The Role of Balancing Nanostructured Silicon Anodes and NMC Cathodes in Lithium-Ion Full-Cells with High Volumetric Energy Density

Abstract

Silicon anodes offer a very promising approach to boost the energy density of lithium-ion batteries. While silicon anodes show a high capacity and, depending on the system, a good cycle stability in half-cells vs lithium, their integration in industrially applicable lithium-ion full-cells is still challenging. Balancing described as the capacity ratio of negative and positive electrode (n/p ratio) is a crucial necessity for the successful design of lithium-ion batteries. In this work, three different silicon based anode systems, namely carbon coated silicon nanowires, columnar silicon thin films and silicon-carbon void structures are compared in LIB full cells containing NMC111 cathodes. By varying the areal capacity of the NMC111 cathode, the influence of the balancing was investigated over a broad n/p range of 0.8−3.2. The aim was to find an ideal compromise between lithium plating suppression, high cycling stability and maximized energy density. To underline the high volumetric energy density, the columnar silicon thin films are additionally analyzed in multilayered pouch cells with NMC622 and NMC811 cathodes resulting in 605 Wh L−1 and 135 Wh kg−1 and even 806 Wh L−1 and 183 Wh kg−1 as demonstrated on stack level.

Exploiting the Degradation Mechanism of NCM523Graphite Lithium‐Ion Full Cells Operated at High Voltage

“…Another important factor which can influence the growth of Li dendrites and, thus, the cycling performance, is the anode to cathode capacity balancing ratio (N/P ratio) [42,81,82] . In the previous chapters, a N/P ratio of 1.35 / 1.00 was used for full cells, while in this chapter the impact of an N/P ratio of 1.05 / 1.00 will be evaluated, and in particular, how it can influence the dendrite growth and cycle life of the NCM523 graphite full cells.…”

Nanostructured Si-C Composites As High-Capacity Anode Material For All-Solid-State Lithium-Ion Batteries

“…[15] The lithium alloy forming element silicon is another attractive alternative to lithium due to its high gravimetric and volumetric capacity (1857 mAh g -1 , 2190 mAh cm -3 ), low delithiation potential (0.4 V vs. Li/Li + ) and high abundance lowering battery production costs. [12,16,17,18] Tesla just recently announced that their future battery technology will be based on cheap and abundant silicon anodes. [19] However, bulk silicon cannot be effectively utilized in a battery.…”

“…The high volume change of silicon during (de)lithiation of about 300 % lead to particle pulverization, loss of electrical contact and an instable solid electrolyte interphase (SEI), resulting in low coulomb efficiency and permanent capacity decay. [4,18,20] In order to compensate the volume changes of silicon, several nano-scaled materials such as silicon nanoparticles [21,22] , nanowires [23,24] , nanotubes [25] , and thin films [26,27] have been developed. It has been shown that crystalline silicon nanoparticles with a diameter < 150 nm do not crack [21] although µm-scaled columnar silicon structures [27,28] are a viable anode system.…”

“…It has been shown that crystalline silicon nanoparticles with a diameter < 150 nm do not crack [21] although µm-scaled columnar silicon structures [27,28] are a viable anode system. To further improve the mechanical stability and the conductivity of the silicon anode, several composites of the silicon nanostructures with carbon [18,29] , transition metal oxides like TiO2 [30] , metals [31] , and polymers [32] have been designed. However, these composites have mostly been analyzed as anode material in conventional LIBs with liquid electrolytes yet.…”

“…Although encouraging results of nano-scaled silicon anodes with liquid electrolytes regarding capacity, initial coulombic efficiency (ICE), rate capability and capacity retention have been published [18,33] , safety issues and also higher costs due to the need of electrolyte additives [34] and special separators [11,35] are still present in conventional lithium ion batteries. Replacing the liquid electrolyte with a SE improves the thermal stability [11] and partially prevents electrolyte depletion as only lithium ions are mobile [11,36,37] in the battery cell.…”