No abstract

Currently widely used carbonate-based electrolytes face difficulty in ensuring that the lithium-ion batteries work beyond 4.2 V for the purpose of energy density improvement. Herein, we report a novel electrolyte that emphasizes the synergistic effect of fluoroethylene carbonate (FEC) and 2-(trifluoromethyl) phenyl boric acid (2-TP) as coadditives, enabling the LiCoO 2 cathode to operate stably under high voltages. With the addition of 1% 2-TP and 10% FEC into a carbonate-based electrolyte, LiCoO 2 shows a significantly improved cyclic stability. Spectral characterizations, electrochemical measurements, and theoretical calculations demonstrate that the improved cyclic stability can be attributed to the cathode−electrolyte interphase (CEI) derived from FEC and 2-TP. These two additives are preferentially oxidized on the LiCoO 2 electrode into their oxidation decomposition products to construct a robust and lowimpedance CEI with inorganic LiF uniformly dispersed in the organic B-containing matrix. This unique CEI construction provides a facile solution to the challenges in developing high-energy-density lithium-ion batteries based on high-voltage cathodes, not limited to LiCoO 2 .

The rate capability of lithium-ion batteries is highly dependent on the interphase chemistry of graphite anodes. Herein, we demonstrate an anode interphase tailoring based on a novel electrolyte additive, lithium dodecyl sulfate (LiDS), which greatly improves the rate capability and cyclic stability of graphite anodes. Upon application of 1% LiDS in a base electrolyte, the discharge capacity at 2 C is improved from 102 to 240 mAh g −1 and its capacity retention is enhanced from 51% to 94% after 200 cycles at 0.5 C. These excellent performances are attributed to the preferential absorption of LiDS and the as-constructed interphase chemistry that is mainly composed of organic long-chain polyether and inorganic lithium sulfite. The long-chain polyether possesses flexibility endowing the interphase with robustness, while its combination with inorganic lithium sulfite accelerates lithium intercalation/deintercalation kinetics via decreasing the resistance for charge transfer.

Lithium-rich layered oxides (LLOs) due to their delivered capacity of over 250 mA h g–1 are regarded as the most attractive cathode for lithium-ion batteries (LIBs) with higher energy density. However, the unstable cycling performance, poor rate capability, and large voltage decay in LLOs hinder their commercial application. Here, we construct a highly conductive electrode where Li1.2Mn0.6Ni0.2O2 (LMN) is wrapped in a N-doped graphene carbon matrix (LMN-NG) to address the fast capacity fading and suppress the voltage decay. The LMN-NG electrode can deliver a capacity of 286.4 mA h g–1 at 0.2 C and maintain a capacity retention of 86% after 200 cycles, which is much higher than the LMN control electrode with values of 268 mA h g–1 and 75%, respectively. The theoretical calculation and differential electrochemical mass spectrometry (DEMS) analysis investigation suggest that the functional group in NG can effectively trap active oxygen species and mitigate the successive electrolyte decomposition, thus protecting LLOs. Transmission electron microscopy and Raman spectroscopy results reveal that the LMN-NG electrode maintains better layered structural stability after long-term cycling and exhibits a less spinel-like disordered phase of 18% compared to 40% of the LMN electrode. The superior electrochemical performance of LMN-NG indicates that enwrapping LLOs in NG has a potential application in LIBs.

The study area is located in Qaidam Basin on Tibetan Plateau, which has very complex geological background sedimentologically and structurally. Building the discrete fracture network (DFN) of study zone is a critical work step for subsequent dual porosity / dual permeability (Dp/Dp) dynamic simulation which further enables the optimized design of field development plan (FDP). The saline lacustrine tight oil reservoirs in study zone were severely deformed by the Neotectonism coupling with the far-field collision between the Indian and Eurasian plates. There were relatively abundant fracture interpretations from image well logs with core calibration and relatively amplitude preserving seismic cube. First, statistics of well fractures were performed in terms of their types and attitudes, which enabled proposing their genetic mechanism together with information of other references and dividing fracture sets more reasonably for subsequent DFN modeling. Then, many efforts were made on fracture driver attribute screening with the aid of neural network (NN) and principal component analysis (PCA) functions. Dozens of possible fracture driver attributes were examined, which were mainly geometric attributes, edge-detection attributes, amplitude/frequency related attributes and lithology/porosity related attributes. Meanwhile, microseismic monitoring (MSM) data were also used to help screen the pertinent fracture drivers. Three fracture driver attributes were finally screened out and they were combined together to produce a fracture intensity trend which was finally used as co-kriging secondary variable together with well fracture intensity logs for modeling the 3D-grids of fracture intensity based on gaussian random function simulation algorithm. Besides the existed fault model (as large-scale fractures) generated when building matrix geomodels, a medium-scale fracture set was built deterministically with "Fault Patch" extraction method based on the seismic edge-detection Ant Cube. Then for small-scale fractures, totally four fracture sets were built stochastically based on split 3D fracture intensity and their own parameters of geometry, orientation, aperture. These five fracture sets were then upscaled to produce the fracture properties with porosity and permeability constraints from wells, i.e., usually less than 0.1% and hundreds of millidarcies respectively. Then these fracture properties were further calibrated and used in Dp/Dp dynamic simulation process. Genuine discrete fracture network and Dp/Dp dynamic simulation were built up and performed for the first time for the complex oil reservoirs on Tibetan Plateau, based on organic multi-disciplinary integration. But more importantly, many useful conclusions and decisions were reached based on the Dp/Dp dynamic simulation which made the field development plan more robust and cost-effective.