Ni-MH battery pack

Discussion on Ni-MH battery pack process technology and production application

In the absence of ammonia water, Ni2+, C02+, and Mn2+ in the solution system of lithium-ion batteries will react with OH- to precipitate. When the complex precipitation method is used to prepare the ternary precursor, Ni(Ⅱ)-Co(Ⅱ)-Mn(Ⅱ)-NH +-NH3-H:0 system is relatively complex. The species present in this system are: Ni(NH3):”(f_o, l, 2, 3, 4, 5, 6), Ni(OH)j2-j(j=l, 2, 3), Co(NH3)k2+Co(oH)f2-7(,=1, 2, 3, 4), Mn(NH3). (m=o, l, 2), Mn(OH). 2-n(yi=l, 2), NH3, NH4+, H+, OH- and H:0. The equilibrium solid phase of the ternary coprecipitation of nickel, cobalt and manganese is Ni(OH)2c.), Co(OH)2c.) and Mn(OH)2c.)'221. NaOH-ammonia solution is added to the reactor at the same time. M2+ first reacts with NH3H20 to form M2+_ammonia complex Compound, and then precipitate with OH- to generate M(OH)2. That is to say, the following complexation reaction and precipitation reaction must occur: l/3N12+(aq)+l/3C02+(aq)+l/3Nj2+(aq)+xNH40H(aq)——,[Ni“3Col/3Mn1／3(NH3)n2+1(aq)+nH20+(x-n)NH40H(aq)[Nil/3Col/3Mnl/3(NH3).2+](aq)+yOH-+zH20～Nil/3Col/3Mnl/3(OH)2cs)+zNH40H(aq)+(n-z)NH3. There is a balance between Ni(Ⅱ)-Co(Ⅱ)-Mn(Ⅱ)-NH4+-NH3-H20. Since a large number of transition metal ions exist in the form of ammine complexes after being added to the reactor, there are few free transition metal ions in the solution, and the supersaturation of the solution is low, which inhibits the rate of nucleation formation, allowing more precipitated ions in the solution to diffuse to the surface of the nucleus particles and precipitate on the surface of the nucleus, promoting grain growth, and obtaining spherical hydroxide products with good crystallinity, reasonable agglomeration and appropriate particle size. Although the solubility products of Ni(OH)2, Co(OH)2 and Mn(OH)2 are different, the solubility product of Mn(OH)2 is two orders of magnitude larger, but because it is two orders of magnitude smaller than ammonia, the system [NH3]T and pH value are controlled well, and Ni2+, C02+, and Mn2+ have similar precipitation conditions and can be co-precipitated. If you want to prepare M(OH)2 with a regular shape, you must control the rate of the precipitation reaction. Only when the rate of the precipitation reaction is controlled within a reasonable range can the precipitated M(OH)2 crystals be arranged regularly, and the specific surface energy of the crystal particles is the highest, which is conducive to the formation of good crystal forms. In the Ni(Ⅱ)-Co(Ⅱ)-Mn(H)-NH4+-NH3-H20 system, the metal ion concentration in the reaction system can be regulated by the complexation of NH, with Ni2+, C02+, and Mn2+, and the reaction nucleation and crystal growth rate can be controlled. Thermodynamic calculations of this system show that the addition of ammonia affects the precipitation reaction of M2+ and hydroxide. In the pH range of 8 to 12, when the reaction is in equilibrium, [Ni2+]T.[C02+]T.[Mn2+]T in the solution increases with the increase of the total ammonia concentration. In other words, M(OH)2 will be reversely dissolved in ammonia water, which shows that the ammonia content in the system can be used to regulate the M2+ concentration in the solution. However, due to the small complexation of Mn2+ with ammonia, the increase of [Mn2+] with [NH3] is much smaller than that of [Ni2+]T and [C02+]. When [NH3]T is Smol. When [NH3]T is 0.01mol. L-1, ammonia has a strong complexing effect on Ni2+, C02+, and Mn2+. At this time, the transition metal ions in the reaction solution mainly exist in the form of ammonia complex ions, and the formation of hydroxide precipitation reaction rate is very low. Only when the pH value increases significantly can a large amount of precipitation be produced. In this case, the process parameters are difficult to control; when [NH3]T is 0.01mol. L-1, ammonia has a small complexing effect on Ni2+, C02+, and Mn2+, and the precipitation reaction cannot be effectively controlled. His research results show that when [NH3]T is 0.010l.Omol. L-1 and the pH value is 10-12, ammonia has a suitable complexing effect on Ni2+, C02+, and Mn2+, which can effectively control the precipitation reaction rate, thereby synthesizing composite precipitation compounds and controlling the morphology of the product. M._H.Lee[25] prepared spherical (Nil/3Col/3Mnl/3)(OH)2 according to the following method: a concentration of 2.0mol. L-1 was added to the mixture under nitrogen protection. L-1 of N1S04, CoS04 and MrlS04 (Ni: Co: Mn = 1: 1: 1) were added to a continuously stirred reactor (CSTR, volume 4L). At the same time, a 2.0mol. L-1 NaOH aqueous solution and a certain amount of NH40H as a complexing agent were also added to the reactor and the solution concentration, pH value, temperature and stirring rate in the reactor were carefully controlled. The article discusses the effects of pH value, ammonia concentration and stirring rate on the performance of (N11/3Col/3Mnl/3)(OH)2. In order to discuss the effect of the complexing agent, they controlled the pH value at 11 during coprecipitation, because the synthesized powder had a higher tap density and larger particle size when the pH value was 11. Therefore, the effect of the amount of complexing agent added on the particle size, morphology and tap density can be observed. They selected three different NH. OH concentrations, which were 0.12mol. L-1, 0.24mol. L-1 and 0.36mol. L-1. There is no big difference in the XRD patterns of these three samples, but their tap density and morphology are quite different (Figure 6-9). NH. + concentration plays an important role in the formation of dense spherical hydroxide particles during the coprecipitation process. As shown in Figure 6-9, the influence of NH. + concentration on particle morphology, particle size, and particle size distribution is obvious. With the increase of NH. + concentration, the particle size becomes larger and the particle size distribution becomes narrower. This is because M2+ and NH. + first form complex ions in ammonia water and form hydroxide precipitation under alkaline conditions. If no complexing agent is used, Ni(OH)2, Co(OH): or Mn(OH): will be generated. The presence of complexing agent prevents phase separation and can generate uniform M(OH)2 (M=Ni, Co, Mn). When NH. + is 0.36mol. L-1, the powder has a spherical morphology, the highest tap density (1.70g.cm-3), a large particle size (about 10 μm) and a narrow particle size distribution. In short, the concentration of ammonia has a great influence on the morphology, particle size distribution and tap density of the precursor. With the increase of total ammonia concentration, the particle size of the precipitation product increases significantly, the surface of the spherical particles becomes smoother and smoother, the sphericity and density also gradually increase, and the dispersion between particles is good. The solubility of nickel and cobalt in the system increases significantly, the supersaturation of the coprecipitation system decreases sharply, the crystal nucleation rate is greatly reduced, and the crystal growth rate is continuously accelerated, resulting in the precipitation product.

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