Lithium titanate material and preparation method thereof, negative pole piece and lithium ion battery

Abstract

The invention discloses a lithium titanate material and a preparation method thereof, a negative pole piece and a lithium ion battery, and relates to the field of lithium ion batteries. The particle size distribution of the lithium titanate material meets the condition that the particle size distribution comprises a plurality of peak values of particle sizes, and the difference of the particle sizes of every two adjacent peak values is larger than 0 mu m and smaller than or equal to 12 mu m. When the material provided by the invention is compacted, materials with different particle sizes are compacted in sequence, and meanwhile, gaps among particles with large particle sizes can be filled with the materials with small particle sizes, so that the compaction density of the material is well improved, and when the material is used for manufacturing a battery, the energy density of the battery is favorably improved, and the performance of the battery is improved.

Description

Technical Field

[0001] The present application relates to the field of lithium-ion batteries, and in particular to a lithium titanate material and a preparation method thereof, a negative electrode sheet and a lithium-ion battery. Background Art

[0002] Lithium-ion battery is a secondary battery (rechargeable battery) including a positive electrode, a negative electrode and a separator. It mainly relies on the reciprocating movement of lithium ions between the positive electrode and the negative electrode to work. There are many known negative electrode materials. Among them, lithium titanate is widely used because of its very flat charging and discharging platform, good safety performance, extremely stable structure and excellent cycle performance during the charging and discharging process. However, the lithium titanate materials currently on the market generally have the problem of low compaction density, which affects the battery performance of lithium titanate batteries. Summary of the invention

[0003] In view of this, the present application provides a lithium titanate material and a preparation method thereof, a negative electrode plate and a lithium ion battery, aiming to provide a lithium titanate material with a higher compaction density.

[0004] The embodiment of the present application is implemented as follows:

[0005] In a first aspect, the present application provides a lithium titanate material, wherein the particle size distribution of the lithium titanate material satisfies: the particle size distribution includes a plurality of particle size peaks, and the difference between the particle sizes of two adjacent peaks is greater than 0 μm and less than or equal to 12 μm.

[0006] Optionally, in some embodiments of the present application, the particle size distribution includes a first peak and a second peak, the first peak appears in a range where the particle size is greater than 0 μm and less than or equal to 5 μm, and the second peak appears in a range where the particle size is greater than 5 μm and less than or equal to 12 μm; and / or,

[0007] The lithium titanate material is a secondary particle structure; and / or,

[0008] The porosity of the lithium titanate material is greater than or equal to 1% and less than or equal to 20%.

[0009] Optionally, in some embodiments of the present application, the first peak appears in a range of particle size greater than or equal to 2 μm and less than or equal to 4 μm, and the second peak appears in a range of particle size greater than or equal to 6 μm and less than or equal to 12 μm.

[0010] Optionally, in some embodiments of the present application, the particle size distribution of the lithium titanate material further satisfies:

[0011] D1 is less than or equal to 1 μm; and / or,

[0012] D10 is greater than or equal to 1 μm and less than or equal to 3 μm; and / or,

[0013] D50 is greater than or equal to 5 μm and less than or equal to 7 μm; and / or,

[0014] D90 is less than or equal to 18 μm; and / or

[0015] D99 is less than or equal to 25μm.

[0016] In a second aspect, the present application also proposes a method for preparing a lithium titanate material, comprising the following steps:

[0017] Providing lithium titanate powders with a plurality of median particle sizes, wherein the median particle sizes of the plurality of lithium titanate powders are arranged in increasing order, and a difference between two adjacent median particle sizes is greater than 0 μm and less than or equal to 12 μm;

[0018] A plurality of the lithium titanate powders are mixed and sintered to obtain a lithium titanate material.

[0019] Optionally, in some embodiments of the present application, in the step of providing lithium titanate powders with multiple median particle sizes, the multiple lithium titanate powders include a first powder and a second powder, the median particle size of the first powder is greater than 0 μm and less than or equal to 5 μm, and the median particle size of the second powder is greater than 5 μm and less than or equal to 12 μm.

[0020] Optionally, in some embodiments of the present application, in the lithium titanate material, a weight ratio of the first powder to the second powder is 1:9 to 9:1.

[0021] Optionally, in some embodiments of the present application, the lithium titanate material is a secondary particle structure; and / or,

[0022] The sintering temperature is 650-780° C.; and / or,

[0023] The sintering time is 0.5 to 5.5 hours; and / or,

[0024] The step of providing lithium titanate powders with a plurality of median particle sizes includes preparing lithium titanate powders, wherein the preparing lithium titanate powders includes:

[0025] Providing lithium titanate particles having a primary particle structure;

[0026] Wet ball milling the lithium titanate particles to obtain a slurry;

[0027] The slurry is spray-dried to obtain lithium titanate powder.

[0028] Optionally, in some embodiments of the present application, the particle size of the lithium titanate particles after the wet ball milling is greater than or equal to 100 nm and less than or equal to 400 nm; and / or,

[0029] The specific surface area of ​​the lithium titanate particles after wet ball milling is greater than or equal to 6 m 2 / g and less than or equal to 9m 2 / g.

[0030] Optionally, in some embodiments of the present application, the plurality of lithium titanate powders include a first powder and a second powder, the median particle size of the first powder is greater than 0 μm and less than or equal to 5 μm, and the median particle size of the second powder is greater than 5 μm and less than or equal to 12 μm; the slurry used to prepare the first powder is the first slurry, and the slurry used to prepare the second powder is the second slurry;

[0031] The step of spray drying the slurry to obtain a powder material comprises:

[0032] Under a first condition, spray drying the first slurry to obtain a first powder;

[0033] Under a second condition, spray drying the second slurry to obtain a second powder;

[0034] Among them, the first condition includes a first inlet air temperature, a first outlet air temperature and a first feed speed, and the second condition includes a second inlet air temperature, a second outlet air temperature and a second feed speed; the first inlet air temperature is lower than the second inlet air temperature, the first outlet air temperature is lower than the second outlet air temperature, and the first feed speed is lower than the second outlet speed.

[0035] Optionally, in some embodiments of the present application, the first air inlet temperature is 250-270° C.; and / or,

[0036] The first air outlet temperature is 100-200° C.; and / or,

[0037] The first feed rate is 15 to 50 mL / min; and / or,

[0038] The second air inlet temperature is 260-300° C.; and / or,

[0039] The second air outlet temperature is 100-200° C.; and / or,

[0040] The second feed rate is 25-50 mL / min.

[0041] In a third aspect, the present application proposes a negative electrode plate, comprising a lithium titanate material, wherein the lithium titanate material comprises the lithium titanate material described above, or the lithium titanate material is prepared by the preparation method described above.

[0042] In a fourth aspect, the present application proposes a lithium-ion battery, comprising a negative electrode plate, wherein the negative electrode plate comprises the negative electrode plate described above.

[0043] The particle size distribution of the lithium titanate material provided in the present application has a multi-peak characteristic, and the particle size difference between two adjacent peaks is within 12μm, so that when the material is compacted, materials of different particle sizes are compacted successively, and at the same time, materials of small particle sizes can be filled in the gaps between particles of large particle sizes, which greatly improves the compaction density of the material. When using this material to make batteries, it helps to improve the energy density of the battery and enhance the performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0045] Figure 1 This is a particle size distribution diagram of a lithium titanate material prepared in Example 1 of the present application;

[0046] Figure 2 is a SEM image of the primary particles prepared in Example 1 of the present application;

[0047] Figure 3 It is a schematic flow chart of a method for preparing a lithium titanate material proposed in an embodiment of the present application. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application. In addition, it should be understood that the specific implementation methods described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0049] In this application, unless otherwise specified, the directional words used, such as "upper" and "lower", refer specifically to the directions of the drawings in the accompanying drawings. In addition, in the description of the specification of this application, the term "including" means "including but not limited to".

[0050] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0051] In this application, "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0052] In the present application, "at least one" means one or more, and "plurality" means two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0053] The technical solution of this application is implemented as follows:

[0054] In the first aspect, the present application embodiment provides a lithium titanate material, see Figure 1 The particle size distribution of the lithium titanate material satisfies: the particle size distribution includes multiple particle size peaks, and the difference between the particle sizes of two adjacent peaks is greater than 0μm and less than or equal to 12μm. For example, the particle size difference can be 0.1μm, 0.2μm, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm.

[0055] The "lithium titanate material" in this application includes the chemical formula Li4Ti5O 12Spherical lithium titanate. Compared with materials with other morphologies, spherical lithium titanate has better powder fluidity and dispersibility, and can eliminate the influence of agglomeration to the greatest extent. In some embodiments, the lithium titanate material is a secondary particle structure, that is, the lithium titanate material can be formed into secondary spherical particles by reorganization of primary particles; wherein, primary particles refer to particles or particles with a primary particle structure, which can be obtained by mixing and sintering raw materials.

[0056] In this application, "multiple" refers to two, three, four or more than four. In some embodiments, the particle size distribution diagram of the lithium titanate material shows two peaks that do not completely overlap, and the difference between the peak values ​​of the two peaks (the particle size corresponding to the highest point) is greater than 0μm and less than or equal to 12μm; in other embodiments, the particle size distribution diagram of the lithium titanate material shows three or more peaks, and the peak values ​​of the three or more peaks are all different. Sorted by peak size, the difference between the peak values ​​of any two adjacent peaks in the sequence is greater than 0μm and less than or equal to 12μm.

[0057] The particle size distribution of the lithium titanate material provided in the present application has a multi-peak characteristic, and the particle size difference between two adjacent peaks is within 12 μm, so that when the material is compacted, materials of different particle sizes are compacted successively, and at the same time, materials of small particle sizes can be filled in the gaps between particles of large particle sizes, which greatly improves the compaction density of the material pole piece. In some embodiments, the compaction density of the lithium titanate material pole piece is greater than or equal to 2.1 g / cm 3 In some other embodiments, the compaction density of the lithium titanate material pole piece can even reach greater than or equal to 2.4g / cm 3 The material can be used to prepare lithium-ion batteries, and when used to prepare batteries, it helps to increase the energy density of the batteries and enhance the performance of the batteries.

[0058] In some embodiments, the multi-peak in the particle size distribution includes at least a first peak and a second peak. The first peak appears in the range of particle size greater than 0 μm and less than or equal to 5 μm. For example, the particle size range of the first peak can be greater than 0 μm and less than or equal to 5 μm, greater than or equal to 0.5 μm and less than or equal to 2 μm, greater than or equal to 0.5 μm and less than or equal to 2.5 μm, greater than or equal to 2 μm and less than 3 μm, greater than or equal to 2 μm and less than or equal to 4 μm, greater than or equal to 4 μm and less than or equal to 5 μm, and so on; specifically, it can be 0.1 μm, 0.2 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, and values ​​between any two of the above-listed values. The second peak appears in the range of particle size greater than 5μm and less than or equal to 12μm; for example, the particle size range of the second peak can be greater than 5μm and less than or equal to 6μm, greater than or equal to 5.5μm and less than or equal to 7μm, greater than or equal to 6μm and less than or equal to 8μm, greater than or equal to 7μm and less than 10μm, greater than or equal to 9μm and less than or equal to 12μm, greater than or equal to 6μm and less than or equal to 12μm, and so on; specifically it can be 5μm, 5.5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm and values ​​between any two of the above-listed values.

[0059] Furthermore, in one embodiment, the first peak appears in the range of particle size greater than or equal to 2 μm and less than or equal to 4 μm, and the second peak appears in the range of particle size greater than or equal to 6 μm and less than or equal to 12 μm. With this particle size distribution, it is beneficial to further improve the compaction density of the lithium titanate material.

[0060] In some embodiments, the multi-peaks may include other peaks with different particle sizes in addition to the first peak and the second peak, for example, a third peak with a particle size distribution of 10 to 20 μm, and the particle size of the third peak may be 10 to 12 μm, 12 to 16 μm, 16 to 19 μm, 18 to 20 μm, etc. The lithium titanate material having the particle size distribution has a higher compaction density.

[0061] In other embodiments, the particle size distribution has a bimodal feature, that is, it has only a first peak and a second peak. When having such a particle size distribution, it is more conducive to improving the compaction density of the lithium titanate material.

[0062] In practice, it is found that in some cases, when two materials have the same multi-peak characteristics and the particle size of each peak corresponds to the same, if there is a difference in one or more of D1, D10, D50, D90 and D99, it will also have a certain degree of impact on the compaction density. In view of this, in some embodiments, the particle size distribution of the lithium titanate material also satisfies: D1 is less than or equal to 1μm, for example, it can be 0.01μm, 0.1μm, 0.2μm, 0.5μm, 0.7μm, 0.9μm, 1μm and any value between the two values ​​listed above. D10 is greater than or equal to 1μm and less than or equal to 3μm, for example, it can be 1μm, 1.1μm, 1.5μm, 2μm, 2.5μm, 2.8μm, 3μm and any value between the two values ​​listed above. D50 (median particle size) is greater than or equal to 5μm and less than or equal to 7μm, for example, it can be 5μm, 5.2μm, 5.5μm, 6μm, 6.5μm, 6.8μm, 7μm and any value between two of the above-mentioned values. D90 is less than or equal to 18μm, for example, it can be 7μm, 10μm, 11μm, 12μm, 15μm, 17μm, 18μm and any value between two of the above-mentioned values; D99 is less than or equal to 25μm, for example, it can be 18μm, 19μm, 19.5μm, 20μm, 21μm, 22μm, 23μm, 25μm and any value between two of the above-mentioned values. By designing the median particle size of the material and the width of the particle size distribution, the overall particle size distribution of the material is within a suitable range, which helps to further improve the compaction density of the material.

[0063] In addition, in some embodiments, the porosity of the lithium titanate material is greater than or equal to 1% and less than or equal to 20%, for example, it can be 1%, 2%, 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20% and values ​​between any two of the above listed values; the porosity refers to the percentage of the total volume of the voids in the deposit formed by the material to the total volume of the deposit.

[0064] In addition, in some embodiments, the lithium titanate material is a secondary particle having a secondary particle structure, which is prepared from primary particles. Figure 2 The primary particles satisfy the following conditions: the particle size is greater than or equal to 100 nm and less than or equal to 400 nm; for example, the particle size can be 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, and any value between any two of the above values. And / or, the specific surface area is greater than or equal to 6 m 2 / g and less than or equal to 9m 2 / g, for example, it can be 6m 2 / g, 6.5m 2 / g, 7m 2 / g, 7.5m 2 / g, 8m 2 / g, 8.5m 2 / g, 9m 2 / g and values ​​between any two of the above listed values. Using primary particles with this particle size design as raw materials can inhibit agglomeration and surface effect phenomena, so that the secondary particles obtained have moderate toughness and are easy to roll. The pole pieces formed after rolling have high compaction characteristics, and the compaction density can even be as high as 2.4g / cm 3 At the same time, the nanoscale material maintains a high rate performance, which helps to improve battery performance.

[0065] In the second aspect, the present application also proposes a method for preparing lithium titanate material, see Figure 3 , including the following steps:

[0066] S100, providing a plurality of lithium titanate powders with median particle sizes, wherein the median particle sizes of the plurality of lithium titanate powders are arranged in increasing order, and a difference between two adjacent median particle sizes is greater than 0 μm and less than or equal to 12 μm;

[0067] S200, mixing a plurality of the lithium titanate powders, and sintering to obtain a lithium titanate material.

[0068] In step S100, lithium titanate powders with multiple median particle sizes refer to multiple lithium titanate powders whose D50 in the particle size distribution is different from each other, and the difference between two adjacent D50 values ​​is greater than 0μm and less than or equal to 12μm. Specifically, it can be two powders, three powders, or more than three powders. It can be selected according to the particle size distribution design of the lithium titanate material to be prepared. For example, if the designed product lithium titanate material has a three-peak feature, it is necessary to prepare a first lithium titanate powder with a first peak, a second lithium titanate powder with a second peak, and a third lithium titanate powder with a third peak, a total of three median particle size powders. In actual operation, you can directly purchase powders with a particle size distribution that meets the above requirements as raw materials, or you can prepare them yourself.

[0069] In some embodiments, in step S100, the plurality of lithium titanate powders include a first powder and a second powder, the first powder has a median particle size greater than 0 μm and less than or equal to 5 μm, and the second powder has a median particle size greater than 5 μm and less than or equal to 12 μm.

[0070] In some embodiments, the lithium titanate material is a secondary particle structure.

[0071] In some embodiments, lithium titanate powder can be prepared by itself for step S100. Accordingly, the step of providing lithium titanate powders with multiple median particle sizes includes preparing lithium titanate powder, and the preparation of lithium titanate powder includes:

[0072] S10, providing lithium titanate particles having a primary particle structure;

[0073] S20, wet ball milling the lithium titanate particles to obtain a slurry;

[0074] S30, spray drying the slurry to obtain lithium titanate powder.

[0075] In step S10, the lithium titanate particles having a primary particle structure can be prepared by the following steps:

[0076] S11, provide a titanium source, a lithium source and water. The titanium source includes but is not limited to one or more of titanium dioxide, titanium hydroxide, metatitanic acid and TiO(OH)2; the lithium source includes but is not limited to one or more of lithium salts, lithium oxide and lithium hydroxide, and the lithium salt includes one or more of lithium carbonate and lithium oxalate; the water can be deionized water. The molar ratio of the titanium source, the lithium source and the water can be 5:4:(1-1000).

[0077] S12, premixing the titanium source, the lithium source and the water to obtain a premix, and then crushing and mixing the premix until the particle size reaches 0.001 to 0.3 μm to obtain a mixed slurry. The crushing and mixing step can be achieved by grinding, ball milling and other methods. In some embodiments, ball milling is used; during the ball milling, the rotation speed of the ball milling device is 2000 to 4000 rpm, and the ball milling time is 1 to 4 hours.

[0078] S13, spray drying the mixed slurry once to obtain a dry material. The spray drying conditions are: a feed rate of 20 to 50 mL / min, an air inlet temperature of 275 to 285°C, and an air outlet temperature of 115 to 120°C.

[0079] S14, sintering the dried material at 550-950°C to obtain lithium titanate particles with a primary particle structure. During sintering, the temperature is first raised to 550-950°C, and then sintered at a constant temperature for 1-3 hours; while controlling the heating rate to 8-12°C / min, so as to ensure that the entire sintering process is within the range of 7-10 hours.

[0080] Returning to step S20:

[0081] The lithium titanate particles with a primary particle structure are obtained and ball-milled again to adjust the particle size distribution and specific surface area of ​​the particles. Specifically, the particle size of the lithium titanate particles after the wet ball milling is greater than or equal to 100 nm and less than or equal to 400 nm; and / or the specific surface area of ​​the lithium titanate particles after the wet ball milling is greater than or equal to 6 m 2 / g and less than or equal to 9m 2 / g. The primary particles designed in this way are used as raw materials to inhibit agglomeration and surface effect phenomena, so that the secondary particles obtained have moderate toughness and are easy to roll. The pole pieces formed after rolling have high compaction characteristics, and the compaction density can even be as high as 2.4g / cm 3 At the same time, the nanoscale material maintains a high rate performance, which helps to improve battery performance.

[0082] In specific operation, the size of the particles can be controlled by controlling the ball milling conditions. For example, the ball milling conditions can be: the rotation speed of the ball milling device is 2000-4000 rpm, and the ball milling time is 3-7 hours.

[0083] In step S30:

[0084] It can be understood that lithium titanate powder with any particle size distribution can be prepared by the above steps S10 to S30. In actual operation, the particle size distribution of the product can be controlled by controlling the process parameters during spray drying so that it has the designed particle size distribution characteristics.

[0085] In some embodiments, the plurality of lithium titanate powders include a first powder and a second powder, the first powder having a median particle size greater than 0 μm and less than or equal to 5 μm, and the second powder having a median particle size greater than 5 μm and less than or equal to 12 μm. For ease of description, the slurry used to prepare the first powder is named the first slurry, and the slurry used to prepare the second powder is named the second slurry.

[0086] Accordingly, step S30 includes:

[0087] S31, spray-drying the first slurry under a first condition to obtain a first powder;

[0088] S32, spray-drying the second slurry under a second condition to obtain a second powder;

[0089] Among them, the first condition includes a first inlet air temperature, a first outlet air temperature and a first feed speed, and the second condition includes a second inlet air temperature, a second outlet air temperature and a second feed speed; the first inlet air temperature is lower than the second inlet air temperature, the first outlet air temperature is lower than the second outlet air temperature, and the first feed speed is lower than the second outlet speed.

[0090] Specifically, in some embodiments, the first air inlet temperature is 250-270°C; for example, it can be 250°C, 255°C, 260°C, 265°C, 270°C, and a value between any two of the above-listed values. The first air outlet temperature is 100-200°C; for example, it can be 100°C, 120°C, 150°C, 180°C, 200°C, and a value between any two of the above-listed values. The first feed rate is 15-50mL / min; for example, it can be 15mL / min, 16mL / min, 17mL / min, 18mL / min, 20mL / min, 25mL / min, 30mL / min, 35mL / min, 40mL / min, 45mL / min, 50mL / min, and a value between any two of the above-listed values.

[0091] Specifically, in other embodiments, the second air inlet temperature is 260-300°C; for example, it can be 260°C, 265°C, 270°C, 280°C, 290°C, 300°C, and a value between any two of the above-listed values. The second air outlet temperature is 100-200°C; for example, it can be 100°C, 120°C, 150°C, 180°C, 200°C, and a value between any two of the above-listed values. The second feed rate is 25-50mL / min; for example, it can be 25mL / min, 30mL / min, 35mL / min, 40mL / min, 45mL / min, 50mL / min, and a value between any two of the above-listed values.

[0092] In addition, before spray drying, the solid content of the slurry can be adjusted by pre-drying or adding deionized water to prepare a slurry with a solid content of 12 to 35% to facilitate spray drying.

[0093] Returning to step S200:

[0094] After the first powder and the second powder are obtained through the second spray drying, the first powder and the second powder need to be mixed in proportion, and then subjected to secondary sintering to obtain the lithium titanate material.

[0095] In some embodiments, in the lithium titanate material, the weight ratio of the first powder to the second powder is 1:9 to 9:1. Further, the weight ratio of the first powder to the second powder can be 6 to 9:4 to 1, and in the mixed mixture, the weight percentage of the first powder is 60% to 90%, for example, 60%, 70%, 80%, 90% and a value between any two of the above values, and the balance is the second powder.

[0096] In some embodiments, in step S200, the sintering temperature is 650-780°C; for example, it can be 650°C, 680°C, 700°C, 720°C, 750°C, 760°C, 780°C, and any value between two of the above-mentioned values. The sintering time refers to the time used for constant temperature sintering after the temperature rises to 650-780°C, and the sintering time is 0.5-5.5h; for example, it can be 0.5h, 1h, 2h, 3h, 4h, 5h, 5.5h, and any value between two of the above-mentioned values.

[0097] In specific implementation, the sintering steps include: first heating to 650-780° C., and then sintering at a constant temperature for 0.5-5.5 hours; while controlling the heating rate to 2-20° C. / min to ensure that the entire sintering process is within 6-8 hours.

[0098] In some embodiments, in step S200, after sintering, a particle size screening step is also included. In specific implementation, the sintered material can be classified by using a sieve or a particle size classification device to obtain a material with a multi-peak particle size distribution and D1, D10, D50, D90, and D99 that meet the requirements.

[0099] In a third aspect, the present application further proposes a negative electrode plate, wherein the negative electrode plate comprises a lithium titanate material, wherein the lithium titanate material comprises the lithium titanate material described above, or the lithium titanate material is prepared by the preparation method described above.

[0100] In a fourth aspect, the present application further proposes a lithium-ion battery, wherein the lithium-ion battery comprises a negative electrode plate, and the negative electrode plate comprises the negative electrode plate described above.

[0101] The technical scheme and technical effects of the present application are described in detail below through specific embodiments and comparative examples. The following embodiments are only some embodiments of the present application and do not specifically limit the present application.

[0102] Example 1

[0103] (1) Mixing: According to the molar ratio of titanium dioxide, lithium carbonate and deionized water being 5:4:800, the materials are weighed and then premixed to obtain a premix. The premix is ​​introduced into a ball mill for ball milling at a fixed ball mill speed of 3000 rpm for 2 h to obtain a mixed slurry.

[0104] (2) Primary spray drying: The mixed slurry was spray dried at a feed rate of 40 mL / min, an air inlet temperature of 280° C., and an air outlet temperature of 120° C. to obtain a dry material.

[0105] (3) Primary sintering: The dried material is sintered to obtain lithium titanate particles with a primary particle structure. During sintering, the temperature is first raised to 780°C, and then sintered at a constant temperature for 1.5 hours; at the same time, the heating rate is controlled to be 10°C / min to ensure that the entire sintering process takes 8 hours.

[0106] (4) Secondary ball milling: The lithium titanate particles obtained in step (3) were fed into a ball mill and the ball mill speed was set to 3000 rpm for 6 h for wet ball milling to obtain a slurry. The slurry was observed by scanning electron microscopy (SEM). Figure 2 As shown, the particle size distribution of lithium titanate particles in the slurry is between 100 and 300 nm.

[0107] (5) Secondary spray drying: The slurry obtained in step (4) is prepared with deionized water to prepare a slurry with a solid content of 25%. The slurry is spray dried under the first condition to obtain a first powder with a D50 of about 2 μm; the slurry is spray dried under the second condition to obtain a second powder with a D50 of about 8 μm; as shown in Table 1. The nozzle of the spray drying device is a direct spray type; the first condition is: inlet air temperature 250°C, outlet air temperature 120°C, and feed rate 20 mL / min; the second condition is: inlet air temperature 270°C, outlet air temperature 150°C, and feed rate 30 mL / min. The first powder and the second powder are mixed in a weight ratio of 7:3 to obtain a mixed powder.

[0108] (6) Secondary sintering: The mixed powder is sintered and then subjected to particle size classification by a particle size classification device to obtain a lithium titanate material having a secondary particle structure. The particle size distribution of the lithium titanate material is measured by a laser diffraction particle size distribution measuring instrument (e.g., Mastersizer 3000) as shown in FIG. Figure 1 As shown in Table 2. During sintering, the temperature was first raised to 730°C, and then sintered at a constant temperature for 1.5 hours; at the same time, the heating rate was controlled to be 10°C / min to ensure that the entire sintering process took 8 hours.

[0109] The porosity of the lithium titanate material was detected and found to be 15%.

[0110] See also Figure 1 As shown in Table 2, the prepared lithium titanate material has a bimodal distribution particle size characteristic, wherein: the first peak appears at about 2.1 μm, the second peak appears at about 7.6 μm, D1 is 0.72 μm, D10 is 2.67 μm, D50 is 6.23 μm, D90 is 12.41 μm, and D99 is 18.62 μm.

[0111] (7) Preparation of negative electrode sheet: The lithium titanate material, super PLL conductive carbon black and N-methylpyrrolidone prepared in step (6) were weighed and mixed in a mass ratio of 94:3:3, and then coated on aluminum foil to form a 112 μm thick film. After vacuum drying, the film was cut into a negative electrode sheet with a diameter of 14 mm.

[0112] (8) Preparation of battery: dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethylene carbonate (EC) were mixed in a volume ratio of 1:1:1 to prepare a solvent; then 1 mol / L LiPF6 conductive salt and DMC:DEC:EC solvent were used as the electrolyte. 0.8 Co 0.1 Mn 0.1 O2 (NCM 811) is used as the positive electrode, the electrode obtained in step (7) is used as the negative electrode, and the polypropylene film is used as the separator. The prepared positive and negative electrode sheets and separators are stacked in the order of negative electrode, separator, and positive electrode to prepare a battery cell, which is then loaded into a shell to obtain a semi-finished battery; the semi-finished battery is vacuum dried at 95°C until the moisture content of the electrode sheet reaches the injection standard, and then the electrolyte is injected to obtain an uncharged battery. The uncharged battery is subjected to static, hot and cold pressing, formation, shaping, and capacity testing in sequence to obtain a lithium-ion battery.

[0113] Examples 2 to 8

[0114] Examples 2 to 8 are substantially the same as Example 1, except that in Examples 2 to 8, the D50 of the first powder and the second powder obtained in step (5) are as shown in Table 1, and the particle size distribution of the lithium titanate material prepared in step (6) is as shown in Table 1.

[0115] Example 9

[0116] This embodiment is basically the same as Embodiment 1, except that, in this embodiment, the porosity of the lithium titanate material prepared in step (6) is 25%.

[0117] Example 10

[0118] This embodiment is basically the same as embodiment 1, except that in step (4) of this embodiment, the particle size of the primary particles is controlled to be 80 to 100 nm.

[0119] Embodiment 11

[0120] This embodiment is basically the same as Embodiment 1, except that in step (5) of this embodiment, the weight ratio of the first powder to the second powder is changed to 6:4.

[0121] Example 12

[0122] This embodiment is basically the same as Embodiment 1, except that in step (5) of this embodiment, the weight ratio of the first powder to the second powder is changed to 9:1.

[0123] Embodiment 13

[0124] This embodiment is basically the same as Embodiment 1, except that in step (5) of this embodiment, the weight ratio of the first powder to the second powder is changed to 5:5.

[0125] Embodiment 14

[0126] This embodiment is basically the same as embodiment 1, except that step (5) of this embodiment further includes a step of preparing a third powder with D50=10.5 μm (the corresponding third condition is an inlet air temperature of 290°C, an outlet air temperature of 105°C, and a feed rate of 10 mL / min), and when preparing the mixed powder, the first powder, the second powder and the third powder are mixed in a weight ratio of 7:2:1 to obtain the mixed powder.

[0127] Comparative Example 1

[0128] This comparative example is basically the same as Example 1, except that in this comparative example, in step (5), only one kind of powder is obtained, and the D50 of the powder is 9.03 μm.

[0129] Comparative Example 2

[0130] This comparative example is basically the same as Example 1, except that in this comparative example, in step (5), only one kind of powder is obtained, and the D50 of the powder is 6.31 μm.

[0131] Comparative Example 3

[0132] This comparative example is basically the same as Example 1, except that in this comparative example, in step (5), only one kind of powder is obtained, and the D50 of the powder is 4.09 μm.

[0133] Comparative Example 4

[0134] This comparative example is basically the same as Example 1, except that in this comparative example, in step (5), only one kind of powder is obtained, and the D50 of the powder is 3.88 μm.

[0135] Table 1 D50 values ​​of the first powder and the second powder in Examples 1-8

[0136]

[0137]

[0138] Performance Testing

[0139] (1) The lithium titanate material prepared in step (6) in the above-mentioned embodiment and comparative example was taken, and the compaction density of the lithium titanate material pole piece was tested according to the method specified in Appendix L of GB / T24533-2009. The results are recorded in Table 2.

[0140] Table 2 Particle size distribution of each embodiment and comparative example

[0141]

[0142]

[0143] It can be seen from the above table that the particle size distribution of the lithium titanate materials obtained in Comparative Examples 1 to 4 has only a single peak characteristic, while the lithium titanate materials obtained in Examples 1 to 14 have multi-peak characteristics, and in the multi-peaks, the difference in particle size between two adjacent peaks is greater than 0 μm and less than or equal to 12 μm; moreover, compared with Comparative Examples 1 to 4, the lithium titanate materials obtained in Examples 1 to 14 have a higher compaction density, indicating that the lithium titanate material proposed in the present application has greatly improved the compaction density of the material by designing its particle size distribution.

[0144] (2) Take the battery prepared in step (8) in the above embodiment and comparative example, and test its energy density, discharge capacity (under the conditions of 1C / 1C, 1.3-2.5V charge and discharge) and first coulomb efficiency, and record the results in Table 3. The test method is as follows:

[0145] The energy density is detected as follows: at 25°C, the lithium-ion batteries prepared in the examples and comparative examples are fully charged at a 1C rate and fully discharged at a 1C rate, and the actual discharge energy at this time is recorded; the ratio of the actual discharge energy of the lithium-ion battery at 1C to the volume of the lithium-ion battery is the actual energy density of the lithium-ion battery.

[0146] The discharge capacity detection method is as follows: place the button-type lithium-ion battery prepared above on a test cabinet, first test the current at 0.5C in a 25°C constant temperature box; let it stand for 3 hours; charge at 0.5C rate until the voltage is ≥2.5V; charge at 2.5V constant voltage until the current is ≤0.05mA; let it stand for 5 minutes; discharge at 0.5C rate until the voltage is ≤1.3V. Record the first discharge capacity of the battery.

[0147] The first coulombic efficiency detection method is: at 25 ° C, the battery prepared in the embodiment and the comparative example is charged to 5mV at a rate of 0.1C and discharged to 1.5V at a rate of 0.1C, and a full charge and discharge test is performed. The ratio of the discharge capacity to the charge capacity is the first efficiency.

[0148] Table 3

[0149]

[0150]

[0151] It can be seen from Table 3 that compared with Comparative Example 1, the lithium-ion batteries made of lithium titanate materials in each embodiment have higher energy density, discharge capacity and first coulombic efficiency, indicating that when the lithium titanate material proposed in the present application is used to make batteries, it is helpful to obtain high energy density and high performance batteries.

[0152] The lithium titanate material and its preparation method, negative electrode plate and lithium-ion battery provided in the embodiments of the present application are introduced in detail above. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea; at the same time, for technical personnel in this field, according to the ideas of the present application, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A lithium titanate material, characterized in that: The particle size distribution of the lithium titanate material satisfies: the particle size distribution includes a plurality of particle size peaks, and the difference between the particle sizes of two adjacent peaks is greater than 0 μm and less than or equal to 12 μm.

2. The lithium titanate material according to claim 1, characterized in that: The particle size distribution includes a first peak and a second peak, the first peak appears in a range where the particle size is greater than 0 μm and less than or equal to 5 μm, and the second peak appears in a range where the particle size is greater than 5 μm and less than or equal to 12 μm; and / or, The lithium titanate material is a secondary particle structure; and / or, The porosity of the lithium titanate material is greater than or equal to 1% and less than or equal to 20%.

3. The lithium titanate material according to claim 2, characterized in that: The first peak appears in a range where the particle size is greater than or equal to 2 μm and less than or equal to 4 μm, and the second peak appears in a range where the particle size is greater than or equal to 6 μm and less than or equal to 12 μm.

4. The lithium titanate material according to claim 1, characterized in that: The particle size distribution of the lithium titanate material also satisfies: D1 is less than or equal to 1 μm; and / or, D10 is greater than or equal to 1 μm and less than or equal to 3 μm; and / or, D50 is greater than or equal to 5 μm and less than or equal to 7 μm; and / or, D90 is less than or equal to 18 μm; and / or, D99 is less than or equal to 25μm.

5. A method for preparing a lithium titanate material, characterized in that: The following steps are involved: Providing lithium titanate powders with a plurality of median particle sizes, wherein the median particle sizes of the plurality of lithium titanate powders are arranged in increasing order, and a difference between two adjacent median particle sizes is greater than 0 μm and less than or equal to 12 μm; A plurality of the lithium titanate powders are mixed and sintered to obtain a lithium titanate material.

6. The preparation method according to claim 5, characterized in that: In the step of providing lithium titanate powders with multiple median particle sizes, the multiple lithium titanate powders include a first powder and a second powder, the first powder has a median particle size greater than 0 μm and less than or equal to 5 μm, and the second powder has a median particle size greater than 5 μm and less than or equal to 12 μm.

7. The preparation method according to claim 6, characterized in that: In the lithium titanate material, the weight ratio of the first powder to the second powder is 1:9 to 9:

1.

8. The preparation method according to claim 5, characterized in that: The lithium titanate material is a secondary particle structure; and / or, The sintering temperature is 650-780° C.; and / or, The sintering time is 0.5 to 5.5 hours; and / or, The step of providing lithium titanate powders with a plurality of median particle sizes includes preparing lithium titanate powders, wherein the preparing lithium titanate powders includes: Providing lithium titanate particles having a primary particle structure; Wet ball milling the lithium titanate particles to obtain a slurry; The slurry is spray-dried to obtain lithium titanate powder.

9. The preparation method according to claim 8, characterized in that: The particle size of the lithium titanate particles after the wet ball milling is greater than or equal to 100 nm and less than or equal to 400 nm; and / or, The specific surface area of ​​the lithium titanate particles after wet ball milling is greater than or equal to 6 m 2 / g and less than or equal to 9m 2 / g.

10. The preparation method according to claim 8, characterized in that: The plurality of lithium titanate powders include a first powder and a second powder, the first powder has a median particle size greater than 0 μm and less than or equal to 5 μm, and the second powder has a median particle size greater than 5 μm and less than or equal to 12 μm; The slurry used to prepare the first powder is the first slurry, and the slurry used to prepare the second powder is the second slurry; The step of spray drying the slurry to obtain a powder material comprises: Under a first condition, spray drying the first slurry to obtain a first powder; Under a second condition, spray drying the second slurry to obtain a second powder; Among them, the first condition includes a first inlet air temperature, a first outlet air temperature and a first feed speed, and the second condition includes a second inlet air temperature, a second outlet air temperature and a second feed speed; the first inlet air temperature is lower than the second inlet air temperature, the first outlet air temperature is lower than the second outlet air temperature, and the first feed speed is lower than the second outlet speed.

11. The preparation method according to claim 10, characterized in that: The first air inlet temperature is 250-270° C.; and / or, The first air outlet temperature is 100-200° C.; and / or, The first feed rate is 15 to 50 mL / min; and / or, The second air inlet temperature is 260-300° C.; and / or, The second air outlet temperature is 100-200° C.; and / or, The second feed rate is 25-50 mL / min.

12. A negative electrode plate, characterized in that: It comprises a lithium titanate material, wherein the lithium titanate material comprises the lithium titanate material according to any one of claims 1 to 4, or the lithium titanate material is prepared by the preparation method according to any one of claims 5 to 11.

13. A lithium ion battery, comprising a negative electrode plate, characterized in that: The negative electrode plate comprises the negative electrode plate according to claim 12.

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