Mechanisms and Synthesis of Materials for Next-Generation Lithium Batteries Using Flame Spray Pyrolysis
Lead Research Organisation:
University of Cambridge
Department Name: Engineering
Abstract
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Organisations
Publications
Park SK
(2022)
Photo-Enhanced Magnesium-Ion Capacitors Using Photoactive Electrodes.
in Small (Weinheim an der Bergstrasse, Germany)
| Description | Battery materials can be synthesised in a number of ways. This project aims to investigate flame spray pyrolysis as a potential alternative method to conventional sol-gel/co-precipitation methods which would reduce the number of manufacturing steps required. We have used flame spray pyrolysis as well as controlled spray pyrolysis (in a furnace) to produce a range of materials involving Lithium as well as Nickel, Manganese, and Cobalt (NMC). The particles produced in the aerosolised materials were annealed at high temperatures, then formed into battery cells, and tested for their battery performance, including ability to be charged, discharged and hold charge over multiple cycles. The precursor materials were a variety of liquid phase metal nitrates and acetates. In flame spray pyrolysis, the key findings were: (a) liquid metal nitrates involving the target metals to produce NMC811 (the numbers refer to the stoichiometry usually used for the respective metals) were produced, and the materials were shaped into battery cells. The battery cells produced charging and discharging capacities comparable to commercial materials (~80%), but the long term, multi-cycle capacity is still lower than required for commercial purposes. (b) the corresponding structure of the materials after pyrolysis, and after annealing revealed that there is some effect of the initial processes for pyrolysis, but that annealing temperatures and times are the most important factor in determining the material performance, allowing clear crystal structures to emerge, coated with the Lithium particles. In high temperature, furnace-based spray pyrolysis, a number of tests were performed comparing the use of nitrates and acetates with additives such as citric acids as precursors. The results showed that acetate precursors always form irregular shape particles. However, when adding a carbon source such as citric acid into the precursor, the particle surface becomes more uniform and smoother. On the other hand, using nitrates with citric acid resulted in porous structure that might not be suitable for good performance battery electrodes. |
| Exploitation Route | The findings will allow a better understanding of how precursors, atomisation and temperature history affect the structure and thus performance of the materials produced in flame spray pyrolysis. |
| Sectors | Energy,Manufacturing, including Industrial Biotechology |
| Description | Enhanced CNTs for High Power Electrodes (EC-HiPE): Creating a Robust UK Battery Material Supply Chain |
| Amount | £546,886 (GBP) |
| Funding ID | 10043701 |
| Organisation | Innovate UK |
| Sector | Public |
| Country | United Kingdom |
| Start | 03/2023 |
| End | 02/2024 |
| Title | Battery electrode evaluation process |
| Description | Creating batteries with industrially relevant properties at a lab scale is a challenging process. It requires making a judicious choice of the battery composition (binder, conductive additives and active material), areal loading (mass of active material per electrode area), and calendaring conditions (electrode porosity). The issue here is that academic work using high amounts of conductive additives, low areal loading and low density can seemingly result in good battery performance per weight of active battery material, but when using the same material in industrial, "lean" battery designs, the same materials can fail. This is because industrial cells require high mass loading and electrode thickness to achieve sufficient energy density. In these designs, transport of Li ions is more challenging and poor electrical conductivity limits rate capability. On the other hand testing new lab materials under conditions that are too close to industrial standards without extensive optimization, can lead to materials being discarded which could perform well after sufficient R&D optimization work. Therefore, we have developed an "in-between" solution that tests new battery materials at the laboratory-scale with an electrode formulation that does not unfairly discards new battery materials while at the same time making sure that no time is wasted on materials that will never find industrial applications. This was applied in particular to spray and flame pyrolsised cathodes. In this work, different cathode materials such as LiCoO2 (LCO) and LiNiMnCoO2 (NMC) fabricated by spray and flame pyrolysis were tested with the electrode formulation discussed above. Areal loadings of 4~5 mg/cm2 were used with a ratio of 90% active material to binder and conductive additive with different electrode densities. Firstly, we found that cathode materials made by spray pyrolysis have a large size distribution and therefore, we first sieved the material to retain a uniform particles size. Then, cathode materials and carbon powder (Super P as conducting additive) were ground in mortar for 10 min and mixed in a centrifugal mixer for 2 min. The cathode slurry was prepared by mixing cathode material, super P and PVDF (6 wt%) dissolved in NMP. The ratio of the cathode materials, super P and PVDF are 90:5:5. The cathode slurry was further homogenized using a centrifugal mixer for 20 min, and then coated on aluminum foil by a doctor blade. The coated electrodes were dried in a vacuum oven at 120 ? overnight. The dried electrode were used as coated or calendared to a reduce the orginal density by 30~35 %. This increases the energy density of the electrode and shortens the Li Ion and electron transport distance. The average mass loading and thickness of the cathode electrode were around 4~5 mg/cm2 and ~40 µm respectively. These electrodes are then assembled in a glove box under Ar gas. Li metal and Celgard were used as a counter electrode and a separator. The electrolyte was 1 M LiPFF6 in EC/DEC (1:1). The electrochemical protocol involves two formation cycles at 0.1 C-rate from 3 to 4.3 V followed by 0.5 C-rate cycling. Further we benchmarked all materials with commercial batteries (MTI company) under the exact same conditions. |
| Type Of Material | Improvements to research infrastructure |
| Year Produced | 2022 |
| Provided To Others? | No |
| Impact | The proposed electrode formulations are not limited to spray pyrolisis and useful for a wide range of new emerging material synthesis and material compositions. This will allow for a fair and rapid evaluation of new materials. |
| Title | Flame spray pyrolysis reactor and sampling methodology |
| Description | A spray pyrolysis flow reactor was constructed to dry and calcine droplets at temperatures between 500-1000 °C, for comparison with flame spray pyrolysis. In the process, the starting solution is atomized by a nebulizer and is introduced into a pre-heating section to evaporate water. The carrier gas can be air, oxygen or nitrogen. Air quenching is used before particle collection in a filter bag. The obtained particles by spray pyrolysis are post-treated at various temperatures to obtain the final crystal structure. Solutions involving a variety of precursor materials have already been tested, leading to the production of Lithium cobalt oxide (LCO), NMC111 and NMC811. A high temperature X-ray diffraction (HT-XRD) was also used in this work to assist in navigating the way to determine the suitable annealing temperatures. |
| Type Of Material | Improvements to research infrastructure |
| Year Produced | 2023 |
| Provided To Others? | Yes |
| Impact | The reactor allows synthesis of battery precursor particles with sufficient residence time and temperature to generate suitable morphology before annealing. There are other reactors around the world with similar capabilities, and this allows the group to compare results from particle synthesis using this method to other methods, such as flame spray pyrolysis in the present project. |
| Title | Flexible stream manifolded burner (FSMB) |
| Description | Understanding flame synthesis requires a well-characterized platform for producing uniform flame temperatures as they mix with various reacting streams to produce particles. Previous studies have used premixed burners using for example the manifolding of hundreds of quartz tubes with fuel, which can stabilize flames (Hencken style) or porous metal burners (McKenna) with one-dimensional characteristics. The study of flame synthesis and in particular the formation of carbon-metal-oxides (CMOs) requires a flexible platform where the fuel and air streams can be manifolded reasonably flexibly. In this work, a novel burner platform is designed and constructed combining the benefits of the conventional Hencken burner's laminar flames with the advantages of simple and flexible assembly methods. While Hencken burner consists of a honeycomb with tubes of small diameters inserted through the pores, the current burner is composed of multiple metal sheets of specially designed patterns. By aligning and stacking the metal sheets together inside the burner shell, flow channels are built separately for fuel and oxidizer gases. The mixing of fuel and oxidizer takes place rapidly above the burner surface and forms multi-element diffusion flames. Conversely, it is possible to use different stacking patterns to produce different manifolding conditions for e.g. premixed or non-premixed streams. An additional central tube is provided to feed spray droplets or vapor precursors for the investigation of flame synthesis. The centerpiece of the burner is realized using developed metal etching technology, offering flexibility to modify the inner structure and sizes without changing the burner shell. Stainless steel is used for fabrication for its chemical integrity and high melting point. The minimum diameter of the holes on metal sheets is 1.2 mm and the thickness of each sheet is 1 mm, limited by the manufacturing technique. The small size of the holes allows for a tight arrangement of the gas channels, which promotes the immediate mixing of fuel and oxidizer. Fuel enters the bottom of the burner, diffuse freely in the chamber before going through the small tubes formed by stacking the oxidiser sheets sequentially. Oxidizer enters the burner through four inlets on the side surface of the burner and distributes evenly before flowing vertically along the height of the burner, promoting uniform gas velocity across the entire burner surface. A water circulation system is employed surrounding the burner shell to improve flame uniformity and burner stability. An illustration of the burner is available at : http://www-g.eng.cam.ac.uk/reactingflows/projects/flame_synthesis/ |
| Type Of Material | Improvements to research infrastructure |
| Year Produced | 2022 |
| Provided To Others? | No |
| Impact | The burner allows stackable manifolding of different configuration, and has significantly saved time for manufacturing and assembly, as well as offering a flexible way to change the manifolding from premixed to diffusion configuration by exchanging the stack without changing the rest of the burner. |
| URL | http://www-g.eng.cam.ac.uk/reactingflows/projects/flame_synthesis/ |