Introduction
All-solid-state lithium batteries (ASSLBs) face the critical challenges of low cathodic loading and poor rate performance, which limits their energy power density. The widely accepted goals of high ionic conductivity and low interface resistance do not appear to be sufficient to overcome these challenges.
Body partBrief introduction of the results
This paper reveals that the efficient ion permeation network in the cathode has a more critical impact on the electrochemical performance of ASSLBs. Construct vertically arranged li0 in a solid-state cathode by magnetic manipulation35la0.55TiO3 nanowires (LTO NWS), which provides a two-fold increase in ionic conductivity at the cathode compared to a cathode consisting of randomly distributed LLTO NWS.
All-solid-state lithium iron phosphate batteries using polyethylene oxide as electrolyte are capable of providing high capacities of 151 mAh g-1 (2C) and 100 mAh g-1 (5C) at 60°C and 108 mAh g-1 at a charge rate of 2C. In addition, the battery can reach a high area capacity of 3 mAh cm-2 even with an actual LFP load of 20 mg cm-2. The prevalence of this strategy is also in lini08co0.1mn0.It was demonstrated in the 1O2 cathode.
This work provides a new avenue for designing ASSLBs with improved energy power density. The research was published in Advanced Materials, a top international journal in the field of materials, with the title of "Efficient ion percolating network for high-performance all-solid-state cathodes".
**Reading guide
Figure 1] Schematic diagram of manufacturing strategies for various cathode structures. COMSOL Simulation 0Lithium ion concentrations along (B) V-LLTO, (C) R-LLTO, and (D) blank cathode thickness directions at 1 and 5 C full charge and simulated at 0CAM utilization at 10% SoC at 1 and 5 C. (e) Simulating the electrochemical performance of V-LLTO, R-LLTO, and blank cathodes at different magnifications.
The magnetic field can adjust the direction of the magnetic vector of the M-LLTO NWS, forcing them to orient themselves vertically in the composite cathode (V-LLTO). For comparison, the R-LLTO cathode was prepared under the same conditions, except for the absence of a magnetic field, and the LFP cathode without M-LLTO NWS (blank) was also prepared. In 0At a low current density of 1 C, the ion concentration gradients within these cathodes are almost identical.
At various rates, the CAM particles in the V-LLTO cathode are efficiently utilized throughout the electrode, whereas in the R-LLTO and blank cathodes, the CAM particles are mainly utilized at the top, and most of the CAM particles at the bottom are unreactive. The potential overcharge of the CAM particles at the top of the electrode leads to low CAM utilization and unstable cycling performance. In 0At a low current density of 1 C, the simulated specific capacities of the three cathodes are close to the theoretical values. The slow rate of charge and discharge allows for more complete ion migration and diffusion in the solid cathode. As the current density gradually increases, the V-110 cathode outperforms other cathodes due to the higher ion permeation efficiency in the low tortuous path.
At a current density of 5 C, the V-LLTO cathode showed a 60% capacity retention, which was significantly higher than that of the R-LLTO (15%). Figure 1. Schematic diagram of manufacturing strategies for various cathode structures. COMSOL Simulation 0Lithium ion concentrations along (B) V-LLTO, (C) R-LLTO, and (D) blank cathode thickness directions at 1 and 5 C full charge and simulated at 0Utilization of CAM at 10% SOC at 1 and 5 C. (e) Simulating the electrochemical performance of V-LLTO, R-LLTO, and blank cathodes at different magnifications.
Directed LLTO precursor nanofibers were synthesized by electrospinning mixed with Ti(OR4), La(NO3)3·6H2O, LiNO3, PVP nanofibers and subsequent thermal annealing, as shown in scanning electron microscopy (SEM) images (Figs. 2A and B). Due to the negative zeta potential on the LLTO surface, positively charged Fe3O4 nanoparticles can spontaneously adsorb on the surface of LLTO NWS to form M-LLTO (Figure 2C). Transmission electron microscopy (TEM) images from M-LLTO confirm surface adsorption.
Fig. 2] Phase, morphology, and structural characteristics of the magnetic packing material and the corresponding electrode. (A-C) SEM images of electrospun LLTO precursor nanofibers (A), LLTO NWS (B), and M-LLTO NWS (C). TEM (D, E) and HAADF TEM (E) images of M-LLTO NWS. XRD plots of LLTO nanowires and M-LLTO nanowires. (G-I) Cross-sectional SEM images of the V-LLTO cathode (G, H) and corresponding EDS spectra (I).
Directed LLTO precursor nanofibers were synthesized by electrospinning mixed with Ti(OR4), La(NO3)3·6H2O, LiNO3, PVP nanofibers and subsequent thermal annealing, as shown in scanning electron microscopy (SEM) images (Figs. 2A and B). Due to the negative zeta potential on the LLTO surface, positively charged Fe3O4 nanoparticles can spontaneously adsorb on the surface of LLTO NWS to form M-LLTO (Figure 2C). Transmission electron microscopy (TEM) images of M-LL confirm the surface adsorption of Fe3O4 nanoparticles (Figure 2D). M-llto nanowires consist of crystalline and twin regions and some amorphous structures (Figure 2E). M-llto grains show highly crystalline properties with a high-resolution crystal structure with a D spacing of 2738, corresponding to the (110) side of the cubic llto.
It is worth noting that M-LLTO shows the same crystal structure as LLTO, indicating that the adsorption of magnetic nanoparticles does not change the crystal structure of LLTO. M-LLTO showed the same X-ray diffraction (XRD) pattern as LLTO, which further confirmed the stability of LLTO after Fe3O4 adsorption. In addition, the ionic conductivity of the CPE composed of LLTO or M-LLTO is basically the same, indicating that a small amount of Fe3O4NPS modified on the surface of LLTO does not affect lithium-ion transmission. Cross-sectional SEM image of the V-LLTO cathode (LFP loading 20 mg cm-2) showing M-LLTO nanowires arranged vertically in the composite cathode. The distribution of Ti and LA elements observed in the Energy Dispersive Spectroscopy (EDS) plotted images is very close to that of LLLTO NWS.
Fig. 3] Charge transport kinetics of different types of cathodes were analyzed by different electrochemical properties. (a-c) stainless steel|Cathode| peo |Cathode|Schematic diagram of an ionic electronically symmetrical battery made of stainless steel (a), Nyquist diagram (b), and the corresponding ionic bending factor and ionic conductivity (c) of various cathodes. （d，e）ss | peo |Cathode|peo|Schematic diagram of an ionic symmetrical cell of SS (D) and corresponding Nyquist diagrams (E) of various cathodes. (f) The peak current density (IP) of the various cathodes has a significant impact on the scan rate (v0.).5) Graph of the square root. Raman spectra of V-LLTO(G) and R-LLTO(H) cathodes at the top and bottom after a full charge at 5 C.
The calculated ionic conductivity (60oC) for V-LLTO, R-LLTO, and blank cathodes are respectively. 9 10-6 and 27×10-6s·cm-1。V-LLTO has the highest ionic conductivity, twice that of R-LLTO and five times that of the blank cathode. V-LLTO's excellent ionic conductivity in the electrode is mainly due to its unique ion transport network, which is due to its short and direct transport path. On the other hand, the electronic conductivity of V-LLTO, R-LLTO, and blank cathodes are respectively. 5 10-5 and 58×10-5s·cm-1。The electronic conductivity of the three electrodes is basically the same, which is mainly determined by the distribution of conductive additives and CAM particles in the composite cathode.
In order to further study the ionic conduction behavior in different cathodes, ionic symmetrical cells considering only the effect of ionic impedance were assembled. Stainless steel| peo |Cathode| peo |The ion impedance in a symmetrical cell made of stainless steel consists of the ionic impedance of the PEO electrolyte, the interface impedance between the cathode and the electrolyte, and the electrode ion transfer impedance. By fitting the total impedance data, the ion transfer impedance of the electrode can be obtained, from which the ionic conductivity of V-LLTO, R-LLTO, and blank cathode (60°C) is calculated, respectively. 9 10-6 and 28×10-6s cm-1。This is consistent with the trend observed in ionic electronically symmetric cells, providing additional evidence for the increase in cathode ion conductivity achieved by vertically oriented LLTO NWS.
Figure 4] Demonstrated electrochemical performance of cathodes with different packing distributions in LFP and NCM systems. (A, B) Rate performance (A) and long-term cycling performance (B) of various LFP PEO lithium batteries at 60 C and 1 C. (c) Cycling performance of V-LLTO batteries under high loads. (d) Comparison of cathode area capacity for different studies (plotted as a function of CAM loading). (h) Rate performance (F, G) of various LFP PEO lithium batteries at 30 and long-term cycle performance (G) of various NCM PEO lithium batteries at 60. (h) Rate performance of various NCM PEO lithium batteries at 30.
In order to determine the feasibility of the cathode structure design, an LFP PEO lithium battery with V-LLTO, R-LLTO, and blank cathodes was assembled and evaluated. The discharge capacitance of the V-LLTO cathode at and 5 C and 100 mAh g-1, respectively, was significantly higher than that of the R-LLTO cathode and 30 mAh G-1 (sequentially numbered) and the corresponding values of the blank cathode and 30 mAh G-1 (sequentially numbered) (Figure 4A) It is worth noting that the V-LLTO cathode exhibits high capacity at 5 C fast charging, more than three times that of the R-LLTO and blank cathode.
Considering that the same anode and electrolyte are used in all three cells, the difference in rate performance is attributed to the different ionic conduction characteristics in the cathode. In addition, the voltage overpotential of the V-LLTO cathode increases slowly with the increase of current density compared to the R-LLTO and blank cathodes, indicating that its ion transfer efficiency is higher. The above results highlight the important role of vertically oriented LLTO NWS in improving rate performance. The V-LLTO cathode also showed stable cycling performance after 300 cycles at 1 C, with a discharge capacity of 113 mAh g-1 and a retention rate of 71%. In contrast, the R-LLTO and blank cathodes showed much lower discharge capacitances, with corresponding retention rates of 52% and 51% after 83 and 63 mAh g-1,300 cycles, respectively.
The vertically oriented LLTO ensures high lithium-ion transfer efficiency, making it promising for high-load cathodes. The V-LLTO cathode with a mass load of 20 mg cm-2 exhibits stable cycling with an area capacity of 3 mAh cm-2. Long-term stability is confirmed by a constant and stable voltage distribution throughout the cycle. The load and area capacity of this study is superior to that of previously reported asslbs.
The authors also tested the magnification performance of different composite cathodes at 30 to evaluate the room temperature (RT) performance of ASSLBs. Compared with the R-LLTO and blank cathode, the rate performance of the V-LLTO cathode is more significantly improved. The discharge capacitance of the V-LLTO cathode at and 5 C and 72 mAh g-1 were significantly higher than those of the R-LLTO cathode and 7 mAh G-1 (in order) and the blank cathode and 2 mAh g-1 (in order).
Summary and outlook
In conclusion, the authors propose a magnetic field-induced alignment strategy to effectively control the orientation of LLTO NWS in the solid-state composite cathode. This strategy allows for efficient ion permeation, even with only 1vol% LTO NWS, thus addressing key challenges in conventional cathodes, such as tortuous ion transport and excess SSE additives.
The simulation results show that the vertically arranged LLTO NWS in the composite cathode has the advantages of reducing the ion concentration gradient and improving the utilization rate of CAM, and is expected to achieve high-performance ASSLBS. The proof-of-concept of all-solid-state LFP lithium batteries with vertically aligned LLTO NWS is capable of exhibiting excellent rate performance at 60°C with a discharge capacity of 151 mAh G-1 at 2C and 100 mAh G-1 at 5C. In addition, even with an actual LFP area load of 20 mg cm-2, there is little capacity loss as the electrode thickness increases, and a high area capacity of 3 mAh cm-2 can be achieved.
Despite the low ionic conductivity of PEO-based electrolytes, solid-state LFP lithium batteries can still maintain a high specific capacity of 108 mAh g-1 at room temperature. This proposed strategy has also proven to be versatile, and the NCM system has further demonstrated its ability to facilitate ion transport kinetics at the electrode level. This study introduces an efficient method to construct an efficient ion permeation network with minimal SSES while achieving fast ion transport and high energy density, and provides a promising solution for practical high-performance ASSLBs.
References
efficient ion percolating network for high-performance all-solid-state cathodes
doi:10.1002/adma.202312927