Analysis of Five Critical Impacts of Electrode Flexibility on Battery Performance

1. Introduction

Lithium-ion batteries (LIBs), serving as the core of modern energy storage, directly determine the performance of electric vehicles and smart devices. The “heart” of the battery: the electrode sheet—relies critically on electrode flexibility, a core metric impacting battery lifespan and safety. Brittle electrode sheets can crack and pulverize during charge/discharge cycles, leading to capacity fade and even safety hazards. How can electrode sheets achieve both strength and pliability? This article unveils the technical key behind battery performance: electrode flexibility, and deciphers IEST Instrument advanced testing solutions.

Figure 1. Lithium Battery Electrode Sheet

2. Electrode Flexibility: The Hidden Arbiter of Battery Performance

2.1 The Lifeline of Cycle Life

• Stress Fluctuations During Cycling: During charge/discharge, electrode materials undergo repeated expansion and contraction (e.g., volume changes in cathode materials like NCM and LFP during Li-ion intercalation/deintercalation). Poor electrode flexibility increases susceptibility to crack initiation and fracture under cyclic stress (Figure 1), degrading electrical contact between the active material and current collector. This elevates internal resistance (IR), ultimately shortening cycle life and potentially triggering safety incidents.

• Powdering Issue: Electrodes with inadequate flexibility are prone to powdering during cycling, causing active material detachment from the current collector and accelerating performance degradation.

Figure 2. Fractured Battery Electrode Sheet Post-Cycling

2.2 The Litmus Test for Manufacturing Processes

• Slitting and Winding Processes: Electrode sheets undergo slitting, hot pressing, winding, or stacking during manufacturing. Sheets with poor flexibility risk burr formation, cracking, or fracture during these processes, reducing yield rates and increasing production costs.

• Electrode-Separator Interface: Flexible electrode sheets conform better to separators, minimizing interfacial gaps. This enhances energy density and cell consistency.

2.3 The Barometer of Performance

• Internal Resistance & Power Performance: Brittle electrodes readily develop cracks during cycling, increasing contact resistance at the active material/current collector interface. This raises the cell’s overall IR, degrading power performance.

• Energy Density: While increasing areal density boosts energy density, insufficient flexibility can cause electrode failure during cycling, paradoxically reducing the practical usable energy density.

2.4 Resolving Design Conflicts

• Electrode Thickness Design: High-energy-density batteries often require increased electrode thickness and areal density, which can compromise flexibility. Design necessitates balancing energy density with sufficient mechanical robustness.

• Material Selection: Flexibility is intrinsically linked to the ratios of binder, conductive additive, and active material. Optimizing formulations and selecting high-performance binders can enhance flexibility without sacrificing energy density.

2.5 The Passport for Application Scenarios

• Traction Batteries: Electric vehicles encounter complex road conditions (vibration, impacts) imposing mechanical stress on battery packs, potentially causing safety incidents (Figure 3). Flexible electrodes better absorb impact energy, mitigating damage risk, thereby enhancing safety and extending pack life.

• Flexible Batteries: Emerging fields like wearables and flexible electronics demand batteries capable of conforming to device deformation. Poor flexibility renders batteries unsuitable for applications like foldable smartphones.

Figure 3. Thermal Runaway Following Impact Damage to EV Underbody

3. How is Electrode Flexibility Tested?

IEST Battery Electrode Flexibility Testing System(BEF1000) provides the answer. The instrument employs the fundamental principle of stress-strain curve measurement: the electrode is bent at a specific angle, secured in the test fixture, and deformed via applied displacement. Stress and strain (force-displacement) at various deformation levels are measured to assess flexibility. As shown in Figure 5, the smooth curve of a high-quality electrode (Sample B) contrasts sharply with the abrupt fracture point of a poor-quality sample (Sample A), clearly differentiating performance.