High-Nickel Ternary Lithium-Ion Batteries have emerged as a cornerstone of advanced energy storage, especially in electric vehicles (EVs), due to their high energy density and superior performance. However, their limited high-temperature cycle life has hindered large-scale adoption in power battery applications, where durability under harsh conditions is critical. Understanding the failure mechanisms behind high-temperature cycling is essential for developing High-Nickel Ternary Lithium-Ion Batteries with extended lifespans, addressing a key challenge in the transition to sustainable transportation.
The Urgency of High-Temperature Longevity Research
As EVs become increasingly prevalent, the demand for batteries that can withstand extreme temperatures—such as those experienced in hot climates or during prolonged operation—continues to grow. High-Nickel Ternary Lithium-Ion Batteries, typically composed of nickel-cobalt-manganese (NCM) cathodes like NCM811, offer high capacity but are prone to capacity fading when cycled at elevated temperatures (e.g., 45℃). This fading stems from multiple interconnected factors, including electrolyte decomposition, structural changes in electrode materials, and ion loss. A study published in the Journal of Power Sources highlighted that high-temperature cycling can reduce battery capacity by 20-30% within 500 cycles, emphasizing the need for targeted research to mitigate these issues.
Experimental Design: Unraveling Degradation Factors
To investigate the high-temperature failure mechanisms of High-Nickel Ternary Lithium-Ion Batteries, researchers conducted systematic experiments using NCM811-based pouch cells. The batteries were fabricated with a cathode mixture of NCM811, PVDF, and conductive carbon black (mass ratio 97.1:1.4:1.5) coated on 15μm aluminum foil, and an anode of artificial graphite, conductive carbon black, CMC, and SBR (mass ratio 97.1:0.5:1.0:1.4) on 8μm copper foil. The cells, with a rated capacity of 3.58Ah, were cycled at 45℃ using a 1.00C charge/discharge rate (4.200V to 2.800V) and subjected to comprehensive tests, including electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD), and inductively coupled plasma atomic emission spectroscopy (ICP-AES).
Key Findings: What Causes Capacity Fading?
After 523 cycles at 45℃, the High-Nickel Ternary Lithium-Ion Batteries retained only 76.05% of their initial capacity, with four primary degradation factors identified:
- Active Lithium Ion (Li⁺) Loss in the Cathode: This was the most significant contributor, accounting for 11.22% of capacity loss. During cycling, Li⁺脱出 from the NCM811 cathode, while transition metals (Ni, Co) oxidized, increasing repulsion between adjacent oxygen layers. This led to changes in the cathode’s crystal structure (e.g., increased c/a ratio) and the formation of microcracks in NCM particles, as observed via scanning electron microscopy (SEM). These cracks exposed new surfaces, accelerating side reactions with the electrolyte and further depleting active Li⁺.
- Cathode Structural Changes: Accounting for 6.55% of capacity loss, structural degradation included the formation of 网状 microcracks in NCM811 particles. Despite the layered structure remaining intact (c/a> 4.9), the cracks created new interfaces between the cathode and electrolyte, promoting electrolyte consumption and increasing internal resistance. Notably, cation mixing (Li/Ni disorder) did not worsen, as indicated by the stable I (003)/I (104) ratio in XRD analysis.
- System Polarization: Contributing 5.25% to capacity loss, polarization increased with cycling, as evidenced by a decreasing constant-current charge ratio. Polarization-induced capacity loss was quantified by comparing discharge capacities at 1.00C and 0.05C (a rate where polarization effects are negligible). The difference in capacity between these rates—0.186Ah—reflected the impact of polarization on energy delivery.
- Metal Accumulation on the Anode: This had a minimal effect (0.11% capacity loss). ICP-AES tests revealed that Ni, Co, and Mn ions dissolved from the cathode and accumulated on the graphite anode, with Ni showing the highest dissolution rate. However, calculations based on Faraday’s law confirmed that these accumulated metals caused negligible capacity loss, and the anode’s structure remained unchanged (XRD analysis) after cycling.
Additionally, electrolyte decomposition played a pivotal role in battery degradation. Failed cells exhibited reduced electrolyte volume, increased thickness (35.3% growth), and higher direct current internal resistance (DCIR). The rise in DCIR was primarily due to increased alternating current internal resistance (ACIR), driven by electrolyte depletion and the accumulation of side reaction products between the separator and electrodes. Electrochemical impedance spectroscopy (EIS) further confirmed that ohmic resistance (Rs) and solid electrolyte interphase (SEI) film resistance (Rsei) increased significantly, while charge transfer resistance (Rct) and Warburg impedance (Rw) remained stable.
Implications for Battery Development
These findings provide critical insights for optimizing High-Nickel Ternary Lithium-Ion Batteries. To enhance high-temperature longevity, researchers and manufacturers can focus on:
- Developing electrolyte additives to suppress decomposition and reduce SEI growth, as suggested by studies on electrolyte modification for high-nickel batteries.
- Designing cathode materials with improved structural stability, such as doped NCM811 or surface-coated particles, to minimize microcrack formation.
- Optimizing cell assembly processes to reduce internal stress and prevent electrode deformation, which exacerbates side reactions.
Conclusion
High-Nickel Ternary Lithium-Ion Batteries hold immense potential for next-generation energy storage, but their high-temperature performance remains a key bottleneck. This research identifies active Li⁺ loss in the cathode as the primary cause of capacity fading, followed by structural changes, polarization, and minimal anode metal accumulation. By addressing these mechanisms through material innovation and process optimization, we can unlock the full potential of High-Nickel Ternary Lithium-Ion Batteries, enabling their widespread use in EVs and other high-demand applications. As the global push for sustainability intensifies, advancing battery technology will continue to be a critical driver of progress, with High-Nickel Ternary Lithium-Ion Batteries leading the way toward more durable, efficient energy storage solutions.
For further reading on battery degradation mechanisms, refer to resources from the Electrochemical Society and the International Battery Association, which provide comprehensive insights into advanced battery research.