Preloading Lithium Ion Negative Electrodes
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Solution Overview
Problem
High capacity active materials like silicon, germanium, and tin are not widely adopted in lithium ion cells due to significant volume changes during cycling, leading to stress, fractures, and lithium loss due to SEI layer formation, which reduces battery capacity and stability.
Innovation Solution
Incorporating a lithium containing material into the negative electrode before the first cycle, with a concentration of 5-25% of the theoretical capacity, to mitigate lithium losses and maintain the electrode in a partially charged state, using nanostructures and varying lithium concentration profiles to minimize mechanical and electrical degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high capacity active materials like silicon are used in negative electrodes, then the theoretical capacity increases significantly, but the volume changes during cycling cause stress, fractures, and lithium loss
Solution Approach 1:
The silicon active material is divided into nanowires with small cross-sectional dimensions. This segmentation reduces the volume change stress within each individual wire during lithiation/delithiation cycling, preventing fractures and pulverization while maintaining high capacity. The nanoscale segmentation allows the material to accommodate volume expansion without structural failure.
Solution Approach 2:
The negative electrode is pre-loaded with lithium before the first cycle at a concentration of 5-25% of theoretical capacity. This preliminary lithium insertion compensates for the lithium that will be consumed during SEI layer formation in subsequent cycles, ensuring that sufficient lithium remains available for charge-carrying functions and maintaining electrode stability.
2Strength
If the active material structure is reduced to small sizes to minimize stress, then fracture resistance improves, but the surface area exposed to electrolyte increases, consuming more lithium for SEI layer formation
Solution Approach 1:
The negative electrode is pre-loaded with lithium before the first cycle at a concentration of 5-25% of theoretical capacity. This preliminary lithium insertion compensates for the lithium that will be consumed during SEI layer formation, ensuring that sufficient lithium remains available for charge-carrying functions while allowing the use of small-scale nanowire structures.
Solution Approach 2:
The lithium concentration in the negative electrode is optimized to a specific range (5-25% of theoretical capacity). This parameter adjustment balances the competing requirements: providing enough lithium to form protective SEI layers on the high-surface-area nanowires while retaining sufficient lithium for electrochemical cycling and maintaining overall cell capacity.
3Duration of action of stationary object
If lithium is added to compensate for SEI layer formation, then capacity retention improves, but the device complexity increases
Solution Approach 1:
The negative electrode is pre-loaded with lithium before the first cycle at a concentration of 5-25% of theoretical capacity. This single preliminary step compensates for lithium losses during SEI formation and maintains capacity retention throughout cycling, avoiding the need for complex ongoing adjustments or additional components.
Solution Approach 2:
The pre-loaded lithium in the negative electrode serves multiple functions automatically: it compensates for SEI layer formation, maintains lithium balance during cycling, and ensures sufficient lithium availability for charge-carrying functions. This self-service approach improves cycle life without requiring external intervention or complex control systems.
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
This approach reduces lithium loss and mechanical stress, enhancing the cycle life and capacity retention of lithium ion cells by maintaining a stable electrode structure and optimizing lithium distribution between electrodes.
Implementation Method 1
an active material disposed on the substrate and configured for inserting and removing lithium ions during battery cycling
Implementation Method 2
Lithium may be integrated into the structure of the active material... The concentration of lithium may differ throughout the thickness of this active layer
Data Source
AI summary
Provided are novel negative electrodes for use in lithium ion cells. The negative electrodes include one or more high capacity active materials, such as silicon, tin, and germanium, and a lithium containing material prior to the first cycle of the cell. In other words, the cells are fabricated with some, but not all, lithium present on the negative electrode. This additional lithium may be used to mitigate lithium losses, for example, due to Solid Electrolyte Interphase (SEI) layer formation, to maintain the negative electrode in a partially charged state at the end of the cell discharge cycle, and other reasons. In certain embodiments, a negative electrode includes between about 5% and 25% of lithium based on a theoretical capacity of the negative active material. In the same or other embodiments, a total amount of lithium available in the cell exceeds the theoretical capacity of the negative electrode active material.