Mechanisms and Synthesis of Materials for Next-Generation Lithium Batteries Using Flame Spray Pyrolysis

Electricity has emerged as a preferred energy vector for both conventional and renewable energy, thanks to its versatility and the vast existing electrical infrastructure. The electrification of the transport sector is a natural development to make use of energy from a wide variety of sources, and to reduce CO2 emissions and combat urban air pollution. The UK government plans to ban sale of all diesel and petrol cars and vans from 2040, following similar moves by France and Germany. Globally, the number of electric vehicles (EVs) is projected to rise from about 1 million in 2015 to 300 million in 2040. Achieving these goals requires dramatically improved performance and lowered costs of batteries for EV use. Lithium-ion batteries (LIBs) are promising, but enhanced materials for electrodes, especially the cathode, are needed to meet the power density and costs requirements for the next-generation EVs and energy storage systems.

The research aims to generate fundamental knowledge and develop experimental and numerical tools for the controlled synthesis of high-performance cathode materials for LIBs with the inherent potential to be scaled to large throughput production. The materials will be based on layered, multi-element metal oxides (MOs) and carbon-metal oxides (CMOs). Among these, the nickel manganese cobalt oxides (NMCs) with various metal contents and surface features, which are favoured by mainstream automotive companies, will be the main target for the research, though the research and production techniques will be applicable for a large class of MOs and CMOs. Conventionally, MOs can be produced via solid state, sol-gel, and co-precipitation methods and combinations thereof, followed by high temperature annealing processes without or with carbon coating. Such multi-step synthesis routes are time- and energy-consuming, and require delicate control of the surrounding conditions. A promising alternative is flame spray pyrolysis (FSP), in which a precursor solution is atomised to produce a large number of evaporating droplets that are carried into a heated reactor or burned with a flame to form nanoparticles. FSP can offer a one-step, high throughput, easy-to-handle, scalable and continuous process, with a wide range of precursor solutions. It allows good control and, importantly, decoupling of the production process from the gas-phase chemistry process, creating the potential to produce designer materials at scale and low cost.

The project is a collaboration between Cambridge University (Simone Hochgreb in flame synthesis; Adam Boies in nanoparticle synthesis; Michael De Volder in nanomaterial and batteries) and UCL (Kai Luo in modelling and simulation). A combined experimental and numerical study will be conducted to reveal the dynamic processes of and controlling mechanisms behind particle formation, growth and coating. At the microscopic level, the detailed transport and chemical reactions will be unravelled; at the mesoscopic level, factors affecting phase change and particle growth will be identified; and at the macroscopic level, the input parameters and time scales of key processes will be linked with quality of MO and CMO products. The experiments involve cutting-edge in-situ and ex-situ measurements to qualify and quantify the synthesis process. The modelling and simulation include advanced mesoscopic simulations of droplet dynamics and evaporation; and atomistic simulations of precursor pyrolysis, particle formation and growth. The fundamental insights gained, and tools and production techniques developed will be exploited for controlled flame synthesis of materials that are directly tied to battery performance metrics, in collaboration with four companies (CATL, Echion Tech, PV3 Technologies and STFET). These companies' activities cover the technology readiness levels (TRLs) from 2 to 9, providing valuable inputs to the research and multiple routes to exploitation of research outputs.

The research will potentially benefit the automotive and energy sectors, which are vital to the UK economy and society. These sectors are undergoing a major transformation to combat air pollution and climate change. This is set in the context that the UK government plans to ban sale of all diesel and petrol cars and vans from 2040, and the UK has an overall target to cut the GHG emissions by 34% by 2020, 50% by 2025 and 80% by 2050, compared to 1990 levels. The global trend towards EVs away from ICEs is emerging and long-term. In the meantime, increasing use of renewables demands high-performance electrochemical devices as energy storage systems.

The research aims to contribute to such a transformation by removing a key technological barrier - poor battery performance due to a lack of advanced electrode materials. The project will open new routes to speed up development of materials via flame spray pyrolysis (FSP) and create new measurement and simulation methods that are accessible by industry and academia. The proposal has strong support from industry and has been formulated in discussion with partners from the very beginning. Four innovative companies have partnered with us in this project, with substantial contributions totalling £315k:

1) PV3 Technologies is specialised in the development and manufacturing of materials for electrochemical applications. It pursues both in-house R & D and collaborative research in order to convert innovative ideas into marketable products. The company will share insights into the synthesis of materials and provide "commercial cathode materials for side by side comparison with the materials developed in this project". It will also help with material characterisation, production scale-up and commercialization of the research.

2) CATL is the world's largest manufacturer of Li-ion batteries for EVs that serves a wide range of companies including BMW, Mercedes, PSA and Toyota. CATL does a substantial amount of research in its three R & D centres. They see a great potential in the present project's ideas and capacity to develop one-step, scalable techniques for NMC synthesis. It will actively participate in the project, helping to test and characterise materials produced in the project for real applications in the automotive industry.

3) Echion Tech is a spin-out from the University of Cambridge which is focusing on next generation anodes for fast charging applications. Echion will support this project through material characterization, as well as supply of anodes to test the performance of our materials in full cells.

4) Finally, STFET conducts R & D and consultancy on advanced materials for fuel cells and batteries, with current focus on Li-ion batteries for EVs. Its clients include major automotive companies such as SAIC, PSA and Toyota. STFET's contributions include: (1) joint assessment and validation of computational models using STFET's experimental database; (2) characterization of materials produced by FSP; (3) tests of new materials in Li-ion battery packs; (3) joint exploration of research outputs for industrial applications and academic publications.

Collaboration with the four companies gives useful industrial steering, facilitates research conduct, and provides multiple routes to exploitation of the results. It helps that the four companies' activities span the scale of technology readiness levels (TRLs) from 2 to 9 while our research is primarily at TRL 1-3. The impact will also arise through the direct training of post-doctoral personnel, as well as extensive dissemination and training in these techniques via the UKCOMES network, the Cambridge Particle Meeting and the newly formed CDT in Aerosol.