Design and Synthesis of Double-Functional Polymer Composite Layer Coating To Enhance the Electrochemical Performance of the Ni-Rich Cathode at the Upper Cutoff Voltage

Abstract

Graphene has been implemented as a desirable additive to improve the electrochemical performance of Ni-rich cathode materials. However, it is not only hard to ensure the intimate interaction between them in practice, which may affect the surface electronic conductivity of the composite, but also a challenge to fabricate cathodes with uniform graphene coating because of its two-dimensional planar structure. Besides, the graphene coating layer is easily peeled off from the cathode material during the cycling process, especially at the upper cutoff voltage. Therefore, we introduced a double-functional layer synergistically modified strategy to facilitate the electrochemical properties of LiNi0.8Co0.1Mn0.1O2 cathode materials. In the designed architecture, the LiNi0.8Co0.1Mn0.1O2 particles were uniformly enwrapped by a functional reduced graphene oxide (RGO)–KH560 polymer composite layer which consists of an inner high-flexibility epoxy-functionalized silane (KH560) layer and an outer RGO layer with high electronic conductivity. The KH560 layer, in the structural system, is especially critical in connecting the layer of outer RGO and the inner surface of the active material, which brings about the perfect and complete double-functional coating layer and in turn fully expresses the modification effect of both KH560 and RGO in the improvement of electrochemical performance. Consequently, higher capacity retention, better rate, and improved high-temperature performances (55 °C) at the upper cutoff voltage (4.5 V) of this composite are identified when compared with the RGO-coated and pristine samples. In particular, the cathode with RGO (0.5%)–KH560 (0.5%) coating exhibits capacity retentions of 95.2 and 81.5% after 150 cycles at 1 C, 4.5 V at room and high temperatures, respectively.

Surface/Interface Structure Degradation of Ni‐Rich Layered Oxide Cathodes toward Lithium‐Ion Batteries: Fundamental Mechanisms and Remedying Strategies

“…Now that the parasitic side reactions start from the interfaces between the solid cathodes and liquid electrolytes, the most effective method is to avoid their direct contact by introducing passive physical protection layer on the cathode surface . In general, the employed coating species can be categorized into i) the chemically and electrochemically inactive coatings, including metal oxides (Al 2 O 3 , TiO 2 , MgO, SiO 2 , ZrO 2 , V 2 O 5 , Nb 2 O 5 , ZnO, MoO 3 , and Y 2 O 3 ,) and phosphates (AlPO 4 , MnPO 4 , Mn 3 (PO 4 ) 2 , La(PO 4 ) 3 , Ni 3 (PO 4 ) 2 , Co 3 (PO 4 ) 2 , ZrP 2 O 7 , and FePO 4 ) as well as some fluorides (AlF 3 and LiF); ii) the Li + conductive coatings, mainly refer to the Li‐containing compounds such as LiAlO 2 , Li 2 ZrO 3 , Li 3 VO 4 , Li 2 MnO 3 , LiMn 2 O 4 , Li 3 PO 4 (LPO), LiFePO 4 (LFP), LiMnPO 4 , Li 2 TiO 3 , LiTiO 2 , Li 2 O‐2B 2 O 3 , LiTi 2 (PO 4 ) 3 , LiZr 2 (PO 4 ) 3 , Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 , Li 0.5 La 0.5 TiO 3 , LiTaO 3 , Li 4 SiO 4 , and LiAlF 4 as well as some heterostructured electrochemical active cathodes (Li 1.2 Ni 0.2 Mn 0.6 O 2 , Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 and NCM333); and iii) the electron conducting coating, representatively, reduced graphene oxide (rGO), permeable poly (3,4‐ethylenedioxythiophene) (PEDOT),…”

Enhanced High‐Temperature Electrochemical Performance of Layered Nickel‐Rich Cathodes for Lithium‐Ion Batteries after LiF Surface Modification

“…However, it is very difficult to obtain uniformly coated compounds via solid state milling process. [42][43][44] Herein, a straightforward surface modification technique is reported for preparing Li-conductive LiF-coated Li-Ni 0.90 Co 0.08 Al 0.02 O 2 (NCA@LiF) using a simple sol-gel method. Since the Li compound remaining on the surface of the Ni-rich material can be as high as 1 % by weight, then LiF coating herein can be constructed by reacting 1-butyl-2,3-dimeth-ylimidazolium tetrafluoroborate (BdmimBF 4 ) solution with residual Li compounds on the surface of the NCA.…”

“…So far, some reported fluoride precursors, such as NH 4 F or NH 4 HF 2 , have been mixed with the original materials via mechanical milling and combined with a following annealing process to form a deep fluorination LiF coating layer. However, it is very difficult to obtain uniformly coated compounds via solid state milling process …”

Surface Architecture Design of LiNi0.8Co0.15Al0.05O2 Cathode with Synergistic Organics Encapsulation to Enhance Electrochemical Stability

“…The comparative result implies that NCA@PK2 has reduced Li 2 CO 3 , which is coincident with the residual alkali contents revealed in Table 1. The C 1s spectrum of NCA@PK2 can be separated into four peaks, the peaks at 284.8, 286.3, 286.8, and 288.5 eV are ascribed to the C−C, C−OH, C−Si, and O−C=O bonds in the amorphous coating layer of NCA@PK2, [60] respectively. The Ni 2p, Co 2p, and Al 2s spectra of NCA and NCA@PK2 are shown in Figure 4d, e, and f. For the Ni 2p spectra, the peak corresponding to Ni 2p 3/2 can be separated into two peaks, one peak at a binding energy of 855.7 eV and the other peak at a binding energy of 854.4 eV are ascribed to Ni 3+ and Ni 2+ .…”