Flexible Morphology Design of 3D‐Macroporous LiMnPO₄ Cathode Materials for Li Secondary Batteries: Ball to Flake

Abstract

Olivine LiMPO 4 (M = Fe and Mn) cathode materials are already present in commercial batteries for diverse applications ranging from tools to electric vehicles due to their excellent thermal stability, compared to LiCoO 2 . [1][2][3][4][5][6][7][8][9][10][11] LiMnPO 4 (LMP) offers a higher energy density than LiFePO 4 due to its higher redox potential (4.1 V vs. Li/Li + ). However, LMP ( > 10 − 10 Scm − 1 ) suffers from lower intrinsic electrical and ionic conductivities than LiFePO 4 ( > 10 − 8 Scm − 1 ), resulting in much poorer electrochemical performance. In response, strategies including carbon coating on LMP, minimizing particle size, and Mn-site substitution have been applied in efforts to improve the electrochemical performance. [12][13][14][15] Several reports have also noted that the electrochemical performance of LMP is not dramatically enhanced, even when the particle size is decreased to the nanoscale ( ∼ 30 nm) and after carbon coating ( > 20 wt%). [16][17][18][19][20][21][22][23][24][25][26][27] Martha et al. [ 17 ] synthesized platelet-like carbon-coated LMP by a polyol method. After ball-milling of the LMP plate with carbon, core-shell composites consisting of < 5 nm carbon coating layer and ∼ 10 nm LMP were obtained. The results showed a practical capacity of 140 mAhg − 1 and 120 mAh g − 1 at 0.1 C; however, this rather rapidly decreased to 70 mAg − 1 at a 5C charge rate at 30 ° C. In general, cathode materials with poor electrical conductivity tend to increase in specifi c capacity with increasing temperature; however, cycling data including rate capability need to show results at 21 ° C.Considering all these factors, a 3D microporous (3DM) structure in which nanoparticles are well dispersed in the carbon matrix is the best choice to maximize the capacity of an LMP cathode. The advantage of 3D electrodes [ 28 , 29 ] are: 1) the solidstate diffusion length of lithium ions is on the order of a few tens of nanometers; 2) there are a large number of active sites for charge-transfer reactions because of the material's high surface area; and 3) reasonable electrical conductivity of the 3DM carbon matrix. These factors lead to signifi cantly improved rate performance compared to other nanoparticles.In this paper, we describe a method for fl exible construction of 3DM-LMP balls and fl akes using a polymethylmethacrylate (PMMA) template. PMMA colloidal crystals provide a fi rm scaffolding onto the dried LMP precursor solution; once removed during calcination, LiMnPO 4 particles feature pores with a diameter of about 250 nm and porewall thickness of about 40 nm. Depending on the impregnation step of the LMP precursor solution, 3DM balls and fl akes with similar porewall size and porewall thickness were obtained. Both samples demonstrated excellent rate capability and capacity retention both at 21 ° C and 60 ° C. Figure 1 shows the schematic view of the preparation procedure for 3DM-LMP balls and fl akes on a Si substrate. A dilute PMMA solution was fi rst poured onto a Si substrate and dried. This was fo...

Basic Electrochemical Performance of Pure LiMnPO4: a Comparison with Selected Conventional Insertion Materials

“…29 Briefly, all diffraction peaks correspond to the olivine type structure with a Pnma space group of the orthorhombic crystal system. The Rietveld refinement showed, however, that our LMP had a slightly smaller cell volume -the difference being in the range ∼0.1-0.6% compared to the previously reported data if compared to LiMnPO 4 samples obtained in earlier studies, 10,12,13,[30][31][32] or to our reference sample with bigger crystallites. This deviation still needs to be explained.…”

Recent Developments on and Prospects for Electrode Materials with Hierarchical Structures for Lithium‐Ion Batteries

“…[86,87] www.advancedsciencenews.com electronic conductivity (less than 10 −10 S cm −1 ), however, and larger volume changes (9.5%) compared with LiFePO 4 . [88] The flakes delivered discharge capacities of 162 mAh g −1 at 0.1 C and 110 mAh g −1 at 10 C. Choi et al synthesized porous LiMnPO 4 /C nanoplates via a solid-state reaction. Preparing nanostructured LiMnPO 4 with a uniform carbon coating is also an effective way to solve these problems.…”

Topotactically synthesized ultralong LiV3O8 nanowire cathode materials for high-rate and long-life rechargeable lithium batteries

“…Such performance is comparable to other layered metaloxide materials and indicates that the LiV 3 O 8 nanowire cathode is a promising candidate for use in high-rate and long-life rechargeable Li batteries. [48][49][50][51] DISCUSSION Calcination temperature has a significant impact on the nanowire size and space between the nanowires, which were reported to greatly influence the electrochemical performance of this material, especially for the high-rate charge/discharge process. 19,20 It was found that 4501C is the best calcination temperature, which may result from the fact that this temperature produces the most suitable degree of crystallinity and the resulting highest surface area (Table 1).…”