Sections were collected and transferred to a Cu TEM grid with carbon film (Ted Pella) using a micromanipulator and a gold-coated human eyelash, with a constant a.c. pulse provided by a CRION antistatic device to facilitate this transfer. STXM measurements were performed at beamline 7.0.1.2 50 at the Advanced Light Source at Lawrence Berkeley National Laboratory using a zone plate with an outer zone width of 45 nm. For purposes of spatially aligning images at different energies, Gaussian smoothing was applied (σ=0.2), followed by a Sobel filter. The resulting images were then aligned using the phase cross-correlation algorithm followed by the enhanced correlation coefficient algorithm, all implemented in custom Python code. Spectroscopic analysis was performed on the raw, but aligned, images, without Gaussian smoothing or Sobel filter. Additional details of the spectroscopic analysis are available in the SI. TGA Thermogravimetric analysis (Setaram THEMYS) was performed following the same temperature and gas profile as in a tube furnace with the addition of a final, active cooling step during which the sample is cooled at a rate of 10 °C/min to room temperature. Typical sample size was 40-60 mg of combined Li 2 CO 3 and TM (oxy)hydroxide precursor. For each TGA run, a blank run with an empty crucible and identical time-temperature profile and gas environment was conducted. This blank run was then subtracted from the relevant experimental run to isolate the signal from mass loss due to calcination from factors such as changes in buoyancy. To ensure that no residual sample from one run impacted the signal on subsequent runs, crucibles were cleaned and burned out between runs. Cleaning entailed rinsing with deionized (DI) water and isopropyl alcohol followed by sonication in DI water for 10 min. Subsequently, the crucible was heated to >100 °C above the top calcination temperature for >10 h.