Organic lithium supplement agent and preparation method thereof, positive electrode material and secondary battery

Abstract

The invention relates to an organic lithium supplement agent and a preparation method thereof, a positive electrode material and a secondary battery, the organic lithium supplement agent comprises a main chain, a first lithium-containing group and a second lithium-containing group, the main chain is a straight chain, the general formula of the main chain is as follows: X2-[Y] m-X1, Y is a repetitive unit, X1 and X2 are end groups connected to the main chain, and m is more than or equal to 10 and less than or equal to 500; the main chain has a grafting point, the first lithium-containing group and the second lithium-containing group are connected to the grafting point, and the lithium release potential of the first lithium-containing group is greater than that of the second lithium-containing group; a molecular chain structure of the organic lithium supplement agent contains a first lithium-containing group and a second lithium-containing group, the lithium release potentials of the first lithium-containing group and the second lithium-containing group are different, and the lithium release potentials of the first lithium-containing group and the second lithium-containing group are different through the combination of the first lithium-containing group and the second lithium-containing group by utilizing the potential difference and structural characteristics of the first lithium-containing group and the second lithium-containing group in different charging and discharging stages. And a collaborative lithium supplement effect is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and particularly relates to an organic lithium supplement agent, a preparation method thereof, a cathode material, and a secondary battery. Background Art

[0002] During the first charge and discharge of a lithium-ion battery, the lithium ions released from the cathode material react with the electrolyte, and a solid electrolyte interface film (SEI) will be formed on the surface of the anode material. This process will irreversibly consume more than 10% of the lithium source in the cathode material, resulting in the Coulombic efficiency of the lithium-ion battery in the first cycle being lower than 90%, and the active lithium in the cathode will also be continuously consumed during the charge and discharge cycles of the lithium-ion battery, leading to a shortened life of the lithium-ion battery.

[0003] In response to this phenomenon, the current solution is to add an appropriate lithium supplement material to the cathode active material, and the active lithium released by the decomposition of the lithium supplement material during the battery charging process is used to reduce the lithium loss during the cycle. Traditional lithium supplement methods mainly focus on lithium supplementation in the first cycle, that is, supplementing the active lithium lost due to the formation of the SEI film during the first charge and discharge of the battery. This means that the organic lithium supplement agent only has a single lithium supplementation effect on the battery. However, this method has some limitations. For example, it cannot effectively supplement the active lithium lost due to side reactions in subsequent cycles, resulting in limited cycle life of the battery. Since the battery will still have active lithium loss during subsequent cycles, the organic lithium supplement agent in the prior art cannot continue to supplement lithium to the battery, resulting in a decrease in the cycle stability of the battery in the prior art. Therefore, how to solve the lithium loss during the cyclic use of existing secondary batteries and achieve continuous lithium supplementation has become the key. Summary of the Invention

[0004] The object of the present invention is to provide an organic lithium supplement agent, a preparation method thereof, a cathode material, and a secondary battery, so as to solve the problem that the existing organic lithium supplement agent cannot supplement lithium during the battery cycle.

[0005] To achieve the object of the present invention, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides an organic lithium supplement agent, which includes a main chain, a first lithium-containing group, and a second lithium-containing group. The main chain is a straight chain, and the general formula of the main chain includes: X2-[Y] m -X1, where Y is a repeating unit, and both X1 and X2 are end groups connected to the main chain, 10 ≤ m ≤ 500; there are grafting sites on the main chain, and the first lithium-containing group and the second lithium-containing group are connected to the grafting sites, and the lithium release potential of the first lithium-containing group is greater than the lithium release potential of the second lithium-containing group.

[0007] In one embodiment, the lithium release potential U1 of the first lithium-containing group and the lithium release potential U2 of the second lithium-containing group satisfy: U1 - U2 ≥ 0.3V.

[0008] In one embodiment, on the molecular chain of the organic lithium supplement, the grafting density ρ2 of the second lithium-containing group and the grafting density ρ1 of the first lithium-containing group satisfy: ρ2 ≥ ρ1.

[0009] In one embodiment, the organic lithium supplement includes a first alkylene chain segment and a second alkylene chain segment, the first alkylene chain segment and the second alkylene chain segment are different, the first alkylene chain segment is located in the repeating unit, the second alkylene chain segment is located in the side chain connected to the main chain, and the first lithium-containing group and / or the second lithium-containing group are connected to the second alkylene chain segment.

[0010] In one embodiment, Y includes -(CH2) n -O-, -(CH2) n -COO-, -(CH2) n -NH-, -(CH2) n -S- or one or more of them, where 1 ≤ n ≤ 4, X1 or X2 includes one or more of -CH3, -CF3, -OH, -NH2; there are multiple grafting sites on the main chain, and there are k repeating units between adjacent two grafting sites, where 1 ≤ k ≤ 5.

[0011] In one embodiment, the first lithium-containing group includes one or more of -COOLi, -SO3Li, -PO4Li2, -BLi, -NO2Li.

[0012] In one embodiment, the second lithium-containing group includes one or more of -OLi, -NHLi, -SiOLi.

[0013] In one embodiment, the grafting density ratio of the first lithium-containing group and the second lithium-containing group is 1:(1 - 5).

[0014] In one embodiment, the polymer precursor of the organic lithium supplement includes one or more of olefin polymers, polyether polymers, polyacrylonitrile polymers, organosilicon polymers.

[0015] In one embodiment, the molecular weight of the organic lithium supplement is 2000 - 5000.

[0016] In one embodiment, the particle size D50 of the organic lithium supplement is 10μm - 15μm.

[0017] In one embodiment, the particle size D100 of the organic lithium supplement is 1 nm to 25 μm.

[0018] In one embodiment, the tap density of the organic lithium supplement is 2 g / cm 3 ~3.5 g / cm 3 .

[0019] In a second aspect, the present invention provides a method for preparing an organic lithium supplement for preparing the organic lithium supplement according to any one of the embodiments in the first aspect. The preparation method includes: dissolving a polymer precursor in a first solvent, adding a first lithium-containing precursor in the first solvent, and obtaining a first organic lithium supplement after reaction. The first organic lithium supplement includes a first lithium-containing group; dissolving the first organic lithium supplement in a second solvent, adding a second lithium-containing precursor in the second solvent, and obtaining a second organic lithium supplement after reaction. The second organic lithium supplement includes the first lithium-containing group and the second lithium-containing group.

[0020] In a third aspect, the present invention provides a positive electrode material. The positive electrode material includes an active material and the organic lithium supplement according to any one of the embodiments in the first aspect, or the positive electrode material includes an organic lithium supplement obtained by the preparation method of the organic lithium supplement according to the second aspect.

[0021] In a fourth aspect, the present invention provides a secondary battery. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode and the negative electrode are disposed in the electrolyte, and the positive electrode includes the positive electrode material according to the third aspect.

[0022] The present invention provides an organic lithium supplement. The molecular chain structure thereof contains a first lithium-containing group and a second lithium-containing group, and the lithium release potentials of the first lithium-containing group and the second lithium-containing group are different. By combining the first lithium-containing group and the second lithium-containing group, a polarization voltage difference exists in the organic lithium supplement. The polarization voltage difference is the actual lithium release potential difference between different lithium-containing groups. Utilizing its potential difference and structural characteristics at different charge and discharge stages, a synergistic lithium supplement effect is achieved; when the battery is first charged and discharged, the second lithium-containing group with a low potential preferentially contributes lithium ions, and can quickly supplement lithium ions by de-lithiation of the second lithium-containing group, thereby improving the first Coulomb efficiency; in subsequent cycles, the second lithium-containing group can also induce the first lithium-containing group to de-lithiate, so as to reduce the lithium release potential of the first lithium-containing group, and continuously and stably release lithium by relying on the first lithium-containing group to maintain the active lithium content, significantly extending the battery cycle life; at the same time, the synergistic effect between functional groups optimizes lithium ion transport, enhances the rate performance, and improves the chemical stability in the electrolyte. Description of the Drawings

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0024] Figure 1 It is a flowchart of the preparation method of an organic lithium supplement agent of an embodiment;

[0025] Figure 2 It is a flowchart of the preparation method of an organic lithium supplement agent with a polyetheramine as the polymer precursor of an embodiment;

[0026] Figure 3 It is a flowchart of the preparation method of an organic lithium supplement agent with polyacrylonitrile as the polymer precursor of an embodiment;

[0027] Figure 4 It is a scanning electron microscope image of the organic lithium supplement agent of Example 1;

[0028] Figure 5 It is a charge curve graph of the battery made in Example 1;

[0029] Figure 6 It is a charge curve graph of the battery made in Example 3;

[0030] Figure 7 It is a charge curve graph of the battery made in Comparative Example 1;

[0031] Figure 8 It is an infrared spectrum of Example 1. Specific Embodiments

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0033] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used in the present invention in the specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used in the present invention includes any and all combinations of one or more of the related listed items.

[0034] It should be noted that the "range" disclosed in the present invention is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The range defined in this way can include or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, ranges of 60 to 110 and 80 to 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In the present invention, unless otherwise specified, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] All steps of the present invention can be carried out sequentially or randomly, and preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0036] The following will, with reference to the accompanying drawings, elaborate on some embodiments of the present invention. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0037] The present invention provides an organic lithium supplement.

[0038] In one embodiment, the organic lithium supplement includes a main chain, a first lithium-containing group, and a second lithium-containing group. The main chain is a straight chain, and the general formula of the main chain includes: X2-[Y] m-X1, where Y is a repeating unit, X1 and X2 are both end groups attached to the main chain, and 10 ≤ m ≤ 500; there are grafting sites on the main chain, and the first lithium-containing group and the second lithium-containing group are attached to the grafting sites. The lithium release potential of the first lithium-containing group is greater than that of the second lithium-containing group. It should be noted that in the technical solution provided by the present invention, the lithium release potentials of the first lithium-containing group and the second lithium-containing group are both referenced to the negative electrode potential in a button cell. In a button cell using metallic lithium as the negative electrode, its potential is defined as 0V.

[0039] In one embodiment, the organic lithium supplement is an organic polymer containing lithium ions, and the chemical formula of the organic lithium supplement is C a H b M c Li d , where M includes one or more of O, N, S, P, and B, 10 ≤ a ≤ 500, 20 ≤ b ≤ 2000, 2 ≤ c ≤ 200, and 2 ≤ d ≤ 200. It should be noted that the chemical formula of the above organic lithium supplement represents the elemental composition of the organic lithium supplement, not the specific molecular structure of the organic lithium supplement. The organic lithium supplement can be classified into linear polymers, branched polymers, three-dimensional polymers (network polymers), hyperbranched polymers, dendritic polymers, etc. according to the molecular structure. Lithium ions can be located at the ends (i.e., on the end groups) or in the middle (i.e., on the functional groups in the end groups) of the molecular structure.

[0040] In a specific embodiment, the organic lithium supplement can be a linear polymer and / or a branched polymer. It should be noted that the advantages of the organic lithium supplement having the above molecular structure include: 1) Stable structure. The atoms in the molecular chain are covalently bonded to form a very long chain, so the molecular stability of the chain structure is higher, and the thermal stability of the chain structure is better; 2) Flexible structure. The molecular chain can be curled, bent or helical, and the spatial distribution of functional groups can be adjusted by flexible design to avoid aggregation; 3) Facilitate transmission. The chain structure is similar to an ion channel, which is conducive to the rapid transmission of lithium ions along the molecular chain; 4) Good compatibility. The chain structure has elasticity and plasticity and can swell or dissolve in an appropriate organic solvent, so it can be compatible with the electrolyte.

[0041] In one embodiment, M includes one or more of O, N, S, P, and B, and 10 ≤ a ≤ 500, 20 ≤ b ≤ 2000, 2 ≤ c ≤ 200, and 2 ≤ d ≤ 200. It can be understood that there are various functional groups in the organic lithium supplement, including but not limited to hydrocarbon groups containing lithium ions (alkyl groups, alkenyl groups, phenyl groups), oxygen-containing functional groups containing lithium ions (hydroxyl groups, ether bonds, ester groups), nitrogen-containing functional groups containing lithium ions (amino groups, nitro groups, cyano groups), halogen-containing functional groups containing lithium ions (fluoro groups, chloro groups, iodo groups), and other functional groups containing lithium ions (sulfonic acid groups, phosphoric acid groups, silicon groups).

[0042] In a specific embodiment, the organic lithium supplement may include one or more of alkyl, ether bond, amino group, and silicon group. It should be noted that the advantages of the organic lithium supplement having the above functional groups include: 1) stable structure, saturated carbon chain or branched chain, not easily broken or chemically reacted; 2) flexible structure, higher rotational freedom, and the molecular chain is more likely to rotate and twist, thus increasing the flexibility of the molecule; 3) easy to process, capable of undergoing addition, neutralization, acylation, diazotization and other reactions, so as to load more lithium ions.

[0043] In one embodiment, the molecular chain of the organic lithium supplement includes a main chain and a branched chain, wherein the branched chain is connected to the main chain, and the branched chain includes a first lithium-containing group and a second lithium-containing group. The main chain includes a terminal group and a plurality of repeating units connected in sequence. The branched chain is connected to the repeating unit or the terminal group. Among them, the general formula of the main chain includes: X2-[Y] m -X1, Y is a repeating unit, and both X1 and X2 are terminal groups connected to the main chain, and 10 ≤ m ≤ 500. In a specific embodiment, m is the degree of polymerization of the organic lithium supplement, and m can be 10, 50, 100, 200, 300, 400, 500.

[0044] In one embodiment, the first lithium-containing group and the second lithium-containing group are lithium-containing functional groups modified by organic functional groups. The elemental compositions of the first lithium-containing group and the second lithium-containing group may be different, and the number of atoms may be different; the first lithium-containing group and the second lithium-containing group are connected to other groups by covalent bonds. It should be noted that the grafting site on the main chain can be understood as the chemical bond formed at the connection of two functional groups. Therefore, the first lithium-containing group and the second lithium-containing group can be directly connected to the grafting site or indirectly connected to the grafting site; the first lithium-containing group and the second lithium-containing group can be directly connected to the same grafting site, or the first lithium-containing group and the second lithium-containing group can be directly connected to two different grafting sites.

[0045] In a specific embodiment, both the first lithium-containing group and the second lithium-containing group are obtained by substituting hydrogen atoms in existing groups (functional groups) with lithium ions. It can be understood that the precursor of the organic lithium supplement is a polymer (or polymer monomer), hereinafter referred to as the polymer precursor; the polymer precursor includes various functional groups, and specific examples can refer to the above functional groups; in the present invention, lithium ions are used to substitute hydrogen atoms in functional groups to obtain lithium-containing groups, and due to the different functional groups substituted by lithium ions, different first lithium-containing groups and second lithium-containing groups are formed.

[0046] In one embodiment, the lithium release potential of the first lithium-containing group is greater than that of the second lithium-containing group; specifically, the lithium release potential of the lithium-containing group refers to the voltage plateau at which lithium ions are deintercalated from the organic lithium supplement. Therefore, the first lithium-containing group can release lithium ions at a higher voltage plateau, and the second lithium-containing group releases lithium ions at a lower voltage plateau. Through the design of the potential difference between lithium release at high potential and lithium release at low potential, the division of labor and cooperation between the first lithium supplementation and the cyclic lithium supplementation are realized.

[0047] It should be noted that the organic lithium supplement provided by the present invention is a chain-like organic lithium supplement, and both the first lithium-containing group and the second lithium-containing group are branched-chain structures connected to the main chain. In terms of molecular structure, the chain-like organic lithium supplement is more conducive to ion and electron transport, and the chain-like organic lithium supplement has greater flexibility and can curl, thereby adjusting the particle size of the product. It can be understood that in the existing cyclic organic lithium supplements, due to the conjugated π bonds on the cyclic carbon chain, the steric hindrance of the molecular structure is large, which is not only not conducive to ion and electron transport, but also the molecular structure is too rigid to curl, resulting in difficulty in adjusting the particle size of the product. In addition, from the perspective of lithium supplementation capacity, in the existing cyclic organic lithium supplements, functional groups can only be grafted at limited positions (such as ortho and para positions) on the ring, resulting in a low grafting density of the organic lithium supplement, and the cyclic carbon chains are closely packed, and it is easy to form a crystalline region after grafting; while the chain-like organic lithium supplement provided by the present invention has more grafting sites, the grafting density of the lithium-containing group is greater, the chain-like carbon chains are not easily stacked, and it is not easy to form a crystalline region after grafting.

[0048] The present invention provides an organic lithium supplement, the molecular chain structure of which contains a first lithium-containing group and a second lithium-containing group, and the lithium release potentials of the first lithium-containing group and the second lithium-containing group are different. Through the combination of the first lithium-containing group and the second lithium-containing group, a polarization voltage difference exists in the organic lithium supplement. The polarization voltage difference is the actual lithium release potential difference between different lithium-containing groups. By using its potential difference and structural characteristics at different charge and discharge stages, the synergistic lithium supplementation effect is realized; when the organic lithium supplement is first charged and discharged in the battery, the second lithium-containing group with a low potential preferentially contributes lithium ions, and can quickly supplement lithium ions by deintercalating lithium from the second lithium-containing group, thereby improving the first Coulomb efficiency; in subsequent cycles, the second lithium-containing group can also induce the first lithium-containing group to deintercalate lithium, so as to reduce the lithium release potential of the first lithium-containing group, and continuously and stably release lithium by relying on the first lithium-containing group to maintain the active lithium content, significantly extending the battery cycle life; at the same time, the synergistic effect between functional groups optimizes lithium ion transport, enhances the rate performance, and improves the chemical stability in the electrolyte.

[0049] In one embodiment, the first lithium-containing group includes one or more of -COOLi, -SO3Li, -PO4Li2, -BLi, -NO2Li. Specifically, the lithium release potentials of the above groups are as follows: lithium carboxylate (-COOLi) = 3.8 V, lithium sulfonate (-SO3Li) = 4.0 V, lithium phosphate (-PO4Li2) = 3.6 - 3.8 V; lithium borate (-BLi) = 3.5 - 3.7 V; lithium nitrite (-NO2Li) = 3.8 - 4.2 V.

[0050] In one embodiment, the second lithium-containing group includes one or more of -OLi, -NHLi, -SiOLi. Specifically, the lithium release potentials of the above groups are as follows: alkoxide (-OLi) = 3.5 V; lithium amide (-NHLi) < 3.0 V; lithium-containing silicon group (-SiOLi) = 2.5 - 3.0 V.

[0051] In a specific embodiment, the first lithium-containing group can be lithium carboxylate (-COOLi), and the second lithium-containing group can be alkoxide (-OLi). Among them, the organic lithium supplement has a first stretching vibration absorption peak at 1550 cm -1 ~1750 cm -1 (carboxylate C=O), and a second stretching vibration absorption peak at 1000 cm -1 ~1300 cm -1 (alkoxide C-O).

[0052] In one embodiment, the lithium release potential U1 of the first lithium-containing group and the lithium release potential U2 of the second lithium-containing group satisfy: U1 - U2 ≥ 0.3 V. Specifically, the first lithium-containing group and the second lithium-containing group can be two different groups provided in the above embodiments, and the lithium release potential difference between the first lithium-containing group and the second lithium-containing group needs to satisfy that it is greater than or equal to 0.3 V. Optionally, 3 V ≥ U1 - U2 ≥ 0.3 V. In a specific embodiment, U1 - U2 can be 0.3 V, 0.5 V, 0.7 V, 0.9 V, 1 V, 1.2 V, 1.4 V, 1.6 V, 1.8 V, 2 V, 2.2 V, 2.4 V, 2.6 V, 2.8 V, 3 V.

[0053] In one embodiment, on the molecular chain of the organic lithium supplement, the grafting density ρ2 of the second lithium-containing group and the grafting density ρ1 of the first lithium-containing group satisfy: ρ2 ≥ ρ1. Specifically, the grafting densities of the first lithium-containing group and the second lithium-containing group refer to that on the molecular chain of any organic lithium supplement, the content of the second lithium-containing group is greater than that of the first lithium-containing group. In a specific embodiment, the total amount of lithium-containing groups connected to the molecular chain of the organic lithium supplement is 100%, and the content (grafting density) of the second lithium-containing group can be 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%. By setting the grafting density of the second lithium-containing group to be greater than that of the first lithium-containing group, the present invention utilizes the fact that the second lithium-containing group can induce the first lithium-containing group to release lithium after partial lithium release, reduces the lithium release potential of the first lithium-containing group, and can utilize the flexible swelling of the organic lithium supplement to compensate for volume changes.

[0054] In one embodiment, at least part of the first lithium-containing group and / or the second lithium-containing group is located on the side chain. Specifically, the organic lithium supplement is a branched polymer as described above, including a main chain and side chains connected to the main chain, and the molecular chain of the organic lithium supplement is dendritic. Among them, on any polymer molecular chain of the organic lithium supplement, a plurality of first lithium-containing groups and a plurality of second lithium-containing groups are included, and at least part of the first lithium-containing group and / or the second lithium-containing group is located on the side chain.

[0055] In a specific embodiment, a plurality of side chains are connected to the main chain, and at least one first lithium-containing group and at least one second lithium-containing group are connected to each side chain. The molecular formula of the organic lithium supplement is as shown in the following (I); alternatively, a plurality of side chains are connected to the main chain, the first lithium-containing group is connected to one of the side chains, and the second lithium-containing group is connected to another of the side chains. The molecular formula of the lithium supplement is as shown in the following (II).

[0056]

[0057] Among them, R in (I) and (II) a is the main chain, and R b (including R b1 and R b2 ) is the side chain, R1Li is the first lithium-containing group, and R2Li is the second lithium-containing group. It should be noted that the main chain R a is a linear structure, and the side chain R b can be connected to any position of the main chain R a (such as the end or the middle); in (II), the side chain R b1 and the side chain R b2 do not need to be connected to the same atom (such as a carbon atom or a nitrogen atom), and the side chain R b1 and the side chain R b2 can be connected to the main chain Ra at different positions

[0058] In one embodiment, the first lithium-containing group and / or the second lithium-containing group are connected to the repeating unit, or the first lithium-containing group and / or the second lithium-containing group are connected to the end group. The polymer precursor of the organic lithium supplement includes a plurality of repeating units (i.e., organic monomers that make up the polymer chain structure). Through a modification reaction, lithium ions are bonded to the molecular chain to form an organic lithium supplement. Of course, the side chain can be a molecular structure originally included in the polymer precursor or a molecular structure grafted onto the polymer precursor through a modification reaction. It can be understood that there are two end groups on the main chain, and the two end groups are respectively located at the ends of the main chain to cap the sequentially connected repeating units.

[0059] In a specific embodiment, the side chain can be connected to the repeating unit, and the molecular formula of the organic lithium supplement is as shown in the following (III); or the side chain can be connected to the end group, and the molecular formula of the organic lithium supplement is as shown in the following (IV); of course, side chains can be simultaneously connected to both the repeating unit and the side chain, and the molecular formula of the organic lithium supplement is as shown in the following (V).

[0060]

[0061] Among them, R in (III), (IV), and (V) a1 is the repeating unit, R a2 and R a3 are end groups (the two can be the same or different), and m is the degree of polymerization. It should be noted that R a2 and R a3 can be the same or different, and side chains R a2 and end group R a3 can both be connected with side chains R b ; all repeating units R a1 can be connected with side chains R b , or side chains R a1 are connected to some of the repeating units R b .

[0062] In one embodiment, the organic lithium supplement includes a first alkylene segment and a second alkylene segment. The first alkylene segment and the second alkylene segment are different. The first alkylene segment is located in the repeating unit, and the second alkylene segment is located in the side chain connected to the main chain. The first lithium-containing group and / or the second lithium-containing group are connected to the second alkylene segment.

[0063] Specifically, the molecular formula of the alkylene segment is -(CH2) n-, where n is a natural number. The difference between the first alkylene chain segment and the second alkylene chain segment means that the degrees of polymerization of the two alkylene chain segments are different. In a specific embodiment, there is a first grafting site on the main chain, the second alkylene chain segment is connected to the first grafting site, and there is a second grafting site on the second alkylene chain segment, and the first lithium-containing group and / or the second lithium-containing group are connected to the second grafting site; therefore, the second alkylene chain segment and the lithium-containing group together form a side chain. It can be understood that both the first grafting site and the second grafting site are chemical bonds formed at the functional group connection, so the lithium-containing group can be indirectly connected to the first grafting site through the second alkylene chain segment.

[0064] There is a second alkylene chain segment on the side chain, and the first lithium-containing group and / or the second lithium-containing group are connected to the second alkylene chain segment, whereby dendrites and pores caused by lithium deposition can be reduced, the formation of uneven lamellae can be avoided, and the organic lithium supplement agent can form a dense and defect-free structure, and the stability of the functional group is improved.

[0065] In a specific embodiment, the repeating unit is a polyether chain segment, the polyether chain segment includes a first alkylene chain segment, the end group can be an amine group, the first lithium-containing group and the second lithium-containing group are each connected to a second alkylene chain segment, and the molecular formula of the organic lithium supplement agent is shown as follows (VI) and (VII).

[0066]

[0067] In one embodiment, Y includes -(CH2) n -O-(polyether), -(CH2) n -COO-(polyester), -(CH2) n -NH-(polyamide), -(CH2) n -S-(polythioether) or more of them, where 1 ≤ n ≤ 4, X1 or X2 includes one or more of -CH3, -CF3, -OH, -NH2; there are multiple grafting sites on the main chain, and there are k repeating units between adjacent two grafting sites, where 1 ≤ k ≤ 5.

[0068] Specifically, Y above refers to the repeating unit that repeats in the main chain, and the number of repeating units is m (degree of polymerization). In a specific embodiment, the main chain can be modified from polyether, polyester, polyamide, or polythioether, and the end groups X1 and X2 can be the same or different. It can be understood that some repeating units have grafting sites for connecting side chains (the first lithium-containing group and the second lithium-containing group), and the number of repeating units between adjacent two grafting sites can be 1 to 5, specifically 1, 2, 3, 4, 5.

[0069] In one embodiment, the grafting density ratio of the first lithium-containing group to the second lithium-containing group is 1:(1 - 5). Specifically, the grafting density ratio of the first lithium-containing group to the second lithium-containing group is ρ1:ρ2 in the above-mentioned embodiment. Meeting the grafting density ratio of the first lithium-containing group to the second lithium-containing group within the above range ensures that the content of the second lithium-containing group is not less than that of the first lithium-containing group. Optionally, the grafting density ratio of the first lithium-containing group to the second lithium-containing group can be 1:1, 1:2, 1:3, 1:4, 1:5.

[0070] In one embodiment, the polymer precursor of the organic lithium supplement includes one or more of olefin polymers, polyether polymers, polyacrylonitrile polymers, and organosilicon polymers. Specifically, olefin polymers include, but are not limited to, polyethylene, polypropylene, polybutene, etc.; polyether polymers include, but are not limited to, polyethylene oxide, polypropylene oxide, polytetrahydrofuran, etc.

[0071] In a specific embodiment, the polymer precursor of the organic lithium supplement is polyethylene ((-CH2-CH2-)), the repeating unit is an alkylene segment, and the molecular formula of the organic lithium supplement is shown as follows (VIII). Alternatively, the polymer precursor of the organic lithium supplement is polyacrylonitrile, the repeating unit is an alkylene segment, and the molecular formula of the organic lithium supplement is shown as follows (IX). Alternatively, the polymer precursor of the organic lithium supplement is an organosilicon polymer, the repeating unit includes a silicon-oxygen bond and an alkylene segment, and the molecular formula of the organic lithium supplement is shown as follows (X).

[0072]

[0073] Among them, m1, m2, and m3 in (VIII), (IX), and (X) are the degrees of polymerization, and m1, m2, and m3 can be different. In addition, the end groups in (VIII), (IX), and (X) are not shown.

[0074] In one embodiment, the molecular weight of the organic lithium supplement is 2000 - 5000. Specifically, meeting the molecular weight of the organic lithium supplement within the above range can ensure the lithium supplement capacity of the organic lithium supplement and reduce the preparation difficulty of the organic lithium supplement. When the molecular weight of the organic lithium supplement is too small, there are fewer lithium-containing groups on the molecular chain, resulting in a decrease in the lithium supplement capacity of the organic lithium supplement. When the molecular weight of the organic lithium supplement is too large, the preparation difficulty of the organic lithium supplement increases and it is not easy to disperse. Optionally, the molecular weight of the organic lithium supplement can be 2000, 2500, 3000, 3500, 4000, 4500, 5000.

[0075] In one embodiment, the D50 of the organic lithium supplement is 10 μm to 15 μm. Specifically, the organic lithium supplement provided by the present invention is solid. Ensuring that the D50 of the organic lithium supplement is within the above range can ensure the tap density of the organic lithium supplement, reduce the preparation difficulty, and fully release lithium ions. Optionally, the D50 of the organic lithium supplement can be 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm.

[0076] In one embodiment, the D100 of the organic lithium supplement is 1 nm to 25 μm. Optionally, the D100 of the organic lithium supplement can be 1 nm, 50 nm, 100 nm, 500 nm, 1 μm, 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm.

[0077] In one embodiment, the tap density of the organic lithium supplement is 2 g / cm 3 ~3.5 g / cm 3 . Optionally, the tap density of the organic lithium supplement can be 2 g / cm 3 , 2.2 g / cm 3 , 2.4 g / cm 3 , 2.6 g / cm 3 , 2.8 g / cm 3 , 3 g / cm 3 , 3.2 g / cm 3 , 3.5 g / cm 3 .

[0078] The present invention also provides a preparation method of an organic lithium supplement for preparing the organic lithium supplement provided in the above embodiment. Please refer to Figures 1-3 .

[0079] In one embodiment, please refer to Figure 1 , the preparation method of the organic lithium supplement specifically includes the following steps:

[0080] Step S10: Dissolve the polymer precursor in the first solvent, add the first lithium-containing precursor in the first solvent, and obtain a first organic lithium supplement after reaction. The first organic lithium supplement includes a first lithium-containing group.

[0081] Step S20: Dissolve the first organic lithium supplement in the second solvent, add the second lithium-containing precursor in the second solvent, and obtain a second organic lithium supplement after reaction. The second organic lithium supplement includes a first lithium-containing group and a second lithium-containing group.

[0082] Specifically, the method for preparing the organic lithium supplement provided by the present invention prepares a first lithium-containing group and a second lithium-containing group on the molecular chain of the polymer through two-step synthesis, wherein the lithium release potential of the first lithium-containing group is greater than that of the second lithium-containing group. The first solvent and the second solvent can be different, and the first lithium-containing precursor and the second lithium-containing precursor can be different. The second organic lithium supplement is the organic lithium supplement provided by the present application, which has a first lithium-containing group and a second lithium-containing group.

[0083] In one embodiment, the polymer precursor is polyetheramine. Please refer to Figure 2 , and the method for preparing the organic lithium supplement specifically includes the following steps:

[0084] Step S100: Dissolve polyetheramine in solvent I, add a modifier to solvent I, and obtain a modified polyetheramine intermediate after reaction.

[0085] Step S110: Dissolve the modified polyetheramine intermediate in solvent II, add a first lithium-containing precursor to solvent II, and obtain a first organic lithium supplement after reaction. The first organic lithium supplement includes a first lithium-containing group.

[0086] Step S120: Dissolve the first organic lithium supplement in solvent III, add a second lithium-containing precursor to solvent III, and obtain a second organic lithium supplement after reaction. The second organic lithium supplement includes a first lithium-containing group and a second lithium-containing group.

[0087] It should be noted that solvent I, solvent II, and solvent III can be the same or different, and solvent II is the first solvent in the above embodiment, and solvent III is the second solvent in the above embodiment. The modifier is an organic solvent used to modify polyetheramine so that additional active groups can be grafted onto it, thereby improving the reaction activity of polyetheramine.

[0088] In a specific embodiment, step S100 is added to modify polyetheramine so that other active groups can be grafted onto polyetheramine, so that the modified polyetheramine intermediate can react with the first lithium-containing precursor and the second lithium-containing precursor to obtain a first lithium-containing group and a second lithium-containing group. Of course, in other embodiments, for some polymer precursors with relatively low reaction activity, the surface modification step can be added to modify them to improve the reaction activity.

[0089] In a specific embodiment, step S100 specifically includes: Dissolve polyetheramine in solvent I, stir and introduce inert gas protection, slowly dropwise add a modifier and a catalyst to the solution, and wash after reacting at a certain temperature for a period of time to obtain a modified polyetheramine intermediate.

[0090] In a specific embodiment, in step S100, the stirring speed is 200 rpm to 600 rpm; the inert gas is nitrogen or argon; the solvent I includes one or more of ether solvents, benzene, toluene, dimethylformamide, and tetrahydrofuran; the modifier includes one or more of acrylic acid, methacrylic acid, benzoic acid, etc.; the catalyst includes one or more of p-toluenesulfonic acid, palladium-carbon, etc.; the reaction temperature is 60 °C to 120 °C, and the reaction time is 2 h - 20 h.

[0091] In a specific embodiment, step S110 specifically includes: dissolving the modified polyetheramine intermediate in solvent II, slowly dropping the first lithium-containing precursor under low temperature and inert gas protection, after the reaction is completed, slowly heating to room temperature and washing the product, and the first organic lithium supplementing agent is obtained after the reaction.

[0092] In a specific embodiment, in step S110, the solvent II includes tetrahydrofuran, anhydrous acetone, toluene, etc.; the low temperature can be achieved by means such as a liquid nitrogen-acetone bath; the first lithium-containing precursor includes n-butyllithium, methyllithium, phenyllithium, etc.

[0093] In a specific embodiment, step S120 specifically includes: dissolving the first organic lithium supplementing agent and the second lithium-containing precursor in solvent III, reacting for a period of time at a certain temperature and then washing, and the second organic lithium supplementing agent is obtained after the reaction.

[0094] In a specific embodiment, in step S120, the second lithium-containing precursor includes one or more of lithium hydroxide, lithium carbonate, and n-butyllithium; the solvent III includes water, alcohol solvents - methanol, ethanol, ethylene glycol, etc.; the reaction temperature is 50 °C to 80 °C, and the reaction time is 1 h to 15 h.

[0095] In one embodiment, the polymer precursor is polyacrylonitrile, please refer to Figure 3 , and the preparation method of the organic lithium supplementing agent specifically includes the following steps:

[0096] Step S210, dissolving polyacrylonitrile in solvent I, adding the first lithium-containing precursor in solvent I, and the first organic lithium supplementing agent is obtained after the reaction, and the first organic lithium supplementing agent includes a first lithium-containing group.

[0097] Step S220, dissolving the first organic lithium supplementing agent in solvent II, adding a modifier in solvent II, and the modified polyacrylonitrile intermediate is obtained after the reaction, and the modified polyacrylonitrile intermediate has a first lithium-containing group.

[0098] Step S230, dissolving the modified polyacrylonitrile intermediate in solvent III, adding the second lithium-containing precursor in solvent III, and the second organic lithium supplementing agent is obtained after the reaction, and the second organic lithium supplementing agent includes a first lithium-containing group and a second lithium-containing group.

[0099] It should be noted that Solvent I, Solvent II and Solvent III can be the same or different. Solvent I is the first solvent in the above-mentioned embodiment, and Solvent III is the second solvent in the above-mentioned embodiment. The modifier is an organic solvent, which is used to modify polyacrylonitrile so that additional active groups can be grafted onto it, thereby improving the reaction activity of polyacrylonitrile.

[0100] In this embodiment, by adding step S210 to modify polyacrylonitrile, other active groups can be grafted onto polyacrylonitrile, so that the modified polyacrylonitrile intermediate can react with the second lithium-containing precursor to obtain a second lithium-containing group. Therefore, in a specific embodiment, the modification reaction can be used to increase the reaction groups with the first lithium-containing precursor and the second lithium-containing precursor, or increase the reaction groups with the first lithium-containing precursor, or increase the reaction groups with the second lithium-containing precursor.

[0101] In one embodiment, the present invention further provides a cathode material, which includes a cathode active material and an organic lithium supplement. The organic lithium supplement is the organic lithium supplement provided in the above-mentioned embodiment. Optionally, the cathode active material can be a phosphate cathode active material or a ternary cathode active material. In a specific embodiment, the cathode active material includes one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium fluorovanadate, lithium titanate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate.

[0102] In one embodiment, the content of the organic lithium supplement in the cathode material can be controlled to be 1% to 6% of the mass of the cathode active material. This ratio can exactly compensate for the loss of active lithium during the first charging process of the battery. If the addition amount of the organic lithium supplement in the cathode material is too low, the lost active lithium in the cathode active material cannot be completely replenished, which is not conducive to improving the energy density and capacity retention rate of the battery. If the addition amount of the organic lithium supplement in the cathode active material is too high, it will occupy the original reversible capacity and increase the cost. In some specific embodiments, in the cathode material, the mass percentage content of the organic lithium supplement can be 1%, 2%, 4%, 6%, etc.

[0103] In one embodiment, the present invention further provides a cathode electrode sheet, which includes a current collector and an active material layer disposed on the current collector. The active material layer includes the organic lithium supplement according to any one of the above-mentioned embodiments. Or the active material layer includes the organic lithium supplement obtained by the preparation method of the organic lithium supplement in the above-mentioned embodiment.

[0104] In one embodiment, the positive electrode plate includes a positive current collector, and a positive active layer is disposed on the positive current collector. The positive active layer includes components such as a positive active material, an organic lithium supplement agent, a conductive agent, and a binder. The present invention does not specifically limit these materials, and appropriate materials can be selected according to actual application requirements. The positive current collector includes, but is not limited to, any one of copper foil and aluminum foil. The conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes, and the content of the conductive agent in the positive active layer is 3 wt% to 5 wt%. The types of the binder include one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethylcellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives, and the content of the binder in the positive active layer is 2 wt% to 4 wt%.

[0105] In one embodiment, the present invention further provides a secondary battery. The secondary battery includes a negative electrode, a positive electrode, and an electrolyte. Among them, the positive electrode includes the above-mentioned positive electrode material; the electrolyte can be an electrolytic solution. In this case, the secondary battery further includes a separator disposed between the positive electrode plate and the negative electrode plate; or, the electrolyte can be a solid electrolyte. In this case, no separator is provided in the secondary battery, and the solid electrolyte is used instead.

[0106] The technical solution of the present invention will be described in detail below through specific examples.

[0107] Example 1

[0108] This example provides an organic lithium supplement agent. The molecular formula of the organic lithium supplement agent is H2N-[CH2CH(COOLi)(OCH2CH2OLi)] m -NH2. -COOLi is the first lithium-containing group, -OLi is the second lithium-containing group, and the grafting density ratio of the first lithium-containing group to the second lithium-containing group is 1:1.86. The polymer precursor of the organic lithium supplement agent is polyetheramine, with a molecular weight of 2000 and a degree of polymerization of 15. The particle size D50 of the organic lithium supplement agent is 10.5 μm, the particle size D100 is 20.3 μm, and the tapped density of the organic lithium supplement agent is 3.2 g / cm 3 .

[0109] The preparation method of the organic lithium supplement agent in this example specifically includes the following steps:

[0110] (1) Dissolve polyetheramine (PEA) in tetrahydrofuran, stir at 600 rpm and protect with an Ar atmosphere, slowly drop acrylic acid and p-toluenesulfonic acid into the solution, react at 60 °C for 12 h, and then wash to obtain a purified carboxyl-containing polyetheramine intermediate (PEA-COOH).

[0111] (2) Re-dissolve PEA-COOH in tetrahydrofuran, protect it under an Ar atmosphere at -78 °C, slowly dropwise add n-butyllithium, after the reaction is completed, slowly warm up to room temperature and wash the product to obtain a polyetheramine product containing alkoxide (PEA-COOH-OLi).

[0112] (3) Dissolve PEA-COOH-OLi and lithium hydroxide in ethylene glycol, react at 80 °C for 8 h and then wash to obtain a polyetheramine organic lithium supplement agent (PEA-COOLi-OLi) containing carboxylate and alkoxide on the branched chain.

[0113] Figure 4 is the scanning electron micrograph of the organic lithium supplement agent in Example 1, and Figure 8 The infrared spectrum of Example 1 is shown; Table 1 shows the infrared test results of the organic lithium supplement agent provided in Example 1. It can be seen from Table 1 that there are four characteristic peaks in the organic lithium supplement agent prepared in this Example 1 at 1640 cm -1 , 1560 cm -1 , 1050 cm -1 , 620 cm -1 . These four characteristic peaks correspond to the first lithium-containing group (-COOLi) and the second lithium-containing group (-OLi), indicating that the organic lithium supplement agent has been synthesized in the present invention.

[0114] Table 1 Infrared spectrum table

[0115]

[0116]

[0117] Example 2

[0118] This example provides an organic lithium supplement agent. The molecular formula of the organic lithium supplement agent is CH3-[CH2CH(COOLi)CH2CH(OLi)] m -CH3. -COOLi is the first lithium-containing group, -OLi is the second lithium-containing group, and the grafting density ratio of the first lithium-containing group to the second lithium-containing group is 1:1.64. The polymer precursor of the organic lithium supplement agent is polyacrylonitrile, with a molecular weight of 2000 and a degree of polymerization of 13. The particle size D50 of the organic lithium supplement agent is 12.3 μm, the particle size D100 is 21.7 μm, and the tapped density of the organic lithium supplement agent is 3.05 g / cm 3 .

[0119] The preparation method of the organic lithium supplement agent in this example specifically includes the following steps:

[0120] (1) Dissolve polyacrylonitrile (PAN) in DMSO. After dissolving at 60 °C, slowly add an aqueous solution of LiOH. Raise the temperature to 90 °C and react for 5 h to promote the full hydrolysis of the cyano group into lithium carboxylate. Precipitate with ice ethanol, wash and dry to obtain lithium carboxylated PAN (PAN-COOLi).

[0121] (2) Dissolve PAN-COOLi, 2-hydroxyethyl acrylate (HEA) and ammonium persulfate (APS) in DMF. After purging with nitrogen to remove oxygen, react at 70 °C for 6 h. Precipitate with ethanol to obtain PAN-COOLi-OH.

[0122] (3) Disperse PAN-COOLi-OH in absolute ethanol, add lithium hydride (LiF). Stir at room temperature for 12 h to ensure complete lithiation of the hydroxyl group. Finally, dry to obtain PAN-COOLi-OLi.

[0123] Example 3

[0124] This example provides an organic lithium supplement. The molecular formula of the organic lithium supplement is [OSi(CH3)2CH2CH(COOLi)CH2CH(OLi)]. m . -COOLi is the first lithium-containing group, -OLi is the second lithium-containing group, and the grafting density ratio of the first lithium-containing group to the second lithium-containing group is 1:1.50. The polymer precursor of the organic lithium supplement is polydimethylsiloxane with a molecular weight of 2000 and a degree of polymerization of 10. The particle size D50 of the organic lithium supplement is 11.8 μm, the particle size D100 is 21.6 μm, and the tapped density of the organic lithium supplement is 3.13 g / cm 3 .

[0125] The preparation method of the organic lithium supplement in this example specifically includes the following steps:

[0126] (1) Dissolve polydimethylsiloxane (PDMS) in toluene, add 3-chloropropyltriethoxysilane (2 mL, molar ratio of PDMS:silane = 1:1.2), and stir and react at 80 °C for 12 hours; add deionized water (10 mL) for hydrolysis to generate PDMS with a chloropropyl side chain (PDMS-Cl). Mix PDMS-Cl with acrylic acid (3 mL, molar ratio 1:2) in tetrahydrofuran, add ammonium persulfate (0.1 g) as an initiator, and react at 60 °C for 8 hours to obtain PDMS with a carboxylic acid group side chain (PDMS-COOH).

[0127] (2) Disperse PDMS-COOH in absolute ethanol (50 mL), add lithium hydroxide (1.2 g, molar ratio of COOH:Li = 1:1.1), and react at 80 °C for 6 hours; filter, wash (ethanol / water = 3:1), and dry in vacuum to obtain PDMS containing lithium carboxylate (PDMS-COOLi).

[0128] (3) Mix PDMS-COOLi with epichlorohydrin (2 mL, molar ratio 1:1.5) in toluene, add triethylamine (1 mL) as a catalyst, and react at 70 °C for 10 hours to form PDMS with epoxy groups in the side chain; add dilute hydrochloric acid (0.1 M, 20 mL) and stir at room temperature for 4 hours to form PDMS with hydroxyl groups in the side chain (PDMS-COOLi-OH); react PDMS-COOLi-OH with lithium hydride (0.5 g, molar ratio OH:Li = 1:1.2) in tetrahydrofuran, stir at room temperature for 12 hours, filter and dry to obtain the final product PDMS-COOLi-OLi.

[0129] Example 4

[0130] This example provides an organic lithium supplement. The molecular formula of the organic lithium supplement is CH3-[CH2CH(SO3Li)CH2CH(NHLi)] m -CH3. -SO3Li is the first lithium-containing group, -NHLi is the second lithium-containing group, and the grafting density ratio of the first lithium-containing group to the second lithium-containing group is 1:1.63. The polymer precursor of the organic lithium supplement is polyacrylonitrile with a molecular weight of 2000 and a degree of polymerization of 12. The particle size D50 of the organic lithium supplement is 11.5 μm, the particle size D100 is 22.4 μm, and the tapped density of the organic lithium supplement is 3.05 g / cm 3 .

[0131] The preparation method of the organic lithium supplement in this example specifically includes the following steps:

[0132] (1) Disperse polyacrylonitrile (PAN) in dichloromethane (DCM), cool it to 0 °C in an ice bath, and slowly dropwise add chlorosulfonic acid while maintaining the temperature ≤ 5 °C; after the addition is complete, raise the temperature to 25 °C and stir and react for 24 h to sulfonate part of the cyano group into sulfonic acid groups (-SO3H); filter, wash, and vacuum dry to obtain sulfonated polyacrylonitrile (PAN-SO3H).

[0133] (2) Add PAN-SO3H and LiOH to water, ultrasonically disperse at 40 °C for 1 h, and then stir and react at 60 °C for 6 h; freeze-dry the reaction solution to obtain lithium sulfonated polyacrylonitrile (PAN-SO3Li).

[0134] (3) Dissolve PAN-SO3Li in THF, add hydrazine hydrate, and reflux and react at 80 °C for 12 h to reduce part of the cyano group to amino groups (-NH2); cool to 0 °C, add LiH in batches, stir and react for 6 h to convert the amino groups into lithium amide (-NHLi); filter, wash, and vacuum dry at 60 °C to obtain the dilithiated polyacrylonitrile organic lithium supplement (PAN-SO3Li-NHLi).

[0135] Example 5

[0136] This embodiment provides an organic lithium supplement. The molecular formula of the organic lithium supplement is CH3-[CH2CH(NO2Li)CH2CH(Si(CH3)2Li)] m -CH3. -NO2Li is the first lithium-containing group, -Si(CH3)2Li is the second lithium-containing group, and the grafting density ratio of the first lithium-containing group to the second lithium-containing group is 1:1.5. The polymer precursor of the organic lithium supplement is polyacrylonitrile with a molecular weight of 2000 and a degree of polymerization of 11. The particle size D50 of the organic lithium supplement is 10.2 μm, the particle size D100 is 20.5 μm, and the tapped density of the organic lithium supplement is 2.95 g / cm 3 .

[0137] The preparation method of the organic lithium supplement in this embodiment specifically includes the following steps:

[0138] (1) Disperse polyacrylonitrile (PAN) in dichloromethane (DCM), cool it to 0 °C in an ice bath, and slowly drop a mixed solution of concentrated nitric acid and sulfuric acid; keep the temperature ≤ 5 °C and stir for 8 h to nitrify part of the cyano group into nitro (-NO2); filter, wash, and vacuum dry to obtain nitrated polyacrylonitrile (PAN-NO2).

[0139] (2) Dissolve PAN-NO2 in THF, add LiH in batches under the protection of an Ar atmosphere, and stir at 25 °C for 12 h; filter to remove unreacted LiH, wash with ether 3 times, and vacuum dry to obtain nitro-lithiated polyacrylonitrile (PAN-NO2Li).

[0140] (3) Add PAN-NO2Li and trimethylchlorosilane to ether, stir at 0 °C for 6 h to silylate the remaining cyano group to form -Si(CH3)2Cl; add Li pieces and react at 25 °C for 8 h to convert -Si(CH3)2Cl to -Si(CH3)2Li; filter, wash, and vacuum dry at 60 °C to obtain a double-lithiated polyacrylonitrile organic lithium supplement (PAN-NO2Li-SiLi).

[0141] Example 6

[0142] This embodiment provides an organic lithium supplement. The molecular formula of the organic lithium supplement is CH3-[CH2CH(COOLi)CH2CH(OLi)] m -CH3. -COOLi is the first lithium-containing group, -OLi is the second lithium-containing group, and the grafting density ratio of the first lithium-containing group to the second lithium-containing group is 1:4.48. The polymer precursor of the organic lithium supplement is polyacrylonitrile with a molecular weight of 2000 and a degree of polymerization of 13. The particle size D50 of the organic lithium supplement is 11.8 μm, the particle size D100 is 23.5 μm, and the tapped density of the organic lithium supplement is 2.82 g / cm3 。

[0143] The preparation method of the organic lithium supplement in this embodiment specifically includes the following steps:

[0144] (1) Dissolve polyacrylonitrile (PAN) in DMSO. After dissolving at 60 °C, slowly add an aqueous LiOH solution; raise the temperature to 60 °C and react for 1 h to promote partial hydrolysis of the cyano group into lithium carboxylate; precipitate with ice ethanol, wash and dry to obtain carboxylate-lithiated PAN (PAN-COOLi).

[0145] (2) Dissolve PAN-COOLi, 2-hydroxyethyl acrylate (HEA), and ammonium persulfate (APS) in DMF; after purging with nitrogen to remove oxygen, react at 80 °C for 12 h; precipitate with ethanol to obtain PAN-COOLi-OH.

[0146] (3) Disperse PAN-COOLi-OH in absolute ethanol, and add lithium hydride (LiF); stir at 40 °C for 24 h to ensure complete lithiation of the hydroxyl groups; finally, dry to obtain PAN-COOLi-OLi.

[0147] Example 7

[0148] This embodiment provides an organic lithium supplement. The molecular formula of the organic lithium supplement is CH3-[CH2CH(COOLi)CH2CH(OLi)] m -CH3. -COOLi is the first lithium-containing group, -OLi is the second lithium-containing group, and the grafting density ratio of the first lithium-containing group to the second lithium-containing group is 1:1.64. The polymer precursor of the organic lithium supplement is polyacrylonitrile, with a molecular weight of 5000 and a degree of polymerization of 32. The D50 of the organic lithium supplement is 15.6 μm, the D100 of the particle size is 24.7 μm, and the tapped density of the organic lithium supplement is 2.73 g / cm 3 。

[0149] The preparation method of the organic lithium supplement in this embodiment specifically includes the following steps:

[0150] (1) Dissolve polyacrylonitrile (PAN) in DMSO, stir at 70 °C for 3 h until completely dissolved, and slowly add an aqueous LiOH solution; raise the temperature to 85 °C and react for 6 h to promote partial hydrolysis of the cyano group into lithium carboxylate; precipitate with ice ethanol, wash and dry to obtain carboxylate-lithiated PAN (PAN-COOLi).

[0151] (2) Dissolve PAN-COOLi, 2-hydroxyethyl acrylate (HEA), and ammonium persulfate (APS) in DMF; after purging with nitrogen to remove oxygen for 40 min, react at 75 °C for 8 h; inject the reaction solution into cold ethanol to precipitate, and dry to obtain high-molecular-weight PAN-COOLi-OH.

[0152] (3) Disperse PAN-COOLi-OH in absolute ethanol, ultrasonically treat for 10 min, and then add lithium hydride (LiF); stir at 35 °C for 18 h to ensure complete lithiation of the hydroxyl groups; finally, dry to obtain high-molecular-weight PAN-COOLi-OLi.

[0153] Example 8

[0154] This example provides an organic lithium supplement. The molecular formula of the organic lithium supplement is CH3-[CH2CH(COOLi)CH2CH(OLi)] m -CH3. -COOLi is the first lithium-containing group, -OLi is the second lithium-containing group, and the grafting density ratio of the first lithium-containing group to the second lithium-containing group is 1:1.64. The polymer precursor of the organic lithium supplement is polyacrylonitrile with a molecular weight of 2000 and a degree of polymerization of 13. The particle size D50 of the organic lithium supplement is 10.1 μm, the particle size D100 is 15.6 μm, and the tapped density of the organic lithium supplement is 3.49 g / cm 3 .

[0155] The preparation method of the organic lithium supplement in this example specifically includes the following steps:

[0156] (1) Dissolve polyacrylonitrile (PAN) in DMSO. After dissolving at 60 °C, slowly add an aqueous solution of LiOH; raise the temperature to 80 °C and react for 4 h to promote partial hydrolysis of the cyano group into lithium carboxylate; quickly stir (1000 rpm) and precipitate in ice ethanol, wash and dry, and then process with an air jet mill and sieve (200 mesh) to obtain fine particles of PAN-COOLi.

[0157] (2) Dissolve PAN-COOLi, hydroxyethyl acrylate (HEA), and ammonium persulfate (APS) in DMF; deoxygenate by passing nitrogen, and react at 70 °C for 6 h; inject the reaction solution into cold ethanol (pre-cooled at -20 °C) to precipitate; then spray-dry the precipitate to obtain spherical PAN-COOLi-OH.

[0158] (3) Add PAN-COOLi-OH and LiH to absolute ethanol containing PEG-400, ball-mill for 4 h (rotation speed 300 rpm, zirconia ball diameter 0.5 mm) to uniformly lithiate the particles; after filtration, perform vacuum hot pressing (pressure 5 MPa, temperature 60 °C) for 1 h to increase the tapped density and obtain high-density PAN-COOLi-OLi.

[0159] Comparative Example 1

[0160] The molecular formula of the organic lithium supplement is H2N-[CH2CH(COOLi)(OCH2CH2OH)] m-NH2. The polymer precursor of the organic lithium supplement is polyetheramine with a molecular weight of 2,000 and a degree of polymerization of 15. The particle size D50 of the organic lithium supplement is 10.2 μm, the particle size D100 is 18.5 μm, and the tapped density of the organic lithium supplement is 3.37 g / cm 3 .

[0161] This comparative example provides a preparation method of polyetheramine containing carboxylate functional groups on the branched chain.

[0162] (1) Dissolve polyetheramine (PEA) in tetrahydrofuran, stir at 600 rpm and protect with an Ar atmosphere. Slowly add acrylic acid and p-toluenesulfonic acid to the solution and react at 60 °C for 12 h, then wash to obtain a purified carboxyl-containing polyetheramine intermediate (PEA-COOH).

[0163] (2) Dissolve PEA-COOH and lithium hydroxide in deionized water, react at 60 °C for 6 h, and then freeze-dry to obtain PEA-COOLi containing only -COOLi.

[0164] Comparative Example 2

[0165] The molecular formula of the organic lithium supplement is H2N-[CH2CH(OH)(OCH2CH2OLi)] m -NH2. The polymer precursor of the organic lithium supplement is polyetheramine with a molecular weight of 2,000 and a degree of polymerization of 15. The particle size D50 of the organic lithium supplement is 11.2 μm, the particle size D100 is 22.1 μm, and the tapped density of the organic lithium supplement is 3.07 g / cm 3 .

[0166] This comparative example provides a preparation method of polyetheramine containing alkoxide functional groups on the branched chain.

[0167] (1) Dissolve polyetheramine (PEA) and cyclohexene oxide in tetrahydrofuran and react at 0 °C for 12 h to obtain hydroxylated PEA (PEA-OH).

[0168] (2) Dissolve PEA-OH and lithium hydroxide in deionized water, stir at room temperature for 24 h, and wash with ethanol to obtain PEA-OLi containing only -OLi.

[0169] The parameters of the organic lithium supplements provided in Examples 1 - 8 and Comparative Examples 1 - 2 are shown in Table 2:

[0170] Table 2 Parameters of the organic lithium supplements provided in the examples and comparative examples

[0171]

[0172] The organic lithium supplements provided in the above Examples 1 - 8 and the organic lithium supplements provided in Comparative Examples 1 - 2 were assembled into positive electrode sheets and lithium - ion batteries respectively according to the following methods:

[0173] Positive electrode sheet: The organic lithium supplement, SP, and PVDF were mixed into a positive electrode slurry by homogenizing according to a mass ratio of 90:4:6. The positive electrode slurry was coated on the surface of aluminum foil and vacuum - dried overnight at 110 °C, and then roll - pressed to obtain the positive electrode sheet;

[0174] Negative electrode sheet: Lithium sheet;

[0175] Electrolyte: Ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7, and LiPF6 was added to form an electrolyte, and the concentration of LiPF6 was 1 mol / L;

[0176] Separator: Polypropylene microporous separator;

[0177] Assembly of lithium - ion battery: Button - type lithium - ion full batteries were assembled in an inert - atmosphere glove box in the order of negative electrode sheet - separator - electrolyte - positive electrode sheet.

[0178] The assembled lithium - ion batteries in the above lithium - ion battery examples were subjected to electrochemical performance tests, and the test conditions were as follows:

[0179] Charge at a rate of 0.1C, with a cut - off voltage of 4.7V; perform constant - voltage charging at 4.7V; after the charging process is completed, stand for 10 minutes and then discharge at a rate of 0.1C, with a cut - off voltage of 2.5V; observe the charging platform during the charging process to obtain the decomposition voltage of the organic lithium supplement.

[0180] The test results of the above lithium batteries are shown in Table 3 below:

[0181] Table 3. Test results of examples and comparative examples

[0182]

[0183] It can be seen from the test results of Example 1, Comparative Example 1, and Comparative Example 2 in Table 3; and Figure 5 the charging curve of Example 1 shown; Figure 7As can be seen from the charging curve of Comparative Example 1 shown, the charge-discharge capacity, cycle life, and first Coulombic efficiency of the organic lithium supplement agent with two lithium-release potentials provided in Example 1 are all higher than those of the organic lithium supplement agent with only one lithium-release potential; and the battery in Example 1 has a polarization voltage difference (0.25 V), which is the actual lithium-release potential difference between the first lithium-containing group and the second lithium-containing group, that is, they release lithium at different voltage platforms, so as to achieve the effect of gradient lithium supplementation. And the transition of this platform is smooth, and there is no steep polarization fluctuation after lithium deintercalation at the first platform, and it can naturally reach the second voltage platform to induce lithium deintercalation; and at Figure 6 the charging curve of Example 3 shown also presents the same law; but due to the difference in the grafting density, the polarization voltage difference is relatively larger, but it can show better performance compared with the comparative examples.

[0184] It can be seen from the test results of Examples 1-5 in Table 3 that the technical solution provided by the present invention can be applied to polymers with different main chains (such as polyetheramine, polyacrylonitrile, and polydimethylsiloxane, etc.), and the performance of the organic lithium supplement agent can be improved by replacing different lithium-containing groups. And different lithium-containing groups can provide different material properties. For example, the silicon-oxygen bond (Example 3) can improve the thermal stability, and the sulfonic acid group (Example 4) can adjust the particle size to increase the tap density. At the same time, it can be seen from the test results that when the second lithium-containing group preferentially releases lithium to compensate for the SEI loss, the first lithium-containing group can still continuously supplement lithium, so as to reduce the cycle attenuation. Therefore, the Coulombic efficiency and cycle life of the organic lithium supplement agent are both good.

[0185] It can be seen from the test results of Examples 1 and 6 in Table 3 that the grafting density ratio of the first lithium-containing group and the second lithium-containing group has an impact on the performance of the organic lithium supplement agent. When the content gap between the first lithium-containing group and the second lithium-containing group is too large, it will lead to a decrease in the continuous lithium supplementation effect provided by the first lithium-containing group, resulting in excessive first lithium supplementation, structural collapse, and a decrease in cycle life.

[0186] It can be seen from the test results of Examples 1 and 7 in Table 3 that the molecular weight and degree of polymerization of the organic lithium supplement agent have an impact on the morphology and performance of the organic lithium supplement agent. When the molecular weight and degree of polymerization of the organic lithium supplement agent increase, it leads to an increase in the particle size of the organic lithium supplement agent, affecting the tap density; and when the molecular weight and degree of polymerization are too large, the chain segments are longer, and the lithium ion transmission path is extended, affecting the release of lithium ions.

[0187] It can be seen from the test results of Examples 1 and 8 in Table 3 that the particle size and tap density of the organic lithium supplement agent have an impact on the performance of the organic lithium supplement agent. By controlling the decrease of the particle size D100 of the organic lithium supplement agent and increasing the tap density, the structure of the electrode can be made dense.

[0188] In the description of the embodiments of the present invention, it should be noted that the orientation or positional relationship of the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0189] The above-disclosed is only a preferred embodiment of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. An organic lithium supplement, characterized in that, The organic lithium supplement includes a main chain, a first lithium-containing group, and a second lithium-containing group. The main chain is a straight chain, and the general formula of the main chain includes: X2-[Y] m -X1, where Y is a repeating unit, and both X1 and X2 are end groups connected to the main chain, 10 ≤ m ≤ 500; there are grafting sites on the main chain, the first lithium-containing group and the second lithium-containing group are connected to the grafting sites, and the lithium release potential of the first lithium-containing group is greater than that of the second lithium-containing group.

2. The organic lithium supplement according to claim 1, wherein The lithium release potential U1 of the first lithium-containing group and the lithium release potential U2 of the second lithium-containing group satisfy: U1 - U2 ≥ 0.3V.

3. The organic lithium supplement according to claim 1, wherein, On the molecular chain of the organic lithium supplement, the grafting density ρ2 of the second lithium-containing group and the grafting density ρ1 of the first lithium-containing group satisfy: ρ2 ≥ ρ1.

4. The organic lithium supplement according to claim 1, wherein The organic lithium supplement includes a first alkylene segment and a second alkylene segment, the first alkylene segment and the second alkylene segment are different, the first alkylene segment is located in the repeating unit, the second alkylene segment is located in the side chain connected to the main chain, and the first lithium-containing group and / or the second lithium-containing group are connected to the second alkylene segment.

5. The organolithium supplement according to claim 1, wherein Y includes -(CH2) n -O-, -(CH2) n -COO-, -(CH2) n -NH-, -(CH2) n -S- or one or more of them, where 1 ≤ n ≤ 4, X1 or X2 includes -CH3, -CF3, -OH, -NH2 or one or more of them; there are multiple grafting sites on the main chain, and there are k repeating units between adjacent two grafting sites, where 1 ≤ k ≤ 5.

6. The organic lithium supplement according to any one of claims 1-5, characterized in that The first lithium-containing group includes one or more of -COOLi, -SO3Li, -PO4Li2, -BLi, -NO2Li; and / or The second lithium-containing group includes one or more of -OLi, -NHLi, -SiOLi; and / or The grafting density ratio of the first lithium-containing group and the second lithium-containing group is 1:(1-5).

7. The organic lithium supplement according to any one of claims 1-6, characterized in that The polymer precursor of the organic lithium supplement includes one or more of an olefin polymer, a polyether polymer, a polyacrylonitrile polymer, an organosilicon polymer; and / or The molecular weight of the organic lithium supplement is 2000-5000; and / or The particle size D50 of the organic lithium supplement is 10μm-15μm; and / or The particle size D100 of the organic lithium supplement is 1nm-25μm; and / or The tap density of the organic lithium supplement is 2 g / cm 3 ~3.5 g / cm 3 .

8. A preparation method of an organic lithium supplement, characterized in that For preparing the organic lithium supplement according to any one of claims 1-7, the preparation method includes: Dissolving the polymer precursor in a first solvent, adding a first lithium-containing precursor in the first solvent, and obtaining a first organic lithium supplement after reaction, the first organic lithium supplement includes a first lithium-containing group; Dissolving the first organic lithium supplement in a second solvent, adding a second lithium-containing precursor in the second solvent, and obtaining a second organic lithium supplement after reaction, the second organic lithium supplement includes the first lithium-containing group and the second lithium-containing group.

9. A cathode material, characterized in that, The positive electrode material includes an active material and the organic lithium supplement according to any one of claims 1-7, or, the positive electrode material includes the organic lithium supplement obtained by the preparation method of the organic lithium supplement according to claim 8.

10. A secondary battery, characterized in that, Including a positive electrode, a negative electrode and an electrolyte, the positive electrode and the negative electrode are arranged in the electrolyte, and the positive electrode includes the positive electrode material according to claim 9.

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