Lithium Alloy Depot for Secondary Cell Capacity Compensation
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Solution Overview
Problem
Lithium-ion cells experience significant capacity loss and aging due to the formation of the Solid Electrolyte Interphase (SEI) during the first charge/discharge cycle, leading to irreversible lithium binding and increased cell impedance over subsequent cycles, which complicates balancing and affects overall performance.
Innovation Solution
Incorporating a lithium alloy as a lithium depot within the cell, with a lithium content ranging from 5% to 46% by weight, which can easily compensate for lithium losses during SEI formation and subsequent cycles, and is easier to handle and dose compared to elemental lithium, with the alloy partner such as aluminum providing additional benefits like corrosion protection and improved reactivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If elemental lithium is used as a lithium depot, then lithium losses during SEI formation can be compensated, but handling and dosing becomes difficult and hazardous
Solution Approach 1:
The patent uses a lithium alloy (composite material of lithium with another metal) instead of pure elemental lithium. This composite material provides the necessary lithium for compensating SEI formation losses while being safer and easier to handle during manufacturing and operation.
Solution Approach 2:
The lithium alloy depot is designed as a consumable component that gradually releases lithium to compensate for ongoing losses. The alloy serves as a reservoir that depletes over time as lithium is released, replacing the need for precise dosing of reactive elemental lithium.
2Ease of operation
If a lithium alloy with low lithium content is used, then handling safety improves, but the capacity to compensate for lithium losses decreases
Solution Approach 1:
The patent optimizes the lithium content parameter within a specific range (5-46 wt%) to achieve the right balance between safety and effectiveness. This parameter optimization ensures sufficient lithium is available for compensation while maintaining acceptable handling characteristics.
Solution Approach 2:
Instead of using pure lithium, the invention uses a lithium alloy that copies the essential function of providing lithium for SEI compensation while improving safety through the addition of another metal element.
3Reliability
If high amounts of lithium are provided in the depot, then lithium losses are fully compensated, but cell impedance increases due to excess lithium
Solution Approach 1:
The lithium alloy depot is designed to provide a controlled excess of lithium that is sufficient to compensate for losses without creating harmful accumulation. The alloy gradually releases lithium at a rate that matches consumption, preventing both deficiency and excessive accumulation that would increase impedance.
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 lithium alloy depot effectively mitigates lithium losses, enhances cell capacity, and improves the service life by ensuring a stable supply of mobile lithium, reducing the need for precise dosing and handling of elemental lithium, while also providing corrosion protection and scavenging harmful substances.
Implementation Method 1
a partial reaction taking place at a comparatively lower redox potential takes place at the negative electrode, one at a comparatively higher redox potential at the positive electrode
Implementation Method 2
a covering layer forms on the surface of the electrochemically active materials in the anode during the first charging/discharging cycle (so-called formation). This top layer is called 'Solid Electrolyte Interphase' (SEI) and usually consists mainly of electrolyte decomposition products
Data Source
Figure 1
AI summary
A secondary electrochemical cell comprises a positive electrode capable of reversibly depositing and removing lithium, a negative electrode capable of reversibly depositing and removing lithium, mobile lithium available for deposition and removal processes in the electrodes, an electrolyte through which the mobile lithium, in the form of ions, can migrate between the positive and negative electrodes, a housing enclosing an interior space in which the electrodes and the electrolyte are arranged, and—in addition to the lithium contained in the electrodes—a lithium reservoir to compensate for lithium losses during cell formation and/or operation. The lithium reservoir is a lithium alloy consisting of lithium and at least one other alloying element, with a lithium content ranging from 5 wt.% to 99.5 wt.%.In addition to the cell itself, a method for producing such a cell and a battery containing such a cell are described. Furthermore, a cell in which the lithium storage capacity has been activated is described.