Silicon Negative Electrode with Silicon Oxide Buffering
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Solution Overview
Problem
Non-aqueous electrolytic secondary batteries using metal lithium as a negative electrode active material face issues with short battery life due to dendrite formation and safety concerns, while alternative materials like silicon offer high energy density but suffer from volume changes that lead to pulverization and capacity deterioration.
Innovation Solution
A negative electrode structure is developed with a current collector and a mixture containing a binder, conductive agents, and active materials like silicon and carbon, where the silicon phase is dispersed in a silicon oxide phase to alleviate volume expansion and maintain particle structure, along with a specific thickness and composition range to enhance cycle life and discharge characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If metal lithium is used as negative electrode active material, then energy density is improved, but dendrite formation occurs causing short battery life and safety problems
Solution Approach 1:
The patent uses a sacrificial aluminum layer that intentionally allows dendrite formation and consumption during initial cycles. This disposable layer protects the main lithium electrode by absorbing dendrite growth, extending the overall battery life while maintaining high energy density from the lithium active material.
2Quantity of substance
If silicon is used as negative electrode active material, then capacity per mass is improved (10 times larger than graphite), but volume change causes pulverization and poor cycle life
Solution Approach 1:
The patent controls the particle size of silicon to 10 μm or less and adjusts the aluminum content to 1-50 mass% of the silicon. These parameter changes reduce the overall volume expansion effect and prevent pulverization, allowing silicon's high lithium occlusion capacity (1:4.4 ratio) to be utilized effectively over many cycles.
Solution Approach 2:
The patent creates a composite material combining silicon particles with aluminum. The aluminum component buffers the volume expansion of silicon during lithium insertion and desorption, preventing pulverization while maintaining the high capacity benefits of silicon. This composite structure resolves the contradiction between high capacity and cycle stability.
3Duration of action of stationary object
If aluminum is added to negative electrode mixture, then cycle characteristics are improved by buffering volume change, but excessive aluminum reduces battery capacity
Solution Approach 1:
The patent precisely controls the aluminum content to be 1-50 mass% of the silicon content in the negative electrode mixture. This optimized ratio ensures sufficient aluminum is present to buffer volume expansion and improve cycle life, while preventing excessive aluminum from occupying too much space and reducing overall battery 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 proposed electrode structure significantly improves cycle life and discharge characteristics by preventing pulverization and maintaining conductivity, while the silicon oxide phase effectively buffers lithium insertion and desorption stress, enhancing the battery's overall performance.
Implementation Method 1
silicon is capable of occluding lithium up to a ratio of a silicon atom to a lithium atom being 1:4.4
Implementation Method 2
silicon makes a large change in volume which accompanies insertion and desorption of lithium in a charge and discharge cycle
Data Source
AI summary
An electrode has a current collector and an electrode mixture containing a binder and an active material particle selected from at least one of a carbonaceous material, a metal particle and a metal oxide particle formed on the current collector. When cutting strength of an interface between the current collector and the electrode mixture is represented by “a” and cutting strength in a horizontal direction within the electrode mixture is represented by “b”, the “a” and “b” satisfy a relation of a/b>1.