Why the First Cycle Defines Irreversible Capacity Loss in High-Nickel Cathodes

Irreversible capacity loss in high-nickel layered oxide cathodes (Ni ≥ 0.8) is disproportionately seeded during the initial charge-discharge cycle, making the formation protocol the most consequential engineering intervention available. During first charge, the cathode surface undergoes oxygen loss that permanently modifies local surface structures. Research from Columbia University (2022) using first-principles surface phase diagram calculations reveals that both the (001) and (104) surfaces of LiNiO₂ experience oxygen loss during the first charge, producing irreversible structural changes before any prolonged cycling occurs. This means that even formation at moderate voltages traps a portion of the lithium inventory in a chemically modified, electrochemically inaccessible surface shell.

The bulk mechanism underpinning irreversible loss is cation disorder driven by oxidation at the solid–electrolyte interface. Research from MIT (2022) demonstrates that nickel with a high concentration of defects is driven into bulk lithium sites by electrostatic forces at potentials above 4.4 V vs. Li/Li⁺, generating a disordered rock-salt shell. Formation protocols that inadvertently push the cathode beyond this threshold during the first charge irreversibly consume both cyclable lithium and active material volume. Once structural disorder is established in the surface layer, subsequent cycling continues to propagate the damaged zone inward.

The structural pathway from the layered phase toward rock-salt is mechanically coupled as well as electrochemical. Research from the University of California (2021) shows that the O1 phase formed at high states of charge acts as a preferential nucleation site for rock-salt transformation via a two-step mechanism: cation mixing followed by lattice shear along (003) planes. Crack nucleation occurs simultaneously from the particle interior and surface along the [100] direction, physically exposing fresh cathode material to electrolyte and amplifying first-cycle irreversibilities if formation drives the cathode through this high-voltage O1 region. Controlling the upper voltage limit during formation is therefore not merely a conservative capacity management measure — it is the primary lever for preventing the O1 phase from forming in the first place.

“Controlling the upper voltage limit during formation is the primary lever for preventing the O1 phase from forming — once rock-salt disorder is established in the surface layer, subsequent cycling continues to propagate the damaged zone inward.”

Mechanical cracking during formation is further governed by the anisotropic volume change of the layered structure along the c-axis during lithium deintercalation. As established by the Korea Electronics Technology Institute (2019), changes in the c-axis length during charging and discharging are the primary cause of microcrack formation and propagation in primary particles of NCM811 (LiNi₀.₈Co₀.₁Mn₀.₁O₂). Cracks formed during high-rate formation expose new electrochemically active surfaces to electrolyte decomposition, increasing impedance and dissolving transition metals. Slow, graduated formation protocols that limit the depth of first-cycle lithium extraction are directly validated by this mechanism.

Formation Protocol Engineering: Rate, Voltage, and Thermal Parameters

Tailored electrochemical protocols — including formation C-rate, voltage window, temperature, and rest steps — provide differentiated degradation pathways, and protocol choice is a primary determinant of long-term capacity loss in nickel-rich cells. This is the central finding of research from the Faraday Institution (2021), which establishes that a detailed mechanistic account of degradation requires matched characterisation methods and that early-life protocol choices set the degradation trajectory for the full lifetime of the cell. In other words, the protocol — not just the material — determines which degradation mechanisms dominate.

A 2024 patent from the University of Michigan (The Regents) introduces a systematic method for optimising formation protocols by comparing the internal resistance of cells formed under different protocols. The invention discloses that internal resistance measured after the first charge is a predictive indicator of long-term aging: a protocol that produces lower first-cycle internal resistance — corresponding to a higher-quality cathode–electrolyte interface (CEI) and less irreversible structural change — yields superior long-term capacity retention. This provides a practical, quantitative handle for selecting among formation variants in a manufacturing context, translating academic degradation insights directly into a factory-floor diagnostic.

At the particle and cell level, a quantitative degradation framework from Imperial College London (2023) distinguishes LAM — driven by phase-transition-induced rock-salt shell formation — from LLI, arising from lithium trapped in degraded surface domains. The cell-level physics-based model demonstrates that LAM dominates usable capacity fade, while LLI primarily shifts the stoichiometric operating range of the negative electrode. Formation protocols that minimise the depth of first-cycle delithiation directly reduce the volume of rock-salt shell formed, limiting LAM. The model quantifies that the trapped lithium in the degraded shell is electrochemically irretrievable once the rock-salt structure is established — reinforcing that formation-stage intervention is more effective than any subsequent remediation.

Residual lithium compounds on the surface of high-nickel cathodes — specifically LiOH and Li₂CO₃, which accumulate due to moisture and CO₂ sensitivity — play a complex role in formation chemistry. A 2020 review identifies that these surface impurities decompose during formation, generating gas and consuming lithium inventory. Formation protocols designed with low initial C-rates and extended constant-voltage hold steps allow more complete decomposition of these residual phases under controlled conditions, preventing gas-induced cell damage and irreversible lithium consumption during high-rate production cycling. According to the US Department of Energy’s Office of Scientific and Technical Information, controlling surface chemistry prior to and during formation is a recognised priority for advanced battery manufacturing.

Pre-formation surface treatment that integrates with the formation protocol is demonstrated by AIST Japan (2019). The CO₂ gas treatment using the cavitation effect (CTCE) for NCA (LiNi₀.₈Co₀.₁₅Al₀.₀₅O₂) neutralises surface alkalinity and forms a uniform Li₂CO₃ layer on NCA particles before formation begins. This pre-conditioning suppressed electrolyte decomposition and charge-transfer resistance growth, achieving 92% capacity retention at the 50th cycle — a direct demonstration of how pre-formation surface conditioning integrates with the formation protocol to limit first-cycle irreversibilities.

Electrolyte Additives as an Integral Component of Formation Protocol Design

Formation protocol optimisation is inseparable from electrolyte composition, because the cathode–electrolyte interface (CEI) formed during the first few cycles is a product of both the electrochemical conditions and the chemical species available in the electrolyte. Research from EMPA Switzerland (2023) on single-crystal LiNi₀.₈₃Co₀.₁₁Mn₀.₀₆O₂ demonstrates that surface reconstruction from layered to disordered spinel/rock-salt structures — the dominant source of impedance growth and irreversible capacity loss — can be mitigated through formation-stage additive-assisted CEI construction. A robust protective layer formed during the first charge acts as a kinetic barrier to continued oxygen loss and cation migration, effectively locking in a more reversible surface configuration.

Fluorinated dual-additive strategies provide quantitative evidence for additive-driven formation quality. Research from Chungnam National University (2022) demonstrates that combining fluoroethylene carbonate (FEC) and di(2,2,2-trifluoroethyl)carbonate (DFDEC) during formation builds a high-quality SEI/CEI that suppresses metal dissolution — a key contributor to irreversible capacity loss in high-nickel full cells. The 228 mAh g⁻¹ capacity at 0.2C achieved in the full cell using optimised dual-additive formation confirms that the electrolyte additive composition defines the quality of the interfacial passivation layer laid down during formation. Standards bodies such as the IEC recognise electrolyte composition as a critical parameter in battery performance qualification.

Oxygen release during formation also drives parasitic reactions at the cathode surface. Research from the Beijing Institute of Technology (2023) shows that released oxygen species at highly delithiated states react with electrolyte, accelerating structural deterioration and triggering thermal degradation. Formation protocols that restrict the upper cutoff voltage or incorporate pre-passivation steps suppress oxygen evolution during the critical first cycle, preventing the formation of resistive electrolyte oxidation products on the cathode surface. The La₂Mo₂O₉ coating approach demonstrated in this work represents one class of pre-passivation strategy that reduces oxygen evolution during formation.

A notable structural trend is the emergence of single-crystal NCM as a formation protocol-friendly material. The absence of grain boundaries in single-crystal particles eliminates intergranular cracking during formation, making the electrode response more predictable and the CEI formation more uniform. This is highlighted by the EMPA study on single-crystal NCM (2023), which notes that the single-crystal morphology reduces the mechanical complexity of the formation response compared to polycrystalline secondary particles, enabling more precise protocol engineering. Research published by Nature has similarly highlighted single-crystal cathode architectures as a structural enabler for improved formation outcomes in high-nickel systems.

Key Institutional Contributors and Emerging Innovation Trends

The research landscape for formation protocol optimisation in high-nickel cathodes spans academic institutions, national laboratories, and industrial R&D groups across multiple continents, with each contributing distinct methodological perspectives. Understanding the institutional map helps R&D teams identify where foundational constraints are established versus where practical protocol engineering is advancing.

Foundational theory and modelling

MIT (2022) contributes foundational theoretical models of disorder-driven degradation that directly inform the voltage and temperature bounds that formation protocols must respect — specifically the 4.4 V vs. Li/Li⁺ threshold above which rock-salt shell formation becomes irreversible. Imperial College London (2023) provides quantitative cell-level degradation modelling that separates LAM and LLI contributions to capacity fade, enabling rational protocol design around minimising rock-salt shell volume during formation. Columbia University (2022) identifies the atomic-scale surface degradation onset during first charge, directly establishing the thermodynamic and kinetic basis for voltage-limited formation protocols.

Protocol engineering and diagnostics

The Faraday Institution (UK, 2021) directly addresses the formation protocol–capacity loss link, establishing the experimental framework for systematic protocol comparison across C-rate, voltage window, temperature, and rest step variables. The University of Michigan (2024) holds a pending patent that translates academic degradation insights into a practical protocol selection methodology based on first-cycle internal resistance diagnostics — a manufacturing-ready approach that bridges laboratory research and production-scale battery formation.

Materials and surface engineering

AIST Japan (2019) demonstrates the practical integration of pre-formation surface treatment with aqueous binder processing in the NCA system, achieving 92% retention at 50 cycles through controlled formation-stage surface chemistry. South China University of Technology (2022) and Central South University (2024) provide comprehensive reviews and experimental studies of surface modification and failure mechanisms in Ni-rich cathodes, supplying the materials science framework within which formation protocols must operate. EMPA Switzerland (2023) advances single-crystal NCM electrolyte optimisation, showing how morphology selection interacts with formation protocol design. According to WIPO‘s global patent data, battery formation and electrode interface engineering is among the fastest-growing patent filing categories in the energy storage sector.

“Internal resistance measured after the first charge is a predictive indicator of long-term aging — a protocol producing lower first-cycle internal resistance yields superior long-term capacity retention.” — University of Michigan patent, 2024

A cross-cutting trend across all institutional contributors is the recognition that formation protocol optimisation cannot be addressed in isolation from material morphology, electrolyte chemistry, and pre-formation surface conditioning. The most effective approaches in the literature combine at least two of these variables simultaneously — for example, single-crystal morphology combined with fluorinated additive formation, or CTCE pre-treatment combined with low-rate constant-voltage formation. This systems-level perspective is increasingly reflected in patent filings, as evidenced by the University of Michigan’s diagnostic patent, which is designed to evaluate the combined outcome of all formation variables through a single measurable quantity: first-cycle internal resistance. For teams tracking this space, PatSnap’s R&D intelligence platform provides structured access to the full landscape of battery formation patents and literature.