A lithium-rich lithium ferrite lithium supplement and its synthesis method and use

Abstract

The present invention belongs to the technical field of battery materials, and provides a lithium-rich lithium ferrite lithium supplementing agent, a synthesis method and a use thereof. In the synthesis method, a solid electrolyte, conductive carbon and elemental sulfur are mixed and subjected to low-temperature heat treatment to form a composite mixture, and then the composite mixture is secondarily mixed with lithium-rich lithium ferrite and subjected to low-temperature heat treatment to form a mixed coating layer on the lithium-rich lithium ferrite, thereby obtaining the lithium-rich lithium ferrite lithium supplementing agent. Sulfur in the mixed coating layer can absorb the surface oxygen released during the charging process of the lithium-rich lithium ferrite, thereby reducing gas generation. The solid electrolyte and the conductive carbon can form an ionic and electronic conductive network, avoiding the difficulty of Li+ extraction and the decrease of lithium supplementing capacity caused by too thick sulfur coating. At the same time, the low-temperature heat treatment causes the elemental sulfur to melt, which can play a role in dispersion and adhesion, realizing the uniform dispersion of the solid electrolyte and the conductive carbon and the effective coating of the composite mixture, which is beneficial to improving the binding property and compatibility. The obtained mixed coating layer can effectively improve the air stability of the lithium supplementing agent.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and relates to a lithium-rich lithium ferrate lithium supplement agent, a synthesis method thereof, and a use thereof. Background Art

[0002] Lithium-ion batteries have been widely used in fields such as portable electronic products and new energy vehicles due to their advantages of high voltage, large energy density, long cycle life, and environmental friendliness. With the rapid expansion of the electronic device and electric vehicle markets, the requirements for the performance of lithium-ion batteries are also continuously increasing. However, existing lithium-ion batteries have the problem of irreversible capacity loss during the first charge and discharge process, which not only affects the energy density of the battery, but also limits its cycle performance, shortens the service life, and affects the actual application effect.

[0003] The problem of irreversible capacity loss mainly stems from the fact that during the first charging process of a lithium-ion battery, the electrolyte will undergo a reduction reaction on the surface of the negative electrode to form a solid electrolyte interface film (SEI). The formation of the SEI film consumes a part of the lithium ions, resulting in irreversible capacity loss; at the same time, since some active substances may undergo irreversible structural changes or decomposition during the first charge and discharge process, the irreversible capacity loss is further increased. To solve this problem, lithium supplementation technology has emerged.

[0004] The core of lithium supplementation technology lies in improving the initial capacity and overall performance of the battery by supplementing an additional lithium source. It mainly includes two methods, namely negative electrode lithium supplementation achieved by pre-depositing lithium metal or lithium alloy on the surface of the negative electrode material, and positive electrode lithium supplementation achieved by adding a lithium supplementation additive to the positive electrode material. Among them, the positive electrode lithium supplementation agent can release lithium ions during the first charging process of the battery, and thus can compensate for the lithium ion loss during the formation of the negative electrode SEI film. Relatively speaking, the use of the positive electrode lithium supplementation agent is relatively more stable and safe, and the process is simple, with a wider range of applicability.

[0005] Common positive electrode lithium supplementation agents include lithium-rich lithium ferrate ( ), lithium-rich lithium manganate ( ), etc. Among them, lithium-rich lithium ferrate has attracted much attention due to its high irreversible lithium supplementation capacity (≥700 mAh / g) and low cost advantages. However, lithium-rich lithium ferrate has poor air stability, which easily leads to the destruction of the material structure and performance degradation. Secondly, the electronic conductivity of lithium-rich lithium ferrate is relatively low, which limits its fast charge and discharge performance in the battery. In addition, lithium-rich lithium ferrate is prone to generating gas during the battery cycle process, affecting the safety and stability of the battery.

[0006] In view of the above problems of lithium-rich lithium ferrate, researchers have proposed to prevent contact with air and maintain structural stability by coating a protective layer of oxides such as Al2O3 and SiO3 on the surface of lithium-rich lithium ferrate. However, such a coating layer will affect the transmission path of lithium ions and further reduce the conductivity and electrochemical performance of the material. To improve the electronic conductivity, researchers have used highly conductive carbon materials, such as carbon nanotubes and graphene, to composite with lithium-rich lithium ferrate. However, the problems of uniform distribution of conductive carbon materials and compatibility with matrix materials need to be further solved. At the same time, the traditional process for synthesizing lithium-rich lithium ferrate requires solid-phase mixing for sintering, and then conductive carbon materials are coated or incorporated by high-temperature sintering. However, high-temperature treatment is likely to trigger a carbothermal reduction reaction, causing Fe 3+ to be reduced to Fe 2+ , resulting in impure phase and capacity decay problems.

[0007] Therefore, it is still necessary to develop and optimize the lithium supplement additive for lithium-rich lithium ferrate to solve the existing problems and provide a more efficient and reliable solution for further promoting its large-scale lithium supplement application. Summary of the Invention

[0008] In view of the problems existing in the prior art, the purpose of the present invention is to provide a lithium supplement agent for lithium-rich lithium ferrate, its synthesis method and uses. The synthesis method includes mixing a solid electrolyte, conductive carbon and elemental sulfur, performing low-temperature heat treatment to form a composite mixture, and then performing secondary mixing and low-temperature heat treatment with lithium-rich lithium ferrate to form a mixed coating layer on the composite mixture, thereby obtaining the lithium supplement agent for lithium-rich lithium ferrate. By adding sulfur to the mixed coating layer in the present invention, the surface oxygen release during the charging process of lithium-rich lithium ferrate is absorbed, thereby reducing gas generation; by adding a solid electrolyte and conductive carbon, an ion and electron conductive network is formed in the sulfur-based mixed coating layer, avoiding the adverse effects of difficult Li + removal and decreased lithium supplement capacity caused by too thick sulfur coating. At the same time, the molten elemental sulfur in the two low-temperature heat treatments can play a role in dispersion and adhesion, realizing the uniform dispersion of the solid electrolyte and conductive carbon and the effective coating of the composite mixture, and being beneficial to improving the binding property and compatibility. The mixed coating layer obtained by the mutual cooperation of the three components can effectively improve the air stability of the lithium supplement agent.

[0009] To achieve this purpose, the present invention adopts the following technical solutions:

[0010] In the first aspect, the present invention provides a synthesis method of a lithium supplement agent for lithium-rich lithium ferrate, and the synthesis method includes:

[0011] Mix a solid electrolyte, conductive carbon, and elemental sulfur, and perform low-temperature heat treatment. The temperature of the low-temperature heat treatment causes the elemental sulfur to melt to bond the solid electrolyte and the conductive carbon, forming a composite mixture based on elemental sulfur. Then, perform secondary mixing and secondary low-temperature heat treatment on the composite mixture and lithium-rich lithium ferrite, so that the composite mixture forms a mixed coating layer on the surface of the lithium-rich lithium ferrite, obtaining a lithium-rich lithium ferrite lithium supplement agent.

[0012] To solve the application problems of lithium-rich lithium ferrite, the synthesis method of the present invention forms a mixed coating layer by coating based on elemental sulfur. The sulfur therein can absorb the surface released oxygen during the charge and discharge process of lithium-rich lithium ferrite to form Li2SO3, effectively inhibiting gas generation. However, considering that only sulfur coating will hinder the lithium ion conduction of the lithium-rich lithium ferrite in the core, and at the same time, in order to further improve the conductivity of lithium-rich lithium ferrite, the synthesis method mixes a solid electrolyte, conductive carbon, and sulfur to form a mixed coating layer, effectively improving the ionic conductivity and electronic conductivity, and can avoid the adverse effects brought by sulfur coating or a large amount of sulfur usage. At the same time, the synthesis method utilizes the characteristic of the low melting point of sulfur, and both of the two low-temperature heat treatments can make the elemental sulfur transform into a molten state, thereby not only improving the dispersion uniformity of the solid electrolyte and conductive carbon, enhancing the binding property and compatibility between various components, making the binding between any two components or with the internal lithium-rich lithium ferrite closer, which is beneficial to the subsequent formation of a denser mixed coating layer, but also effectively ensuring that the composite mixture forms a tightly bound mixed coating layer on the surface of the lithium-rich lithium ferrite. Since elemental sulfur also has hydrophobicity, the mixed coating layer formed by the combination of the three components can further effectively improve the air stability of the overall lithium supplement agent.

[0013] The following are the preferred technical solutions of the present invention, but do not constitute limitations to the technical solutions provided by the present invention. Through the following technical solutions, the technical purposes and beneficial effects of the present invention can be better achieved and realized.

[0014] As a preferred technical solution of the present invention, the method for preparing the lithium-rich lithium ferrite includes: performing solid-phase mixing of a lithium source and an iron source, and then performing pre-sintering and sintering in sequence to obtain the lithium-rich lithium ferrite.

[0015] As a preferred technical solution of the present invention, the lithium source includes at least one of lithium hydroxide monohydrate, anhydrous lithium hydroxide, lithium oxide, lithium carbonate, or lithium nitrate. For example, typical but non-limiting combination examples include the combination of lithium hydroxide monohydrate and anhydrous lithium hydroxide, the combination of lithium hydroxide monohydrate and lithium oxide, the combination of lithium hydroxide monohydrate and lithium carbonate, the combination of lithium hydroxide monohydrate and lithium nitrate, the combination of lithium oxide and lithium carbonate, or the combination of lithium nitrate and lithium carbonate, etc.

[0016] Preferably, the iron source includes nano-iron oxide.

[0017] Preferably, the particle size D of the nano iron oxide 50 is 0.02 - 1 μm, such as 0.02 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm, etc.

[0018] Preferably, the amounts of the lithium source and the iron source are controlled such that the molar ratio of the lithium element in the lithium source to the iron element in the iron source is (5 - 5.6):1, such as 5:1, 5.1:1, 5.2:1, 5.3:1, 5.4:1, 5.5:1 or 5.6:1, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0019] As a preferred technical solution of the present invention, the method for preparing the lithium - rich lithium ferrate further includes solid - phase mixing of an additive with the lithium source and the iron source to dope the obtained lithium - rich lithium ferrate.

[0020] The present invention preferably forms Li - site defects by metal cation doping to anchor lattice oxygen, further improving air stability and ionic conductivity.

[0021] Preferably, the additive includes at least one of zirconia, alumina, tungsten oxide, titanium oxide or magnesia. For example, typical but non - restrictive combination examples include the combination of zirconia and alumina, the combination of zirconia and tungsten oxide, the combination of alumina and titanium oxide, the combination of alumina and magnesia, the combination of tungsten oxide and titanium oxide, etc.

[0022] Preferably, the amount of the additive accounts for 0.1% - 1.2% of the mass of the lithium - rich lithium ferrate theoretically generated from the lithium source and the iron source, such as 0.1%, 0.3%, 0.5%, 0.8%, 0.9%, 1%, 1.1% or 1.2%, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0023] As a preferred technical solution of the present invention, the temperature of the pre - calcination is 400 - 550 °C, such as 400 °C, 430 °C, 440 °C, 450 °C, 480 °C, 500 °C, 520 °C or 550 °C, etc., and the time is 5 - 40 h, such as 5 h, 8 h, 10 h, 12 h, 15 h, 18 h, 20 h, 23 h, 25 h, 28 h, 30 h, 33 h, 35 h, 38 h or 40 h, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0024] As a preferred technical solution of the present invention, the sintering temperature is 700-850°C, such as 700°C, 720°C, 750°C, 780°C, 800°C, 830°C or 850°C, etc., and the time is 5-15h, such as 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h or 15h, etc. However, it is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0025] As a preferred technical solution of the present invention, the amount of the solid electrolyte is a, and a accounts for 0.3%-2% of the mass of the lithium-rich lithium ferrite, such as 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2%, etc. Preferably, it is 0.3%-1.4%, and more preferably 0.5%-1%. However, it is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0026] Preferably, the amount of the conductive carbon is b, and b accounts for 1%-2.5% of the mass of the lithium-rich lithium ferrite, such as 1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.%, 2.2%, 2.3%, 2.4% or 2.5%, etc. Preferably, it is 1.2%-2.1%, and more preferably 1.3%-1.7%. However, it is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0027] Preferably, the amount of the elemental sulfur is c, and c accounts for 1%-10% of the mass of the lithium-rich lithium ferrite, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc. Preferably, it is 2%-8.5%, and more preferably 3%-7%. However, it is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0028] Preferably, the amount a of the solid electrolyte, the amount b of the conductive carbon and the amount c of the elemental sulfur satisfy 1≤c / b≤5 and 3≤c / a≤10.

[0029] In this application, if c / b > 5 and / or c / a > 10, the sulfur content is too high, while the content of the solid electrolyte and / or conductive carbon is too low, making it impossible to form an effective ionic and electronic conductive network in elemental sulfur, which affects the lithium-ion insertion and extraction. If c / b < 1 and / or c / a < 3, the sulfur content is too low, while the content of the solid electrolyte and / or conductive carbon is too high, which not only affects the effect of low-temperature coating, but also results in insufficient adhesion and dispersion provided by molten elemental sulfur. At the same time, the formed mixed coating layer cannot effectively improve the gas generation problem, and the excessive content of the solid electrolyte and / or conductive carbon will also lead to a decrease in the lithium compensation capacity and an increase in cost.

[0030] It should also be noted that, compared with lithium-rich lithium ferrite, the total amount of the solid electrolyte, conductive carbon and elemental sulfur will also affect the thickness of the mixed coating layer. The thickness of the mixed coating layer should be at least 5 nm to ensure uniform wrapping, and the capacity attenuation caused by too thick coating should also be avoided.

[0031] As a preferred technical solution of the present invention, the temperature of the low-temperature heat treatment is 110~130 °C, such as 110 °C, 113 °C, 115 °C, 118 °C, 120 °C, 123 °C, 125 °C, 128 °C or 130 °C, etc., and the time is 1~3 h, such as 1 h, 1.3 h, 1.5 h, 1.8 h, 2 h, 2.2 h, 2.5 h, 2.8 h or 3 h, etc., but it is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0032] In the second aspect, the present invention provides a lithium-rich lithium ferrite lithium compensator, which is obtained according to the synthesis method described in the first aspect.

[0033] In the third aspect, the present invention provides a battery, which contains the lithium-rich lithium ferrite lithium compensator described in the second aspect.

[0034] It should be noted that the lithium-rich lithium ferrite lithium compensator of the present invention is applicable to the existing tablet manufacturing and battery assembly processes without additional process improvement.

[0035] Compared with the existing technical solutions, the present invention has at least the following beneficial effects:

[0036] Mix the solid electrolyte, conductive carbon and elemental sulfur, and perform low-temperature heat treatment to form a composite mixture, and then perform secondary mixing and low-temperature heat treatment with lithium-rich lithium ferrite to form a mixed coating layer on the composite mixture, thereby obtaining a lithium-rich lithium ferrite lithium compensator. By adding sulfur to the mixed coating layer, the present invention absorbs the surface oxygen released during the charging process of lithium-rich lithium ferrite, thereby reducing gas generation; by adding a solid electrolyte and conductive carbon, an ionic and electronic conductive network is formed in the sulfur-based mixed coating layer, avoiding Li caused by too thick sulfur coating. +The adverse effects of difficult extraction and decreased lithium supplementation capacity. At the same time, the molten elemental sulfur in the two low-temperature heat treatments can play a role in dispersion and adhesion, achieving uniform dispersion of the solid electrolyte and conductive carbon and effective coating of the composite mixture, and is beneficial to improving the binding property and compatibility. The mixed coating layer obtained by the mutual cooperation of the three components can effectively improve the air stability of the lithium supplement agent. Brief Description of the Drawings

[0037] Figure 1 It is a schematic structural diagram of the lithium-rich lithium iron ferrite lithium supplement agent obtained in Example 1. Detailed Embodiments

[0038] The technical solutions of the present invention will be further described below through specific embodiments.

[0039] Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0040] Example 1

[0041] This example provides a synthesis method of a lithium-rich lithium iron ferrite lithium supplement agent, and the synthesis method includes:

[0042] Solid-phase mixing of the lithium source lithium hydroxide anhydrous, the iron source nano-iron oxide, and the additive zirconia, controlling the usage amounts of the lithium source and the iron source according to the molar ratio of lithium element in the lithium source to iron element in the iron source being 5.2:1, and the usage amount of the additive accounting for 0.4% of the mass of the lithium-rich lithium iron ferrite theoretically generated by the lithium source and the iron source. Pre-burning the obtained solid-phase mixture at 470 °C for 20 h, and then sintering at 810 °C for 7 h to obtain lithium-rich lithium iron ferrite doped with zirconium element; pulverizing the obtained lithium-rich lithium iron ferrite, and then first solid-phase mixing 0.7% of the solid electrolyte LATP by mass of the lithium-rich lithium iron ferrite, 1.5% of the conductive carbon SP (conductive carbon black) by mass of the lithium-rich lithium iron ferrite, and 3% of the elemental sulfur by mass of the lithium-rich lithium iron ferrite, and then performing low-temperature heat treatment at 120 °C in a rotary kiln for 2 h, cooling to form a composite mixture, and then adding lithium-rich lithium iron ferrite for secondary solid-phase mixing. After the mixing is completed, the obtained solid-phase mixture is placed in a rotary kiln and then subjected to secondary low-temperature heat treatment at 120 °C for 2 h. The temperatures of the low-temperature heat treatment and the secondary low-temperature heat treatment can make the elemental sulfur melt to bond the solid electrolyte and the conductive carbon, and jointly (i.e., the composite mixture) form a mixed coating layer on the outer surface of the lithium-rich lithium iron ferrite to obtain a lithium-rich lithium iron ferrite lithium supplement agent.

[0043] Figure 1It is a schematic structural diagram of the lithium-rich lithium iron phosphate lithium supplement obtained in Example 1. In the obtained lithium-rich lithium iron phosphate lithium supplement, lithium-rich lithium iron phosphate serves as the matrix of the core, and its surface is coated with a mixed coating layer. In the mixed coating layer, elemental sulfur with a relatively higher content serves as the matrix, and a relatively lower content of solid electrolyte and conductive carbon are uniformly dispersed in the elemental sulfur. The solid electrolyte and conductive carbon respectively form an ion conductive network and an electron conductive network, and jointly form a composite coating network in the elemental sulfur matrix to form a uniform mixed coating layer.

[0044] Example 2

[0045] This example provides a synthesis method of a lithium-rich lithium iron phosphate lithium supplement. In the synthesis method, the dosage of elemental sulfur is adjusted from 3% of the mass of the lithium-rich lithium iron phosphate to 0.5%. Except for the above, other conditions are exactly the same as those in Example 1.

[0046] Example 3

[0047] This example provides a synthesis method of a lithium-rich lithium iron phosphate lithium supplement. In the synthesis method, the dosage of elemental sulfur is adjusted from 3% of the mass of the lithium-rich lithium iron phosphate to 1%. Except for the above, other conditions are exactly the same as those in Example 1.

[0048] Example 4

[0049] This example provides a synthesis method of a lithium-rich lithium iron phosphate lithium supplement. In the synthesis method, the dosage of elemental sulfur is adjusted from 3% of the mass of the lithium-rich lithium iron phosphate to 5%. Except for the above, other conditions are exactly the same as those in Example 1.

[0050] Example 5

[0051] This example provides a synthesis method of a lithium-rich lithium iron phosphate lithium supplement. In the synthesis method, the dosage of elemental sulfur is adjusted from 3% of the mass of the lithium-rich lithium iron phosphate to 7%. Except for the above, other conditions are exactly the same as those in Example 1.

[0052] Example 6

[0053] This example provides a synthesis method of a lithium-rich lithium iron phosphate lithium supplement. In the synthesis method, the dosage of elemental sulfur is adjusted from 3% of the mass of the lithium-rich lithium iron phosphate to 10%. Except for the above, other conditions are exactly the same as those in Example 1.

[0054] Example 7

[0055] This example provides a synthesis method of a lithium-rich lithium iron phosphate lithium supplement. In the synthesis method, the dosage of elemental sulfur is adjusted from 3% of the mass of the lithium-rich lithium iron phosphate to 13%. Except for the above, other conditions are exactly the same as those in Example 1.

[0056] Example 8

[0057] This embodiment provides a method for synthesizing a lithium-rich lithium iron phosphate lithium supplement. In this synthesis method, the dosage of the solid electrolyte is adjusted from 0.7% of the mass of the lithium-rich lithium iron phosphate to 0.1%. Except for this, other conditions are exactly the same as those in Embodiment 1.

[0058] Example 9

[0059] This embodiment provides a method for synthesizing a lithium-rich lithium iron phosphate lithium supplement. In this synthesis method, the dosage of the solid electrolyte is adjusted from 0.7% of the mass of the lithium-rich lithium iron phosphate to 0.3%. Except for this, other conditions are exactly the same as those in Embodiment 1.

[0060] Example 10

[0061] This embodiment provides a method for synthesizing a lithium-rich lithium iron phosphate lithium supplement. In this synthesis method, the dosage of the solid electrolyte is adjusted from 0.7% of the mass of the lithium-rich lithium iron phosphate to 1.4%. Except for this, other conditions are exactly the same as those in Embodiment 1.

[0062] Example 11

[0063] This embodiment provides a method for synthesizing a lithium-rich lithium iron phosphate lithium supplement. In this synthesis method, the dosage of the solid electrolyte is adjusted from 0.7% of the mass of the lithium-rich lithium iron phosphate to 2%. Except for this, other conditions are exactly the same as those in Embodiment 1.

[0064] Example 12

[0065] This embodiment provides a method for synthesizing a lithium-rich lithium iron phosphate lithium supplement. In this synthesis method, the dosage of the solid electrolyte is adjusted from 0.7% of the mass of the lithium-rich lithium iron phosphate to 2.3%. Except for this, other conditions are exactly the same as those in Embodiment 1.

[0066] Example 13

[0067] This embodiment provides a method for synthesizing a lithium-rich lithium iron phosphate lithium supplement. In this synthesis method, the dosage of the conductive carbon is adjusted from 1.5% of the mass of the lithium-rich lithium iron phosphate to 0.5%. Except for this, other conditions are exactly the same as those in Embodiment 1.

[0068] Example 14

[0069] This embodiment provides a method for synthesizing a lithium-rich lithium iron phosphate lithium supplement. In this synthesis method, the dosage of the conductive carbon is adjusted from 1.5% of the mass of the lithium-rich lithium iron phosphate to 1%. Except for this, other conditions are exactly the same as those in Embodiment 1.

[0070] Example 15

[0071] This embodiment provides a method for synthesizing a lithium-rich lithium ferrate lithium supplement. In this synthesis method, the dosage of conductive carbon is adjusted from 1.5% of the mass of the lithium-rich lithium ferrate to 2%. Except for the above, other conditions are exactly the same as those in Example 1.

[0072] Example 16

[0073] This embodiment provides a method for synthesizing a lithium-rich lithium ferrate lithium supplement. In this synthesis method, the dosage of conductive carbon is adjusted from 1.5% of the mass of the lithium-rich lithium ferrate to 2.5%. Except for the above, other conditions are exactly the same as those in Example 1.

[0074] Example 17

[0075] This embodiment provides a method for synthesizing a lithium-rich lithium ferrate lithium supplement. In this synthesis method, the dosage of conductive carbon is adjusted from 1.5% of the mass of the lithium-rich lithium ferrate to 3%. Except for the above, other conditions are exactly the same as those in Example 1.

[0076] Example 18

[0077] This embodiment provides a method for synthesizing a lithium-rich lithium ferrate lithium supplement. In this synthesis method, the temperature of low-temperature heat treatment is adjusted from 120 °C to 100 °C. Except for the above, other conditions are exactly the same as those in Example 1.

[0078] Example 19

[0079] This embodiment provides a method for synthesizing a lithium-rich lithium ferrate lithium supplement. In this synthesis method, the temperature of low-temperature heat treatment is adjusted from 120 °C to 110 °C. Except for the above, other conditions are exactly the same as those in Example 1.

[0080] Example 20

[0081] This embodiment provides a method for synthesizing a lithium-rich lithium ferrate lithium supplement. In this synthesis method, the temperature of low-temperature heat treatment is adjusted from 120 °C to 130 °C. Except for the above, other conditions are exactly the same as those in Example 1.

[0082] Example 21

[0083] This embodiment provides a method for synthesizing a lithium-rich lithium ferrate lithium supplement. In this synthesis method, the temperature of low-temperature heat treatment is adjusted from 120 °C to 160 °C. Except for the above, other conditions are exactly the same as those in Example 1.

[0084] Example 22

[0085] This embodiment provides a method for synthesizing a lithium-rich lithium ferrate lithium supplement. In this synthesis method, the additive is not used. Except for the above, other conditions are exactly the same as those in Example 1.

[0086] Comparative Example 1

[0087] This comparative example provides a method for synthesizing a lithium-rich lithium ferrate lithium supplement. The synthesis method does not use the elemental sulfur. Except for the above, other conditions are exactly the same as those in Example 1.

[0088] Comparative Example 2

[0089] This comparative example provides a method for synthesizing a lithium-rich lithium ferrate lithium supplement. The synthesis method does not use the solid electrolyte. Except for the above, other conditions are exactly the same as those in Example 1.

[0090] Comparative Example 3

[0091] This comparative example provides a method for synthesizing a lithium-rich lithium ferrate lithium supplement. The synthesis method does not use the conductive carbon. Except for the above, other conditions are exactly the same as those in Example 1.

[0092] Comparative Example 4

[0093] This comparative example provides a method for synthesizing a lithium-rich lithium ferrate lithium supplement. The synthesis method does not use the solid electrolyte and the conductive carbon. Except for the above, other conditions are exactly the same as those in Example 1.

[0094] Characterization and testing:

[0095] Ⅰ. The lithium-rich lithium ferrate lithium supplement obtained in the examples and comparative examples is used as the cathode material to form a cathode sheet, and then an assembled button cell is subjected to a charging test.

[0096] Ⅱ. Record the mass of the active material of the fully charged button electrode sheet, inject the electrolyte according to the injection coefficient of 3.5 g / Ah, encapsulate it with an aluminum-plastic bag, and then store it at 60 °C, and record the gas production after 7 days of storage.

[0097] Ⅲ. Perform a transmission electron microscope test on the sample and record the thickness of the coating layer.

[0098] The above results are shown in Table 1.

[0099]

[0100] It can be seen from Table 1 that:

[0101] When the content and ratio of the elemental sulfur, solid electrolyte, and conductive carbon and the process conditions of the synthesis method are all relatively appropriate, the obtained lithium-rich lithium ferrate lithium supplement can balance the capacity performance and air stability, and the gas production after 7 days of storage at 60 °C is all < 5 mL / Ah, and further can be less than < 3 mL / Ah, and the lowest can be as low as < 1.5 mL / Ah.

[0102] Compared with Example 1, in Example 2, due to the too low dosage of elemental sulfur, the uniformity of the mixed coating layer formed by low-temperature coating was affected, resulting in a decrease in the capacity of the obtained lithium supplement agent. At the same time, due to the low content of elemental sulfur in the mixed coating layer, its gas production during storage was relatively high; in Example 7, due to the too high content of elemental sulfur, both c / a and c / b were relatively large, resulting in the inability to form an effective ion and electron conductive network of the solid electrolyte and conductive carbon in the coating layer based on elemental sulfur, with a low capacity. At the same time, although the total coating amount was relatively high, the amount of Li released during charging was small. Therefore, the content of residual lithium in the electrode plate after charging was relatively high, and it was unstable during storage, instead causing an increase in gas production.

[0103] Compared with Example 1, in Example 8, due to the too low content of the solid electrolyte, the ionic conductivity was affected, resulting in a decrease in the charging specific capacity, and further causing an increase in gas production; in Examples 11 and 12, due to the too high content of the solid electrolyte, the c / a value was relatively low. Since the solid electrolyte itself did not have electrochemical activity, it caused a decrease in capacity, and further caused an increase in gas production.

[0104] Compared with Example 1, in Example 13, due to the too low content of conductive carbon, the electronic conductivity was affected, resulting in a decrease in the charging specific capacity, and further causing an increase in gas production; in Example 17, due to the too high content of SP, the c / b value was too low. Since the conductive carbon itself did not have electrochemical activity, it caused a decrease in capacity, and further caused an increase in gas production.

[0105] Compared with Example 1, in Example 18, due to the too low heat treatment temperature, the elemental sulfur could not melt, resulting in a very poor coating effect, an extremely low capacity, and a relatively high gas production at the same time; in Example 21, due to the too high treatment temperature of elemental sulfur, it was easy to have side reactions with oxygen, resulting in the loss of elemental sulfur and affecting the performance capacity and gas production. Therefore, for elemental sulfur with a melting point of 112.8 °C under standard conditions, the temperatures of the low-temperature heat treatment and the secondary low-temperature heat treatment described in the present invention are preferably from 110 to 130 °C, and more preferably from 118 to 126 °C.

[0106] In Example 22, due to the lack of doping, to a certain extent, the ionic conductivity and air stability of the material were reduced, resulting in a decrease in capacity and an increase in gas production; in Comparative Example 1, due to the lack of elemental sulfur coating, the gas production increased sharply, which was the highest among all examples and comparative examples. In Comparative Examples 2, 3, and 4, due to the lack of addition of solid electrolyte and / or conductive carbon, the capacity decreased significantly, and it also caused an increase in gas production.

[0107] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0108] In addition, it should be noted that, for each of the specific technical features described in the above specific embodiments, they can be combined in any appropriate manner without conflict. To avoid unnecessary repetition, the present invention will not separately describe various possible combination manners.

[0109] In addition, any combinations can be made among various different embodiments of the present invention, as long as they do not violate the idea of the present invention, and they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for synthesizing a lithium-rich lithium ferrite lithium supplement, characterized in that, The synthesis method includes: Mixing a solid electrolyte, conductive carbon, and elemental sulfur, wherein the dosage of the solid electrolyte is a, the dosage of the conductive carbon is b, and the dosage of the elemental sulfur is c, 1 ≤ c / b ≤ 5, 3 ≤ c / a ≤ 10, and performing low-temperature heat treatment. The temperature of the low-temperature heat treatment melts the elemental sulfur to bond the solid electrolyte and the conductive carbon to form a composite mixture based on elemental sulfur. Then, the composite mixture is secondarily mixed and secondarily heat-treated at low temperature with lithium-rich lithium ferrite to form a mixed coating layer on the surface of the lithium-rich lithium ferrite, obtaining a lithium-rich lithium ferrite lithium supplement agent.

2. The synthesis method of the lithium-rich lithium ferrite lithium supplement agent according to claim 1, wherein The method for preparing the lithium-rich lithium ferrite includes: solid-phase mixing a lithium source and an iron source, and then performing pre-sintering and sintering in sequence to obtain the lithium-rich lithium ferrite.

3. The synthesis method of the lithium-rich lithium iron oxide lithium supplement according to claim 2, characterized in that, The lithium source includes at least one of lithium hydroxide monohydrate, anhydrous lithium hydroxide, lithium oxide, lithium carbonate, or lithium nitrate; The iron source includes nano iron oxide with a particle size D 50 of 0.02 to 1 μm; The dosages of the lithium source and the iron source are controlled such that the molar ratio of lithium element in the lithium source to iron element in the iron source is (5 - 5.6):

1.

4. The synthesis method of the lithium-rich lithium iron ferrite lithium supplement agent according to claim 2, characterized in that The method for preparing the lithium-rich lithium ferrite further includes solid-phase mixing an additive with the lithium source and the iron source to dope the obtained lithium-rich lithium ferrite; The additive includes at least one of zirconia, alumina, tungsten oxide, titanium oxide, or magnesia; The dosage of the additive accounts for 0.1% - 1.2% of the mass of the lithium-rich lithium ferrite theoretically generated from the lithium source and the iron source.

5. The synthesis method of the lithium-rich lithium ferrite lithium supplement agent according to claim 2, characterized in that, The temperature of the pre-sintering is 400 - 550 °C, and the time is 5 - 40 h; The temperature of the sintering is 700 - 850 °C, and the time is 5 - 15 h.

6. The synthesis method of the lithium-rich lithium ferrite lithium supplement agent according to claim 2, characterized in that The dosage of the solid electrolyte is a, and a accounts for 0.3% - 2% of the mass of the lithium-rich lithium ferrite; The dosage of the conductive carbon is b, and b accounts for 1% - 2.5% of the mass of the lithium-rich lithium ferrite; The dosage of the elemental sulfur is c, and c accounts for 1% - 10% of the mass of the lithium-rich lithium ferrite.

7. The synthesis method of the lithium-rich lithium iron ferrite lithium supplement agent according to claim 6, characterized in that The thickness of the mixed coating layer is 5 - 20 nm.

8. The synthesis method of the lithium-rich lithium iron ferrite lithium supplement agent according to claim 1 or 2, characterized in that, The temperature of the low-temperature heat treatment is 110 - 130 °C, and the time is 1 - 3 h.

9. A lithium-rich lithium iron phosphate lithium supplement, characterized in that, The lithium-rich lithium ferrite lithium supplement agent is obtained according to the synthesis method described in any one of claims 1 - 8.

10. A battery, characterized in that, The battery contains the lithium-rich lithium ferrite lithium supplement agent described in any one of claims 1 - 9.

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