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Sodium ion batteries (NIBs) are an attractive alternative to lithium‐ion batteries in applications that require large‐scale energy storage due to sodium's high natural abundance and low cost. Hard carbon (HC) is the most promising anode material for NIBs; however, there is a knowledge gap in the understanding of the sodium binding mechanism that prevents a rational design of HC. This study tunes sucrose‐derived HC via synthesis temperature then evaluates the structural, physical, and electrochemical properties. Neutron total scattering is used to generate structural models by fitting pair distribution functions (PDF) with a combination of molecular dynamics and reverse Monte Carlo methods. From this model, the number and type of structural features are identified, quantified, and correlated to the galvanostatic charge/discharge. A method of PDF “fingerprinting” binding sites using Na probe atoms is developed and analyzing these PDFs reveals an atomistic view of ion binding sites responsible for “defect” storage mechanisms. Combining these techniques results in an atomic‐level study that provides a big picture of the Na‐binding mechanism in NIBs, which allows for more precise tuning of the structure–property relationships in the future. The methodologies developed will also enable new strategies for the analysis of amorphous functional materials.

Aqueous rechargeable batteries are promising solutions for large‐scale energy storage. Such batteries have the merit of low cost, innate safety, and environmental friendliness. To date, most known aqueous ion batteries employ metal cation charge carriers. Here, we report the first “rocking‐chair” NH₄‐ion battery of the full‐cell configuration by employing an ammonium Prussian white analogue, (NH₄)_1.47Ni[Fe(CN)₆]_0.88, as the cathode, an organic solid, 3,4,9,10‐perylenetetracarboxylic diimide (PTCDI), as the anode, and 1.0 maqueous (NH₄)₂SO₄as the electrolyte. This novel aqueous ammonium‐ion battery demonstrates encouraging electrochemical performance: an average operation voltage of ca. 1.0 V, an attractive energy density of ca. 43 Wh kg⁻¹based on both electrodes’ active mass, and excellent cycle life over 1000 cycles with 67 % capacity retention. Importantly, the topochemistry results of NH₄⁺in these electrodes point to a new paradigm of NH₄⁺‐based energy storage.