Temporary Lithium Additives in Positive Electrodes for Capacity Compensation
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Solution Overview
Problem
Lithium ion cells face capacity loss due to undesirable reactions during initial cycling, such as the formation of a solid-electrolyte interphase (SEI) layer, which permanently traps lithium ions, making it challenging to maintain cell capacity.
Innovation Solution
Introducing a temporary lithium additive into the positive electrode, which decomposes to release additional lithium ions during initial cycling, complementing primary lithium ions from the active material, thereby compensating for losses and optimizing lithium utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium metal is introduced directly into the negative electrode to compensate for lithium ion losses, then cell capacity can be maintained, but uniform distribution is difficult to achieve and safety risks increase due to lithium dendrite formation
Solution Approach 1:
The patent extracts the lithium source function from the negative electrode and relocates it to the positive electrode through temporary lithium additives. This separation allows the negative electrode to focus on uniform lithium ion acceptance while the positive electrode provides controlled lithium ion release, eliminating the safety risks associated with lithium metal in the negative electrode.
Solution Approach 2:
The patent introduces temporary lithium additives as intermediary substances in the positive electrode that decompose to release lithium ions. These additives act as a buffer between the positive active material and the electrolyte, providing controlled lithium ion release without requiring lithium metal in the negative electrode, thus maintaining safety while compensating for lithium ion losses.
2Quantity of substance
If lithium metal is introduced directly into the negative electrode to compensate for lithium ion losses, then cell capacity can be maintained, but handling complexity and costs increase due to reactivity with ambient air
Solution Approach 1:
The patent inverts the conventional approach by placing the lithium source in the positive electrode rather than the negative electrode. Instead of adding lithium metal to the negative electrode, temporary lithium additives are incorporated into the positive electrode slurry, which then release lithium ions during initial cycling. This inversion eliminates the need for special handling and environment controls required for lithium metal.
Solution Approach 2:
The patent uses temporary lithium additives that are consumed during initial cycling to provide the necessary lithium ions. These additives serve a specific temporary purpose (compensating for lithium ion losses during SEI formation) and are then depleted, after which the cell operates normally. This disposable approach is simpler and more cost-effective than maintaining lithium metal in the negative electrode throughout the cell lifecycle.
3Quantity of substance
If additional lithium ions are introduced to compensate for SEI layer formation losses, then cell capacity is maintained, but the mechanism must ensure uniform distribution to prevent lithium clusters and dendrites
Solution Approach 1:
The patent applies local quality by incorporating temporary lithium additives uniformly throughout the positive active material matrix. This ensures that lithium ion release occurs at multiple distributed locations within the positive electrode during initial cycling, preventing concentration at specific points and thereby avoiding lithium cluster and dendrite formation in the negative electrode.
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 method effectively enhances lithium ion availability for cycling, maintaining cell capacity by strategically releasing additional lithium ions, thus addressing the issue of capacity fade and ensuring uniform distribution without the safety risks associated with lithium metal introduction.
Implementation Method 1
The temporary lithium additive is operable to release additional lithium ions during its decomposition, but not to receive any lithium ions thereafter. The temporary lithium additive may decompose when applying a voltage between the electrodes, e.g., during initial cycling.
Implementation Method 2
applying a voltage between the positive electrode and the negative electrode thereby decomposing the temporary lithium additive to produce the additional lithium ions and a decomposition product
Data Source
AI summary
Provided are methods of introducing additional lithium ions into lithium-ion electrochemical cells as well as positive electrodes, comprising these additional lithium ions. A method may involve introducing a temporary lithium additive into a positive electrode, such as mixing the additive into slurry used for coating the electrode. The positive electrode also comprises a positive active material, different from the temporary lithium additive and used as a source of primary lithium ions. The positive active material is operable to release and also later to receive lithium ions during cycling. The temporary lithium additive is operable to release additional lithium ions during its decomposition, but not to receive any lithium ions thereafter. The amount of these additional lithium ions may be selected based on expected lithium ion losses in the cell. The temporary lithium additive may decompose when applying a voltage between the electrodes, e.g., during initial cycling.