A preparation method of lithium iron phosphate precursor or lithium iron phosphate and hydrogen and its application

Abstract

The present invention relates to the field of electrochemical materials, and in particular to a method for synchronously and continuously preparing a lithium iron phosphate precursor and hydrogen and its application. The preparation method uses iron metal as a working electrode and a hydrogen evolution reaction counter electrode material as a counter electrode, and electrolysis occurs in an acidic electrolyte or a neutral electrolyte to prepare hydrogen and a lithium iron phosphate precursor. The method has the advantages of low cost, high safety, good cycle performance, good reaction sustainability, and high yield.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical materials, and in particular to a preparation method of a lithium iron phosphate precursor or lithium iron phosphate and hydrogen and applications thereof. Background Art

[0002] With the development of economy, science and technology, and the improvement of productivity, people's demand for energy is also increasing. Traditional fossil energy can no longer meet the demand and will cause environmental pollution. Therefore, the current development of new clean energy is a top priority, and hydrogen energy and lithium-ion secondary batteries with lithium iron phosphate as the positive active material are the most important technical solutions for electrochemical energy storage.

[0003] Hydrogen energy has the advantages of being clean and pollution-free, having high calorific value, and being used in various forms. The development of hydrogen energy is very promising. At present, the production and preparation of hydrogen in industry is mainly through the reforming of fossil fuels, but the production of hydrogen by this method will cause carbon emissions. Water electrolysis is another important way to produce hydrogen, which has the advantages of no carbon emissions and simple process. However, the traditional water electrolysis is limited by the kinetic and thermodynamic disadvantages of the anode OER (oxygen evolution reaction) process and encounters bottlenecks. On the one hand, the OER process has a high overpotential due to the involvement of four-electron transfer and kinetic hysteresis; on the other hand, the standard potential of OER itself is high, especially under acidic and neutral conditions. The energy barrier that needs to be overcome by the OER process occupies the vast majority of the actual applied voltage of electrolysis, and expensive precious metals need to be used as electrocatalysts, and the added value of oxygen produced by the OER byproduct is low. Especially low, in actual operation, oxygen and hydrogen at the two poles may penetrate the diaphragm, resulting in hydrogen-oxygen mixing, which may cause major safety hazards such as explosion and fire, and bring great burden to the safety management of water electrolysis hydrogen production tanks. Therefore, it is urgent to adopt appropriate strategies to avoid the problems existing in OER in traditional water electrolysis hydrogen production systems.

[0004] On the other hand, lithium iron phosphate is one of the most widely used positive electrode materials for lithium-ion batteries. It has the advantages of low cost, high safety, and good cycle performance. Currently, the commonly used preparation methods for lithium iron phosphate include high-temperature solid phase method, carbon thermal reduction method, hydrothermal method, etc., and materials such as iron salts and iron oxides are important precursors for synthesizing lithium iron phosphate. How to obtain lithium iron phosphate precursors efficiently and at low cost is a problem that has attracted much attention in the production process of lithium iron phosphate. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for preparing a lithium iron phosphate precursor and hydrogen and applications thereof.

[0006] In a first aspect, the present invention provides a method for preparing a lithium iron phosphate precursor and hydrogen.

[0007] A method for preparing a lithium iron phosphate precursor or lithium iron phosphate and hydrogen, comprising: in the presence of an anode and a cathode, using iron metal electrooxidation as an anode reaction and hydrogen evolution reaction as a cathode reaction, electrolyzing in a reaction container containing an acidic electrolyte with or without an external voltage, wherein the acidic electrolyte contains acid, a working electrode generates free iron ions, a counter electrode generates hydrogen, and the hydrogen is drawn out of the reaction container for storage;

[0008] The acidic electrolyte is led out of the reaction container, a precipitant or an alkali is added, and then solid-liquid separation is performed, and the solid obtained by solid-liquid separation is a lithium iron phosphate precursor; or the acidic electrolyte is led out of the reaction container, lithium phosphate is added, and then solid-liquid separation is performed, and the solid obtained by solid-liquid separation is lithium iron phosphate;

[0009] The liquid obtained by solid-liquid separation is added with an acidic electrolyte containing a certain concentration of acid and then fed into the reaction vessel as a feed liquid to maintain the stability of the components, volume and pH of the acidic electrolyte in the reaction vessel. The flow rate of the feed liquid into the reaction vessel is the same as the flow rate of the acidic electrolyte in the reaction vessel. The method can simultaneously produce lithium iron phosphate precursors and H2. The working electrode of the present invention uses an electro-oxidation reaction of iron to replace the OER process in the traditional water reaction vessel, and couples hydrogen evolution with the cathode end. At the same time, the iron ions produced by the oxidation of the electrode enter the acidic electrolyte, and iron salts in different states are obtained according to the pH value of the acidic electrolyte and the additive composition, which are further used as precursors for preparing lithium iron phosphate. Under acidic conditions, a particularly excellent hydrogen production rate can be obtained, and the product of the working electrode exists in the solution as free iron ions or ferrous ions. After separation from the reaction vessel, lithium iron phosphate precursors in different forms can be prepared by adding corresponding precipitants.

[0010] In some embodiments, the cathode is a hydrogen evolution reaction counter electrode material.

[0011] In some embodiments, the hydrogen evolution reaction counter electrode material is platinum metal. In some embodiments, the hydrogen evolution reaction counter electrode material is a platinum-based material such as platinum mesh or carbon-supported platinum.

[0012] In some embodiments, the anode is iron metal.

[0013] In some embodiments, the acid is hydrochloric acid or phosphoric acid.

[0014] In some embodiments, the reaction vessel is diaphragm-free.

[0015] In some embodiments, the preparation method may perform electrolysis without using a catalyst.

[0016] In some embodiments, the acidic electrolyte contains sodium chloride. In some embodiments, the acidic electrolyte contains natural seawater. In some embodiments, the acidic electrolyte contains sodium chloride and buffer salt. In some embodiments, the solvent of the acidic electrolyte is water.

[0017] In some embodiments, the buffer salt is disodium hydrogen phosphate and / or sodium dihydrogen phosphate. In some embodiments, the buffer salt is disodium hydrogen phosphate and sodium dihydrogen phosphate.

[0018] In some embodiments, the concentration of sodium chloride in the acidic electrolyte is 0 to 5 mol / L. In some embodiments, the concentration of sodium chloride in the acidic electrolyte is 0 to 2 mol / L. In some embodiments, the concentration of sodium chloride in the acidic electrolyte is 0 to 1 mol / L. In some embodiments, the concentration of sodium chloride in the acidic electrolyte is 0.5 to 5 mol / L. In some embodiments, the concentration of sodium chloride in the acidic electrolyte is 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, 4.5 mol / L or 5.0 mol / L. In some embodiments, the concentration of sodium chloride in the acidic electrolyte is 0.5 mol / L, which is used to simulate the sodium chloride concentration in seawater; in some embodiments, sodium chloride may not be added or a higher concentration of sodium chloride may be added to further improve conductivity.

[0019] In some embodiments, the acidic electrolyte includes 0.10mol / L-0.40mol / L of buffer salt. In some embodiments, the acidic electrolyte contains 0.05mol / L-0.20mol / L of sodium dihydrogen phosphate and 0.005mol / L-0.020mol / L of disodium hydrogen phosphate. In some embodiments, the acidic electrolyte contains 0.10mol / L-0.20mol / L of sodium dihydrogen phosphate and 0.01mol / L-0.05mol / L of disodium hydrogen phosphate. In some embodiments, the acidic electrolyte contains 0.10mol / L-0.15mol / L of sodium dihydrogen phosphate and 0.01mol / L-0.02mol / L of disodium hydrogen phosphate. In some embodiments, the concentration of buffer salt in the acidic electrolyte contains 0.1mol / L sodium dihydrogen phosphate and 0.01mol / L disodium hydrogen phosphate.

[0020] In some embodiments, the concentration of the acid in the acidic electrolyte in the reaction container is ≤1.0mol / L. In some embodiments, the concentration of the acid in the acidic electrolyte in the reaction container is 0.2mol / L to 1.0mol / L. In some embodiments, the concentration of the acid in the acidic electrolyte in the reaction container is 0.3mol / L to 1.0mol / L. In some embodiments, the concentration of the acid in the acidic electrolyte in the reaction container is 0.5mol / L to 1.0mol / L. In some embodiments, the concentration of the acid in the acidic electrolyte in the reaction container is 0.7mol / L to 1.0mol / L. In some embodiments, the concentration of the acid in the acidic electrolyte in the reaction container is 0.8mol / L to 1.0mol / L. In some embodiments, the concentration of the acid in the acidic electrolyte in the reaction container is 0.9mol / L to 1.0mol / L. In some embodiments, the concentration of acid in the acidic electrolyte in the reaction container is 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1.0 mol / L.

[0021] In some embodiments, the concentration of acid in the feed solution satisfies the following conditions:

[0022] c1=c2+2V0 / V;

[0023] in,

[0024] c1 is the concentration of acid in the feed solution, mol / L;

[0025] c2 is the acid concentration in the acidic electrolyte in the reaction vessel, mol / L;

[0026] V0 is the molar yield of hydrogen per unit time (which can be obtained by the formula V0 = j / 2F (j is the current flowing through the two electrodes of the electrolytic cell, and F is the Faraday constant)), mol / s;

[0027] V is the volume flow rate of the acidic electrolyte out of the reaction vessel, L / s. Replenishing the acidic electrolyte in the reaction vessel with a feed solution of this concentration is conducive to continuous renewal of the acidic electrolyte, maintaining the dynamic stability of the acidic electrolyte components, and is conducive to the continuous reaction, thereby increasing the reaction speed and reaction yield.

[0028] In some embodiments, the precipitating agent is an alkaline agent.

[0029] In some embodiments, the alkaline agent or the base includes at least one alkaline substance such as sodium hydroxide or ammonia.

[0030] In some embodiments, the lithium iron phosphate precursor includes iron hydroxide.

[0031] In some embodiments, the pH of the acidic electrolyte in the reaction container is 0 to 6. In some embodiments, the pH of the acidic electrolyte in the reaction container is 0, 1, 2, 3, 4, 5 or 6.

[0032] In some embodiments, the method for preparing the lithium iron phosphate precursor and hydrogen further includes stirring the acidic electrolyte in the reaction container.

[0033] In some embodiments, the applied voltage is -0.5V to 1.0V. In some embodiments, the applied voltage is -0.3V to 0.4V. In some embodiments, the applied voltage is 0V to 0.4V. In some embodiments, the applied voltage is 0.1V to 0.4V. In some embodiments, the applied voltage is 0.2V to 0.4V. In some embodiments, the applied voltage is 0.3V to 0.4V. In a second aspect, the present invention provides another method for preparing a lithium iron phosphate precursor and hydrogen.

[0034] A method for preparing a lithium iron phosphate precursor and hydrogen comprises: using iron metal as a working electrode and a hydrogen evolution reaction counter electrode material as a counter electrode, electrolyzing in a reaction container containing an electrolyte under an external voltage condition, wherein the electrolyte is neutral or weakly acidic, and the electrolyte is a saturated sodium chloride aqueous solution or a saturated sodium chloride aqueous solution to which a buffer salt and / or phosphate ions are added, the working electrode generates iron oxide or iron hydroxide, the counter electrode generates hydrogen, and the hydrogen is led out of the reaction container for storage; the electrolyte is led out of the reaction container, solid-liquid separation is performed, the solid obtained by the solid-liquid separation is a lithium iron phosphate precursor, and the liquid obtained by the solid-liquid separation is fed into the reaction container as a feed liquid, and the flow rate of the feed liquid into the reaction container is the same as the flow rate of the electrolyte led out of the reaction container.

[0035] In some embodiments, the hydrogen evolution reaction counter electrode material is platinum metal. In some embodiments, the hydrogen evolution reaction counter electrode material is a platinum-based material such as platinum mesh or carbon-supported platinum.

[0036] In some embodiments, the lithium iron phosphate precursor is at least one of ferrous phosphate, ferric hydroxide, ferric oxyhydroxide, or ferrosoferric oxide.

[0037] In some embodiments, the electrolyte further contains a buffer salt.

[0038] In some embodiments, the buffer salt is disodium hydrogen phosphate and / or sodium dihydrogen phosphate.

[0039] In some embodiments, the electrolyte comprises 0.10mol / L-0.40mol / L of buffer salt. In some embodiments, the electrolyte comprises phosphate ions. In some embodiments, the electrolyte comprises 0.05mol / L-0.20mol / L of sodium dihydrogen phosphate and 0.005mol / L-0.020mol / L of disodium hydrogen phosphate. In some embodiments, the electrolyte comprises 0.10mol / L of sodium dihydrogen phosphate and 0.01mol / L of disodium hydrogen phosphate.

[0040] In some embodiments, the pH of the electrolyte is 4.0-7.0. In some embodiments, the pH of the electrolyte is 4.0-6.0. In some embodiments, the pH of the electrolyte is 4.0, 4.5, 5.0, 5.5, 6.0, 6.5 or 7.0.

[0041] In some embodiments, the applied voltage is 0.4V to 2.0V. In some embodiments, the applied voltage is 0.4V to 1.5V. In some embodiments, the applied voltage is 0.6V to 1.2V. In some embodiments, the applied voltage is 1.0V to 2.0V. In some embodiments, the applied voltage is 1.0V to 1.2V. In some embodiments, the applied voltage is 1.0V to 2.0V. In some embodiments, the applied voltage is 0.4V, 0.5V, 0.6V, 0.7V, 0.8V, 0.9V, 1.0V, 1.1V, 1.2V, 1.3V, 1.4V, or 1.5V.

[0042] In a third aspect, the present invention provides an application of the lithium iron phosphate precursor prepared by the aforementioned method.

[0043] A use of the lithium iron phosphate precursor prepared by the method of the first aspect in the preparation of lithium iron phosphate or battery positive electrode materials.

[0044] In a fourth aspect, the present invention provides a method for preparing lithium iron phosphate.

[0045] A method for preparing lithium iron phosphate comprises: mixing a lithium iron phosphate precursor prepared by the method described in the first aspect or a lithium iron phosphate precursor prepared by the method described in the second aspect with ammonium phosphate, lithium carbonate and glucose, and then calcining the mixture to prepare lithium iron phosphate.

[0046] Beneficial Effects

[0047] Compared with the prior art, a certain embodiment of the present invention has at least one of the following beneficial technical effects:

[0048] (1) When electrolysis is performed in an alkaline electrolyte, the working electrode is prone to severe passivation, and the electrolytic cell voltage increases significantly, resulting in the inability of the working electrode electro-oxidation reaction to proceed further; when electrolysis is performed in a neutral electrolyte, the working electrode is also passivated to a certain extent. Therefore, compared with electrolysis in a neutral or alkaline electrolyte, the present invention uses an acidic electrolyte for electrolysis, which is beneficial to avoid passivation of the iron sheet and is beneficial to the long-term continuous and efficient electrolysis reaction.

[0049] (2) When electrolysis is carried out in a neutral electrolyte, the working electrode also has a certain degree of passivation. The present invention uses a saturated sodium chloride aqueous solution as the electrolyte, which is beneficial to reducing the passivation of the iron sheet and improving the long-term, continuous and efficient electrolysis reaction.

[0050] (3) The present invention uses an acidic electrolyte and iron as the working electrode for electrolysis, which can significantly reduce the theoretical voltage required for hydrogen production, which is much lower than the 1.23V of the traditional water electrolysis system; the working electrode does not produce oxygen, thus avoiding the safety hazard of explosion caused by the mixing of hydrogen and oxygen.

[0051] (4) The method of the present invention can obtain the key precursors required for lithium iron phosphate and H2, two high value-added energy material products required for the current mainstream electrochemical energy storage. Continuous operation is also more in line with industrial application scenarios and has the potential for large-scale industrial production.

[0052] (5) The preparation method of the present invention does not require a diaphragm in the electrolytic cell, and the working electrode does not require a catalyst, which is beneficial to reducing costs. In the preparation method using an acidic electrolyte, no external voltage is required, which is beneficial to further reducing costs.

[0053] (6) After the electrolyte flowing out of the reaction vessel of the present invention is separated by iron salt, fresh electrolyte with a specific acid concentration is added and then partially refluxed, which can maintain the pH value and composition stability in the electrolytic cell, achieve continuous and stable production of hydrogen and lithium iron phosphate precursor, and reduce the preparation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 A schematic diagram of a device for preparing a lithium iron phosphate precursor and hydrogen using a neutral or weakly acidic electrolyte according to the present invention is shown;

[0055] Figure 2 A schematic diagram of a device for preparing a lithium iron phosphate precursor and hydrogen using an acidic electrolyte according to the present invention is shown;

[0056] Figure 3 1 is a polarization curve diagram obtained under acidic conditions according to Example 1 of the present invention;

[0057] Figure 4FIG. 1 is a graph showing an it curve (current versus time curve) obtained under acidic conditions in Example 1 of the present invention;

[0058] Figure 5 A comparison diagram showing the actual hydrogen production measured by chromatography in Example 1 of the present invention and the theoretical production calculated based on the current;

[0059] Figure 6 2 shows the polarization curve obtained under neutral conditions in Example 2 of the present invention;

[0060] Figure 7 2 shows an it curve diagram obtained under neutral conditions in Example 2 of the present invention;

[0061] Figure 8 1 is a graph showing the SEM (scanning electron microscope) test result of the iron metal compound obtained in Example 2 of the present invention;

[0062] Fig. 9 1 is a graph showing the XRD (X-ray diffraction) test result of the iron metal compound obtained in Example 2 of the present invention;

[0063] Fig.10 1 is an it curve diagram obtained in phosphate buffer solution according to Example 3 of the present invention;

[0064] Fig.11 1 is a SEM test result diagram of the iron metal compound obtained in Example 3 of the present invention;

[0065] Fig.12 1 is a graph showing the XRD test result of the iron metal compound obtained in Example 3 of the present invention;

[0066] Fig.13 2 is a SEM test result diagram of lithium iron phosphate prepared in Example 3 of the present invention;

[0067] Fig.14 1 is a graph showing the XRD test result of the lithium iron phosphate prepared in Example 3 of the present invention;

[0068] Fig.15 1 is a graph showing the full spectrum test result of XPS (X-ray photoelectron spectroscopy) of lithium iron phosphate prepared in Example 3 of the present invention;

[0069] Fig.16 Graph showing the XPS-Fe2p test results of lithium iron phosphate prepared in Example 3 of the present invention;

[0070] Fig.17 CV curve (current-voltage curve) of the lithium iron phosphate assembled battery of Example 5 of the present invention is shown;

[0071] Fig.18 The graph shows the cycle performance of the lithium iron phosphate assembled battery of Example 5 of the present invention.

[0072] Definition of terms:

[0073] In the present invention, "room temperature" refers to ambient temperature, which may be 20°C-30°C; in some embodiments, 22°C-28°C; in some embodiments, 24°C-26°C; in some embodiments, 25°C.

[0074] In the above text of the present invention, regardless of whether the words "about" or "approximately" are used, all the numbers disclosed herein are approximate values. Based on the disclosed numbers, the value of each number may vary by less than ±10% or reasonable differences considered by those skilled in the art, such as ±1%, ±2%, ±3%, ±4% or ±5%.

[0075] The term "optional", "optional" or "optionally" means that the subsequently described event or circumstance may but need not occur. For example, "optional surfactant" means that a surfactant may or may not be present.

[0076] The term "weight percent" or "percent by weight" or "wt %" is defined as the weight of a single component in a composition divided by the total weight of all components of the composition multiplied by 100.

[0077] The term "and / or" should be understood to mean any one of the optional items or a combination of any two or more of the optional items.

[0078] The term "wt%" means percent by mass.

[0079] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction. DETAILED DESCRIPTION

[0080] In order to enable those skilled in the art to better understand the technical solution of the present invention, some non-limiting embodiments are further disclosed below to further illustrate the present invention in detail.

[0081] The reagents used in the present invention can be purchased from the market or prepared by the method described in the present invention.

[0082] The term "M" means mol / L, ie moles per liter.

[0083] Example 1

[0084] Under acidic conditions (pH = 0), a mixed solution containing 0.5 M NaCl (sodium chloride) and 1.0 M HCl (hydrochloric acid) was used as the electrolyte. 2 The iron sheet was used as the working electrode, the platinum mesh electrode was used as the counter electrode and the reference electrode, and electrolysis was carried out in a two-electrode system with magnetic stirring. First, a linear voltammetric scan was performed at a scanning rate of 10 mV / s in the potential range of -0.3 to 0.4 V to obtain the polarization curve, see Figure 3 It can be seen that the starting potential of the reaction is lower than 0V, that is, theoretically, the reaction can proceed spontaneously without the need for an external voltage; when the cell voltage is 0.4V, the current can reach nearly 400mA. Then, electrolysis is carried out at a constant potential of 0.4V for 6000s to obtain the it curve, see Figure 4 It can be seen that at 0.4V, the electrolyzer can maintain a large current for a long time to produce hydrogen. The actual hydrogen production was measured by gas chromatography and compared with the theoretical production calculated based on the current, see Figure 5 Under this condition, the product of the electro-oxidation of the working electrode iron sheet mainly exists in the form of free iron ions. The solution after the reaction is collected and the pH is adjusted with sodium hydroxide or ammonia water, and it can be used as lithium iron phosphate precursor iron hydroxide to further prepare lithium iron phosphate.

[0085] Example 2

[0086] Under neutral conditions (pH = 7), saturated NaCl aqueous solution was used as the electrolyte, and the size of the electrolyte was 3 × 2 cm 2 The iron sheet was used as the working electrode, the platinum mesh electrode was used as the counter electrode and the reference electrode, and electrolysis was carried out in a two-electrode system with magnetic stirring. First, a linear voltammetric scan was performed at a scanning rate of 10 mV / s in the potential range of 0-1.2 V to obtain the polarization curve, see Figure 6 It can be seen that when the applied voltage is 1.2V, the current can reach more than 250mA. Then electrolysis is carried out at a constant potential of 1.2V to obtain the it curve, see Figure 7 , it can be seen from the figure that the electrolytic cell can maintain a high current density and stably produce hydrogen for more than 12 hours. Under this condition, the product of the electrooxidation of the working electrode iron sheet mainly exists in the form of nano iron oxide or nano iron hydroxide (such as iron oxyhydroxide) or their mixture. After the product is collected and centrifuged, washed and dried, the morphology and composition of the material are analyzed by SEM and XRD, see Figure 8 and Fig. 9 The product can be mixed with ammonium phosphate, lithium carbonate, glucose and other materials and then calcined to prepare lithium iron phosphate.

[0087] Example 3

[0088] Under near-neutral conditions (pH 4-6), a buffer solution containing 0.1 mol / L sodium dihydrogen phosphate and 0.01 mol / L sodium dihydrogen phosphate was used as the electrolyte. 2 The iron sheet was used as the working electrode, the platinum mesh electrode was used as the counter electrode and the reference electrode, and electrolysis was carried out in a two-electrode system with magnetic stirring. Electrolysis was carried out at a constant potential of 1 V to obtain the it curve, see Fig.10 , and can stably produce hydrogen for more than 4 hours at a current of nearly 200mA. Under this condition, the product of the electro-oxidation of the working electrode iron sheet mainly exists in the form of nano-ferrous phosphate. After the product is collected and centrifuged, washed and dried, the morphology and composition of the material are analyzed by SEM and XRD, see Fig.11 , 12. The product was uniformly mixed with ammonium phosphate, lithium carbonate and glucose by sand milling, and then granulated by spray drying and calcined at 750°C to prepare lithium iron phosphate. The SEM, XRD and XPS results of the obtained lithium iron phosphate are shown in Fig.13 , Fig.14 , Fig.15 , Fig.16 The obtained lithium iron phosphate precursor nano-ferrous phosphate can also be used to prepare lithium iron phosphate by undergoing lithiation and granulation according to conventional lithium iron phosphate preparation methods.

[0089] Example 4

[0090] In order to ensure continuous and stable hydrogen production and produce nano-scale lithium iron phosphate precursors with stable particle size, the concentration of each component and pH value of the electrolyte in the device must be kept dynamically stable. Figure 1 or Figure 2The process in the above, combined with the material balance in the electrolytic cell, can achieve dynamic stabilization of the components and concentrations of the electrolyte. Taking acidic conditions as an example, it is sufficient to keep the hydrogen ion concentration in the electrolyte stable. If the flow rate of the electrolyte pumped from the electrolyte regeneration cell to the electrolytic cell is V1, its hydrogen ion concentration is c1; the hydrogen ion concentration of the electrolyte in the electrolytic cell under dynamic stability conditions is c2; then the hydrogen ion concentration of the discharge from the discharge port of the electrolytic cell is c2, and the volume flow rate is V2. Because the replenishment of hydrogen ions in the system only comes from the feed, the consumption of hydrogen ions goes to the discharge and the precipitation of hydrogen, and the hydrogen production rate v0 can be measured by gas chromatography or flow meter, then the hydrogen ions consumed due to hydrogen production per unit time is 2v0. Therefore, the material balance is c1V1t=c2V2t+2V0t. If the volume of the electrolyte in the device is to be maintained unchanged, the flow rates of the feed and the discharge must be the same, that is, V1=V2=V. Simplifying the above formula, the material balance condition can be obtained as c1=c2+2V0 / V, that is, by adding concentrated acid to the electrolyte regeneration pool so that its pH value satisfies the above balance condition, the pH value in the electrolytic cell can be maintained constant. In addition, considering that the complexity of the dynamic system in actual operation may cause the steady state to be destroyed, the sodium hydrogen phosphate / sodium dihydrogen phosphate buffer pair solution can be used as the electrolyte in Example 3 to further maintain the stability of the pH value in the system. If a neutral system is used, that is, a saturated sodium chloride aqueous solution is used as the electrolyte, the precipitation of hydrogen in the electrolyte and the precipitation of hydroxide ions only come from water, so the pH value in the electrolyte is basically unchanged, and it is only necessary to maintain the same flow rate of feed and discharge.

[0091] Example 5

[0092] The lithium iron phosphate obtained in Example 3 was used as the positive electrode material to assemble button lithium-ion batteries and test the electrochemical performance. The specific implementation plan is as follows: lithium iron phosphate was mixed with SuperP conductive carbon black and PVDF in a weight ratio of 8:1:1, and NMP was added as a solvent. After ball milling for 6 hours, the resulting slurry was evenly coated on a carbon-coated aluminum foil and then vacuum dried. The coated aluminum foil was punched into small discs and used as the positive electrode to assemble button batteries in an argon-filled glove box; the lithium sheet was used as the negative electrode, and an ester electrolyte containing LiPF6 was used. The reaction was carried out at 0.1mVs in the range of 2.7 and 4.4V. -1 Cyclic voltammetry (CV) measurements were performed at a scan rate of Fig.17 At room temperature, 0.5C (1C is 170mAhg -1 ) was tested with a constant current charge / discharge rate between 2.7 and 4.4 V. The battery cycle performance is shown in Fig.18 .

[0093] The method of the present invention has been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein within the content, spirit and scope of the present invention to implement and apply the technology of the present invention. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters. It is particularly important to point out that all similar replacements and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention.

Claims

1. A method for preparing a lithium iron phosphate precursor or lithium iron phosphate and hydrogen, characterized in that: include: In the presence of an anode and a cathode, electrolysis is performed in a reaction vessel containing an acidic electrolyte with iron metal electrooxidation as an anode reaction and hydrogen evolution reaction as a cathode reaction, with or without an external voltage, wherein the acidic electrolyte contains acid, the working electrode generates free iron ions, the counter electrode generates hydrogen, and the hydrogen is drawn out of the reaction vessel for storage; The acidic electrolyte is led out of the reaction container, an alkaline reagent is added, and then solid-liquid separation is performed, and the solid obtained by solid-liquid separation is a lithium iron phosphate precursor; or the acidic electrolyte is led out of the reaction container, lithium phosphate is added, and then solid-liquid separation is performed, and the solid obtained by solid-liquid separation is lithium iron phosphate; The liquid obtained by solid-liquid separation is added with an acidic electrolyte containing a certain concentration of acid and then fed into the reaction container as a feed liquid to maintain the stability of the composition, volume and pH of the acidic electrolyte in the reaction container. The flow rate of the feed liquid into the reaction container is the same as the flow rate of the acidic electrolyte out of the reaction container. The acid concentration in the acidic electrolyte in the reaction container is 0.2 mol / L to 1.0 mol / L; The concentration of acid in the feed solution satisfies the following conditions: c1=c2+2V0 / V; in, c1 is the concentration of acid in the feed solution, mol / L; c2 is the acid concentration in the acidic electrolyte in the reaction vessel, mol / L; V0 is the molar yield of hydrogen per unit time, mol / s; V is the volume flow rate of the acid electrolyte out of the reaction vessel, L / s.

2. The preparation method according to claim 1, characterized in that: The cathode is a counter electrode material for hydrogen evolution reaction; and / or the counter electrode material for hydrogen evolution reaction is platinum metal.

3. The preparation method according to claim 1, wherein the electrode material for the hydrogen evolution reaction is a platinum mesh or carbon-supported platinum; and / or the anode is iron metal.

4. The method according to claim 1, characterized in that: The acid is hydrochloric acid or phosphoric acid; and / or The acidic electrolyte contains sodium chloride.

5. The method according to claim 4, characterized in that The concentration of sodium chloride in the acidic electrolyte is 0-5 mol / L.

6. The method according to claim 4, characterized in that The concentration of sodium chloride in the acidic electrolyte is 0.5 mol / L.

7. The method according to claim 1, characterized in that The alkaline agent includes at least one of sodium hydroxide or ammonia water.

8. The method according to any one of claims 1 to 5, characterized in that: The lithium iron phosphate precursor includes iron hydroxide.

9. The method according to any one of claims 1 to 5, characterized in that: The pH of the acidic electrolyte in the reaction container is 0-6.

10. The method according to any one of claims 1 to 5, characterized in that: The method further includes stirring the acidic electrolyte in the reaction container.

11. The method according to any one of claims 1 to 5, characterized in that: The applied voltage is -0.5V~1.0V.

12. The method according to any one of claims 1 to 5, characterized in that: The applied voltage is -0.3V~0.4V.

13. A method for preparing a lithium iron phosphate precursor and hydrogen, characterized in that: include: With iron metal as a working electrode and a hydrogen evolution reaction counter electrode material as a counter electrode, electrolysis is performed in a reaction container containing an electrolyte under an external voltage condition, wherein the electrolyte is a saturated sodium chloride aqueous solution or a saturated sodium chloride aqueous solution to which a buffer salt of 0.10 mol / L-0.40 mol / L is added, the electrolyte is neutral or weakly acidic, and the pH value of the electrolyte is 4.0-7.

0. The working electrode generates iron oxide or iron hydroxide, and the counter electrode generates hydrogen, which is led out of the reaction container for storage; the electrolyte is led out of the reaction container, solid-liquid separation is performed, the solid obtained by the solid-liquid separation is a lithium iron phosphate precursor, and the liquid obtained by the solid-liquid separation is fed into the reaction container as a feed liquid, and the flow rate of the feed liquid into the reaction container is the same as the flow rate of the electrolyte led out of the reaction container.

14. The method according to claim 13, wherein the counter electrode material for the hydrogen evolution reaction is platinum metal.

15. The method according to claim 13, wherein the hydrogen evolution reaction counter electrode material is platinum mesh or carbon-supported platinum. The method according to claim 13 , wherein the electrolyte contains a buffer salt.

17. The method according to claim 16, wherein the buffer salt is disodium hydrogen phosphate and / or sodium dihydrogen phosphate.

18. The method according to claim 13, wherein the electrolyte comprises 0.05 mol / L-0.20 mol / L of sodium dihydrogen phosphate and 0.005 mol / L-0.020 mol / L of disodium hydrogen phosphate.

19. The method according to claim 13, wherein the electrolyte comprises 0.10 mol / L of sodium dihydrogen phosphate and 0.01 mol / L of sodium hydrogen phosphate.

20. The method of claim 13, wherein the electrolyte comprises phosphate ions.

21. The method according to claim 13, wherein the lithium iron phosphate precursor comprises at least one of ferrous phosphate, ferric hydroxide, ferric oxyhydroxide, and ferrosoferric oxide.

22. The method according to claim 13, wherein the pH of the electrolyte is 4.0-6.

0.

23. The method according to claim 13, wherein the applied voltage is 0.4V to 2.0V.

24. The method according to claim 13, wherein the applied voltage is 0.4V to 1.5V.

25. The method according to claim 13, wherein the applied voltage is 0.6V to 1.2V.

26. The method according to claim 13, wherein the applied voltage is 1.0V to 2.0V.

27. The method according to claim 13, wherein the applied voltage is 1.0V to 1.2V.

28. Use of a lithium iron phosphate precursor prepared by the method of any one of claims 1 to 12 or a lithium iron phosphate precursor prepared by the method of any one of claims 13 to 27 in preparing lithium iron phosphate or battery positive electrode materials.

29. A method for preparing lithium iron phosphate, characterized in that: include: The lithium iron phosphate precursor prepared by the method according to any one of claims 1 to 12 or the lithium iron phosphate precursor prepared by the method according to any one of claims 13 to 27 is mixed with ammonium phosphate, lithium carbonate and glucose and then calcined to prepare lithium iron phosphate.

Images