The development of high-performance binders for silicon (Si) anodes in lithium-ion batteries (LIBs) remains critical due to silicon’s severe volume expansion (>300%) during lithiation/delithiation. This study introduces a cross-linked binder (C-PEI-10%) synthesized through electrostatic interactions between anionic carboxymethyl cellulose sodium (CMC-Na) and cationic polyethyleneimine (PEI). Compared with conventional polyvinylidene fluoride (PVDF) and pure CMC-Na binders, C-PEI-10% demonstrates superior mechanical stability and electrochemical performance, addressing key challenges in Si-based LIBs.
Mechanical and Structural Characterization
The 3D network structure of C-PEI-10% was confirmed through FTIR and XPS analyses. The interaction between CMC-Na’s carboxylate groups (−COO−) and PEI’s protonated amines (−NH3+) enhanced binder cohesion, as evidenced by zeta potential measurements:
$$ \Delta \zeta = \zeta_{\text{C-PEI-10\%}} – (\zeta_{\text{CMC-Na}} + \zeta_{\text{PEI}}) = -30.8 – (-76.2 + 14.6) = -30.8 + 61.6 = 30.8 \, \text{mV} $$
| Binder | Peel Strength (N) | Capacity Retention (0.2C, 100 cycles) |
|---|---|---|
| PVDF | 0.57 ± 0.12 | 10.86% |
| CMC-Na | 1.52 ± 0.21 | 58.33% |
| C-PEI-10% | 2.42 ± 0.18 | 82.54% |
Electrochemical Performance
The Si@C-PEI-10% electrode exhibited exceptional cycling stability in lithium-ion batteries, retaining 82.54% capacity after 100 cycles at 0.2C (2,249.1 mAh·g−1). The lithium-ion diffusion coefficient (DLi+) was calculated using GITT:
$$ D_{\text{Li}^+} = \frac{4}{\pi\tau} \left( \frac{m_B V_m}{M_B S} \right)^2 \left( \frac{\Delta E_s}{\Delta E_\tau} \right)^2 $$
where τ = relaxation time, mB = active material mass, and S = electrode surface area. C-PEI-10% showed enhanced DLi+ values compared to CMC-Na:
| State | DLi+ (C-PEI-10%) | DLi+ (CMC-Na) |
|---|---|---|
| Discharge | 10−12.1 cm2·s−1 | 10−13.4 cm2·s−1 |
| Charge | 10−14.2 cm2·s−1 | 10−15.8 cm2·s−1 |
Interface Stability
XPS analysis revealed that C-PEI-10% facilitated stable solid electrolyte interphase (SEI) formation in lithium-ion batteries, with 92.05% LiF content versus 69.07% for CMC-Na. The SEI composition directly impacts LIBs’ long-term cyclability:
$$ \text{LiF content} = \frac{I_{\text{LiF}}}{I_{\text{LiF}} + I_{\text{LixPFy}}} \times 100\% $$
where I = XPS peak intensity.
Rate Capability
At 1C, Si@C-PEI-10% delivered 2,030.5 mAh·g−1, outperforming conventional binders in lithium-ion battery applications:
| Current Density | C-PEI-10% | CMC-Na | PVDF |
|---|---|---|---|
| 0.1C | 2,414.4 | 2,099.3 | 928.9 |
| 1C | 2,030.5 | 1,477.3 | 16.7 |
Conclusion
The C-PEI-10% binder demonstrates three key advantages for lithium-ion battery silicon anodes: 1) Enhanced adhesion through 3D cross-linking, 2) Improved Li+ transport via amine coordination, and 3) Stable SEI formation with high LiF content. This biomaterial-based approach provides a sustainable pathway for high-energy-density LIBs while addressing silicon’s intrinsic degradation mechanisms.