Tuning Dopant Distribution for Stabilizing the Surface of High‐Nickel Layered Oxide Cathodes for Lithium‐Ion Batteries

Abstract

Layered oxide cathodes with a high‐nickel (Ni ≥ 0.9) content exhibit great potential for enabling high‐energy‐density lithium‐ion batteries. However, their practical feasibility and cycle life are hampered by severe surface reactivity with the electrolyte. A LiNi0.90Co0.05Al0.05O2 cathode is presented enriched with Al on the surface (S‐NCA) and benchmark it against a LiNi0.90Co0.05Al0.05O2 cathode obtained by a conventional co‐precipitation method that has a uniform Al distribution throughout the bulk (B‐NCA). The S‐NCA cathode greatly outperform with an impressive capacity retention of 84% after 1000 cycles in pouch full cells with graphite anode compared to 62% retention for B‐NCA. Advanced surface characterization methodologies, including time‐of‐flight secondary‐ion mass spectrometry, reveal that the Al‐enriched surface morphology facilitates the formation of a robust, thin electrode‐electrolyte interphase (EEI), effectively suppressing the oxidative decomposition of the electrolyte, gas generation, and metallic dead lithium formation on graphite anode. The results illustrate that surface reactivity with the electrolyte is the primary factor limiting the cycle of cells with high‐Ni cathodes. The work provides valuable insights toward the practical viability of ultrahigh‐Ni cathodes in lithium‐ion batteries.

Factors Influencing Gas Evolution from High‐Nickel Layered Oxide Cathodes in Lithium‐Based Batteries

“…All cathodes were evaluated with OEMS with a CC-CV charging protocol to charge at a 0.1 C rate to an upper cutoff voltage of 4.4 V (CC), followed by holding at CV for 6 h and allowing to rest for 10 h. Additional details on the characterization techniques employed to validate the cathode composition and Al distribution are provided in our previous article. [70] The total amount of gas evolution from the coated sample, NCA-S (213 μmol m −2 ), is found to be less than that from the uncoated sample, NCA-B (266 μmol m −2 ). The normalization of the gas evolution from the NCA cathodes was conducted assuming a surface area of 0.2514 m 2 g −1 that was measured for NCA-90 with BET measurement.…”

“…All cathodes were evaluated with OEMS with a CC‐CV charging protocol to charge at a 0.1 C rate to an upper cutoff voltage of 4.4 V (CC), followed by holding at CV for 6 h and allowing to rest for 10 h. Additional details on the characterization techniques employed to validate the cathode composition and Al distribution are provided in our previous article. [ 70 ]…”

“…[68,69] To highlight the importance of mitigating cathode surface reactivity, we present OEMS data conducted on two samples of LiNi 0.9 Co 0.05 Al 0.05 O 2 (NCA-90) from our previous work that were synthesized in two different ways (Figure 7). [70] The first synthesis method employs coprecipitation to distribute Al at an atomic level throughout the bulk of the NCA cathode precursor (referred to as NCA-B). The second synthesis method coats an LiNi 0.95 Co 0.05 O 2 hydroxide precursor with enough aluminum isopropoxide dispersed in isopropanol solution to achieve the same average molar composition as NCA-90, although the surface of the cathode will be enriched with Al (referred to as NCA-S).…”

“…The total amount of gas evolved is provided in the gas evolution plot and is the sum of CO 2 , O 2 , and CO gases evolved from the cathode. Reproduced with permission [70]. Copyright 2023, Wiley-VCH.…”