Feb 27, 2019 Pageview:1495
LiFePO4 batteries just different from other lithium battery of the anode material, it’s process similar to other lithium.Big process is as follows: ingredients - coated - rolling - cutting - production - winding - assembly - laser welding - baking - filler - activation - into - seal - cleaning - - sorting.The main difference in the LiFePO4 material conductive performance is poor, so do more fine material particles, large surface area, causing ingredients dispersion was difficult, and easy to water absorption.The other difference is really small.
Lithium ion batteries As a kind of high performance second green battery, high voltage, high energy density (including volume energy and mass ratio), the use of low self-discharge rate, wide temperature range, long cycle life, environmental protection, no memory effect, and can the advantages of large current charge and discharge.To improve the performance of lithium ion batteries, to a large extent depends on to improve the performance of electrode materials, especially the anode material.The most widely studied nowadays cathode material LiCoO2, LiNiO2, LiMn2O4, but as a result of cobalt toxic and limited resources, lithium nickel acid preparation is difficult, poor circulation performance and high temperature performance of manganese acid lithium factors, restricting their application and development.Therefore, the development of the new type high-energy cheap is very important for the development of the anode materials for lithium ion batteries.
1997, Padhi reported with olivine structure such as LiFePO4 (LiFePO4) can be reversibly embedded lithium, and have high specific capacity and good cycle performance, electrochemical performance is stable, the price is low wait for a characteristic, is the first choice of a new generation of green anode materials, especially as power lithium ion battery materials.The discovery of the LiFePO4 caused electrochemical both at home and abroad academic circles the attention of many researchers, in recent years, with the more and more widely application of lithium batteries, the study of LiFePO4 is increasing.
The structure of the LiFePO4
LiFePO4 (LiFePO4) has olivine structure, for a slightly twisted the six-party close packing, the space group is Pmnb type,
LiFePO4 by FeO6 cathedral and PO4 tetrahedron form space frame, P tetrahedron position, while Fe and Li fill in cathedral gap, the Fe Angle of cathedral position, Li octahedron of edge position.Lattice a FeO6 octahedron with two FeO6 cathedral and join a PO4 tetrahedral edge, while the PO4 tetrahedron with a FeO6 two LiO6 octahedron octahedron and edge.Because almost six party closely arranged, the oxygen atoms of the accumulation of making lithium ion can only be embedded in the two-dimensional plane to take off, and therefore has a relatively high theoretical density (3.6 g/cm3).In this structure, Fe2 + / Fe3 + relatively metallic lithium voltage of 3.4 V, the theory of material specific capacity is 170 ma · h/g.In the material form strong P - O - M covalent bond, greatly stability of the crystal structure of materials, leading to materials with high thermal stability.
Wang on the electrochemical performance of LiFePO4 made detailed analysis, figure 2.2 is the cycle load voltammograms LiFePO4, formed in C - V figure two peak, at the anode scan Li + emerge from LixFePO4 structure and oxidation peak at 3.52 V formation;When scanning in 4.0 ~ 4.0 Li + embedded in LixFePO4 structure, the corresponding reduction peak at 3.32 V formation;C - V curves show that the REDOX peak in LiFePO4 electrode embedded with reversible lithium ion reaction.
The performance of LiFePO4
1) high energy density
Its theoretical specific capacity is 170 mAh/g, actual specific capacity of product can be more than 140 mAh/g (0.2 C, 25 ° C).
2) security
Is the safety of lithium ion battery cathode material;Do not contain any harmful heavy metals;
3) long life
Under the condition of 100% DOD, can charge and discharge more than 2000 times;(reason: LiFePO4 lattice stability is good, the lithium ions embedded and emergence of lattice impact is not big, so it has good reversibility.The deficiencies are ionic conductivity electrode is poor, not suitable for large current charge and discharge, stuck in applications.Solution: the electrodes coated on the surface of conductive material, doped with electrode modification.)
The service life of the LiFePO4 battery with temperature, temperature too low or too high in the charging and discharging process and use process produce greatly bad hidden trouble.Electric cars use especially in northern China, in the fall and winter normal power supply of the LiFePO4 batteries or power supply is too low, need to adjust its working environment temperature to maintain its performance.At present, the domestic solve the LiFePO4 battery temperature working environment should be considered space limitations, the common solution is to use the aerogel blanket as a thermal insulation layer.
4) charging performance
LiFePO4 cathode material of lithium battery, can use big charge ratio, the fastest will be in 1 hour to the battery is full.
, 1, iron phosphate drying in addition to water
: (1) drying room drying process sager filled with stainless steel raw materials iron phosphate into chamber, regulate the drying room temperature to 220 +
20 ℃, 6-10 hours to dry.Discharge to the next working procedure to the rotary kiln sintering.
(2) the rotary kiln sintering process: after met the requirement of the rotary kiln temperature, nitrogen, feed (from the process chamber
Material), adjust the temperature to 540 + 20 ℃, sintering 8 to 12 hours.
2, grinding machine mixing process
Normal production, two grinding machine in operation at the same time, two specific feeding device and the same operation (when debugging a separate operation can be), program is as follows:
(1) lithium carbonate grinding: 13 kg weigh lithium carbonate, sucrose 12 kg, 50 kg of pure water, mixed grinding 1 to 2 hours.Pause.
(2) grinding: add iron phosphate in the mixture of 50 kg, 25 kg of pure water, mixed grinding 1-3 hours.Downtime, discharging into dispersion machine).Sample particle size measurement.
(3) cleaning: weighing 100 kg of pure water, wash lapping machine for 3 to 5 times, lotion all into dispersion machine).
3, scattered pattern material dispersion process
(1) 2.2 two grinding machine mix well (or 1 grinding machine two hybrid) of the material about 500 kg (including cleaning materials grinding machine) together into the dispersion machine, then add 100 kg of pure water, adjust the stirring speed, fully mixing dispersion 1 to 2 hours, waiting for the pump into the spray drying equipment.
4, spray drying process
(1) adjusting the spray drying equipment inlet temperature of 220 + 20 ℃, the outlet temperature to 110 + 10 ℃, the feed speed is 80 kg/hr, then begin to feed spray drying, dry material.
(2) can be regulated in accordance with the spray particle size and solid content is 15% ~ 30%.
5, hydraulic pressure piece of charging material, regulate the pressure of the hydraulic press is 150 tons and 175 tons, in the spray drying material in the mould, the holding time, compacted into squares.Loading of sagger into pushing plate furnace).At the same time, in the groups of bulk samples, compared with pressure into a block of materials.
6, pushing plate furnace sintering temperature first, nitrogen, meet the atmosphere requirements 100 parts per million, push the sagger push plate furnace, according to the heating period of 300-550 ℃, 4 to 6 hours.Constant temperature 750 ℃ 8 to 10 hours;Cooling period of six to eight hours, discharging.
7, superfine grinding roller pressure
Will push plate furnace superfine grinding burn good material input, adjust speed, grind after rolled into ultra fine grinding mill.Each batch sampling test particle size.
8, screening, packaging
The grinding material screening and packaging.5 kg, 25 kg two specifications.
9, inspection, warehousing
Label the product inspection, warehousing.Including: product name, inspection, material batch, date.
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