Coordination of dissolved transition metals in pristine battery electrolyte solutions determined by NMR and EPR spectroscopy.

The solvation of dissolved transition metal ions in lithium-ion battery electrolytes is not well-characterised experimentally, although it is important for battery degradation mechanisms governed by metal dissolution, deposition, and reactivity in solution. This work identifies the coordinating species in the Mn and Ni solvation spheres in LiPF/LiTFSI-carbonate electrolyte solutions by examining the electron-nuclear spin interactions, which are probed by pulsed EPR and paramagnetic NMR spectroscopy. These techniques investigate solvation in frozen electrolytes and in the liquid state at ambient temperature, respectively, also probing the bound states and dynamics of the complexes involving the ions.

Quantifying Dissolved Transition Metals in Battery Electrolyte Solutions with NMR Paramagnetic Relaxation Enhancement.

Transition metal dissolution is an important contributor to capacity fade in lithium-ion cells. NMR relaxation rates are proportional to the concentration of paramagnetic species, making them suitable to quantify dissolved transition metals in battery electrolytes. In this work, Li, P, F, and H longitudinal and transverse relaxation rates were measured to study LiPF electrolyte solutions containing Ni, Mn, Co, or Cu salts and Mn dissolved from LiMnO.

Solution NMR of Battery Electrolytes: Assessing and Mitigating Spectral Broadening Caused by Transition Metal Dissolution.

NMR spectroscopy is a powerful tool that is commonly used to assess the degradation of lithium-ion battery electrolyte solutions. However, dissolution of paramagnetic Ni and Mn ions from cathode materials may affect the NMR spectra of the electrolyte solution, with the unpaired electron spins in these paramagnetic solutes inducing rapid nuclear relaxation and spectral broadening (and often peak shifts). This work establishes how dissolved Ni and Mn in LiPF electrolyte solutions affect H, F, and P NMR spectra of pristine and degraded electrolyte solutions, including whether the peaks from degradation species are at risk of being lost and whether the spectral broadening can be mitigated.

Determining the oxidation states of dissolved transition metals in battery electrolytes from solution NMR spectra.

Dissolved transition metal ions can induce peak shifts in the NMR spectra of degraded battery electrolytes. Here, we exploit this staightforward, accessible method to calculate magnetic moments for dissolved Ni, Mn, Co, and Cu; subsequent analysis of dissolution from LiMnO, LiNiO, and LiNiMnO shows that the dissolved metals are exclusively divalent.

Electrolyte Reactivity at the Charged Ni-Rich Cathode Interface and Degradation in Li-Ion Batteries.

The chemical and electrochemical reactions at the positive electrode-electrolyte interface in Li-ion batteries are hugely influential on cycle life and safety. Ni-rich layered transition metal oxides exhibit higher interfacial reactivity than their lower Ni-content analogues, reacting via mechanisms that are poorly understood. Here, we study the pivotal role of the electrolyte solvent, specifically cyclic ethylene carbonate (EC) and linear ethyl methyl carbonate (EMC), in determining the interfacial reactivity at charged LiNiMnCoO (NMC111) and LiNiMnCoO (NMC811) cathodes by using both single-solvent model electrolytes and the mixed solvents used in commercial cells.