Extremely Durable High‐Rate Capability of a LiNi_0.4Mn_0.4Co_0.2O₂ Cathode Enabled with Single‐Walled Carbon Nanotubes

Abstract

wileyonlinelibrary.comAdv. Energy Mater. 2011, 1, [58][59][60][61][62] Extensive studies on intercalation electrodes have enabled rapid development of lithium-ion batteries for electronic applications. However, limited cycle life and moderate rate-capability as well as the high-cost of electrode materials still restrict penetration of Li-ion cells for vehicular applications. [ 1 ] LiCoO 2 , the most commonly employed cathode in portable electronics with a capacity of ~135 mAh g − 1 , is expensive, toxic and unstable at higher voltages ( > 4.3 V). [2][3][4] Recently, Ni and Mn substituted compounds (LiNi y Mn y Co 1-2y O 2 (0 < y ≤ 0.5)) have been explored. [ 2 , 5-8 ] Unfortunately, the instability of de-lithiated Li x NiO 2 and LiMnO 2 limits their usage as Li-ion cathodes. [9][10][11] Although, the LiNi y Mn y Co 1-2y O 2 (0 < y ≤ 0.5) compounds show better thermal stability in organic electrolytes, [ 12 , 13 ] the electronic conductivity and structural stability are lower than that of LiCoO 2 , thereby negatively affecting rate capability and lifetime, respectively. Different compounds with variations in y (LiNi y Mn y Co 1-2y O 2 ) including the one discussed here have been studied, but it has still not been possible to demonstrate stable high rates with conventional electrodes. [ 14 , 15 ] Recent research in the Whittingham group has shown that LiNi y Mn y Co 1-2y O 2 (y = 0.4, 0.45) compounds have higher capacities than other compositions but still exhibit low rate-capability. [ 16 ] Many efforts to enhance the conductivity of layered structures that improves the rate performance of Ni and Mn substituted compounds have been undertaken. Carbon coatings have been successfully employed to improve electronic conductivity. [17][18][19] The use of nanoscale materials is also considered an effective way to ameliorate rate performance due to shorter lithium diffusion paths. [ 20 , 21 ] But, the large surface area of nanomaterials can cause undesirable side reactions that ultimately impair cycling performance. [ 22 ] Surface coatings with stable chemicals such as Al 2 O 3 and ZrO 2 have been employed to protect the surface resulting in a longer cycle-life. [ 2 , 23 ] However, the electronic conductivity may be reduced if the coating is an insulating material. [ 24 ] In our previous work we demonstrated that single-walled carbon nanotubes (SWNTs) could be employed as a fl exible net enabling reversible cycling for a high volume expansion materials. [ 25 ] In this work the cathode material does not undergo volume expansion but suffers from poor electrical conductivity and surface over-charge/over-discharge causing capacity fade, especially at high rate. We now demonstrate that the SWNTs can improve both conductivity and also stabilize the surface at an exceptionally high rate of 10C (charge/discharge in 6 min). Specifi cally, by constructing an LiNi 0.4 Mn 0.4 Co 0.2 O 2 cathode (NMCSWNT) with 5 wt.% SWNTs, the cathode is shown to have a capacity of ˜130 mAh g − 1 at 5C and nearly 120 mAh g − 1 at 10C, both for...

Synthesis and Electrochemical Performance of Reduced Graphene Oxide/AlPO4-coated LiMn1.5Ni0.5O4for Lithium-ion Batteries

“…8,9 The surface modification including conductive agents like carbon and aluminum has been successfully applied to the cathodes, where the formation of conductive coating layers consisting of nanostructured carbon materials leads to improved electronic conductivity, cyclability, and rate capability. [15][16][17] Based on these approaches, graphene has been considered as an effective conductive coating material due to its outstanding physical properties including high specific surface area, high electronic conductivity, and excellent structural stability. 18,19 In this study, we report the LMNO cathode material with a conductive hybrid coating layer consisting of reduced graphene oxide (rGO)/aluminum phosphate (AlPO 4 ).…”

Carbon Nanomaterials in Different Dimensions for Electrochemical Energy Storage

“…Many hybrids composed of CNTs and LiCoO 2 , [58] LiNi 0.4 Mn 0.4 Co 0.2 O 2 , [59] LiMn 2 O 4 , [60] or olivine [61,62] have been fabricated, and shown good rate and cycling performance as predicted. For example, Dillon et al fabricated a SWNT wired LiNi 0.4 Mn 0.4 Co 0.2 O 2 hybrid electrode using a vacuum filtration approach with the assistance of sodium dodecyl sulfate.…”

“…For example, Dillon et al fabricated a SWNT wired LiNi 0.4 Mn 0.4 Co 0.2 O 2 hybrid electrode using a vacuum filtration approach with the assistance of sodium dodecyl sulfate. [59] In the hybrid, SWNTs form flexible networks that seamlessly stick onto the particle surface of LiNi 0.4 Mn 0.4 Co 0.2 O 2 , possibly due to charge-transfer between them. This strong surface connectivity ensures the fast diffusion of ions and electrons during cycling, resulting in a robust (120 mAh g −1 at 10 C rate) and sustainable capacity delivery (91% over 500 cycles).…”

Advances in Lithium-Ion Battery Technology Based on Functionalized Carbon Nanotubes for Electrochemical Energy Storage

“…The composite cathodes exhibited superior properties such as high conductivity, great flexibility, and outstanding cycling stability (151.4 at 10C, both for over 500 cycles, and showed significantly higher capacity as compared with the pristine NMC at rates of 5-10C. Addition of SWNTs to NMC improved both conductivity and surface stability at an exceptionally high rate of 10C (charge/discharge in 6 min) [55]. …”