Microbattery Testing with Lithium Formation for Wafer-Level Sorting
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Solution Overview
Problem
Current electrical testing methods for microbatteries, particularly those with a metallic lithium anode (Li-free configuration), are inadequate as they require cycling, which causes structural variations and sensitivity to air, making intermediate sorting and cost-effective testing challenging, and existing methods like OCV measurement and pulse testing are not suitable for Li-free microbatteries.
Innovation Solution
A test method involving sequential steps: initial voltage measurement, controlled charging to form a lithium layer, stabilization, and retention phase measurements to determine valid device parameters without degrading the microbattery, allowing for rapid and non-degrading testing of micro-energy storage devices, including those with metallic lithium anodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complete charge-discharge cycling is performed to test microbatteries, then reliable electrical sorting can be achieved, but structural variations occur and metallic lithium formation makes devices sensitive to air
Solution Approach 1:
The patent applies preliminary action by performing the complete charge-discharge cycling test before encapsulation, when the microbattery is still in a protected environment during manufacturing. This allows reliable electrical sorting to be conducted on wafer-level devices before they are exposed to air, eliminating the harmful sensitivity issue while maintaining test reliability.
2Reliability
If complete charge-discharge cycling is performed, then reliable electrical sorting can be achieved, but testing time and manufacturing cost increase significantly
Solution Approach 1:
The patent performs the time-consuming complete charge-discharge cycling test at an early stage in the manufacturing process, before encapsulation. By conducting the full testing sequence (formation charge, rest period, discharge, rest period) on wafer-level microbatteries, the invention achieves reliable sorting without requiring post-encapsulation testing, thereby reducing total manufacturing time and cost.
3Productivity
If Open Circuit Voltage (OCV) measurement is used for sorting, then testing is rapid and non-degrading, but OCV shows significant variability and no correlation with state of charge in Li-free microbatteries
Solution Approach 1:
The patent changes the measurement parameter from Open Circuit Voltage (OCV) to terminal voltage during controlled charge and discharge phases. By measuring voltage during active electrochemical processes rather than at open circuit, the method obtains readings that correlate with state of charge and battery health, achieving both measurement precision and productivity.
4Productivity
If internal resistance measurement is used for sorting, then testing is rapid and non-degrading, but internal resistance is not relevant for Li-free microbatteries before lithium anode formation
Solution Approach 1:
The patent performs a formation charge step before measurement that creates the metallic lithium anode in Li-free microbatteries. This preliminary action transforms the battery from a state where internal resistance measurement is irrelevant to a state where the lithium anode is formed and internal resistance becomes a meaningful sorting parameter, enabling both rapid testing and reliable sorting.
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
Enables rapid and non-degrading testing of microbatteries, allowing for early identification of faulty devices and reducing manufacturing costs by applying the test sequence in parallel, without the need for complete cycling or encapsulation, thus overcoming the limitations of existing methods.
Implementation Method 1
a metallic lithium anode is formed during the first charge of the battery by electrodeposition of Li+ ions (from the cathode) between the electrolyte and the second current collector
Data Source
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AI summary
The invention relates to a method for testing at least one micro-energy storage device comprising a metallic lithium anode formed by electrodeposition of ions on a metal inert to lithium ions, the method comprising a succession of steps during the manufacture of said anode: ∘ a step of measuring the initial voltage OCV of the micro-energy storage device; ∘ a first charge step comprising the application of a current, the measurement of the voltage and the internal resistance of the device to verify the conformity of the measurements on a very thin layer of lithium formed as an anode; ∘ a second charge stabilization step comprising the application of a current and the measurement of the voltage of the device to verify the conformity of the measurements on a thin layer of lithium formed as an anode;• a zero-current retention step and voltage measurement to confirm the conformity of the micro-energy storage device. The invention also relates to a system for implementing the method;