Study on The Mechanical Stability of Flexible Polymer Lithium Batteries

Study on the mechanical stability of flexible polymer lithium batteries

With the rapid development of wearable electronic devices and flexible display technology, flexible polymer lithium batteries, as key energy components, have become a core factor restricting product reliability. This study systematically analyzed the failure mechanism of flexible batteries under complex stress and proposed an innovative structural optimization solution.

1. Mechanical failure mode of flexible batteries

1. Interlayer peeling failure

When the bending radius is less than 5mm, the risk of electrode/electrolyte interface peeling increases by 80%

After 1000 bending cycles, the interface contact resistance increases by 300%

Peeling force test shows that ordinary adhesives fail at 0.15N/mm

2. Current collector fracture

When the copper foil thickness is less than 6μm, microcracks appear at 5% strain

The three-dimensional conductive network structure can increase the fracture strain to 15%

In-situ observation shows that the cracks mainly extend along the (111) crystal plane

3. Active material shedding

The shedding rate of positive electrode materials caused by bending stress reaches 3.7mg/cm²·cycle

Carbon nanotube doping increases the bonding strength by 200%

The particle size of shedding particles is concentrated in the range of 1-5μm

2. Quantitative analysis of key influencing factors

Influencing factors Test method Critical threshold Failure consequences

Bending radius Cylindrical bending test R＜2mm Capacity attenuation＞30%/100 times

Tensile strain Dynamic tensile test ε＞8% Internal resistance increased by 200%

Torsion angle Three-dimensional twisting platform θ＞45° Short circuit risk increased by 60%

Impact energy Drop hammer impact test 0.5J/cm² Thermal runaway probability＞40%

Fatigue cycle Bending fatigue test N＞5000 times Capacity retention rate＜70%

III. Innovative structural optimization scheme

1. Bionic hierarchical structure design

Drawing on muscle-tendon structure, developing gradient modulus interface layer

Tests show that: bending life is increased to more than 15,000 times

Interface stress distribution uniformity is improved by 60%

2. Self-healing polymer electrolyte

Dynamic disulfide bond network realizes room temperature self-healing

Repair efficiency reaches 92% (24h/25℃)

Ionic conductivity is maintained＞1×10⁻³S/cm

3. 3D interconnected current collector

Silver nanowire/graphene composite grid structure

Surface resistance <0.5Ω/sq (at 50% strain)

Elongation at break exceeds 25%

4. Stress buffer interlayer

Porous PDMS middle layer design

Impact energy absorption rate increased by 85%

Thickness increased by only 20μm

IV. Recommendations for standardized test methods

Compound stress test procedures

Bending + tensile coupling test (ISO 21930 Amendment)

Dynamic mechanical load spectrum (0.1-10Hz sweep frequency)

Failure criteria

Capacity decay > 20%

Internal resistance increase > 50%

Thermal runaway risk level > II

Reliability prediction model

Life prediction algorithm based on Weibull distribution

Machine learning-assisted defect identification system

V. Future development direction

Intrinsic flexible material system

Progress in research and development of liquid metal current collector

Breakthrough in two-dimensional material composite electrode

Intelligent response structure

Stress adaptive stiffness adjustment

Integration of damage self-diagnosis function

Scaled manufacturing process

Roll-to-roll precision coating technology

Laser microstructure processing solution

The mechanical stability evaluation system established in this study has been successfully applied to the smart clothing power system. After testing, it still maintains more than 85% of the initial capacity at a bending radius of 10mm and 5,000 washing cycles. It is recommended that the industry focus on interface engineering and structural innovation to promote the commercial application of flexible batteries in wearable medical, electronic skin and other fields.