Non-graphitizable Carbon Negative Electrode Thickness Design
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Solution Overview
Problem
When non-graphitizable carbon is used as the negative active material in energy storage devices to increase capacity, it leads to a decrease in durability due to low electrode potential and increased resistance after charge-discharge cycles.
Innovation Solution
An energy storage device design where the negative active material layer on the electrode substrate has a thicker end edge than the central portion, and the true density of non-graphitizable carbon is within specific ranges, along with a porosity of 50% or more in the separator and the use of a cellulose derivative binder, to suppress the deposition of metallic lithium and maintain capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If non-graphitizable carbon is used as negative active material to increase capacity, then the chargeable/dischargeable capacity per unit mass increases, but the potential becomes low causing metallic lithium deposition and deterioration in durability
Solution Approach 1:
The negative active material layer is designed with non-uniform thickness where at least one end edge side is thicker than the central portion. This local variation in thickness creates different electrical characteristics in different regions of the electrode, preventing uniform lithium deposition and improving durability while maintaining high capacity
Solution Approach 2:
The patent introduces asymmetric thickness distribution in the negative active material layer by making at least one end edge side thicker than the central portion. This asymmetric structure disrupts the uniform potential distribution during charging, preventing metallic lithium deposition and improving battery durability
2Quantity of substance
If the depth of charge of the negative electrode is increased to increase capacity, then the capacity increases, but the potential becomes low causing metallic lithium deposition and increased resistance
Solution Approach 1:
By creating regions of different thickness in the negative active material layer, the patent establishes local variations in electrical potential and current density. This prevents uniform lithium ion insertion and reduces the risk of metallic lithium deposition even at high depth of charge
Solution Approach 2:
The non-uniform thickness structure is pre-designed into the negative active material layer before battery operation. This preliminary structural arrangement ensures that during subsequent charging cycles, lithium ions are distributed more uniformly, preventing deposition before it can occur
Data Source
AI summary
An energy storage device according to one aspect of the present invention includes: a negative electrode including a negative electrode substrate and a negative active material layer layered directly or indirectly on a surface of the negative electrode substrate; and a positive electrode. The negative active material layer contains a negative active material. The negative active material contains non-graphitizable carbon. In one direction of the negative electrode substrate, at least one end edge side of the negative active material layer is thicker than a central portion present between the one end edge side and the other end edge side facing the one end edge side. When a true density of the non-graphitizable carbon is A [g/cm3], an amount of charge B [mAh/g] of the negative electrode in a fully charged state satisfies the following formula 1.−173XA+1588≤B≤-830A+1800