Analysis On Rapid Capacity Degradation At Early Cycles Of Lithium‑Iron‑Phosphate Batteries And Performance Improvement
Aug 14, 2026
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Lithium‑iron‑phosphate (LFP) batteries have been widely adopted in new‑energy‑vehicle industries owing to their outstanding cycling performance, high safety level and relatively low cost. Nevertheless, their capacity‑fading curve exhibits a characteristic of fast degradation in early cycles and moderate fading in mid‑to‑late cycles. Compared with NCM‑based ternary batteries, LFP batteries suffer more prominent capacity loss during the initial cycling stage, which limits their application potential in long‑lifespan scenarios. Investigating early‑stage degradation mechanisms and exploring improvement approaches is of great significance for enhancing their market competitiveness.
I. Analysis of Degradation Mechanisms
1. Comparison with Ternary Batteries
Under identical test conditions, LFP batteries retain 95 % capacity after 200 cycles, while ternary batteries achieve 97 %. Research reveals that the fundamental origin for the discrepancy in fading rate lies in the difference of initial Coulombic efficiency (ICE):
a. Ternary batteries deliver low cathode ICE (~88 %) and high anode ICE (~92 %). Approximately 4 % surplus active lithium remains in the anode after the first charge‑discharge cycle, which can compensate for partial active‑lithium consumption in subsequent cycles.
b. LFP batteries feature high cathode ICE (~95 %) yet low anode ICE (~92 %). No spare active lithium is reserved in the anode upon completion of the initial cycle, rendering LFP cells more susceptible to active‑lithium loss during early cycling.
Further characterizations via ICP and XRD confirm that the lithium content in the anode of ternary batteries is persistently higher than that of LFP batteries. The anode lithium content of ternary batteries gradually declines as cycling proceeds, demonstrating that the pre‑stored lithium inside the anode is progressively consumed to retard capacity degradation.
2. Early‑cycle Degradation Mechanism of LFP Batteries
Capacity loss measured at 1 C and 0.05 C rates shows nearly identical loss ratios, indicating that capacity fading is dominated by irreversible consumption of active lithium rather than polarization effects.
The anode solid‑electrolyte interphase (SEI) films were further characterized by ICP, EDS, DSC and other analytical tools. Key findings are summarized as follows:
a. As cycling progresses, lithium content in the anode rises, lithium concentration within SEI films increases, and exothermic heat from SEI films grows accordingly.
b. Within the first 50 cycles, the capacity degradation rate reaches 3.3 %, electrode‑sheet expansion rate 3.3 %, and pressure increment rate 33.6 %. By contrast, over cycles 50‑100, the degradation rate drops to 1.2 %, electrode‑sheet expansion rate to 1.6 %, and pressure increment rate to merely 1.4 %.
These results demonstrate that drastic volume expansion of the anode in early cycles triggers frequent rupture and self‑repair of SEI films, consuming massive active lithium and constituting the primary driver for rapid capacity decay. As cycling continues, electrode‑sheet structures stabilize, SEI damage is mitigated, and the degradation rate slows down consequently.
II. Improvement Strategies
Based on the above‑mentioned mechanisms, multiple mitigation strategies are proposed from the perspectives of cathode/anode material design and manufacturing‑process optimization, with their effectiveness verified by experiments.
1.Reduce cathode specific surface area: suppress side‑reactions and cut active‑lithium consumption to slow down capacity fading.
2.Optimize anode orientation index (OI): lower OI values correspond to reduced graphite volume expansion upon lithium intercalation and alleviated SEI‑film damage. Experiments indicate that when OI decreases from 9.33 to 5.55, the capacity decay rate after 100 cycles drops from 3.3 % to 2.4 %.
3.Regulate anode coating mass loading: excessive coating loading aggravates electrode‑sheet expansion and raises risks of SEI fracture. A 30 % increase in coating loading leads to a 9 % rise in electrode‑sheet rebound rate and a 1.0 % increment in capacity degradation rate.
4.Lower expansion rate of anode binder: a 20 % reduction in binder‑film expansion rate yields a 2 % drop in electrode‑sheet rebound rate and a 0.5 % decrease in capacity degradation rate.
Validated by ICP, EDS, DSC and other characterization methods, optimized cells exhibit obvious improvements in anode lithium content, lithium concentration in SEI films and heat release from SEI films, proving the effectiveness of the foregoing countermeasures.
