transportation emissions account for nearly one-quarter of all greenhouse gases. [1] However, the current fleet of EVs, mainly powered by lithium-ion batteries (LIBs), still falls short of performance standards, especially in driving range per charge, that are required for broad consumer appeal. A driving range comparable to that of an ICEV requires a substantial increase in the energy density of LIBs, whose capacity is largely limited by the cathode. [2][3][4] Archetypal cathodes for LIBs deployed in current EVs are layered Li[Ni x Co y (Al or Mn) 1−x−y ]O 2 (Al = NCA or Mn = NCM) oxide materials. [4][5][6][7] Both cathodes were derived from LiNiO 2 , which has a high theoretical capacity of 270 mAh g −1 . Multiple phase transitions during delithiation quickly deteriorate the reversible capacity of LiNiO 2 ; this inherent structural instability renders the cathode unsuitable for EV applications. NCA cathodes were developed by introducing Co 3+ and Al 3+ to LiNiO 2 to prevent multistep phase transitions and stabilize the structure, resulting in the Li[Ni 0.8 Co 0.15 Al 0.05 ]O 2 cathode, which currently powers the Tesla Model S. [8] In another example, Ni was partially replaced with Co and Mn to develop Li[Ni 1/3 Co 1/3 Mn 1/3 ]O 2 ; this cathode exhibited excellent capacity retention and thermal stability but its capacity was limited to 160 mAh g −1 . [9] To compensate for inferior capacity, Ni content was increased to x = 0.6; this cathode is also widely commercialized. Although both NCA and NCM cathodes are adequate, the energy density of 350 Wh kg −1 required to provide a drive range threshold of 300 miles per charge requires a new class of layered oxide cathodes. As Ni content exceeds x = 0.8, NCA and NCM cathodes are plagued by increasingly compromised battery life and thermal safety, due to rapid capacity fading and an abundance of unstable Ni 4+ species, as observed in LiNiO 2 . [4,[10][11][12][13] To overcome the inherent instability of Ni-rich NCM and NCA cathodes, we propose a new type of layered oxide cathode, Li[Ni x Co y W 1−x−y ]O 2 . Previous work indicates that W doping of LiNiO 2 substantially improved its cycling stability without sacrificing energy density. [14,15] In this study, we show that replacement of Al ions with W ions in a Ni-rich NCA layered oxide cathode markedly modifies the cathode microstructure through particle refinement and greatly improves the cycling stability of the cathode. We compare the electrochemical performance of the Li[Ni 0.9 Co 0.09 W 0.01 ]O 2 cathode (NCW90) to the well-characterized Li[Ni 0.885 Co 0.1 Al 0.015 ]O 2 (NCA89) to demonstrate its superior structural and thermal stability compared to the commercialized NCA cathode.Substituting W for Al in the Ni-rich cathode Li[Ni 0.885 Co 0.10 Al 0.015 ]O 2 (NCA89) produces Li[Ni 0.9 Co 0.09 W 0.01 ]O 2 (NCW90) with markedly reduced primary particle size. Particle size refinement considerably improves the cathode's cycling stability such that the NCW90 cathode retains 92% of its initial capacity after 1000 cycles (c...