Deep learning of experimental electrochemistry for battery cathodes across diverse compositions

Artificial intelligence (AI) has emerged as a powerful tool in the discovery and optimization of novel battery materials. However, the adoption of AI in battery cathode representation and discovery is still limited due to the complexity of optimizing multiple performance properties and the scarcity of high-fidelity data. In this study, we present a comprehensive machine-learning model (DRXNet) for battery informatics and demonstrate the application in discovery and optimization of disordered rocksalt (DRX) cathode materials. We have compiled the electrochemistry data of DRX cathodes over the past five years, resulting in a dataset of more than 30,000 discharge voltage profiles with 14 different metal species. Learning from this extensive dataset, our DRXNet model can automatically capture critical features in the cycling curves of DRX cathodes under various conditions. Illustratively, the model gives rational predictions of the discharge capacity for diverse compositions in the Li--Mn--O--F chemical space and high-entropy systems. As a universal model trained on diverse chemistries, our approach offers a data-driven solution to facilitate the rapid identification of novel cathode materials, accelerating the development of next-generation batteries for carbon neutralization

Design principles for high transition metal capacity in disordered rocksalt Li-ion cathodes

The discovery of facile Li transport in disordered, Li-excess rocksalt materials has opened a vast new chemical space for the development of high energy density, low cost Li-ion cathodes. We develop a strategy for obtaining optimized compositions within this class of materials, exhibiting high capacity and energy density as well as good reversibility, by using a combination of low-valence transition metal redox and a high-valence redox active charge compensator, as well as fluorine substitution for oxygen. Furthermore, we identify a new constraint on high-performance compositions by demonstrating the necessity of excess Li capacity as a means of counteracting high-voltage tetrahedral Li formation, Li-binding by fluorine and the associated irreversibility. Specifically, we demonstrate that 10–12% of Li capacity is lost due to tetrahedral Li formation, and 0.4–0.8 Li per F dopant is made inaccessible at moderate voltages due to Li–F binding. We demonstrate the success of this strategy by realizing a series of high-performance disordered oxyfluoride cathode materials based on Mn²+/⁴+ and V⁴+/⁵+ redox.Vehicle Technologies Program (U.S.) (Contract No. DE-AC02-05CH11231)United States. Department of Energy. Office of Energy Efficiency and Renewable Energy. Advanced Battery Materials Research Program (Subcontract No. 7056411)National Science Foundation (U.S.) (Reward No. OCI-1147503)National Science Foundation (U.S.) (grant number ACI- 105357)National Science Foundation (U.S.) (NSF DMR 172025)United States. Department of Energy (Contract No. DE-AC02-06C H11357)United States. Department of Energy. Office of Science (contract no. DE-AC02-05CH11231

Short-range order and macroscopic Lithium transport in cation-disordered rocksalt cathodes

The tremendous success and growth of Lithium (Li)-ion based energy storage in a broad range of applications is likely to strain our natural resources. Projected growth of Li-ion production towards 1 TWh/year will require more than a million tons of Co/Ni combined, which constitutes a very sizeable fraction of the annual production of these metals. The recent development of Li-excess cation-disordered rocksalt (DRX) cathodes, which require no separate Li layer and transition metal (TM) layer in the cation sublattice, is providing an avenue for the Li-ion battery field to develop high energy density cathodes with more abundant and less expensive metals, such as Mn, Fe and Ti. Unlike the traditional layered NCM cathodes in which Li ions transport within the well-defined Li layers, the Li ions diffuse through a “3-D” Li rich pathway (‘0-TM’ channel) in DRX cathodes, i.e., the feasible Li hops require that the intermediate tetrahedral sites along the Li diffusion path are coordinated only by Li (no transition metal). The complexity of this class of DRX cathodes mainly lies in the fact that lacking in long-range order though, DRX cathodes, in most cases, present various types of cation short-range order (SRO), which controls the frequency and connectivity of Li migration channels, thus, macroscopic Li transport.In this thesis, two general strategies to engineer the cation SRO in DRX cathodes will be demonstrated through compositional design, combining electrochemical tests, advanced characterizations and computational investigations. The first part of the thesis will talk about the control of SRO in DRX cathodes through fluorine doping on anion sublattices. The strong Li-F interaction modifies the cation SRO in DRX materials by forming Li-rich domains around F ions. Four well-chosen compositions within the Li–Mn–O–F DRX chemical space with different Li content and F content were synthesized, characterized, electrochemically tested and modeled: Li1.333Mn(III)0.667O1.333F0.667 (HLF67), Li1.333Mn(III)0.5Mn(IV)0.167O1.5F0.5 (HLF50), Li1.333Mn(III)0.333Mn(IV)0.333O1.667F0.333 (HLF33), and Li1.25Mn(II)0.167Mn(III)0.583O1.333F0.667 (LLF67). While all compositions tested achieve higher than 200 mAh/g initial capacity the material with high Li-excess (1.333 per formula unit, LixMn2-xO2-yFy) and moderate fluorination (0.333 per formula unit) achieves 349 mAh/g initial capacity and 1068 Wh/kg specific energy. Higher fluorination (0.667 per formula unit) leads to a less efficient Li diffusion network, resulting in a decrease in capacity (specific energy) to be 256 mAh/g (822 Wh/kg). However, the activation of Mn2+/Mn4+ redox enabled by F substitution significantly improve the cycle life of DRX cathodes, with more than 85% retained after 30 cycles even upon charging to 5.0V. It can thus be concluded that the Li-site distribution, which can be significantly modified by fluorine substitution, plays a more important role than the metal-redox capacity in determining the initial capacity, whereas the metal-redox capacity is more closely related to the cyclability of the materials. A design map will also be presented, which shows that the macroscopic Li transport is strongly controlled by the Li-excess level and F content within a fixed DRX chemical space and can be correlated to the observed capacities of a DRX cathode, as corroborated by electrochemical tests. Similar computational evaluations will also be shown in various different DRX chemistries to demonstrate that fluorination is a generalized strategy to engineering SRO in DRX cathodes. The second part of the thesis will talk about the control of SRO in DRX cathodes through TM doping on cation sublattices. With a fixed Li and F content, TM doping can frustrate the cation SRO in DRX cathodes by increasing configurational entropy to form so-called high-entropy (HE) DRX, thus improve the Li transport, i.e. capacity and rate capability in a significant way. As a demonstration, a group of DRX cathodes containing two, four or six TM species are designed. It is shown that SRO in these DRX cathodes systematically decreases, as a consequence, energy density and rate capability systematically increase as more metal cations are mixed together, even though the total metal content are fixed. Remarkably, a HE DRX cathode with six TM species achieves 307 mAh g−1 (955 Wh kg−1) at a low rate (20 mA g−1), and retains more than 170 mAh g−1 when cycling at a high rate of 2,000 mA g−1. The compatibility between various TM ions in DRX compounds is also investigated to facilitate future experimental design and a phase-pure HE DRX compound containing twelve TM species was successfully synthesized as a proof-of-concept

Oxygen Vacancy Introduction to Increase the Capacity and Voltage Retention in Li‐Excess Cathode Materials

Li-rich rocksalt oxides are promising cathode materials for lithium-ion batteries due to their large capacity and energy density, and their ability to use earth-abundant elements. The excess Li in the rocksalt, needed to achieve good Li transport, reduces the theoretical transition metal redox capacity and introduces a labile oxygen state, both of which lead to increased oxygen oxidation and concomitant capacity loss with cycling. Herein, it is demonstrated that substituting the labile oxygen in Li-rich cation-disordered rocksalt materials with a vacancy is an effective strategy to inhibit oxygen oxidation. It is found that the oxygen vacancy in cation-disordered lithium manganese oxide favors high Li coordination thereby reducing the concentration of unhybridized oxygen states, while increasing the theoretical Mn capacity. It is shown that in the vacancy-containing compound, synthesized by ball milling, the Mn valence is lowered to less than +3, providing access to more than 300 mAh g−1 capacity from the Mn2+/Mn4+ redox reservoir. The increased transition metal redox and decreased O oxidation are found to improve the capacity and voltage retention, indicating that oxygen vacancy creation to remove the most vulnerable oxygen ions and reduce transition metal valence provides a new opportunity for the design of high-performance Li-rich rocksalt cathodes

Oxygen Vacancy Introduction to Increase the Capacity and Voltage Retention in Li‐Excess Cathode Materials

Li‐rich rocksalt oxides are promising cathode materials for lithium‐ion batteries due to their large capacity and energy density, and their ability to use earth‐abundant elements. The excess Li in the rocksalt, needed to achieve good Li transport, reduces the theoretical transition metal redox capacity and introduces a labile oxygen state, both of which lead to increased oxygen oxidation and concomitant capacity loss with cycling. Herein, it is demonstrated that substituting the labile oxygen in Li‐rich cation‐disordered rocksalt materials with a vacancy is an effective strategy to inhibit oxygen oxidation. It is found that the oxygen vacancy in cation‐disordered lithium manganese oxide favors high Li coordination thereby reducing the concentration of unhybridized oxygen states, while increasing the theoretical Mn capacity. It is shown that in the vacancy‐containing compound, synthesized by ball milling, the Mn valence is lowered to less than +3, providing access to more than 300 mAh g−1 capacity from the Mn2+/Mn4+ redox reservoir. The increased transition metal redox and decreased O oxidation are found to improve the capacity and voltage retention, indicating that oxygen vacancy creation to remove the most vulnerable oxygen ions and reduce transition metal valence provides a new opportunity for the design of high‐performance Li‐rich rocksalt cathodes

Supporting data for "Operando visualization of kinetically induced lithium heterogeneities in single-particle layered Ni-rich cathodes"

This data set contains all the data presented in the main text figures and extended data figures (for the manuscript titled ‘Operando visualization of kinetically-induced lithium heterogeneities in single-particle layered Ni-rich cathodes’). The information on how the data was acquired and processed is detailed in the open access manuscript which has been deposited in this repository. The check-list ‘Repository_list_Joule.xlsx’ contains the information on the repository files and folders. Main Figures: Figure1: Monolithic NMC cathode and operando optical microscopy. (A) Schematic drawing of the key components of the electrochemical cell for optical microscopy. The cathode is a self-standing electrode composed of numerous NMC particles, carbon black and polytetrafluoroethylene (PTFE) binder. Aluminium mesh is used as a current collector. (WE = working electrode, CE = counter electrode). (B) Optical image of an active NMC particle in the electrochemical cell. (C) SEM image of the same monolithic NMC particle shown in (B), obtained after the optical measurements. (D) Schematic illustration of the crystal structure of the NMC cathode illustrating the alternating layers of LiO6 and TMO6 octahedra, where TM denotes transition metal. (E) Voltage (black) and current (blue) profile (top panel) and the normalised optical intensity of the active particle shown in (B) (bottom panel) during one charge-discharge cycle (comprising a C/3 constant-current (CC) charge and discharge between 4.3 and 3 V, followed by a two-hour constant-voltage (CV) hold at 3 V). Three C/3 cycles were performed prior to this cycle, finishing with two-hour voltage holds at 3 V. The C-rate was calculated based on a practical capacity of 210 mA h g-1, i.e., the current density for C/3 rate is 70 mA g-1. Scale bars, 1 μm. Figure2: Lithium heterogeneity in single-particle NMC at the beginning of charge. (A) Voltage and current profiles during the first one hour of charge at C/3 (top panel), and the normalised intensity changes, obtained by integrating over the whole active particle shown in (B) (bottom panel). (B) Normalised differential images of the active particle during the initial charging, for the time points indicated by black circles in (A). The total contrast is shown, which represents the fractional intensity change between the current frame and the first frame of the cycle (i.e., with no current applied). The colour scale is centred at zero (white), with positive values indicating an overall intensity increase (red) and negative values indicating a decrease (blue). (C) Voltage and current profiles during the first 20 min of charge at C/3 followed by a rest period (top panel), and the normalised intensity changes of a second active particle (bottom panel). (D) Normalised differential images of the active NMC particle during the charge-rest experiment. Scale bars, 1 μm. Figure3: Comparing modelling and experiments. (A) Sketch of the particle used in the modelling. (B) The effective lithium diffusion coefficient D_Li^eff≡D_Li/S as a function of lithium content (S=3.5). (C) Comparison of simulation and experimental imaging results, both conducted at a delithiation rate of C/3. The predicted degree of delithiation (1-θ) on the basal plane of the particle at various times during the charge. (D, E) Evolution of (D) the degree of delithiation in the simulation and (E) the total contrast in the optical images along the horizontal dotted line marked in (C). In (E) we include the corresponding predictions (shown with dashed curves) of the total contrast. (F) Evolution of measurements and predictions of total contrast at the centre of the particle (shown by the vertical dashed lines in (D)). Figure4: Lithium heterogeneity at the end of discharge. (A) Voltage and current profile (top panel) and normalised intensity changes of the active particle during a 1C rate CC charge and CCCV discharge cycle. CV was performed at 3 V for two hours. The dashed grey line (bottom panel) is a guide for the eye, representing 0 intensity change. The initial lithium content is estimated to be ~97% based on the open circuit voltage (OCV, ~3.5 V vs. Li/Li+). Note this near-full lithiation state was achieved by applying a two-hour voltage hold at 3 V after the end of CC discharge in the previous cycle. (B) Differential images of an NMC active particle during the discharge, at the times indicated by black circles in (A) (where a, b, c, d, e and f are at 90, 104, 140, 180, 224 and 298 min, respectively). Scale bars, 1 μm. The current at the end of the CV period was -7.59 μA (equivalent to ~C/200; negative sign denotes discharging current). Figure5: Summary of the lithium-ion distribution within the single active particle at various lithium contents. The circles show schematic representations of single-particle Ni-rich materials at various SoCs. The voltage profile is illustrative of the single-crystal NMC material used in this work, and was obtained in a half-cell cycled with a CC charge and CC discharge (C/20 rate) and a discharge CV hold at 3 V (for 24 hours)

Experimental discharge voltage profiles of disordered rocksalt cathodes

An open-source dataset of disordered rocksalt cathode electrochemical discharge voltages.</p