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Method for Battery Cell Latent Particle Short Detection Subsequent to Formation and Prior to Pack Assembly

IP.com Disclosure Number: IPCOM000250311D
Publication Date: 2017-Jun-27
Document File: 3 page(s) / 375K

Publishing Venue

The IP.com Prior Art Database

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Method for Battery Cell Latent Particle Short Detection Subsequent to Formation and Prior to Pack Assembly

Battery cell particle shorts occur when a small piece of conductive material penetrates the cell separator and creates a lower than normal resistance path between the cell electrodes. These failures are difficult to prevent since they are caused by microscopic debris that can originate from both foreign materials as well as pieces of the cell itself. The occurrence of these shorts is exacerbated as cell separators are thinned and ceramic overcoats are removed in the course of cell cost reduction. To complicate matters, the shorts are not realized until the internal pressure of the cell increases (due to increasing SOC, temperature, and age) beyond the point where the particle is forced through the separator. Often times, the short does not exhibit until after battery pack assembly and charge, and may not be detected until after vehicle assembly. Our detection method artificially increases the internal cell pressure directly after cell manufacturing through the application of a calibrated external load to each cell (or array of cells). This load simulates the internal pressures the cell would experience later on, forces any problem particles through the separator, and allows them to be detected by monitoring the open circuit voltage of the cell over time.

Method

In our method, a calibrated external load is applied to a cell (or array of cells) in order to reproduce the internal pressure that the cell will experience after pack assembly and full charge. This load is selected to achieve the required internal pressure without damaging the cell. A close up, internal cell view is shown in Figure 1 where the particle is forced through the separator by a calibrated load.

Figure 1: Internal cell view for a) no particle b) non-exhibited particle short c) particle short induced through the application of a calibrated external load

Figure 2: Example of external load application fixture - a calibrated linear actuator applies the prescribed force directly after cell manufacturing

Max In-Vehicle Force

 

Figure 3: Calibrated load target compressed thickness derivation method

Implementation Example – Application of calibrated external load to...