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  • H01M4/36—Selection of substances as active materials, active masses, active liquids
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  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/24—Alkaline accumulators
  • H01M10/28—Construction or manufacture
• • H—ELECTRICITY
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
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  • H01M4/24—Electrodes for alkaline accumulators
  • H01M4/244—Zinc electrodes
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/24—Electrodes for alkaline accumulators
  • H01M4/32—Nickel oxide or hydroxide electrodes
• • H—ELECTRICITY
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  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
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  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
• • H—ELECTRICITY
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  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
  • H01M4/624—Electric conductive fillers
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  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/027—Negative electrodes
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  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/028—Positive electrodes
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  • H01M2300/0014—Alkaline electrolytes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• DESCRIPTION TITLE SECONDARY ELECTROCHEMICAL GENERATOR ZINC - MANGANESE DIOXIDE - NICKEL HYDROXIDE
• the present invention relates to the field of accumulators and more particularly that of alkaline electrochemical generators. It is especially related to secondary zinc-manganese dioxide generators having a high number of charge-discharge cycles. BACKGROUND OF THE INVENTION Primary Zn/MnO 2 cells are commonly used even though the secondary batteries of this Zn/MnO 2 system remain a challenge. The reversibility of this system is considered to be very limited.
• the MnO2 cathode On the side of the positive pole, the MnO2 cathode, irreversible compounds are formed during the discharge such as hausmannite (Mn 3 O 4 ) and heterolite (ZnMn2O4) leading to a rapid and significant loss of capacity.
• the Zn anode On the side of the negative pole, the Zn anode, phenomena of changes in shape, passivation, and formation of dendrites limit the reversibility in particular when the zinc anodes are charged-discharged at high current densities and that the theoretical capacity utilization rate is greater than 10% 2.3 .
• the reduction of MnO2 in the alkaline medium takes place in two steps: First reduction step: MnO2 + H2O+ e- -> MnOOH + OH- (1) Second reduction step: MnOOH + H 2 O + e- -> Mn( OH) 2 + OH-(2)
• the first reduction step is characterized by a voltage drop from 1.5 V to 0.9 V.
• the electrode potential of MnO2 continuously decreases in accordance with the homogeneous solid-state insertion of electron-protons into MnO2, reducing the oxidation state of Mn atoms from 4+ to 3+, resulting in the formation of MnOOH.
• this process is also associated with a mechanism of partial amorphization of the host crystallographic structure following steric constraints linked to the insertion of protons (H + ) and to the increase in the ionic radiation of the Mn cation (Mn 3 + vs Mn 4+ ).
• This insertion can be reversible within a limited range of H + insertion consistent with a limited amorphization process, up to H0.7MnO2 (1.1-1 V) according to Patrice 5 or H0.79MnO2 according to Gallaway 6 .
• MnOOH can further be reduced below 0.9 V, to Mn(OH)2 in the so-called second-step electron and via a heterogeneous process of dissolution (MnOOH to Mn 3+ )-reduction (Mn 3+ to Mn 2+ )-precipitation (Mn 2+ to Mn(OH)2).
• the second step can take place before the completion of the first step (the insertion of the first electron), due to the instability of MnOOH and the dissolution of Mn3+ in the electrolyte.
• Mn(OH)2 forming in reaction (2) is considered as a reversible discharge product, but it is not the/only product which forms in practical cases and against a Zn electrode.
• MnOOH is capable of reacting with the ions of the electrolyte according to a mechanism described by the chemical reactions (3) and (4) involving the formation of electrochemically inert reaction products, heterolite (ZnMn 2 O 4 ) and hausmannite ( Mn3O4): 2 MnOOH + Zn(OH)4 2- -> ZnMn2O4 + 2OH- + 2H2O (3) 2 MnOOH + Mn(OH) 4 2- -> Mn 3 O 4 + 2OH- + 2H 2 O (4) The irreversibility of the MnO2 reduction is therefore strongly correlated with the formation of the Mn 3 O 4 and ZnMn 2 O 4 compounds.
• Mn3O4 is formed during the first discharge, this compound can only be partially reduced to Mn(OH)2 while ZnMn2O4 is not reduced to Mn(OH)2 at all.
• Kordesch et al. 1,7,8,9 showed that ⁇ -MnO2 is rechargeable with a higher number of cycles only if the discharge is limited to less than 35% of the first stage reduction.
• Ingale et al. 10 followed this strategy to improve cyclability with a limited capacity of 5% to 20% DoD (depth of discharge). With inexpensive battery materials, they show stable capacity for 3000 cycles for 10% DoD and 500 cycles for 20% DoD.
• MnO 2 electrodes are still susceptible to Zn poisoning (irreversibly forming ZhMh 2 q 4 ) and also required an initial procedure against a Ni(OH) 2 electrode to "form" the electrodes before they can be paired with a Zn anode to form the Zn/Mn0 2 battery.
• Zn poisoning irreversibly forming ZhMh 2 q 4
• Ni(OH) 2 electrode to "form" the electrodes before they can be paired with a Zn anode to form the Zn/Mn0 2 battery.
• only 900 cycles are obtained in front of a zinc electrode 19 .
• this last result is obtained with the addition of a Ca(OH) 2 membrane making it possible to trap the zincate ions and to limit the formation of ZnMn 204 .
• the object of the present invention is to provide a new answer to the limits of ability of accumulators based on MnO 2 electrodes to provide a large number of cycles.
• tests relate to the addition of Ni(OH) 2 compounds in the composition of the positive electrode based on Mn0 2 , this electrode becoming de facto hybrid, Mn02 and Ni(OH) 2 together being electrochemically active.
• the idea is to provide, through the presence of stable Ni(OH) 2 /N1OOH crystallites in the alkaline electrolyte, a crystal growth substrate for the Mn00H/Mn02 compounds.
• This crystal growth medium is likely to increase the reversibility of the MnOOH/MnO 2 electrochemical couple by an increase in the coherence domains of these compounds, which limits the reactivity of MnOOH with the ions of the electrolyte and de facto the formation of parasitic reactions (3) formation of heterolite (ZnMn 2 04) and (4) Hausmannite formation (MnsCh).
• TN Ramesh et al. indicates that a mixture of MnO 2 and Ni(OH) 2 materials is not ready to be used in an electrochemical storage application.
• a composite phase NiO (OH)/MnO 2 obtained by common coprecipitation of Ni 2+ and Mn 2+ ions is mentioned as being capable of greatly increasing the capacity up to 2.25 electrons per metal atom equivalent to 650 mAh/g. Only 20 cycles are demonstrated.
• Ni(OH) 2 in the composition of the Mn0 2 cathode is reported, to limit the manganese dioxide overload and the formation of oxygen, which are the result of premature failures of the manganese dioxide cathode.
• the addition of Ni(OH) 2 is a reserve of materials capable of reversing the consequences of overloads of the Mn0 2 cathode. No table of values is provided to support the beneficial action of the addition of Ni(OH) 2 .
• the Ni(OH) 2 content is very low, less than 2%. The number of cycles demonstrated is only 5.
• Ni(OH) 2 is not described but it is reasonable to believe that the action sought is similar to US patent 5011752, with a limitation of the manganese dioxide overload and the formation of oxygen.
• patent JP H1074511 A mention is made of the addition of nickel hydroxide and nickel oxide in a rechargeable MnO 2 electrode.
• the composition of the MnO 2 electrode is such that the atomic ratio of the Ni atom to the Mn atom corresponds to a range of 2% to 35%.
• this invention relates to the recharging of MnO 2 electrodes in an alkaline solution while limiting the generation of oxygen.
• a figure is given making it possible to compare the voltages during charging with and without the addition of Ni(OH) 2 .
• the charge curve is characterized by a double plateau before a final increase correlated with the evolution of oxygen.
• the second plateau above 1.85V, corresponds to the Ni(OH) 2 charge.
• the very pronounced voltage difference between the first and second plateau allows better detection of the end of charge and a reduction in the evolution of oxygen.
• the number of cycles is 18.
• the addition of Ni(OH) 2 makes it possible to increase this number of cycles to 54 and 62 respectively for 9.1 % and 10 atomic % for the Ni/(Mn+Ni) ratio.
• the number of cycles decreases to be 37 when the Ni/(Mn+Ni) ratio is 45%.
• the quantity of nickel must remain low in order to preserve the discharge quantity of the Mn0 2 compound.
• the addition of Ni (OH) 2 in the rechargeable Mn0 2 electrode is all related to a reduction in the formation of oxygen at the end of the charge.
• the object of the present invention is to increase the cycle life of secondary electrochemical generators. It therefore aims to provide a new response to the limits of ability of the MnO 2 electrode to provide a large number of cycles, with a discharge greater than 35% of the first reduction stage, response provided by modifying the loss conditions capacitance of the MnO 2 electrode by limiting the formation of an electrochemically inert crystal structure.
• Zinc-manganese dioxide hybrid secondary electrochemical generator in accordance with statement 1 below: 1.
• Zinc-manganese dioxide hybrid secondary electrochemical generator this generator being distinguished in that it comprises: a) a positive hybrid electrode containing a mixture of manganese dioxide (MnO 2 ) and nickel hydroxide
• Ni (OH) 2 the mass of Ni (OH) 2 preferably being greater than 5% of the sum of the masses of Ni (OH) 2 and Mn0 2 , and b) an electrolyte which is an alkaline aqueous solution of which the molarity is between 4 M and 15 M of hydroxyl anions (OH-).
• This hybridization by constitution of a positive electrode associating manganese dioxide and nickel hydroxide makes it possible to produce an economical secondary system, thanks to the low cost of MnCk, and benefiting from good cycling ability, thanks to the excellent reversibility between Ni (OH) 2 and NiOOH.
• Secondary electrochemical generator according to statement 3 in which the zinc negative electrode contains titanium nitride. 5. Secondary electrochemical generator according to one of the statements 1 to 4, the molarity of the alkaline solution is between 7 and 13 M.
• FIG. 2 the evolution of the capacitance as a function of the number of cycles of the electrochemical cells of examples 2, 3 and
• FIG. 3 the evolution of the capacitance as a function of the number of cycles of the electrochemical cells of examples 1, 2 and
• FIG. 5 the voltage-capacitance profiles at cycle No. 5 for the electrochemical cells of examples 2 to 7
• FIG. 6 the voltage-capacitance profiles at cycle No. 50 for the electrochemical cells of examples 2 to 7
• FIG. 7 the electrochemical cell X-ray diffraction diagrams of examples 1 to 6.
• the active material of the positive electrode comprises a mixture of manganese dioxide and nickel hydroxide, the mass of Ni( OH)2 being greater than 5% of the sum of the masses of Ni(OH)2 and Mn0 2 and, preferably, greater than 20% of the sum of the masses of Ni(OH)2 and Mn0 2 .
• Manganese dioxide can be brought to the preparation of the cathode by all chemical and electrochemical varieties of Mn0 2 .
• nickel hydroxide can be provided therein by all varieties of Ni(OH)2, including all usual crystallographies and additives.
• the electrolyte used according to the present invention is an aqueous alkaline solution whose molarity is between 4 and 15 M, and preferably between 7 and 13 M, of hydroxyl anions. It may be composed of lithium, sodium or potassium hydroxides taken alone or in mixtures.
• the electrolyte may also contain zincates, borates, silicates and/or aluminates, in varying proportions.
• the zinc negative electrode preferably incorporates conductive ceramic powders, which can be chosen from borides, carbides, nitrides and silicides of various metals such as: hafnium, magnesium, niobium, titanium and vanadium. It may thus advantageously be nitride and/or hafnium carbide, and/or carbide and/or nitride and/or magnesium silicide, and/or carbide and/or niobium nitride, and/or carbide and/or nitride and/or titanium silicide, and/or vanadium nitride.
• ceramic materials such as titanium sub-oxides of general formula Ti n 02n-i, where n is between 4 and 10.
• these ceramics can be retained for use in the context of the present invention, insofar as they are conductive, chemically inert in the accumulator, and have a high hydrogen overvoltage.
• these conductive powders used should be fine and dispersed as homogeneously as possible in the active mass.
• a prismatic format electrochemical cell consists of two zinc electrodes flanking an MnO 2 electrode. Each zinc electrode has an active surface of 26 cm 2 for a capacity of 1.5 Ah.
• the MnÜ2 electrode with an active surface of 24 cm 2 and a capacity of 0.588 Ah calculated for the equivalent of an exchanged electron corresponding to the first stage of reduction between MnO 2 and MnOOH or 308 mAh/g, consequently has a capacity limiting the capacity of the Zn/MnO 2 electrochemical cell.
• Each zinc and MnO 2 electrode is enveloped by a membrane in order to confine the threshold of the surface of the electrodes both Zn and Mn soluble ions.
• a felt is also positioned between each electrode as a separator and electrolyte reservoir.
• the composition of the active material of the zinc electrode includes conductive ceramics of TiN, as described in the patent FR 2788 887, to eliminate the problems of cyclability of the zinc electrode.
• the composition of the active material of the MnO 2 electrode consists, expressed in masses, of 60% of MnCb-EMD (electrolytic manganese dioxide), 6% of B12O3, 30% of carbon and 4% of a binder-plasticizer (PTFE). To the mixture of the previous constituents is added alcohol to obtain a compact paste which is then prepared in the form of strips, which are deposited on each side of a current collector, the whole being compacted to obtain an electrode of MnC> 2.
• the electrolyte is an alkaline aqueous solution with a molarity of 10 M, obtained from a mixture of NaOH and KOH.
• the electrolyte also contains 0.25 M of zincate ions obtained by the addition of ZnO.
• the first two cycles at the C/20 regime are used as a training step.
• the ZnMnO 2 accumulator thus made is first discharged at the rate of C/20, down to 1 V or the equivalent of 20% of the capacity. Charging is done at C/20 with no voltage limit up to an equivalent of 21% of capacity.
• the element of example 1 is cycled with the same conditions as the first two cycles but with a current rate equivalent to C/10.
• Example 1 The capacity of Example 1 as a function of the number of cycles is shown in Figure 1.
• the rate of use of MnO 2 is 20% compared to 308 mAh/g and leads to an average surface capacity for the first 150 cycles of 5 mAh/cm 2 .
• the lifetime is estimated at 786 cycles.
• the capacity is particularly stable during the first 150 cycles.
• Example 2 (prior art): The cell of example 2 is identical to that of example 1.
• the capacity of the Mn0 2 electrode is 0.644 Ah.
• the rate of use of the MnO 2 electrode is increased to have a surface capacity greater than 10 mAh/cm 2 .
• the accumulator of example 2 thus made is first discharged at the rate of C/20, up to 1 V or the equivalent of 43% of the capacity calculated by considering an exchanged electron or 308 mAh/g of MnO 2 . Charging is done at C/20 with no voltage limit up to an equivalent of 45% of capacity.
• the element of example 2 is cycled with the same conditions as the first two cycles but with a current rate equivalent to C/10.
• Example 2 The capacity of Example 2 is presented in FIG. 1.
• the discharge of MnO2 at 43% makes it possible to have an initial surface capacity of 11.6 mAh/cm 2 .
• the average surface capacity of the first 150 cycles is 10.3 mAh/cm 2 .
• Only 155 cycles, instead of 786 for example 1, are performed before a recoil greater than 30% of the initial capacity. Capacity is stable for 20 cycles.
• Example 2 demonstrates that for a surface capacity greater than 10 mAh/cm 2 , a discharge of 43% MnO 2 is necessary under the experimental conditions of Examples 1 and 2.
• Doubling the surface capacity of 5 mAh/ cm 2 for Example 1 to 10 mAh/cm 2 for Example 2 is associated with a drastic drop in lifetime. This is divided by 5, going from 786 to 155 cycles. This drop in lifetime with increasing discharge of the MnO 2 compound is consistent with previous observations reporting the formation of parasitic compounds Mh 3 q 4 and ZhMh 2 q 4 following reactions (3) and (4).
• Example 3 is similar to example 2 with a positive electrode modified by the addition of 3.75% Ni(OH) 2 in the electrode of Mn0 2 .
• the composition of the active material of the positive electrode modified by the addition of nickel hydroxide to replace part of the Mn0 2 is, by mass, 56.25% MnO 2 - EMD, 3.75% of Ni(OH)2, 6% of B1 2 O 3 , 30% of carbon and 4% of binder-plasticizer.
• the positive electrode becomes hybrid with 2 electrochemically active materials in the voltage range between 1 V and 2.3 V.
• the capacity is calculated by considering for this voltage range one electron exchanged for each active material, i.e. 308 mAh/g for Mn0 2 and 289 mAh/g for Ni(OH) 2 .
• the capacity of the hybrid electrode of Example 3 is 0.690 Ah.
• Example 3 is formed and cycled under the same conditions as Example 2 with a 43% discharge. With this discharge at 43%, the minimum discharge of Mn0 2 is 40% considering a discharge of 100% for the nickel hydroxide.
• the capacity of Example 3 is shown in Figure 2. The life of this example is measured at 226 cycles, higher than that of Example 2 at 155 cycles. The average surface capacity of the first 150 cycles of example 3 is 12.1 mAh/cm 2 , higher than that of example 2 by 10.3 mAh/cm 2 . With the addition of 3.75% of Ni(OH) 2 , example 3 compared to example 2, increases the surface capacity by 17% and the service life by 46%.
• Example 4 comparativative:
• Example 4 is identical to example 3 with a positive electrode modified by the addition of 7.5% Ni(OH)2 in the electrode of Mn0 2 .
• the composition of the positive Mn0 2 electrode becomes, by mass, 52.5% Mn0 2 - EMD, 7.5% Ni (OH)2, 6% B12O3, 30% carbon and 4% binder - plasticizer.
• the capacity of the electrode of Example 4 is 0.654 Ah.
• Example 4 is formed and cycled under the same conditions as example 2 but with a greater discharge (47%), allowing a minimum discharge of Mn0 2 to 40%, identical to that of examples 2 and 3.
• the discharge nickel hydroxide is considered to be 100%.
• the capacity of Example 4 is shown in Figure 2.
• the lifetime of this example is measured at 224 cycles identical to that of Example 3.
• the average areal capacity of the first 150 cycles of Example 4 is 12 .1 mAh/cm 2 , identical to that of example 3.
• example 4 gives results similar to those of example 3, with a increase in surface capacity by 17% and lifespan by 45%, compared to example 2.
• This identical result of example 4 is obtained with a discharge of 47%, greater than that of 43% of Example 3, suggesting that the presence of Ni(OH)2 in the composition of the MnO 2 electrode limits the capacity losses of this MnC>2 compound.
• Example 5 is similar to example 3 with a positive electrode modified by the addition of 15% Ni(OH)2 in the MnO 2 electrode.
• the composition of the positive MnO 2 electrode becomes, by mass, 45% MnO 2 - EMD, 15% Ni (OH)2, 6% B12O3, 30% carbon and 4% binder- plasticizer.
• the capacity of the electrode of Example 5 is 0.616 Ah.
• Example 5 is cycled with the same conditions as Example 2. With this same 43% discharge, the minimum MnO 2 discharge is 26% for Example 5, considering a 100% discharge for the nickel hydroxide.
• example 5 The capacity of example 5 is shown in figure 3.
• the life of this example 5 is measured at 673 cycles, higher than that of example 2 at 155 cycles.
• the average surface capacity of the first 150 cycles of example 5 is 11.1 mAh/cm 2 , higher than that of example 2 by 10.3 mAh/cm 2 .
• example 5 compared to example 2 increases the surface capacity by 8% and the lifetime by 334%. This increase, 7 times greater than that measured in examples 3 and 4, is to be linked to the discharge of MnO 2 at 26%, lower than the 40% of examples 3 and 4.
• the number of cycles during which the initial capacity is perfectly stable in example 5 is superior to example 1 with 243 and 139 cycles respectively.
• Ni(OH) 2 in the MnO 2 electrode makes it possible to increase this area of perfect stability of the positive electrode by 75% even though the minimum discharge of the MnO 2 compound is increased by 30% going from 20% to 26%.
• the addition of 15% Ni(OH) 2 remarkably increases the stability of the MnO 2 electrode, even with an increase in the percentage discharge of the MnO 2 phase
• the service life is increased by more than 300% with surface capacities greater than 10 mAh/cm 2 .
• Example 6 is similar to Example 2 with a positive electrode modified by the addition of Ni(OH) 2 replacing completely the compound MnCt by Ni(OH)2.
• the composition of the positive electrode becomes, by mass, 60% Ni(OH)2, 6% B12O3, 30% carbon and 4% binder - plasticizer.
• the capacity of the electrode of Example 6 is 0.533 Ah.
• Example 6 is cycled at the same current regime as example 2, with a charge at C/10102% of the capacity without voltage limit and a discharge at C/10 down to 1 V. These cycling conditions reproduce a complete charge and discharge of the nickel hydroxide identical to that of examples 3, 4, and 5.
• the discharge capacity obtained from example 6 is characterized by an average value over the first 150 cycles of 95%, lower at 100% assumed for Examples 3, 4 and 5.
• the average surface capacity over the first 150 cycles of Example 6 is 22.1 mAh/cm 2 .
• the capacitor for Example 6 is provided in Figure 4.
• Example 7 is similar to example 3 with a positive electrode modified by the addition of 30% Ni(OH)2 in the electrode of Mn0 2 .
• the composition of the positive Mn0 2 electrode becomes, by mass, 30% Mn0 2 - EMD, 30% Ni(OH)2, 6% B12O3, 30% carbon and 4% binder-plasticizer.
• the capacity of the hybrid electrode of Example 7 is 0.529 Ah.
• Example 7 is formed and cycled with the same conditions as Example 2 with a 66% discharge. With this discharge at 66%, the minimum discharge of MnO 2 is 37% considering a discharge of 100% for the nickel hydroxide.
• example 6 demonstrates that for a discharge of 100% Ni(OH)2, the capacity obtained is not 100% but 95% implying a minimum discharge for MnO2 of 41% very close to the 43% of example 2.
• the capacity of example 7 is shown in Figure 4.
• the life of this example 7 is measured at 457 cycles, greater than that of Example 2 at 155 cycles.
• the average surface capacity of the first 150 cycles of example 7 is 14.6 mAh/cm 2 , higher than that of example 2 by 10.3 mAh/cm 2 .
• the addition of 30% of Ni (OH) 2 in example 7 increases compared to example 2 the surface capacity of 42% and the service life of 195%.
• Example 6 which does not contain MnCt, has a discharge profile of only nickel hydroxide, very different from the discharge profile of example 2, which is purely MnCt.
• Ni(OH) 2 of 3.75% and 7.5% respectively for examples 3 and 4 do not modify the discharge profile of example 2.
• Ni(OH) 2 contributes very little to the discharged capacity.
• the 43% discharge of example 5 should be distributed to 21% on Ni (OH) 2 and 22% on MnO 2 .
• the shoulder of example 5 is in agreement with a contribution to the discharge of Ni(OH) 2 of less than 3%. This difference between a calculated maximum contribution (21%) and what could be deduced from the discharge curves (3%) can be explained by the fact that Ni(OH) 2 is not completely charged under the conditions of applied cycling.
• the voltage does not increase sufficiently in the charge curves to arrive at the voltages corresponding to the Ni(OH) 2 charge.
• the discharge profile is hybrid with a wide shoulder up to 30%, characteristic of the discharge voltage of Ni (OH) 2 then a fairly slow drop in voltage corresponding to the discharge of Mn0 2 .
• the 66% discharge of example 7 should be distributed at 44% on Ni(OH)2 and 22% on MnO 2 .
• the discharge voltages of cycle n° 50, as a function of the capacitor discharged, for examples 2 to 7 are presented in figure 6.
• the profiles of the discharge voltages of examples 3, 4, 5 and 7 are strongly modified with the presence of an increasing shoulder with the Ni (OH)2 content.
• This shoulder is correlated to the discharge of Ni (OH)2.
• the shoulders of examples 5 and 7 are respectively around 25% and 45%, values close to the calculation of a maximum contribution of Ni(OH)2, respectively of 21% and 44%.
• the reason for a better agreement here between the calculated maximum contribution of Ni(OH)2 and the values deduced from the curve could be explained by the fact that Ni(OH)2 becomes more charged than at the start of cycling, due to the causes MnO 2 to gradually lose its cycling performance.
• the continuation of the discharge is correlated with the contribution of the MnO 2 discharge, but the voltage is higher than for cycles n° 5, demonstrating a significant modification in the behavior of the discharge of this Mn02 phase.
• the X-ray diffraction diagram of preparation 1 is characterized by the diffraction peaks of the b-Ni(OH)2 and B12O3 phases.
• the diffraction peaks of the Mn0 2 phase are not identified, indicating that this Mn02 phase is insufficiently crystallized to be visible in the presence of the other b-N ⁇ (OH)2 and B12O3 phases.
• preparations 4 and 5 without Ni(OH)2 in the active material, preparations 4 and 5, the diagrams are similar, with very few diffraction peaks, attesting to the weak crystallization in agreement with the initial Mn0 2 phase.
• the parasitic phase ZhMh2q4 is not identified in these diagrams.
• the X-ray diffraction diagrams show, with respect to preparation 1, a significant crystallographic transformation with the presence of peaks at low angles around 11-13 degrees, suggesting lamellar crystallized phases with insertion.
• Diagram 3 is distinguished from diagram 2 by the formation of a shoulder in the first peak, which indicates an evolution structural.
• This physico-chemical analysis associates the stabilization of the capacity with an in-situ crystallographic transformation between the initial active phases MnO 2 / ⁇ -N ⁇ (OH)2.
• substantial additions of Ni(OH)2 such as 50% relative to Mn0 2 , example 7, stabilizes the capacity of the hybrid electrode.

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