Battery-grade lithium phosphate and preparation method thereof, positive electrode material, electrolyte and battery

Abstract

The present invention relates to the technical field of secondary battery materials, specifically to a battery-grade lithium phosphate, its preparation method, cathode material, electrolyte, and battery. By heating the leachate after sulfuric acid leaching at three different temperatures, the aluminum in the lithium ore is effectively solidified in the slag, while the sulfur content in the slag is reduced. Leaching is then followed by impurity removal and lithium extraction. This method has the advantages of a high lithium extraction rate, a single impurity component, a simple process, and low lithium extraction costs. The resulting battery-grade lithium phosphate has an impurity content of less than 50 ppm, meeting the requirements for battery-grade lithium phosphate.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary battery materials, and in particular to battery-grade lithium phosphate and a preparation method thereof, a positive electrode material, an electrolyte and a battery. Background Art

[0002] Battery-grade lithium phosphate is a versatile phosphate with unique optical, catalytic, and electrochemical properties, resulting in a wide range of applications. It can be used as the primary raw material for preparing LiFePO4, the cathode material for lithium-ion batteries; as a target material for preparing LiPON all-solid-state electrolyte thin films, a key component of all-solid-state lithium batteries; or as an additive to lithium battery electrolytes, promoting ion transport during the charge and discharge processes of high-voltage electrode materials and improving their electrochemical cycling stability. The development and utilization of low-cost lithium sources for battery-grade lithium phosphate has become a research hotspot, including the extraction of lithium from lithium clays.

[0003] Currently, the main processes for extracting lithium from lithium clay include sulfuric acid leaching, additive roasting, chloride roasting, and alkaline digestion. The sulfuric acid method converts components in lithium clay into soluble sulfates, offering high lithium extraction rates. However, this process leaches most of the impurities in the ore into the lithium solution, significantly increasing the burden of subsequent impurity removal and purification. While the additive roasting method can solidify aluminum, it often requires the introduction of additives containing impurities such as Na, K, Ga, F, and Cl, similarly increasing the burden of subsequent battery-grade lithium phosphate purification.

[0004] Existing patent CN114875250A provides a method for purifying lithium from lithium-containing clay. The lithium-containing clay is activated; after activation, the lithium-containing clay is subjected to acidification and solid aluminum treatment; the lithium-containing clay after acidification and solid aluminum treatment is subjected to solution leaching to purify lithium, and the activator used is one or more of sodium sulfate, potassium sulfate, sodium bisulfate, potassium bisulfate, calcium sulfate, ferrous sulfate, and ferric sulfate. This patent scheme introduces a large amount of soluble impurities, and the subsequent removal of impurities is very complicated. Patent CN103849761A provides a method for extracting lithium from low-grade lithium-containing clay ore, which also adds roasting auxiliary materials such as calcium sulfate, calcium fluoride, and sodium sulfate to increase the source of soluble impurities.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The first objective of the present invention is to provide a method for preparing battery-grade lithium phosphate. By heating the leachate after sulfuric acid leaching at three different temperatures, the aluminum in the lithium ore is effectively solidified in the slag, while simultaneously reducing the sulfur content in the slag. Impurity removal and lithium extraction are then performed. This method offers the advantages of a high lithium extraction rate, a single impurity profile, a simple process, and low lithium extraction costs.

[0007] The second object of the present invention is to provide a battery-grade lithium phosphate whose impurity content is less than 50 ppm, meeting the requirements of battery-grade lithium phosphate.

[0008] The third object of the present invention is to provide a positive electrode material prepared from the battery-grade lithium phosphate prepared as above.

[0009] A fourth object of the present invention is to provide an electrolyte comprising the battery-grade lithium phosphate prepared as described above.

[0010] A fifth object of the present invention is to provide a battery comprising a positive electrode sheet and / or an electrolyte made from the positive electrode material as described above.

[0011] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0012] The present invention provides a method for preparing battery-grade lithium phosphate, comprising the following steps:

[0013] (a) mixing lithium ore with sulfuric acid to obtain a mineral acid mixture, and sequentially performing a first roasting, a second roasting, and a third roasting on the mineral acid mixture to obtain a roasting material;

[0014] Wherein, the temperature of the first calcination is 200-350°C; the temperature of the second calcination is 600-740°C; the temperature of the third calcination is 770-850°C;

[0015] (b) soaking the roasted material in water to obtain a first mixed solution, and performing impurity removal treatment on the first mixed solution to obtain a second mixed solution;

[0016] (c) adding a precipitant to the second mixed solution to precipitate lithium phosphate to obtain battery-grade lithium phosphate.

[0017] Furthermore, in step (a), the mass concentration of the sulfuric acid is 30% to 98%.

[0018] Furthermore, in step (a), the mass ratio of the sulfuric acid to the lithium ore is 0.1 to 8:1.

[0019] Furthermore, in step (a), the first calcination time is 1 to 5 hours.

[0020] Furthermore, in step (a), the second roasting time is 1 to 5 hours.

[0021] Furthermore, in step (a), the third roasting time is 1 to 60 minutes.

[0022] Furthermore, in step (b), the water immersion temperature is 60-90°C.

[0023] Furthermore, in step (b), before the impurity removal treatment, the first mixed solution is concentrated to a Li concentration of no more than 5500 ppm.

[0024] Furthermore, in step (b), the impurity removal treatment includes a first extraction treatment, a second extraction treatment and a back extraction treatment performed in sequence.

[0025] Further, in step (b), the extractant of the first extraction treatment and / or the second extraction treatment includes at least one of Mextral3936H, P204, P507, Cyanex272, N503, and DNNSA;

[0026] Furthermore, in step (b), the O / A ratio of the first extraction treatment and / or the second extraction treatment is 1 to 10:1.

[0027] Furthermore, in step (b), the temperature of the first extraction treatment and / or the second extraction treatment is 5 to 50°C.

[0028] Furthermore, in step (b), the time of the first extraction treatment and / or the second extraction treatment is 1 to 60 minutes.

[0029] Furthermore, in step (b), the number of extraction stages of the first extraction treatment and / or the second extraction treatment is 1 to 50.

[0030] Furthermore, in step (b), the stripping agent of the stripping treatment includes a primary acid, a precipitation acid and a phosphorus source;

[0031] The main acid includes at least one of nitric acid, hydrochloric acid and sulfuric acid; the precipitation acid includes at least one of oxalic acid and carbonic acid; and the phosphorus source includes at least one of phosphoric acid, hypophosphorous acid, metaphosphoric acid, ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

[0032] Furthermore, the phosphorus source is calculated as P, the lithium in the first mixed solution is calculated as Li, and the molar ratio of P to Li is 1:3-6.

[0033] Furthermore, the mass ratio of the main acid to the phosphorus source is 0.5 to 10:1.

[0034] Furthermore, the mass ratio of the precipitated acid to the phosphorus source is 0.1 to 10:1.

[0035] Furthermore, the back extraction treatment ratio O / A is 1-10:1-10.

[0036] Furthermore, the stripping temperature is 5-50°C.

[0037] Furthermore, the back extraction treatment time is 1 to 60 minutes.

[0038] Furthermore, the number of stages of the back-extraction treatment is 1 to 50.

[0039] Furthermore, in step (c), during the precipitation of the lithium phosphate, the pH of the solution system is ≥6.

[0040] The present invention provides a battery-grade lithium phosphate, which is mainly prepared by the preparation method of the battery-grade lithium phosphate.

[0041] The present invention provides a positive electrode material, which is mainly prepared from the battery-grade lithium phosphate.

[0042] The present invention provides an electrolyte comprising the battery-grade lithium phosphate.

[0043] The present invention provides a battery comprising a positive electrode sheet prepared from the positive electrode material and / or the electrolyte.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) The preparation method of battery-grade lithium phosphate provided by the present invention can convert the components into sulfates and leachable substances under low temperature conditions, and the reaction conditions are simple and mild.

[0046] (2) The method for preparing battery-grade lithium phosphate provided by the present invention effectively solidifies the Al in the lithium ore in the slag by heating the leachate after sulfuric acid leaching at three different temperatures, while simultaneously reducing the sulfur content in the slag. The temperature of the second roasting is appropriately controlled to volatilize the free sulfate ions as much as possible without converting the sulfate into oxides.

[0047] (3) The preparation method of battery-grade lithium phosphate provided by the present invention reasonably controls the temperature of the third roasting to ensure that aluminum sulfate is just converted into aluminum oxide; moreover, the roasting structure collapse and kiln over-burning caused by the sintering time being too long will not occur, thereby avoiding the problem of lithium sulfate being coated inside the aluminum oxide and unable to be leached.

[0048] (4) The preparation method of battery-grade lithium phosphate provided by the present invention uses a composite stripping agent of "main acid + precipitation acid + phosphorus source" for stripping, which further precipitates and removes the remaining trace Ca impurities that cannot be extracted, and at the same time, replenishes the phosphorus source.

[0049] (5) The preparation method of battery-grade lithium phosphate provided by the present invention adopts a composite stripping agent of "primary acid + precipitation acid + phosphorus source". Both the precipitation acid and the phosphorus source can supplement hydrogen ions, thereby reducing the amount of primary acid used and reducing the subsequent processing burden of the residual solution of lithium precipitation.

[0050] (6) The preparation method of battery-grade lithium phosphate provided by the present invention effectively solidifies Al in lithium ore in slag, while reducing the S content in the slag, thereby improving the utilization rate of the slag.

[0051] (7) In the preparation method of battery-grade lithium phosphate provided by the present invention, since impurities are solidified in the slag, no additional waste is generated during the entire impurity removal process.

[0052] (8) The preparation method of battery-grade lithium phosphate provided by the present invention has the advantages of high lithium extraction rate, no additional introduction of soluble impurities, single impurity composition, simple process, and low lithium extraction cost.

[0053] (9) The battery-grade lithium phosphate provided by the present invention has low extraction cost and low impurity content, with the impurity content being less than 50 ppm, meeting the requirements of battery-grade lithium phosphate and can be used as a raw material for making batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0055] Figure 1 This is a process flow chart of the method for preparing lithium phosphate provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0056] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments. However, it will be understood by those skilled in the art that the following embodiments are only some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially. In addition, the terms "first", "second", "third", "fourth" etc. are only used to distinguish descriptions and should not be understood as indicating or implying relative importance.

[0057] A first aspect of the present invention provides a method for preparing battery-grade lithium phosphate, comprising the following steps:

[0058] (a) mixing lithium ore with sulfuric acid to obtain a mineral acid mixture, and sequentially performing a first roasting, a second roasting, and a third roasting on the mineral acid mixture to obtain a roasting material;

[0059] The temperature of the first calcination is 200-350°C; the temperature of the second calcination is 600-740°C; the temperature of the third calcination is 770-850°C;

[0060] (b) soaking the roasted material in water to obtain a first mixed solution, and performing impurity removal treatment on the first mixed solution to obtain a second mixed solution;

[0061] (c) adding a precipitant to the second mixed solution to precipitate lithium phosphate to obtain battery-grade lithium phosphate.

[0062] Among them, the main function of the first roasting is the further reaction and dissolution of the components in the lithium ore with sulfuric acid. The main reactions include: 2LiAlSi4O 10 +4H2SO4→Li2SO4+Al2(SO4)3+4H2O+8SiO2, the temperature of the first calcination is 200-350℃, for example, any point value among 200℃, 220℃, 240℃, 260℃, 280℃, 300℃, 325℃, 350℃ or a range value consisting of any two point values.

[0063] The temperature of the second roasting is reasonably controlled so that the free sulfate ions are volatilized as much as possible without converting the sulfate into oxides. The main reactions include: H2SO4→H2O+SO3. The temperature of the second roasting is 600-740°C, for example, any point value among 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, and 740°C, or a range consisting of any two points.

[0064] Reasonably control the temperature of the third roasting to ensure that aluminum sulfate is transformed into aluminum oxide, effectively solidify the Al in the lithium ore in the slag, and avoid the collapse of the roasting structure and over-burning of the kiln due to too long sintering time, thereby avoiding the problem of lithium sulfate being coated inside the aluminum oxide and unable to be leached. The main reactions in this process include: Al2(SO4)3→Al2O3+3SO3; Fe2(SO4)3→Fe2O3+3SO3. At the same time, this step can also reduce the S content in the slag and improve the utilization rate of the slag. The temperature of the third roasting is 770~850℃, for example, any point value among 770℃, 780℃, 790℃, 800℃, 820℃, 830℃, 840℃, 850℃ or a range value consisting of any two point values.

[0065] The method for preparing battery-grade lithium phosphate provided in this application effectively solidifies the Al in the lithium ore in the slag by heating the leachate after sulfuric acid leaching at three different temperatures, while reducing the S content in the slag and improving the Li extraction rate. Secondly, because the impurities are solidified in the slag, no additional waste is generated during the entire impurity removal process, and no new soluble impurities are introduced. This method has the advantages of being simpler, more convenient, and having a low cost for lithium extraction.

[0066] In a preferred embodiment, the lithium ore includes clay-type lithium ore and / or spodumene.

[0067] In a preferred embodiment, the lithium ore is crushed to facilitate leaching of components.

[0068] In a preferred embodiment, the mass concentration of sulfuric acid is 30% to 98%, for example, any one of 30%, 40%, 50%, 60%, 70%, 75%, 80%, 85%, 90%, 95%, 98% or a range consisting of any two of the values.

[0069] In a preferred embodiment, the mass ratio of sulfuric acid to lithium ore is 0.1 to 8:1, for example, any one of 0.1:1, 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, and 8:1, or a range consisting of any two of the ratios.

[0070] In a preferred embodiment, the first roasting time is selected based on the first roasting temperature to allow sufficient reaction between the sulfuric acid and the components in the lithium ore. The first roasting time is 1 to 5 hours, for example, any one of 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours, or a range consisting of any two of these values.

[0071] In a preferred embodiment, the second roasting time is selected based on the second roasting temperature so that the sulfate is not converted into oxides and the free sulfate radical is volatilized as much as possible. The second roasting time is 1 to 5 hours, for example, any one of 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours, or a range consisting of any two of these values.

[0072] In a preferred embodiment, the time of the third roasting should be selected according to the temperature of the third roasting, and aluminum sulfate is transformed into aluminum oxide as much as possible to effectively solidify the Al in the lithium ore in the slag. The time of the third roasting is 1 to 60 min, for example, any point value among 1 min, 2 min, 5 min, 8 min, 10 min, 15 min, 18 min, 20 min, 25 min, 28 min, 30 min, 33 min, 35 min, 40 min, 45 min, 50 min, 55 min, and 60 min, or a range value consisting of any two point values.

[0073] In a preferred embodiment, which is beneficial to the leaching efficiency of water immersion, the water immersion temperature is 60-90°C, for example, any value among 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, and 90°C, or a range consisting of any two values. Furthermore, to accelerate dissolution, stirring can be performed during the water immersion process. Furthermore, the stirring speed is 300-1000 rpm, for example, any value among 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, and 1000 rpm, or a range consisting of any two values; the stirring time is 1-4 hours, for example, any value among 1 hour, 2 hours, 3 hours, and 4 hours, or a range consisting of any two values.

[0074] In a preferred embodiment, to ensure the yield of precipitated lithium phosphate, the first mixed solution is concentrated to a Li concentration of no more than 5500 ppm, preferably 4900-5100 ppm.

[0075] In a preferred embodiment, the impurity removal treatment includes a first extraction treatment, a second extraction treatment, and a back extraction treatment, performed sequentially. Furthermore, the extractant for the first extraction treatment and / or the second extraction treatment includes at least one of Mextral3936H, P204, P507, Cyanex272, N503, and DNNSA. A single extractant or a composite extractant comprising several different extractants may be used. Mextral3936H is a new energy battery metal extractant from Comp Chemical, suitable for extracting lithium from salt lake brine with a low magnesium (calcium) to lithium content ratio, ore leachate, lithium-containing wastewater, and used lithium batteries. DNNSA is dinonylnaphthalenesulfonic acid.

[0076] In a preferred embodiment, the extract may further include a diluent in addition to the extractant, or may have been subjected to a saponification treatment with a strong base; preferably, the volume concentration of the extractant is 5 Vol% to 90 Vol%, for example, any value among 5 Vol%, 10 Vol%, 15 Vol%, 20 Vol%, 25 Vol%, 30 Vol%, 35 Vol%, 40 Vol%, 50 Vol%, 55 Vol%, 60 Vol%, 65 Vol%, 70 Vol%, 75 Vol%, 80 Vol%, 85 Vol%, 90 Vol%, or a range consisting of any two values.

[0077] In a preferred embodiment, the O / A ratio of the first extraction treatment and / or the second extraction treatment is 1 to 10:1, for example, any ratio of 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 9:1, 10:1 or a range consisting of any two ratios.

[0078] In a preferred embodiment, the temperature of the first extraction treatment and / or the second extraction treatment is 5 to 50° C., for example, any one of 5° C., 10° C., 15° C., 20° C., 25° C., 30° C., 35° C., 40° C., 45° C., and 50° C., or a range consisting of any two of these values. The duration of the first extraction treatment and / or the second extraction treatment is 1 to 60 min, for example, any one of 1 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, and 60 min, or a range consisting of any two of these values.

[0079] In a preferred embodiment, the number of extraction stages in the first extraction treatment and / or the second extraction treatment is 1 to 50, for example, any point value among stage 1, stage 3, stage 5, stage 10, stage 15, stage 20, stage 22, stage 25, stage 28, stage 30, stage 35, stage 40, stage 45, and stage 50, or a range value consisting of any two point values.

[0080] In a preferred embodiment, the stripping agent used in the stripping treatment includes a primary acid, a precipitating acid, and a phosphorus source, effectively reducing trace amounts of calcium impurities in the stripping solution. The primary acid primarily provides an acidic liquid environment and includes at least one of nitric acid, hydrochloric acid, and sulfuric acid; the precipitating acid primarily precipitates residual calcium ions and includes at least one of oxalic acid and carbonic acid; and the phosphorus source includes at least one of phosphoric acid, hypophosphorous acid, metaphosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. Furthermore, both the precipitating acid and the phosphorus source can replenish hydrogen ions, reducing the amount of primary acid used and the subsequent processing burden of the lithium precipitation residual solution.

[0081] In a preferred embodiment, to ensure that lithium phosphate precipitates as much as possible, the phosphorus source is calculated as P, the lithium in the first mixed solution is calculated as Li, and the molar ratio of P to Li is 1:3 to 6, for example, any ratio of 1:6, 2:6, 3:6, or a range value consisting of any two ratios.

[0082] In a preferred embodiment, the mass ratio of the main acid to the phosphorus source is 0.5 to 10:1, for example, any ratio or any two ratios of 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, and 10:1.

[0083] In a preferred embodiment, the mass ratio of the precipitating acid to the phosphorus source is 0.1 to 10:1, for example, any one of 0.1:1, 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, and 10:1, or a range consisting of any two of the ratios.

[0084] In a preferred embodiment, the back extraction treatment ratio O / A is 1 to 10:1 to 10, for example, any ratio of 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 9:1, 10:1, 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, 1:1, 2:7, 3:5, 4:3, 7:9, 6:5, 5:8, 4:5, 3:7, 2:9, and 9:2, or a range of any two ratios.

[0085] In a preferred embodiment, the stripping treatment is carried out at a suitable temperature, for example, 5 to 50°C, further any value among 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C, or a range consisting of any two values. Furthermore, the stripping treatment time is 1 to 60 min, for example any value among 1 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, and 60 min, or a range consisting of any two values. Furthermore, the number of stripping treatment stages is 1 to 50 stages, for example any value among 1, 3, 5, 10, 15, 20, 22, 25, 28, 30, 35, 40, 45, and 50 stages, or a range consisting of any two values.

[0086] In a preferred embodiment, the precipitant includes but is not limited to a pH adjuster.

[0087] In a preferred embodiment, during the precipitation of lithium phosphate, the pH of the solution system is ≥ 6, preferably 6 to 11, for example, any one of 6, 7, 8, 9, 10, and 11, or a pH range consisting of any two of these values, to ensure that lithium phosphate is precipitated as much as possible. Preferably, the pH can be adjusted using a pH adjuster, such as common ammonia, sulfuric acid, or hydrochloric acid, and the pH adjuster should minimize the introduction of excessive impurities.

[0088] The second aspect of the present invention provides a battery-grade lithium phosphate, which is mainly prepared by the preparation method of the battery-grade lithium phosphate provided by the present invention. The battery-grade lithium phosphate has low extraction cost and low impurity content, with the impurity content being less than 50 ppm, meeting the requirements of battery-grade lithium phosphate and can be used as a raw material for making batteries.

[0089] A third aspect of the present invention provides a positive electrode material, which is mainly made of battery-grade lithium phosphate, including lithium iron phosphate, lithium manganese iron phosphate or other positive electrode composite materials.

[0090] A fourth aspect of the present invention provides an electrolyte comprising the battery-grade lithium phosphate described above. The lithium phosphate can be used as an additive or as a raw material for producing the electrolyte, for example, to prepare lithium difluorophosphate or lithium hexafluorophosphate.

[0091] A fifth aspect of the present invention provides a battery comprising a positive electrode sheet, a separator, and a negative electrode sheet stacked in sequence, with the separator positioned between the positive and negative electrode sheets to provide isolation, followed by winding to form an electrode assembly; the electrode assembly is placed in an outer foil packaging, the electrolyte is injected into the dried outer foil packaging, and the battery is vacuum packaged, allowed to stand, formed, and shaped to form a single cell. The positive electrode sheet is made from a positive electrode slurry comprising the above-mentioned positive electrode material.

[0092] In the embodiment of the present invention, the content of each element is tested using an inductively coupled plasma spectrometer (ICP).

[0093] Example 1

[0094] The preparation method of battery-grade lithium phosphate provided in this embodiment has the following process: Figure 1 As shown, the following steps are included:

[0095] Step 1: Take 50g of clay lithium ore and crush it into -74μm particles. The composition of the clay lithium ore is shown in Table 1:

[0096] Table 1

[0097]

[0098] Step 2: Add 80 g of 50% sulfuric acid solution to the clay ore and stir evenly; place the ore-acid mixture in a muffle furnace and calcine it according to the following heating temperature and heating time:

[0099] 200℃, 2.5h→740℃, 1.5h→770℃, 10min;

[0100] Step 3: Add 500 g of desalted water to the roasted ore after roasting, place in a water bath, and stir and heat at 90°C and 600 rpm for 2.5 hours; after stirring, filter to obtain 493 g of mixed solution ①. The composition data of mixed solution ① are shown in Table 2:

[0101] Table 2

[0102]

[0103] According to the data of mixed solution ①, the Li leaching rate is close to 93%, the Al solidification rate is 99.5%, it contains a small amount of Ca / Mg impurities, the Li / S molar ratio is 2 / 1, and the sulfate in the solution is completely volatilized;

[0104] Step 4: The mixed solution ① was concentrated to a Li content of 5070 ppm to obtain 82 g of mixed solution ②. The composition data of the mixed solution ② are shown in Table 3:

[0105] Table 3

[0106]

[0107] Step 5: Mextral 3936H extractant, which had been saponified with NaOH, was added to the mixed solution ②. The extractant preferentially extracted divalent, trivalent, or higher-valent metal ions. The O / A ratio was 1:8, the extraction temperature was 40°C, the extraction time was 10 min, and the extraction stage was 1. After removing the organic phase, a mixed solution ③ was obtained. The composition data of the mixed solution ③ are shown in Table 4:

[0108] Table 4

[0109]

[0110] Step 6: After the extraction of divalent or trivalent ions is completed, Mextral3936H extractant saponified with NaOH is added to the mixture ③ for Li + The extraction was carried out at an O / A ratio of 1:1, an extraction temperature of 40°C, an extraction time of 10 min, and a first extraction stage. The mixed solution containing sulfate ions (aqueous phase) was removed to obtain a second organic phase containing lithium.

[0111] Step 7: A stripping agent was prepared by mixing nitric acid (2 g) + oxalic acid (0.5 g) + phosphoric acid (2.3 g) + water (15.2 g). The stripping agent was added to the second organic phase containing lithium for stripping. O / A = 4:1. The stripping temperature was 40° C., the time was 10 min, and the stripping stage was 1. After removing the third organic phase, a mixed solution containing a precipitate ⑤ was obtained. The clear solution was filtered to obtain a mixed solution ⑥. The composition data of the mixed solution ⑥ are shown in Table 5:

[0112] Table 5

[0113]

[0114] Step 8: Ammonia water was added to the mixed solution ⑥ to adjust the pH to 8.5, and the mixture was heated at 90° C. and aged for 2 h until lithium phosphate was precipitated. The mixed solution ⑦ was removed by filtration to obtain wet-based lithium phosphate, which was dried to obtain battery-grade lithium phosphate. The composition data of the lithium phosphate is shown in Table 6:

[0115] Table 6

[0116]

[0117] The impurity content of the lithium phosphate prepared in this embodiment is less than 50 ppm, meeting the requirements of battery-grade lithium phosphate.

[0118] Example 2

[0119] The method for preparing battery-grade lithium phosphate provided in this embodiment includes the following steps:

[0120] Step 1: Take 100 g of clay lithium ore and crush it into -74 μm particles. The composition of the clay lithium ore is the same as Table 1 in Example 1;

[0121] Step 2: Add 800 g of 80% sulfuric acid solution to the clay ore and stir evenly; place the ore-acid mixture in a muffle furnace and calcine it according to the following heating temperature and heating time:

[0122] 200℃, 2.5h→720℃, 2h→790℃, 5min;

[0123] Step 3: Add 500 g of desalted water to the roasted ore after roasting, place in a water bath, and stir and heat at 70°C and 600 rpm for 2.5 h. After stirring, filter to obtain 488 g of mixed solution ①. The composition data of mixed solution ① are shown in Table 7:

[0124] Table 7

[0125]

[0126] According to the data of mixed solution ①, the Li leaching rate is close to 91%, the Al solidification rate is 99.2%, it contains a small amount of Ca / Mg impurities, the Li / S molar ratio is 2 / 1, and the sulfate in the solution is volatilized;

[0127] Step 4: The mixed solution ① was concentrated to a Li content of 5085 ppm to obtain 162 g of mixed solution ②. The composition data of the mixed solution ② are shown in Table 8:

[0128] Table 8

[0129]

[0130] Step 5: Mextral 3936H extractant saponified with NaOH was added to mixed solution ②, with O / A = 1:1, extraction temperature at 25°C, extraction time for 10 min, and extraction stage 2. After removing the organic phase, mixed solution ③ was obtained. The composition data of mixed solution ③ are shown in Table 9:

[0131] Table 9

[0132]

[0133] Step 6: Add Mextral 3936H, which has been saponified with NaOH, to the mixture (3) at an O / A ratio of 1:1, an extraction temperature of 40°C, an extraction time of 10 min, and a first extraction stage to remove the sulfate-containing mixture (4) (aqueous phase) to obtain a second organic phase containing lithium.

[0134] Step 7: A stripping agent was prepared by mixing nitric acid (4 g) + oxalic acid (0.5 g) + monoammonium phosphate (5 g) + water (30.5 g). The stripping agent was added to the second organic phase containing lithium for stripping. O / A = 4:1. The stripping temperature was 40° C., the time was 10 min, and the stripping stage was 1. After removing the third organic phase, a mixed solution containing a precipitate ⑤ was obtained. The clear solution was filtered to obtain a mixed solution ⑥. The composition data of the mixed solution ⑥ are shown in Table 10:

[0135] Table 10

[0136]

[0137] Step 8: Ammonia water was added to the mixed solution ⑥ to adjust the pH to 9, and the mixture was heated to 60° C. and aged for 2 h until lithium phosphate was precipitated. The mixed solution ⑦ was removed by filtration to obtain wet-based lithium phosphate, which was then dried to obtain battery-grade lithium phosphate. The composition data of the lithium phosphate is shown in Table 11:

[0138] Table 11

[0139]

[0140] The impurity content of the lithium phosphate prepared in this embodiment is less than 50 ppm, meeting the requirements of battery-grade lithium phosphate.

[0141] Example 3

[0142] The method for preparing battery-grade lithium phosphate provided in this embodiment includes the following steps:

[0143] Step 1: Take 100g of clay lithium ore and crush it into -74μm particles. The composition of the clay lithium ore is as shown in Table 1 in Example 1:

[0144] Step 2: Add 800 g of 98% sulfuric acid solution to the clay ore and stir evenly; place the ore-acid mixture in a muffle furnace and calcine it according to the following heating temperature and heating time:

[0145] 300℃, 2.5h→720℃, 2h→850℃, 2min;

[0146] Step 3: Add 500 g of desalted water to the roasted ore after roasting, place in a water bath, and stir and heat at 70°C and 600 rpm for 2.5 h. After stirring, filter to obtain 490 g of mixed solution ①. The composition data of mixed solution ① are shown in Table 12:

[0147] Table 12

[0148]

[0149] According to the data of mixed solution ①, the Li leaching rate is close to 90%, the Al solidification rate is 99.9%, it contains a small amount of Ca / Mg impurities, the Li / S molar ratio is 2 / 1, and the sulfate in the solution is volatilized;

[0150] Step 4: The mixed solution ① was concentrated to a Li content of 5004 ppm to obtain 162 g of mixed solution ②. The composition data of the mixed solution ② are shown in Table 13:

[0151] Table 13

[0152]

[0153] Step 5: P204 extractant saponified with NaOH was added to mixed solution ②, with O / A = 2:1, extraction temperature at 25°C, extraction time for 10 min, and extraction stage 1. After removing the organic phase, mixed solution ③ was obtained. The composition data of mixed solution ③ are shown in Table 14:

[0154] Table 14

[0155]

[0156] Step 6: Add NaOH-saponified P507 extractant to the mixed solution ③, with an O / A ratio of 2:1, an extraction temperature of 40°C, an extraction time of 10 min, and an extraction stage of 1, to remove the mixed solution ④ (aqueous phase) containing sulfate, thereby obtaining a second organic phase containing lithium;

[0157] Step 7: A stripping agent was prepared by mixing nitric acid (4 g) + oxalic acid (0.5 g) + monoammonium phosphate (5 g) + water (30.5 g). The stripping agent was added to the second organic phase containing lithium for stripping. O / A = 4:1. The stripping temperature was 40° C., the time was 10 min, and the stripping stage was 1. After removing the third organic phase, a mixed solution containing a precipitate ⑤ was obtained. The clear solution was filtered to obtain a mixed solution ⑥. The composition data of the mixed solution ⑥ are shown in Table 15:

[0158] Table 15

[0159]

[0160] Step 8: Ammonia water was added to the mixed solution ⑥ to adjust the pH to 9, and the mixture was heated to 70° C. and aged for 2 h until lithium phosphate was precipitated. The mixed solution ⑦ was removed by filtration to obtain wet-based lithium phosphate, which was dried to obtain battery-grade lithium phosphate. The composition data of the lithium phosphate is shown in Table 16:

[0161] Table 16

[0162]

[0163] The impurity content of the lithium phosphate prepared in this embodiment is less than 50 ppm, meeting the requirements of battery-grade lithium phosphate.

[0164] Comparative Example 1

[0165] Comparative Example 1 is substantially the same as Example 1, except that the heating temperature and heating time in step 1 are set as follows: 200° C., 2.5 h→740° C., 100 min.

[0166] The composition data of the prepared lithium phosphate are shown in Table 17:

[0167] Table 17

[0168]

[0169] The experimental results show that when only the first and second sintering processes are performed, even if the sintering time of the second sintering process is extended, the Al content in the lithium phosphate obtained in Comparative Example 1, which does not undergo the third sintering process, is significantly higher than that in Example 1. Even if the subsequent steps are exactly the same, the impurity contents of Ca, Mg, and Si are also relatively high and cannot meet the battery-grade standards.

[0170] Comparative Example 2

[0171] Comparative Example 2 is substantially the same as Example 3, except that the stripping agent in step 7 is composed of nitric acid (9.5 g) + water (30.5 g).

[0172] The composition data of the prepared lithium phosphate are shown in Table 18:

[0173] Table 18

[0174]

[0175] The experimental results show that during the stripping process, if only the main acid is added, that is, the total amount of stripping agent used is the same, the impurity removal effect is significantly different from that in Example 3, the impurity content is too high, and the battery-grade standard cannot be met. In particular, the residual Ca content is too high, affecting the quality of lithium phosphate.

[0176] Although the present invention has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are merely intended to illustrate the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and scope of the present invention. However, these modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing battery-grade lithium phosphate, characterized in that: The following steps are involved: (a) mixing lithium ore with sulfuric acid to obtain a mineral acid mixture, and sequentially performing a first roasting, a second roasting, and a third roasting on the mineral acid mixture to obtain a roasted material; The temperature of the first calcination is 200-350°C; the temperature of the second calcination is 600-740°C; the temperature of the third calcination is 770-850°C; (b), soaking the roasted material in water to obtain a first mixed solution, and subjecting the first mixed solution to an impurity removal treatment to obtain a second mixed solution; in step (b), the impurity removal treatment includes a first extraction treatment, a second extraction treatment, and a stripping treatment performed in sequence; the stripping agent of the stripping treatment includes a primary acid, a precipitating acid, and a phosphorus source; in step (b), the primary acid includes at least one of nitric acid, hydrochloric acid, and sulfuric acid, and the precipitating acid includes at least one of oxalic acid and carbonic acid; (c) adding a precipitant to the second mixed solution to precipitate lithium phosphate to obtain battery-grade lithium phosphate; the precipitant comprises aqueous ammonia.

2. The method for preparing battery-grade lithium phosphate according to claim 1, wherein: In step (a), at least one of the following features (1) to (5) is included: (1) The mass concentration of the sulfuric acid is 30% to 98%; (2) The mass ratio of the sulfuric acid to the lithium ore is 0.1 to 8:1; (3) The first roasting time is 1 to 5 hours; (4) The second roasting time is 1 to 5 hours; (5) The third roasting time is 1 to 60 minutes.

3. The method for preparing battery-grade lithium phosphate according to claim 1, wherein: In step (b), at least one of the following features (1) to (2) is included: (1) The water immersion temperature is 60-90°C; (2) Before the impurity removal treatment, the first mixed solution is concentrated to a Li concentration of no more than 5500 ppm.

4. The method for preparing battery-grade lithium phosphate according to claim 1, wherein: Contains at least one of the following features (1) to (5): (1) The extractant of the first extraction treatment and / or the second extraction treatment includes at least one of Mextral3936H, P204, P507, Cyanex272, N503, and DNNSA; (2) The O / A ratio of the first extraction treatment and / or the second extraction treatment is 1 to 10:1; (3) The temperature of the first extraction treatment and / or the second extraction treatment is 5 to 50°C; (4) The duration of the first extraction treatment and / or the second extraction treatment is 1 to 60 minutes; (5) The number of extraction stages of the first extraction process and / or the second extraction process is 1 to 50.

5. The method for preparing battery-grade lithium phosphate according to claim 1, wherein: In step (b), at least one of the following features (1) to (8) is included: (1) The phosphorus source includes at least one of phosphoric acid, hypophosphorous acid, metaphosphoric acid, ammonium dihydrogen phosphate and diammonium hydrogen phosphate; (2) The phosphorus source is calculated as P, the lithium in the first mixed solution is calculated as Li, and the molar ratio of P to Li is 1:3-6; (3) The mass ratio of the primary acid to the phosphorus source is 0.5-10:1; (4) The mass ratio of the precipitated acid to the phosphorus source is 0.1 to 10:1; (5) The stripping treatment has an O / A ratio of 1-10:1-10; (6) The stripping temperature is 5-50°C; (7) The stripping time is 1 to 60 minutes; (8) The number of stages of the stripping treatment is 1 to 50.

6. The method for preparing battery-grade lithium phosphate according to claim 1, wherein: In step (c), during the precipitation of lithium phosphate, the pH of the solution system is ≥6.

7. Battery-grade lithium phosphate, characterized in that The battery-grade lithium phosphate is mainly prepared by the preparation method of any one of claims 1 to 6.

8. A cathode material, characterized in that Mainly prepared from the battery-grade lithium phosphate as claimed in claim 7.

9. An electrolyte, characterized in that Comprising the battery-grade lithium phosphate as claimed in claim 7.

10. A battery, characterized in that Comprising a positive electrode sheet made of the positive electrode material as claimed in claim 8 and / or an electrolyte as claimed in claim 9.

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