Anisotropic Intermediate Layer for Nonaqueous Battery Safety
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Solution Overview
Problem
Nonaqueous batteries face the challenge of short-circuiting during nail penetration, which generates excessive heat due to insufficient protection of the current collector by the intermediate layer, and the existing intermediate layers with conductivity issues lead to increased short-circuit currents.
Innovation Solution
Incorporating graphite particles with a specific alignment and structure in the intermediate layer, where the basal planes are parallel to the thickness direction, and using insulating particles in higher proportions to minimize in-plane conductivity, thereby reducing the likelihood of short-circuit currents during nail penetration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an intermediate layer with high conductivity is used to ensure good conduction between active material layer and current collector, then battery capacity is improved, but short-circuit current increases during nail penetration
Solution Approach 1:
The intermediate layer is designed with spatially varying conductivity: high conductivity in the thickness direction (parallel to current flow during normal operation) and low conductivity in the in-plane direction (parallel to current flow during nail penetration). This is achieved by using plate-like graphite particles with specific orientation, creating anisotropic electrical properties that simultaneously satisfy both conduction and safety requirements
Solution Approach 2:
The intermediate layer combines plate-like graphite particles with insulating particles to create a composite structure. The graphite particles provide conductivity in the thickness direction while the insulating particles reduce in-plane conductivity during nail penetration. This composite approach enables the layer to exhibit different electrical properties in different directions, resolving the contradiction between capacity and safety
2Reliability
If an intermediate layer with high electrical resistance is used to prevent short-circuiting, then safety is improved, but conduction between active material layer and current collector becomes insufficient
Solution Approach 1:
The intermediate layer exhibits different electrical resistance in different directions: low resistance in the thickness direction for adequate conduction during normal operation, and high resistance in the in-plane direction to prevent short-circuiting during nail penetration. This directional resistance control resolves the contradiction between safety and capacity
Solution Approach 2:
The electrical resistance parameter of the intermediate layer is changed from being isotropic (same in all directions) to anisotropic (different in different directions) by controlling the orientation of plate-like graphite particles. This parameter transformation enables the layer to provide both low resistance for conduction and high resistance for safety simultaneously
3Reliability
If the intermediate layer contains only insulating particles, then protection of current collector is improved, but conductivity becomes insufficient
Solution Approach 1:
The intermediate layer combines insulating particles for protection with plate-like graphite particles for conduction, creating a composite structure where different regions serve different functions. The graphite particles provide conductivity in the thickness direction while the insulating particles provide protection, resolving the contradiction between protection and conduction
4Ease of manufacture
If graphite particles are randomly oriented in the intermediate layer, then manufacturing is simplified, but short-circuit current increases during nail penetration
Solution Approach 1:
The plate-like graphite particles are pre-oriented in a specific direction (with basal planes parallel to the thickness direction of the intermediate layer) before the layer is finalized. This preliminary orientation action ensures low in-plane conductivity during nail penetration while maintaining manufacturing feasibility through controlled particle alignment processes
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 aligned graphite particles and insulating particles effectively prevent short-circuit currents and reduce heat generation by ensuring minimal current flow in the in-plane direction of the intermediate layer, enhancing the safety and performance of nonaqueous batteries.
Implementation Method 1
a short-circuit current is thought to flow in the nail and there is greater Joule heat
Implementation Method 2
The graphite crystal has anisotropy in conductivity. That is, a current is likely to flow in a direction parallel to the basal plane, and a current is unlikely to flow in the c axis direction
Data Source
AI summary
A nonaqueous battery includes a positive electrode and a negative electrode. At least one of the positive electrode and the negative electrode includes a current collector, an intermediate layer, and an active material layer. The intermediate layer is interposed between the current collector and the active material layer and includes graphite particles and insulating particles. In a cross section of the intermediate layer in a thickness direction, a major axis diameter of the graphite particles is equal to or greater than the thickness of the intermediate layer. In X-ray diffraction measurement of the intermediate layer by an out-of-plane method, a ratio of an intensity of an 110 diffraction line of a graphite crystal to an intensity of a 002 diffraction line of the graphite crystal is 0.0011 or more.