)≦2.0 (formula 1)1.1≦D90(B)/D90(A)≦2.4 (formula 2)1.0≦D10(B)/D10(A)≦1.8 (formula 3)(b) assuming that the value of 110(A)/004(A) which is the ratio between 110 plane and 004 plane measured from XRD of the (A) is x and the value of 110(B)/004(B) which is the ratio between 110 plane and 004 plane measured from XRD of the (B) is y, the ratio z therebetween is defined by the following formula and z is from 1.2 to 3.5:z=y/x.