Advanced Automotive Battery Conferences

Session 2:
 

Key Lithium-Ion Materials R&D

Dr. Kang Xu is a senior chemist at Electrochemistry Branch of U. S. Army Research Laboratory. He received his Ph. D. under the tutelage of Prof. Austen Angell in Arizona State University, and has been conducting research on electrolytes and interphasial chemistry in various energy storage devices for the past 20 years. His work has received numerous recognitions and awards. In addition to the numerous new salts, solvents and additives he invented and the concept of Li+-solvation-interphasial chemistry correlation he proposed, he is best known in the field for his two comprehensive reviews on electrolytes published at Chemical Reviews in 2004 and 2014 respectively.

1. Current Research on High-Energy Lithium-Ion at Argonne National Laboratory
   Jason Croy, Materials Scientist, Argonne National Laboratory
   

   Lithium-ion batteries have been successfully developed and improved upon for more than two decades and have been pushed very close to what may be their practical limit. However, the promise of an electrified vehicle fleet, and energy storage in general, justifies continued, scientific interest in this already robust technology. This presentation will highlight some of the current, DOE-sponsored research taking place at Argonne National Laboratory aimed at enabling the next generation of Li-ion cells. Topics of discussion include:

   • Establishment of baselines and protocols for the “bench-scale” researcher
   • Characterization efforts on complex cathode materials
   • “New” materials efforts for high energy cathodes
2. High-Voltage Spinel Cathode Materials, Opportunities and Challenges
   Katharine Chemelewski, Senior Battery Scientist and Team Leader, Axium Battery LLC
   

   The high-voltage LiMn_1.5Ni_0.5O₄ spinel is an attractive cathode candidate for next generation lithium-ion batteries, as it offers high power capability with an operating voltage of 4.7 V, excellent rate capability, and a reversible capacity of 135 mA h g⁻¹. However, its commercialization has continued to be plagued by severe capacity fade, particularly at elevated temperatures, in full cells employing a graphite anode. This presentation provides an overview of the recent developments on understanding various crystallographic, morphological, and electrochemical factors that influence the cycling performance of the high-voltage spinel cathodes. These factors include:

   • Cation ordering and presence of rocksalt impurity
   • Phase transitions during cycling
   • Particle morphology and surface planes
   • Recent trends in electrolyte and surface modifications
   • Summary: Identification of key challenges facing the high-voltage spinel technology and opportunities for improvement
3. New High-Capacity Silicon-Graphene Anode for Li-Ion Batteries
   Rob Privette, Vice President, Energy Markets, XG Sciences
   

   Consumer electronics users are increasingly choosing smart phones that provide a web-connected experience together with a high degree of portability. User activities such as web surfing and gaming consume significant amounts of stored energy, far greater than that of simple mobile phones. Additionally, the portability of these devices requires a small size and weight compared with traditional laptop computers. This combination of increased energy consumption from smaller and lighter weight devices presents a significant challenge for the lithium batteries that provide the onboard energy storage. Cell volumetric and gravimetric energy density targets for advanced devices cannot be met with traditional carbon anodes due to the materials inherent low capacity. A new class of “beyond graphite” anodes are required. Silicon, a promising graphite replacement due to its capacity (4,200 mAh/g) and lithiation voltage range (0.0 ~ 0.4 V) but poor cycle life and excessive volumetric expansion have slowed commercial adoption. A high-performance & low-cost Si-based anode remains a crucial need of the battery industry.

   XG Sciences (XGS) is launching a new generation of its SiG silicon-graphene anode material. The new generation of material delivers substantial improvements in cycle life and volumetric expansion compared to the first generation material. The new anode incorporates several changes to the material physical properties and manufacturing process that are responsible for the performance improvements. Tap density of 0.88 g/cc and reduced surface area continue to provide good processability. The new material is produced in the existing ton-scale manufacturing plant ensuring availability in volumes necessary for commercial cell programs. Typical full cell cycling performance (Silicon anode/ NCA cathode) is shown in Figure 1. SiG electrodes compressed to 1.6 g/cc have demonstrated swelling of less than 35 percent.

   
   Figure 1 New XGS Silicon-based anode material cycled in full cell (C/2) between 3 - 4.2 V.

   In addition, the new material has shown comparable cycling capacity stability over wide voltage ranges which normally present significant challenges for silicon-based anodes. The wide operating voltage range enables cell manufactures to maximize energy density for their high energy products.

   Dispersion of the new SiG anode material has also been improved and demonstrated using typical industrial double planetary mixers. SiG anode slurry formulated with aqueous CMC/SBR binder and has been successfully coated using pilot scale commercial coaters. Coating quality has been confirmed through inspection of electrodes compressed to 1.8 g/cc. This presentation will include details of the new SiG nanocomposite anode material, dispersion and mixing developments using industrial scale equipment and full cell cycling performance information.

   The stable cycling performance of the new SiG silicon-graphene anode material confirms the effectiveness of XGS’ anode material design strategy utilizing graphene nanoplatelets in mitigating the detrimental effects of Silicon particle expansion and contraction and improving the cycle life of the Silicon anode.

   XG Sciences acknowledges the U.S. Department of Energy SBIR program that provided support for this work.

4. Rate Determining Steps during Charging of LIB Anodes
   Takeshi Abe, Professor, Kyoto University
   

   Since lithium-ion batteries were commercialized in 1991, the energy densities of LIB have creased and now the champion value is above 250 Wh/kg for 18650-type. In contrast, LIBs for automobile use show smaller energy densities ranging from 80 - 130 Wh/kg. This is principally due to the charging time. LIBs for portable devices need 1 – 2 h for a complete charge, while fast charge must be required for EVs. If we can use high-density-LIBs, the cruising distance of EVs can be twice as long. We have so far focused how to decrease the internal resistances of LIBs. In this conference, I will report rate determining steps at graphite anode by considering the charge transfer resistances, ion transport resistances inside composite electrode, diffusion coefficients of lithium-ion inside active materials, and surface film resistances on the active materials.
5. Expanding Electrochemical Stability Window of Electrolytes to Enable More Energetic Battery Chemistries
   Kang Xu, Senior Chemist, Electrochemistry Branch, U. S. Army Research Laboratory
   

   As the essential component in any energy storage device, electrolyte determines a number of key performances of the device, including temperature range for service, rate of electrochemical reaction, safety under both normal and abusive operations, cycle/calendar life as well as the maximum voltage allowed. Among these, the electrochemical stability window is perhaps the most intriguing property, because in almost all electrochemical devices, the electrodes operate at potentials far beyond what thermodynamics allowed. This group at ARL has been trying to understand this basic phenomenon and exploring various means to affect the surface chemistry at electrode/electrolyte junctions, so that this stability window could be expanded to enable more powerful battery chemistries. This talk will summarize these recent efforts.