High‐nickel LiNi1−x−yMnxCoyO2 and LiNi1−x−yCoxAlyO2 cathodes are receiving growing attention due to the burgeoning demands on high‐energy‐density lithium‐ion batteries. The presence of both cobalt and manganese in them, however, triggers multiple issues, including high cost, high toxicity, rapid surface deterioration, and severe transition‐metal dissolution. Herein, a Co‐ and Mn‐free ultrahigh‐nickel LiNi0.93Al0.05Ti0.01Mg0.01O2 (NATM) cathode that exhibits 82% capacity retention over 800 deep cycles in full cells, outperforming two representative high‐Ni cathodes LiNi0.94Co0.06O2 (NC, 52%) and LiNi0.90Mn0.05Co0.05O2 (NMC, 60%) is presented. It is demonstrated that a titanium‐enriched surface along with aluminum and magnesium as the stabilizing ions in NATM not only ameliorates unwanted side reactions with the electrolyte and structural disintegrity, but also mitigates transition‐metal dissolution and active lithium loss on the graphite anode. As a result, the graphite anode paired with NATM displays an ultrathin (≈8 nm), monolayer anode‐electrolyte interphase architecture after extensive cycling. Furthermore, NATM displays considerably enhanced thermal stability with an elevated exothermic temperature (213 °C for NATM vs 180 and 190 °C for NC and NMC, respectively) and remarkably reduced heat release. This work sheds light on rational compositional design to adopt ultrahigh‐Ni cathodes in lithium‐based batteries with low cost, long service life, and improved thermal stability.

High-Ni layered oxides with Ni contents greater than 90% are promising cathode candidates for high-energydensity Li-ion batteries. However, drastic electrode−electrolyte reactions and mechanical degradation issues limit their cycle life and practical viability. We demonstrate here that Li-Ni 0.94 Co 0.04 Zn 0.02 O 1.99 (NCZ), obtained by incorporating 2 mol % Zn 2+ into an ultrahigh-Ni baseline cathode material LiNi 0.94 Co 0.06 O 2 (NC), delivers superior cell performance. NCZ retains 74% of the initial capacity after 500 cycles in a full cell assembled with a graphite anode, outperforming NC (62% retention). NCZ also possesses a higher average discharge voltage relative to NC with an outstanding average voltage retention of over 99% after 130 cycles in half cells. Bulk structural investigations unveil that Zn doping promotes a smoother phase transition, suppresses anisotropic lattice distortion, and maintains the mechanical integrity of cathode particles. Furthermore, NCZ shows an enhanced interphase stability after long-term cycling, in contrast to the seriously degraded surface chemistry in NC. This work provides a practically viable approach for designing higher-energy-density high-Ni layered oxide cathodes for lithium-ion batteries.

Bulk, surface, and interfacial instabilities that impact the cycle and thermal performances are the major challenges with high‐energy‐density LiNi1−x–yMnxCoyO2 (NMC) cathodes with high nickel contents. It is generally believed that the instabilities and performance losses become exponentially aggravated as the nickel content increases. Disparate from this prevailing belief, it is herein demonstrated that NMC cathodes with higher Ni contents may imply better overall stability than “lower‐Ni” cathodes under an identical degree of delithiation (charging) conditions. With two representative cathodes, LiNi0.8Mn0.1Co0.1O2 and LiNiO2, a systematic investigation into their stabilities with control of the degree of delithiation is presented. Electrochemical tests indicate that LiNiO2 displays better cyclability than LiNi0.8Mn0.1Co0.1O2 at the same delithiation state. Comprehensive structural and interphase investigations unveil that the inferior cyclability of LiNi0.8Mn0.1Co0.1O2 predominantly results from aggravated parasitic reactions, and the interphase stability may be more critical than lattice stability in dictating cyclability. Also, LiNiO2 delivers similar or better thermal behavior than LiNi0.8Mn0.1Co0.1O2. The findings demonstrate a strong correlation of the stability of NMC cathodes to the degree of delithiation state rather than the Ni content itself, highlighting the importance of reassessing the true implications of Ni content and structural and interphasial tuning on the stabilities of NMC cathodes.

LiNiO 2 (LNO) is a high-capacity and model cathode first discovered in the 1980s that fell out of favor due to its intrinsic instabilities. However, research activities toward LNO are once again on the rise as the push for higher-energy-density cells marches on. We demonstrate here that with appropriate modern electrolytes, major performance improvements can be achieved with LNO with no additional modifications. Cells with a localized high concentration electrolyte (LHCE) deliver 92% capacity retention after 200 cycles compared with 56% capacity retention in a baseline carbonate electrolyte, maintain 94% capacity after high-voltage storage compared with 77% capacity, and display a higher onset temperature of thermal runaway of 244 °C compared with 188 °C. These improvements are attributed to the LHCE's high oxidative stability and its formation of fluorine-rich interphases. Although further characterization of this new class of electrolyte is necessary, this work demonstrates that modern electrolytes can be dropin enablers of high-capacity, long-cycle-life cells.

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