Graphite Composite Electrode for Lithium Deposition Suppression
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Solution Overview
Problem
Lithium-ion secondary batteries for electric vehicles face challenges in achieving high energy density while suppressing metallic lithium deposition during overcharge, as existing negative electrode materials compromise between charge/discharge capacity and deposition resistance.
Innovation Solution
An electrode comprising graphite, a binding agent, and a non-graphitic carbonaceous material, optimized with specific structural and compositional features such as a CV area ratio, electrode mixture density, and pore volume, to enhance lithium ion storage and suppress metallic lithium deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If non-graphitic carbonaceous material is mixed in graphite to suppress metallic lithium deposition, then resistance to deposition of metallic lithium is improved, but energy density decreases
Solution Approach 1:
The invention applies local quality by creating a specific surface structure on graphite particles where non-graphitic carbonaceous material is selectively positioned on the surface rather than uniformly mixed throughout. This surface-localized approach provides lithium deposition suppression at the critical interface while preserving the bulk graphite's high capacity for lithium insertion, thus maintaining energy density.
Solution Approach 2:
The invention uses composite materials by combining graphite and non-graphitic carbonaceous material in a specific configuration where the non-graphitic material forms a surface layer or coating on graphite particles. This composite structure leverages the high capacity of graphite and the deposition-suppressing properties of non-graphitic carbon, achieving both goals simultaneously.
2Reliability
If non-graphitic carbonaceous material is added to suppress lithium deposition, then safety in repeated charge/discharge is improved, but charge/discharge capacity per volume decreases
Solution Approach 1:
The invention applies partial action by using a controlled, limited amount of non-graphitic carbonaceous material specifically on the particle surfaces rather than bulk mixing. This partial incorporation provides sufficient safety benefits for repeated charge/discharge while minimizing the impact on volumetric capacity, avoiding excessive addition that would unnecessarily reduce energy density.
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 optimized electrode achieves a high charge/discharge capacity per volume while effectively preventing metallic lithium deposition, ensuring safer and longer battery life for electric vehicles.
Implementation Method 1
a non-graphitic carbonaceous material... can be expected to exhibit a certain degree of the suppression effect of metallic lithium deposition in overcharge
Data Source
AI summary
The present invention relates to an electrode including at least graphite, a binding agent, and a non-graphitic carbonaceous material, in which, in a half-cell produced with the electrode as a working electrode, Li foil as a counter electrode, and a solution in which lithium hexafluorophosphate is dissolved at a concentration of 1 mol/L in a mixed solution of ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate at a volume ratio of 1/1/1, as an electrolytic solution:(A) a ratio of an area of a region A to an area of a region B (A/B) is 4.0% or more, in which the areas are calculated based on the following reference points in a cyclic voltammogram obtained by doping the electrode with lithium until a cell voltage of 0.01 V is achieved, and then sweeping the cell voltage from +0.01 V to −0.05 V toward the reduction side and further sweeping the cell voltage to +0.5 V toward the oxidation side at a sweeping rate of 0.01 mV/s in cyclic voltammetry:E1: a point at which an absolute value of current in a range of −0.05 V≤E1≤0.01 V in a current-voltage curve on the reduction side is minimumE2: an intersection point of a tangent line on which a slope in a range of −0.05 V≤E2≤0.01 V in a current-voltage curve on the reduction side is maximum, with a coordinate axis of voltage (current=0 mA)E3: a point at which an absolute value of current in a range of 0.05 V≤E3≤0.1 V in a current-voltage curve on the oxidation side is minimumE4: a point at which a voltage of 0.3 V is achieved in a current-voltage curve on the oxidation side;the region A:a region surrounded by the current-voltage curve on the reduction side, a straight line passing through the reference point E1 and orthogonal to the coordinate axis of voltage (current=0 mA), a straight line passing through the reference point E2 and orthogonal to the coordinate axis of voltage (current=0 mA), and the coordinate axis of voltage (current=0 mA); andthe region B:a region surrounded by the current-voltage curve on the oxidation side, a straight line passing through the reference point E3 and orthogonal to the coordinate axis of voltage (current=0 mA), a straight line passing through reference point E4 and orthogonal to the coordinate axis of voltage (current=0 mA), and the coordinate axis of voltage (current=0 mA); and(B) an electrode mixture density at a charge depth of 50% is 1.30 g/cm3 or more under the assumption that a capacity in doping of the electrode with lithium until a cell voltage of 0.05 V is achieved is a charge depth of 100%.