One-Precursor Coating Tames Fading Cobalt-Free Lithium-Rich Cathodes

Lithium-ion batteries are on the verge of a materials revolution, and one of the most tantalizing candidates has long been the cobalt-free lithium-rich manganese-based oxide cathode, known in the field as LRMO. These compounds promise an extraordinary specific capacity and a remarkably low cost, because they lean on abundant manganese instead of scarce, ethically fraught cobalt. Yet for all their promise, LRMOs have been haunted by three stubborn demons: their operating voltage decays with every charge-discharge cycle, their capacity fades steadily, and the kinetics at the electrode-electrolyte interface are painfully sluggish. A team of researchers at Northeastern University in China has now reported a strikingly simple fix, described in the Journal of Materials Science, that addresses all three problems at once with a single precursor and an elegant in situ surface treatment.

The strategy, developed by Yanni Li, Zhigui Zhang, Yu Chen, and colleagues under the supervision of corresponding authors Dan Wang and Zhiyuan Wang, hinges on constructing a dual-function surface coating composed of lithium phosphate, Li3PO4, and a spinel phase directly on the surface of the LRMO particles. What makes the approach remarkable is its economy: ammonium dihydrogen phosphate, NH4H2PO4, serves as the sole precursor. During a facile thermal treatment, this single compound orchestrates the simultaneous formation of two structurally distinct surface layers, each tackling a different failure mode of the cathode. No exotic reagents, no multi-step deposition sequences, no vacuum processes—just one salt, one heat treatment, and a carefully tuned chemistry.

The electrochemical results are impressive. The optimized sample, designated LP-1% for its one percent precursor loading, retains a discharge capacity of 194 milliampere-hours per gram after 200 cycles at a demanding 1C rate, corresponding to a capacity retention of 94 percent. For context, untreated pristine LRMO particles typically bleed capacity far more rapidly under identical conditions, and their voltage curves sag in ways that erode the usable energy of a full battery pack. The coated material also shows significantly improved rate capability, meaning it can deliver its charge faster without collapsing—a property that matters enormously for electric vehicles that need to accelerate and fast-charge.

To understand why the coating works, it helps to dissect the two layers independently. The outer Li3PO4 layer acts as a chemical shield. In an uncoated LRMO, the highly reactive surface of the cathode particle is in direct contact with the liquid electrolyte, and at the high operating voltages these materials demand, that contact triggers a cascade of parasitic side reactions. Electrolyte decomposition products build up, oxygen atoms escape from the lattice, and the surface gradually transforms into an electrochemically dead layer. The Li3PO4 coating interrupts this process by physically isolating the active material from the electrolyte, suppressing the interfacial side reactions that would otherwise consume both lithium inventory and electrolyte over hundreds of cycles.

The inner spinel phase performs a subtler but equally vital role. Spinel-structured oxides offer three-dimensional channels through which lithium ions can diffuse rapidly, in contrast to the more constrained pathways of the layered rock-salt structure that dominates the LRMO bulk. By converting the outermost shell of each particle into spinel, the treatment effectively builds a fast-ion highway around every grain, explaining the improved rate performance. Even more importantly, the spinel shell reduces the unit cell volume change that the particle experiences as lithium ions shuttle in and out during cycling. Repeated expansion and contraction is what drives mechanical fatigue in cathode particles: microscopic cracks nucleate, propagate, and eventually fracture the particle into electrically disconnected fragments. By damping this volume change, the spinel layer substantially mitigates particle cracking and the structural degradation that follows.

The synergy between the two layers is the conceptual heart of the work. Interfacial instability and bulk structural decay have traditionally been treated as separate problems requiring separate solutions—perhaps a protective oxide here, a dopant there. The NH4H2PO4 treatment demonstrates that a single, well-chosen precursor can address both simultaneously, because the phosphate chemistry naturally yields a lithium-ion-conducting insulator while the reaction with the underlying oxide reconstructs the surface into the spinel framework. The authors also note that the coating suppresses oxygen release from the lattice and intergranular cracking, two processes that are tightly coupled: when lattice oxygen escapes at high voltage, it leaves behind vacancies and structural disorder that weaken the particle and accelerate voltage decay.

The significance of this work is amplified by the broader context of battery materials research. Cobalt has become the industry’s problem child: its supply chain is concentrated in politically unstable regions, mining practices raise serious human rights concerns, and its price volatility destabilizes cell economics. Cobalt-free lithium-rich manganese-based oxides sidestep all of these issues while offering capacities that exceed conventional layered cathodes by a wide margin, thanks in part to the participation of anionic oxygen redox in charge storage. But the very oxygen redox chemistry that grants LRMOs their high capacity is also the source of their instability, because highly oxidized lattice oxygen is prone to irreversible loss. Surface engineering strategies like the one reported here are therefore among the most actively pursued routes to making these materials practical, and the field has seen a wave of related approaches, from alumina and lithium aluminate coatings to aluminum phosphate dual shells and lithium titanate or lithium zirconium phosphate modifications.

What distinguishes the new study within this crowded landscape is the in situ character of the coating. Many conventional coating methods deposit a foreign material onto pre-synthesized cathode particles, which raises questions about adhesion, uniformity, and unwanted interfacial reactions between coating and substrate. An in situ treatment, by contrast, grows the protective layers out of the cathode’s own surface chemistry, ensuring intimate contact and structural compatibility. The result is a coating that is not merely painted on but integrated into the particle, which likely explains why the LP-1% sample outperforms both the pristine material and the other coating loadings tested in the study—too little precursor leaves the surface exposed, while too much presumably adds resistive dead weight.

The research was carried out at the School of Materials Science and Engineering at Northeastern University in Shenyang and the School of Resources and Materials at Northeastern University at Qinhuangdao, with support from the Key Laboratory of Dielectric and Electrolyte Functional Material of Hebei Province. Funding came from the National Natural Science Foundation of China, the Hebei Natural Science Foundation, the Fundamental Research Funds for the Central Universities, and several provincial and university programs. The team’s earlier publications reveal a sustained campaign against LRMO degradation mechanisms, including work on spinel-carbon composite coatings, oxygen vacancy and stacking fault engineering, and dual-element substitution strategies to suppress voltage decay—efforts that have now converged on this streamlined single-precursor solution.

For the battery industry, the practical appeal is obvious. A coating process that requires only ammonium dihydrogen phosphate and a thermal treatment slot could, in principle, be grafted onto existing cathode manufacturing lines with minimal capital investment, unlike approaches that demand atomic layer deposition equipment or multiple sintering steps. If the 94 percent capacity retention over 200 cycles can be extended to the thousands of cycles demanded by electric vehicle warranties, and if the voltage stability proves durable at the pack level, cobalt-free lithium-rich manganese cathodes could finally graduate from laboratory curiosity to commercial contender. The work is a reminder that in materials science, the most transformative advances sometimes arrive not as exotic new compounds but as clever, economical treatments that coax existing materials into behaving like the versions we always hoped they could be.

Subject of Research: In situ surface coating of cobalt-free lithium-rich manganese-based cathode materials for lithium-ion batteries

Article Title: In situ construction of surface coating for boosting the electrochemical performance of cobalt-free Li-rich Mn-based cathode

Article References: Li, Y., Zhang, Z., Chen, Y., Zheng, R., Wang, D., Song, Z., Sun, H., Liu, Y., & Wang, Z. (2026). In situ construction of surface coating for boosting the electrochemical performance of cobalt-free Li-rich Mn-based cathode. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13804-7

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13804-7

Keywords: lithium-ion batteries, cathode materials, lithium-rich manganese oxide, cobalt-free, surface coating, Li3PO4, spinel phase, voltage decay, capacity retention, electrolyte interface, NH4H2PO4 precursor, energy storage