Solvent-Free Manufacturing of Electrodes for Lithium-Ion Batteries

Lithium ion battery electrodes were manufactured using a new, completely dry powder painting process. The solvents used for conventional slurry-cast electrodes have been completely removed. Thermal activation time has been greatly reduced due to the time and resource demanding solvent evaporation process needed with slurry-cast electrode manufacturing being replaced by a hot rolling process. It has been found that thermal activation time to induce mechanical bonding of the thermoplastic polymer to the remaining active electrode particles is only a few seconds. Removing the solvent and drying process allows large-scale Li-ion battery production to be more economically viable in markets such as automotive energy storage systems. By understanding the surface energies of various powders which govern the powder mixing and binder distribution, bonding tests of the dry-deposited particles onto the current collector show that the bonding strength is greater than slurry-cast electrodes, 148.8 kPa as compared to 84.3 kPa. Electrochemical tests show that the new electrodes outperform conventional slurry processed electrodes, which is due to different binder distribution

GREENLION Project: Advanced Manufacturing Processes for Low Cost Greener Li-Ion Batteries

GREENLION is a Large Scale Collaborative Project within the FP7 (GC.NMP.2011-1) leading to the manufacturing of greener and cheaper Li-Ion batteries for electric vehicle applications via the use of water soluble, fluorine-free, high thermally stable binders, which would eliminate the use of VOCs and reduce the cell assembly cost. The project has 6 key objectives: (i) development of new active and inactive battery materials viable for water processes (green chemistry); (ii) development of innovative processes (coating from aqueous slurries) capable of reducing electrode production cost and avoid environmental pollution; (iii) development of new assembly procedures (including laser cutting and high temperature pre-treatment) capable of substantially reduce the time and the cost of cell fabrication; (iv) lighter battery modules with easier disassembly through eco-designed bonding techniques; (v) waste reduction, which, by making use of the watersolubility of the binder, allows the extensive recovery of the active and inactive battery materials; and (vi) development of automated process and construction of fully integrated battery module for electric vehicle applications with optimized electrodes, cells, and other ancillaries. Achievements during the first 18 months of the project, especially on materials development and water-based electrode fabri cation are reported herein

A Review of Lithium-Ion Battery Electrode Drying: Mechanisms and Metrology

Lithium-ion battery manufacturing chain is extremely complex with many controllable parameters especially for the drying process. These processes affect the porous structure and properties of these electrode films and influence the final cell performance properties. However, there is limited available drying information and the dynamics are poorly understood due to the limitation of the existing metrology. There is an emerging need to develop new methodologies to understand the drying dynamics to achieve improved quality control of the electrode coatings. A comprehensive summary of the parameters and variables relevant to the wet electrode film drying process is presented, and its consequences/effects on the finished electrode/final cell properties are mapped. The development of the drying mechanism is critically discussed according to existing modeling studies. Then, the existing and potential metrology techniques, either in situ or ex situ in the drying process are reviewed. This work is intended to develop new perspectives on the application of advanced techniques to enable a more predictive approach to identify optimum lithium-ion battery manufacturing conditions, with a focus upon the critical drying process

Solvent-free additive manufacturing of electrodes for Li-ion batteries

A new Li-ion battery electrode manufacturing process using a solvent free additive manufacturing method has been developed. Li-ion battery electrodes consist of active material particles, a binder additive, and a conductive additive. Traditionally, Li-ion battery electrodes are manufacturing using the slurry casting technique. In this method, the electrode materials are mixed with a solvent to create a slurry. Electrodes fabricated in this method are readily implemented for small platforms, such as portable electronics. However, this method isn\u27t as economically viable in large platforms due to high material and manufacturing costs. High material and manufacturing costs are mostly attributed to the use of organic solvents, typically N-methyl-pyrrolidone, to dissolve the binder additive. A drying line is needed to evaporate the solvent from the electrode layer and an expensive recovery system is needed to collect the evaporated solvent. In total, the use of NMP attributes ~14.5% to the overall Li-ion battery cell costs. The solvent-free manufacturing method has been developed to eliminate these problems. In this method, the electrode materials are dry mixed and directly deposited on to the current collector. Therefore, uniform distribution of the electrode particles during the mixing process is the driving factor for the solvent-free additive manufactured batteries. The distribution of dry electrode materials was studied through experimental mixing studies, mixing models, and mixing simulations to better understand how the electrode material\u27s surface properties effect the final distribution of electrode particles. Afterwards, Li-ion batteries were assembled with solvent-free manufactured electrodes and compared to slurry-cast electrodes with similar specifications --Abstract, page iv

Development and management of advanced batteries via additive manufacturing and modeling

The applications of Li-ion batteries require higher energy and power densities, improved safety, and sophisticated battery management systems. To satisfy these demands, as battery performances depend on the network of constituent materials, it is necessary to optimize the electrode structure. Simultaneously, the states of the battery have to be accurately estimated and controlled to maintain a durable condition of the battery system. For those purposes, this research focused on the innovation of 3D electrode via additive manufacturing, and the development of fast and accurate physical based models to predict the battery status for control purposes. Paper I proposed a novel 3D structure electrode, which exhibits both high areal and specific capacity, overcoming the trade-off between the two of the conventional batteries. Paper II proposed a macro-micro-controlled Li-ion 3D battery electrode. The battery structure is controlled by electric fields at the particle level to increase the aspect ratio and then improve battery performance. Paper III introduced a 3D model to simulate the electrode structure. The effect of electrode thickness and solid phase volume fraction were systematically studied. Paper IV proposed a low-order battery model that incorporates stress-enhanced diffusion and electrolyte physic into a Single Particle model that addresses the challenges of battery modeling for BMS: accuracy and computational efficiency. Paper V proposed a single particle-based degradation model by including Solid Electrolyte Interface (SEI) layer formation coupled with crack propagation. Paper VI introduced a single-particle-based degradation model by considering the dissolution of active materials and the Li-ion loss due to SEI layer formation with crack propagation for LiMn₂O₄/Graphite battery --Abstract, page iv

Improved Synthesis and Material Processing of Black Phosphorus for Using as Lithium-ion Battery Anode

Recent studies show that black phosphorus (BP) is a promising candidate anode material for Li-ion batteries (LIB), exhibiting much higher theoretical capacity (2,596 mAh/g) compared to commercialized graphite anode (372 mAh/g). Application of BP in LIB requires scalable material synthesis procedure, in-depth understanding of degradation mechanism and novel predictive models. In this work, a variety of synthesis, characterization, and modeling methods are developed to optimize the BP quality and promote its electrochemical performance in LIB. BP is not naturally available. High energy mechanical milling (HEMM) is a conventional method which transforms red phosphorus (RP) precursor into BP. To precisely control the quality of BP, the effects of processing time, power, ball-to-powder ratio and atmosphere on BP’s particle size distribution and crystallinity are systematically studied. A multistep milling technique combining planetary and shaking ball millings is developed. The produced BP and BP-graphite (BPG) composite have homogeneous size distribution, coherent bonding connection and high specific surface area. The as-synthesized material is used to fabricate half coin cell to test its electrochemical performance. The optimal sample cell achieves high initial capacity of 2000 mAh/g at 0.1C rate. After 150 cycles, more than 80% capacity is still reversible. Disassembly analysis reveals electrode cracks and particle fractures cause capacity degradation. To address the bulk phase BP’s intrinsic limitation of volume expansion and contraction upon cycling, 2D phosphorene (an analogy of graphene to graphite) is exfoliated from HEMM-synthesized BP particles. The laser-assisted liquid phase exfoliation is found to be superior than existing methods for its low cost, high productivity and significantly promoting phosphorene stability. The as-exfoliated phosphorene is very durable against oxidation and humidity. Which relies on the polycrystalline properties of phosphorene and liquid protective layer. A novel top-down co-exfoliation method to produce phosphorene-graphene heterostructure is developed. An ultrasonication system with moderate processing power is used to do liquid phase exfoliation. Instead of BP crystal, BPG composite from HEMM is directly utilized as precursor. The 2D layered material is found to be ultrathin (~10 nm) and ultrasmall ( 1500 mAh/g), long cycling life (> 500 cycles), and high capacity retention ratio (>80%). Galvanostatic Intermittent Titration Technique (GITT) shows fast solid-phase diffusion. Impedance evolution progress is investigated by Electrochemical Impedance Spectroscopy (EIS) test. The improvement doesn’t only come from conventional conversion/alloying reaction between lithium and phosphorus, but also electrode-electrolyte interface pesudocapacitive effect due to high surface area of 2D phosphorene. This effect is quantified by properly designed Cyclic Voltammetry (CV) test. A non-destructive 3D micro-CT rendering is built to track the electrode structural change after battery cycling. A data-driven machine learning framework is proposed to aggregate both cycling-related and material-related features into a predictive model. Which is able to estimate failed/alive batteries and identify important material influencers. 90 in-lab made BP-based coin cells from 16 batches are cycled to extract degradation patterns. Combining the material and electrode properties, the most comprehensive alternative anode database is formed. The insights from modeling can further optimize the material/electrode design.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/155253/1/zjianyu_1.pd

Continuous Freezecasting

In electric vehicle manufacturing, battery electrodes are made using roll-to-roll manufacturing, a continuous process in which an electrode mixture is moved along a roller-based processing line. It is efficient and cost-effective. Freeze casting is a process used to manufacture ceramic materials by using a temperature gradient to cast. The gradient aligns the grains in such a way that makes the material very conductive. The goal of this project is to design a mechanism to allow continuous freeze casting to be used in electrode manufacturing.Wenda TanUM Mechanical Engineering departmenthttp://deepblue.lib.umich.edu/bitstream/2027.42/192012/1/UM_Tan_F23_Team08_Continous-Freeze-Casting.pd

Fragmented Carbon Nanotube Macrofilms as Adhesive Conductors for Lithium-Ion Batteries

Polymer binders such as poly(vinylidene fluoride) (PVDF) and conductive additives such as carbon black (CB) are indispensable components for manufacturing battery electrodes in addition to active materials. The concept of adhesive conductors employing fragmented carbon nanotube macrofilms (FCNTs) is demonstrated by constructing composite electrodes with a typical active material, LiMn₂O₄. The adhesive FCNT conductors provide not only a high electrical conductivity but also a strong adhesive force, functioning simultaneously as both the conductive additives and the binder materials for lithium-ion batteries. Such composite electrodes exhibit superior high-rate and retention capabilities compared to the electrodes using a conventional binder (PVDF) and a conductive additive (CB). An <i>in situ</i> tribology method combining wear track imaging and force measurement is employed to evaluate the adhesion strength of the adhesive FCNT conductors. The adhesive FCNT conductors exhibit higher adhesion strength than PVDF. It has further been confirmed that the adhesive FCNT conductor can be used in both cathodes and anodes and is proved to be a competent substitute for polymer binders to maintain mechanical integrity and at the same time to provide electrical connectivity of active materials in the composite electrodes. The organic-solvent-free electrode manufacturing offers a promising strategy for the battery industry