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The drying of electrodes for lithium-ion batteries is one of the most energy- and cost-intensive process steps in battery production. Laser-based drying processes have emerged as promising candidates for electrode manufacturing due to their direct energy input, spatial homogeneity within the laser spot, and rapid controllability. However, it is unclear to what extent electrode and cell quality are affected by higher heating and drying rates. Hybrid systems as a combination of laser- and convection-based drying were investigated in an experimental study with water-processed LFP cathodes. The manufactured electrodes were compared with purely laser-dried and purely convection-dried samples in terms of drying times and quality characteristics. The electrodes were characterized with regard to physical properties like adhesion and electronic conductivity, as well as electrochemical performance using the rate capability. Regarding adhesion and electronic conductivity, the LFP-based cathodes dried in the hybrid-drying process by laser and convection showed similar quality characteristics compared to conventionally dried cathodes, while, at the same time, significantly reducing the overall drying time. In terms of electrochemical performance, measured by the rate capability, no significant differences were found between the drying technologies used. These findings demonstrate the great potential of laser- and convection-based hybrid drying of LFP cathodes to enhance the electrode-drying process in terms of energy efficiency and operational costs. [ABSTRACT FROM AUTHOR]

Porosity is frequently specified as only a value to describe the microstructure of a battery electrode. However, porosity is a key parameter for the battery electrode performance and mechanical properties such as adhesion and structural electrode integrity during charge/discharge cycling. This study illustrates the importance of using more than one method to describe the electrode microstructure of LiNi0.6Mn0.2Co0.2O2 (NMC622)-based positive electrodes. A correlative approach, from simple thickness measurements to tomography and segmentation, allowed deciphering the true porous electrode structure and to comprehend the advantages and inaccuracies of each of the analytical techniques. Herein, positive electrodes were calendered from a porosity of 44-18% to cover a wide range of electrode microstructures in state-of-the-art lithium-ion batteries. Especially highly densified electrodes cannot simply be described by a close packing of active and inactive material components, since a considerable amount of active material particles crack due to the intense calendering process. Therefore, a digital 3D model was created based on tomography data and simulation of the inactive material, which allowed the investigation of the complete pore network. For lithium-ion batteries, the results of the mercury intrusion experiments in combination with gas physisorption/pycnometry experiments provide comprehensive insight into the microstructure of positive electrodes. [ABSTRACT FROM AUTHOR]

Lithium metal is considered to be the most promising anode for the next generation of batteries if the issues related to safety and low coulombic efficiency can be overcome. It is known that the initial morphology of the lithium metal anode has a great influence on the cycling characteristics of a lithium metal battery (LMB). Lithium‐powder‐based electrodes (Lip‐electrodes) are reported to diminish the occurrence of high surface area lithium deposits. Usually, ultra‐thin lithium foils (<50 µm) and Lip‐electrodes are prepared on a copper substrate, thus a metal–metal contact area is generated. The combination of these two metals in the presence of an electrolyte, however, can lead to galvanic corrosion. Herein, the corrosion behavior of Lip‐electrodes is studied. The porosity of such electrodes leads to a high amount of accessible Cu surface in contact with electrolyte. As a consequence, Lip‐electrodes aged for 1 week in the electrolyte show spontaneous lithium dissolution near the junction to copper and void formation on the lithium‐powder particles. This corrosion process affects the delivered capacity of Lip‐electrodes and increases the overvoltage of the lithium electrodissolution process. The occurrence of corrosion at the Cu|Lip interface raises concerns about the practicality of multi‐metallic component systems for LMBs. [ABSTRACT FROM AUTHOR]

The high specific capacity of Li-rich layered oxides of up to 300 mAh g−1 renders them a promising class of positive electrode materials for high energy lithium ion batteries (LIBs). However, this material class suffers from poor capacity retention, voltage fade and structural degradation. The degradation phenomena include phase transformation and particle cracking during operation and take place in the bulk as well as the active material’s surface. In this work, we demonstrate a straightforward approach for the surface modification of Li1.15Ni0.15Co0.15Mn0.55O2 for LIB cells. This strategy is based on a bis(carboxyethylgermanium)-based (Ge-132) coating, which is prepared via a simple sol-gel process. The coating layer is composed of a Ge-132 polymer network, which can coordinate on the oxygen atoms at the material’s surface. As a result, LIB full-cells with coated Li-rich NCM vs a graphite negative electrode provide reversible capacities of ≈180 mAh g−1 within a voltage range of 2.5–4.65 V for more than 200 cycles. The coated positive electrode exhibits a capacity retention improved by more than 20% compared to the uncoated reference material, which can be attributed to the suppression of parasitic side reactions at the cathode/electrolyte interface, less particle cracking upon electrochemical load and reduced manganese dissolution. [ABSTRACT FROM AUTHOR]

Lithium Metal Batteries: Galvanic Corrosion of Lithium-Powder-Based Electrodes (Adv. Keywords: electrodeposition; electrodissolution; galvanic corrosion; lithium metal batteries; lithium-powder-based electrodes EN electrodeposition electrodissolution galvanic corrosion lithium metal batteries lithium-powder-based electrodes 1 1 1 04/23/20 20200421 NES 200421 In article number 2000017, Martin Winter, Marian Cristian Stan and co-workers demonstrate that Cu|Li interfaces create favorable pre-conditions for galvanic corrosion. Electrodeposition, electrodissolution, galvanic corrosion, lithium metal batteries, lithium-powder-based electrodes. [Extracted from the article]

Investigation of reactions that determine safety properties of LIB cells is key for understanding degradation (aging) effects of the cell system e.g. via deciphering thermally induced reactions of active materials. In this study, an approach is conducted to determine thermal profiles of anodes and cathodes at different states of charge (SOCs) after electrochemical aging. Thermal profiling is performed using three different methods to determine temperature-related loss of mass, detection of m / z , and heat flow. After determination of thermal profiles, detailed analysis using pyrolysis-GC-MS is accomplished. Main points that were concluded from this study are that electrophilic lithiated anodes show intense decomposition behavior and reactions with electron-rich binder molecules. Moreover, it is possible to prove thermally induced de-lithiation as it was suggested before. De-lithiated cathodes (layered material) are prone to phase changes which can be obtained via detection of distinct oxygen release. Different decomposition properties of the solid electrolyte interphase is obtained depending on the SOC. The cathode electrolyte interphase exposes a SOC-dependent detection behavior; oligocarbonates are obtained for SOC 100%, solely CO 2 at high temperatures (>515 °C) for SOC 0%. Eventually, we provide a set of methods for thermal profiling to unravel reactions that determine safety properties of LIBs. Image 1 • Combination of different methods for the thermal profiling of LIB electrodes. • Determination of SOC-dependent particular influences of the electrodes. • Hypothesis of a high temperature-stable polycarbonate film. [ABSTRACT FROM AUTHOR]

Commercial 18650-type lithium ion cells employing an Al 2 O 3 coating on the anode surface as a safety feature are investigated regarding cycling behavior at low temperatures and related safety. Due to irreversible lithium metal deposition, the cells show a pronounced capacity fading, especially in the first cycles, leading to a shortened lifetime. The amount of reversibly strippable lithium metal decreases with every cycle. Post-mortem analysis of electrochemically aged anodes reveals a thick layer of lithium metal deposited beneath the coating. The Al 2 O 3 coating on the electrode surface is mostly intact. The lithium metal deposition and dissolution mechanisms were determined combining electrochemical and post-mortem methods. Moreover, the cell response to mechanical and thermal abuse was determined in an open and adiabatic system, revealing a similar behavior of fresh and aged cells, thus, demonstrating no deterioration in the safety behavior despite the presence of a thick lithium metal layer on the anode surface. [ABSTRACT FROM AUTHOR]

We introduce a novel formulation concept to prepare high capacity graphite electrodes for lithium ion batteries. The concept is based on the capillary suspension phenomenon: graphite and conductive agent are dispersed in an aqueous binder solution and the organic solvent octanol is added as immiscible, secondary fluid providing the formation of a sample-spanning network resulting in unique stability and coating properties. No additional processing steps compared to conventional slurry preparation are required. The resulting ultra-thick electrodes comprise mass loadings of about 16.5 mg cm −2 , uniform layer thickness, and superior edge contours. The adjustment of mechanical energy input ensures uniform distribution of the conductive agent and sufficient electronic conductivity of the final dry composite electrode. The resulting pore structure is due to the stable network provided by the secondary fluid which evaporates residue-free during drying. Constant current-constant potential (CC-CP) cycling clearly indicates that the corresponding microstructure significantly improves the kinetics of reversible Li + (de-) intercalation. A double layer electrode combining a conventionally prepared layer coated directly onto the Cu current collector with an upper layer stabilized with octanol was prepared applying wet-on-wet coating. CC-CP cycling data confirms that staged porosity within the electrode cross section results in superior electrochemical performance. [ABSTRACT FROM AUTHOR]

Due to its high theoretical capacity, silicon is a promising active material candidate for the negative electrode of lithium ion batteries. One way to reduce the severe degradation of silicon during charge/discharge cycling, is to use blends of different active materials and a well-balanced ratio of active and inactive materials. To ensure high-energy densities while still maintaining good electronic conductivity and ionic mobility, the necessity of nano-scale conductive carbons within a graphite/silicon composite was evaluated in this study. In particular, the correlation of silicon particle size and the presence of conductive additive was studied in electrodes, predominantly consisting of graphite (15 wt% silicon). Carbon black as conductive additive has a high contact surface area, which can enhance the electronic conductivity within the electrode and thus the rate capability, however, it can also propagate parasitic side reactions. It was determined that composite electrodes containing micron-sized silicon particles depend on the addition of conductive additives with regard to electrochemical performance. Due to high contact area and small transport distances, electrodes based on nano-sized silicon showed comparable capacity retention and a higher specific discharge capacity. Omitting conductive particles from these composite electrodes allowed lower binder amounts, while maintaining a good mechanical electrode integrity. [Display omitted] • Optimization of C/Si-based composite electrode formulation. • Impact of different Si particle sizes varying from nano-to micro-scale. • Evaluation of the necessity of conductive additives in C/Si-based electrodes. • Reduction of inactive material content to maximize energy density. [ABSTRACT FROM AUTHOR]

Electrode processing and performance strongly depend on the active material. Maximizing the active material content of positive composite electrodes enables low cost and high energy density. However, this maximization cannot reach 100%, as composite electrodes additionally consist of binder to provide mechanical integrity and conductive additive to enhance electronic conductivity, which in combination create a flexible porous microstructure for appropriate electron and lithium transport. In this study, the influence of three positive active material classes, layered oxide LiNi 0.6 Mn 0.2 Co 0.2 O 2 , spinel-type LiMn 2 O 4 and olivine-type carbon-coated LiFePO 4 , were investigated regarding the optimum amount of polyvinylidene difluoride as binder and carbon black as conductive additive to achieve high mechanical stability as well as high electronic and ionic conductivity within composite electrodes. Formulation optimization was conducted and compared to a reference electrode formulation with regard to physical, mechanical, electronic and electrochemical properties. In a first step, the binder amount was optimized for each active material class by varying the ratio of binder content to surface area of the solid electrode components. In a second step, the critical conductive additive content was determined. Overall, this strategy allows to decipher material class dependent optimized electrode formulations for high energy density composite electrodes with maximized active material content. [Display omitted] • Strategy to develop material class dependent electrode formulations. • Active material particle surface and size affects binder and conductive additive amount. • Carbon-coated LiFePO 4 based composite electrodes show a high SOH with low conductive additive content. [ABSTRACT FROM AUTHOR]

The influence of the preset pH value of the binder solution on aqueous processing of LiNi 0.5 Mn 0.3 Co 0.2 O 2 positive electrodes is studied. The processed electrodes are investigated by means of electrochemical charge/discharge cycling, potentiostatic electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. The results show major impact of the pH value of the binder solution on the cycling performance of lithium ion cells. Low binder solution pH values (here 7.6) lead to faster capacity fading within the first 100 cycles. In comparison, higher binder solution pH values (here 12.5) show similar fading compared to the reference electrodes based on poly(vinylidene difluoride) and N-methyl pyrrolidone as solvent. Positive electrode materials undergo a lithium-proton exchange, when in contact with water or other proton sources. Post-mortem analysis revealed that lower pH values of the binder solution potentially lead to more pronounced lithium-proton exchange. The previously inserted protons are extracted from the active material during electrochemical cycling, potentially initiate decomposition of the conductive salt LiPF 6 and hence degrade the cell performance. In combination with LiPF 6 , inter alia HF might be formed, which then reacts with lithium from LiNi 0.5 Mn 0.3 Co 0.2 O 2 or other active and inactive components and precipitate as M -F or other resistive interphases on the LiNi 0.5 Mn 0.3 Co 0.2 O 2 surface. Image 1 • Significantly improved long term stability of aqueous processed NMC positive electrodes. • Increased rate capability of aqueous processed NMC positive electrodes. • Discovery of possible degradation mechanism. • Discovery of dependence of binder pH value. [ABSTRACT FROM AUTHOR]