Functional Role of Aramid Coated Separator for Dendrite Suppression in Lithium-Ion Batteries

The separator is an essential important key material in lithium-ion batteries (LIBs) because it is in contact with the positive and negative electrodes and the electrolyte. Aramid coated separators (ACS) are widely used in automotive and consumer batteries as high-performance separators for LIBs with high safety and excellent lifetime characteristics. Although much effort has been made to improve the electrolyte composition, the lithium deposition on the surface of the graphite electrode at low temperature and the high charge rate is still an unsolved problem in LIBs. In this work, lithium metal is used as a counter electrode, and a separator was placed between lithium metal and graphite composite electrode. The lithium was deposited on the surface of the graphite composite electrode through the separator. Then, the functional role of ACS in the initial deposition process was investigated. The dendrite blocking effect of ACS was studied by the observation of dendrite growth and pulse cycle performance.

The Role of Silicon in Silicon-Graphite Composite Electrodes Regarding Specific Capacity, Cycle Stability, and Expansion

One promising way of compensating for the repeated volume expansion and contraction of silicon as an anode active material in lithium ion batteries (LIBs) is to embed silicon within a graphite matrix. Silicon-graphite (SiG) composites combine the advantageous properties of graphite, i.e., large electrical conductivity and high structural stability, with the advantageous properties of silicon, i.e., high theoretical capacity. Graphite has a much lower volume expansion upon lithiation (≈ 10%) than pure silicon (≈ 300%) and provides a mechanically stable matrix. Herein, we present an investigation into the electrochemical performance and thickness change behavior of porous SiG anode compositions with silicon contents ranging from 0 wt% to 20 wt%. The electrode composites were studied using two methods: in situ dilatometry for the thickness change investigation and conventional coin cells for the assessment of electrochemical performance. The measurements show that the initial thickness change of SiG electrodes increased significantly with the silicon content, but it leveled off during cycling for all compositions. There appears to be a correlation between silicon content and capacity loss, but no clear correlation between thickness change and capacity loss rate was found.

The Effect of Silicon Grade and Electrode Architecture on the Performance of Advanced Anodes for Next Generation Lithium-Ion Cells

To increase the specific capacity of anodes for lithium-ion cells, advanced active materials, such as silicon, can be utilized. Silicon has an order of magnitude higher specific capacity compared to the state-of-the-art anode material graphite; therefore, it is a promising candidate to achieve this target. In this study, different types of silicon nanopowders were introduced as active material for the manufacturing of composite silicon/graphite electrodes. The materials were selected from different suppliers providing different grades of purity and different grain sizes. The slurry preparation, including binder, additives, and active material, was established using a ball milling device and coating was performed via tape casting on a thin copper current collector foil. Composite electrodes with an areal capacity of approximately 1.70 mAh/cm² were deposited. Reference electrodes without silicon were prepared in the same manner, and they showed slightly lower areal capacities. High repetition rate, ultrafast laser ablation was applied to these high-power electrodes in order to introduce line structures with a periodicity of 200 µm. The electrochemical performance of the anodes was evaluated as rate capability and operational lifetime measurements including pouch cells with NMC 622 as counter electrodes. For the silicon/graphite composite electrodes with the best performance, up to 200 full cycles at a C-rate of 1C were achieved until end of life was reached at 80% relative capacity. Additionally, electrochemical impedance spectroscopies were conducted as a function of state of health to correlate the used silicon grade with solid electrolyte interface (SEI) formation and charge transfer resistance values.