Carbon/Polymer Bilayer-Coated Si-SiOx Electrodes with Enhanced Electrical Conductivity and Structural Stability
ACS APPLIED MATERIALS & INTERFACES
Authors: Guo, Junpo; Zhao, Guangming; Xie, Tian; Dong, Dongqi; Ma, Chuanli; Su, Linghao; Gong, Liangyu; Lou, Xiangdong; Guo, Xuyun; Wang, Jie; Zhu, Ye
Abstract
Si-based electrodes offer exceptionally high capacity and energy density for lithium-ion batteries (LIBs),but suffer from poor structural stability and electrical conductivity that hamper their practical applications. To tackle these obstacles, we design a C/polymer bilayer coating deposited on Si-SiOx microparticles. The inner C coating is used to improve electrical conductivity. The outer C-nanoparticle-reinforced polypyrrole (CNP-PPy) is a polymer matrix composite that can minimize the volumetric expansion of Si-SiOx and enhance its structural stability during battery operation. Electrodes made of such robust Si-SiOx@C/CNP-PPy microparticles exhibit excellent cycling performance: 83% capacity retention (794 mAh g(-1)) at a 2 C rate after more than 900 cycles for a coin-type half cell, and 80% capacity retention (with initial energy density of 308 Wh kg(-1)) after over 1100 cycles for a pouch-type full cell. By comparing the samples with different coatings, an in-depth understanding of the performance enhancement is achieved, i.e., the C/CNP-PPy with cross-link bondings formed in the bilayer coating plays a key role for the improved structural stability. Moreover, a full battery using the Si-SiOx@C/CNP-PPy electrode successfully drives a car model, demonstrating a bright application prospect of the C/polymer bilayer coating strategy to make future commercial LIBs with high stability and energy density.
Finite-dimensional approximations for Nica-Pimsner algebras
ERGODIC THEORY AND DYNAMICAL SYSTEMS
Authors: Kakariadis, Evgenios T. A.
Abstract
We give necessary and sufficient conditions for nuclearity of Cuntz-Nica-Pimsner algebras for a variety of quasi-lattice ordered groups. First we deal with the free abelian lattice case. We use this as a stepping-stone to tackle product systems over quasi-lattices that are controlled by the free abelian lattice and satisfy a minimality property. Our setting accommodates examples like the Baumslag-Solitar lattice for n = m > 0 and the right-angled Artin groups. More generally, the class of quasi-lattices for which our results apply is closed under taking semi-direct and graph products. In the process we accomplish more. Our arguments tackle Nica-Pimsner algebras that admit a faithful conditional expectation on a small fixed point algebra and a faithful copy of the coefficient algebra. This is the case for CNP-relative quotients in-between the Toeplitz-Nica-Pimsner algebra and the Cuntz-Nica-Pimsner algebra. We complete this study with the relevant results on exactness.