Enhanced Safety Coating (ESC) and CPACK/Steel‑Sheet Battery Solutions for Mobile Phone Batteries

During everyday use, mobile phones can suffer accidental battery damage that leads to thermal runaway and fire. To address this, the article introduces a safety‑focused battery design, covering the currently feasible Enhanced Safety Coating (ESC) solution for soft‑pack cells and future research directions such as CPACK and steel‑sheet batteries.

1. Soft‑pack cell ESC safety solution

Most phone batteries use soft‑pack polymer cells where the anode and cathode foils are separated by a membrane and wound together. Puncture can cause four short‑circuit modes, with the anode‑foil‑to‑aluminum‑foil contact generating rapid heat and fire risk.

Typical mitigation involves coating the separator with ceramic or low‑melting‑point layers that shrink under heat to form a thermal barrier. However, these provide limited advantage against puncture.

The ESC technology applies a protective coating on the cathode aluminum foil. When punctured, the coating isolates the foil from the anode, preventing short‑circuit‑induced fire. The following sections detail safety and reliability tests of ESC cells.

Needle‑penetration test

Needle penetration is one of the toughest battery safety tests. Using a 2.5 mm steel needle at 150 mm/s, three groups of fully‑charged cells were punctured. Ordinary cells ignited, while ESC‑treated cells remained normal.

Temperature monitoring at three points near the puncture showed peak temperatures staying below 35 °C, with no abrupt rise.

Voltage measurements during and after puncture revealed no rapid drop; after 48 h storage the voltage remained above 3.9 V, indicating no severe internal short.

90° bending test

Ten ESC cells were bent 90° to simulate accidental flexing. Post‑test, no smoke, fire, explosion, or leakage was observed, and voltage and internal resistance remained unchanged.

Cycle performance at different temperatures

Capacity retention was compared between ESC and conventional cells under two temperature regimes: 25 °C (800 cycles) vs 45 °C (500 cycles) and low‑temperature 10 °C/0 °C cycles. Results showed comparable capacity retention and swelling for ESC cells.

Additional safety tests—including thermal abuse, high‑rate discharge, low‑temperature discharge, high‑temperature storage, and float‑charge—were all passed, confirming the overall reliability of the ESC design.

2. CPACK and steel‑sheet cell solutions

2.1 CPACK solution

The ESC coating adds about 5 µm to the electrode stack, reducing capacity by roughly 3.5 %. To compensate, the CPACK packaging reduces the cell’s end‑cap length by ~2 mm, improving energy density (ED) by about 3 %.

Critical to CPACK is controlling the folding/rolling process at the cell’s top edge to avoid damage to the overhang area, and using aging tests to assess aluminum‑plastic film integrity.

2.2 Steel‑sheet cell solution

Soft‑pack cells are wrapped in an aluminum‑plastic film (nylon/aluminum/PP) that offers limited puncture resistance. Replacing the film with a steel sheet greatly improves puncture resistance and can increase volume utilization, raising capacity by ~2‑3 %.

Proper adhesion between the cell core and steel sheet is essential; using a high‑temperature hot‑melt adhesive minimizes core shift and short‑circuit risk during device operation.

2.3 Steel‑sheet battery integration

A metal structural sheet can be bonded to the cell surface, providing robust protection without sacrificing capacity because the conventional peel‑off wrapper is eliminated. This approach also improves adhesion when the device is used with the screen facing up. Further reliability verification is required for full‑device integration.

Overall, the article outlines current mobile‑phone battery technologies, focusing on ESC safety coating, CPACK packaging, and steel‑sheet cell concepts, while acknowledging that solid‑state batteries remain a promising but longer‑term direction due to current density and cost challenges.