Battery, battery separator, and separator manufacturing method

Abstract

The present invention provides a battery, a battery separator, and a method for preparing the separator. The battery separator includes a base film and a coating structure disposed on the base film. The coating structure contains multiple material layers, each material layer having a one-dimensional nanomaterial. Along the direction away from the base film, the average length of the one-dimensional nanomaterial in each material layer decreases layer by layer.

Description

Technical Field

[0001] This invention relates to the field of batteries, and more particularly to a battery, a battery separator, and a method for preparing the separator. Background Technology

[0002] The separator is one of the core components of a lithium-ion battery, and its performance has a significant impact on the overall performance of the battery, making it a key technology restricting the development of lithium-ion batteries. With the continuous expansion of lithium-ion battery applications and the deepening influence of lithium-ion battery products in people's lives, the requirements for lithium-ion battery performance are also increasing. To meet these development requirements, the separator, as a crucial component of lithium-ion batteries, should not only possess good chemical stability and low manufacturing costs, but improving the safety performance of lithium-ion batteries is also a significant trend in current lithium battery development.

[0003] In existing related technologies, the separator of a lithium-ion battery may include a base film and a coating covering at least one surface of the base film. The coating may contain one-dimensional nanomaterials. However, the stacking mode of one-dimensional nanomaterials is disordered, which can easily cause problems such as too many voids and too few contact points, thereby affecting the thermal stability of the separator. Summary of the Invention

[0004] This invention provides a battery, a battery separator, and a method for preparing the separator, in order to solve problems such as excessive voids and insufficient contact points.

[0005] According to a first aspect of the present invention, a separator for a battery is provided, comprising: a base film and a coating structure disposed on the base film, the coating structure containing multiple material layers, each material layer containing a one-dimensional nanomaterial, and the average length of the one-dimensional nanomaterial in each material layer decreasing layer by layer along a direction away from the base film.

[0006] Optionally, for the one-dimensional nanomaterials in the coating structure, the following conditions must be met: 5≥L50 / L10≥1.3, 4≥L90 / L50≥1.3;

[0007] L10 represents the length description value of the one-dimensional nanomaterial in the coating structure when 10% is the first target percentage.

[0008] The L50 characterizes the length description value of the one-dimensional nanomaterial in the coating structure when 50% is the first target percentage.

[0009] L90 represents the length description value of the one-dimensional nanomaterial in the coating structure when 90% is taken as the first target proportion.

[0010] The length description value of the one-dimensional nanomaterial in the coating structure indicates that when the number of one-dimensional nanomaterials in the coating structure is gradually accumulated in order from shortest to longest, the length of the one-dimensional nanomaterial corresponds to the ratio of the accumulated number to the total number of one-dimensional nanomaterials in the coating structure when the ratio reaches the first target proportion.

[0011] Optional,

[0012] The length of L10 of the one-dimensional nanomaterial in the coating structure is between 100 and 300 nm.

[0013] The length of the L50 of the one-dimensional nanomaterial in the coating structure is between 250 and 400 nm.

[0014] The length of the L90 of the one-dimensional nanomaterial in the coating structure is between 350 and 900 nm.

[0015] Optionally, the proportion of one-dimensional nanomaterials in different material layers relative to the same second target results in different length description values;

[0016] The length description value of the one-dimensional nanomaterial in the material layer indicates that:

[0017] When the number of one-dimensional nanomaterials in the corresponding material layer is gradually accumulated in order of length from shortest to longest, the length of the corresponding one-dimensional nanomaterial is such that the ratio of the accumulated number to the total number of one-dimensional nanomaterials in the corresponding material layer reaches the second target percentage. The second target percentage is not 50%.

[0018] Along the direction away from the base film, for the same second target proportion, the length description value of the one-dimensional nanomaterial of each material layer gradually decreases.

[0019] Optionally, the second target percentage is in the range of 5%-40%, or in the range of 60%-99%.

[0020] Optionally, the one-dimensional nanomaterial includes at least one of the following: nanocellulose, aramid nanofibers, and polyimide nanofibers.

[0021] Optionally, in the adjacent first material layer and second material layer, the voids of the one-dimensional nanomaterial in the first material layer are partially or completely filled by the one-dimensional nanomaterial in the second material layer; wherein, the first material layer is located on the side of the second material layer facing the base film.

[0022] According to a second aspect of the invention, a battery is provided, comprising the separator described in the first aspect and its alternatives.

[0023] According to a third aspect of the present invention, a method for preparing a diaphragm is provided for preparing the diaphragm involved in the first aspect and its alternative embodiments, the method comprising:

[0024] Dispersing one-dimensional nanomaterials of different lengths in the same or different dispersants yields at least one dispersion.

[0025] Based on the at least one dispersion, at least one corresponding slurry is formed;

[0026] The at least one slurry is coated onto the base film, and the base film and the slurry are dried to obtain the diaphragm.

[0027] Optionally, before dispersing the one-dimensional nanomaterials of different lengths in the same or different dispersants to obtain at least one dispersion, the method further includes:

[0028] The raw material or the broken one-dimensional nanomaterial is broken apart, and one-dimensional nanomaterials of at least some different lengths are formed by breaking them apart once or multiple times.

[0029] Optionally, before dispersing one-dimensional nanomaterials of different lengths in the same or different dispersants to obtain at least one dispersion, the method further includes:

[0030] Perform at least one of the bonding processes a), b), and c), and through one or more bonding operations, form one-dimensional nanomaterials of at least partially different lengths:

[0031] a) Joining the raw material of a one-dimensional nanomaterial to one end of another raw material;

[0032] b) The joined one-dimensional nanomaterial is joined to one end of the raw material;

[0033] c) Join the joined one-dimensional nanomaterial to one end of another joined one-dimensional nanomaterial.

[0034] Optionally, the engagement includes:

[0035] The one-dimensional nanomaterial to be bonded is mixed with a material rich in hydroxyl functional groups in a solution;

[0036] Molecular sieve particles are added to the solution as a catalyst;

[0037] The solution is heated, then cooled, and the molecular sieve particles are removed by filtration to obtain the bonded one-dimensional nanomaterial.

[0038] Optionally, based on the at least one dispersion, at least one corresponding slurry is formed, including:

[0039] Adhesive and additives are added to the dispersion in sequence.

[0040] Optionally, the adhesive comprises at least one of the following: polyacrylic acid, lithium polyacrylate, polyvinyl alcohol, polyvinylpyrrolidone, and carboxymethyl cellulose;

[0041] The adjuvants include at least one of the following: glycerol, fluoroalkyl ethoxylate, sodium butadiene naphthalene sulfonate, sodium hydroxyethyl sulfate, and sodium dodecyl sulfate.

[0042] Optionally, the preparation method further includes:

[0043] Poly-N-isopropylacrylamide is added to the dispersion or the slurry.

[0044] In the battery, battery separator, and separator preparation method provided by this invention, since the length of the one-dimensional nanomaterial is related to its surface energy, and thus to its adhesion to the base film, compared to randomly distributed one-dimensional nanomaterials, this invention achieves an ordered distribution based on adhesion through layer-by-layer distribution. Because it is ordered, it avoids the formation of potentially large voids due to random or disordered distribution and ensures a sufficient number of contact points. Furthermore, since the voids in the one-dimensional nanomaterial of the first material layer are partially or completely filled by the one-dimensional nanomaterial of the second material layer, and the first material layer is located on the side of the second material layer facing the base film, the voids are further reduced and the number of contact points is increased while maintaining the orderliness of the one-dimensional nanomaterials. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a partial structural schematic diagram of the separator of a battery in one embodiment of the present invention;

[0047] Figure 2 This is a schematic flowchart of a membrane preparation method according to an embodiment of the present invention;

[0048] Figure 3 This is a schematic diagram illustrating how the length of the material layer l50 varies with the coating position in a specific example of the present invention.

[0049] Explanation of reference numerals in the attached figures:

[0050] 1-Diaphragm

[0051] 11-Base film;

[0052] 12-Coating structure. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] In the description of this invention, it should be understood that the terms "upper part", "lower part", "upper end", "lower end", "lower surface", "upper surface", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention.

[0055] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

[0056] In the description of this invention, "a plurality of" means multiple, such as two, three, four, etc., unless otherwise explicitly specified.

[0057] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" and other such terms should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a mechanical connection, an electrical connection, or a connection that allows communication between the components; it can refer to a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0058] The technical solution of the present invention will be described in detail below with reference to specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0059] Please refer to Figure 1This invention provides a battery separator 1, comprising: a base film 11 and a coating structure 12 disposed on the base film 11. The coating structure 12 contains multiple material layers, each of which contains a one-dimensional nanomaterial. Along the direction away from the base film, the average length of the one-dimensional nanomaterial in each material layer decreases layer by layer. Correspondingly, the average size of the voids in the one-dimensional nanomaterial in each material layer also gradually decreases.

[0060] The coating has the following characteristics: Figure 1 The three-layer material shown has a bottom-layer one-dimensional nanomaterial with an average length longer than the middle layer, and the middle layer has an average length longer than the top layer. The difference in average length between the layers can be arbitrarily configured, and the lengths of the one-dimensional nanomaterials within the same layer can be the same or different. In one embodiment, the one-dimensional nanomaterial includes at least one of the following: cellulose nanofibers, aramid nanofibers, and polyimide nanofibers. The material selection for the one-dimensional nanomaterial in this embodiment is not limited to the examples above.

[0061] In one embodiment, the proportion of one-dimensional nanomaterials in different material layers relative to the same second target forms different length description values;

[0062] The length description value of the one-dimensional nanomaterial in the material layer indicates that:

[0063] When the number of one-dimensional nanomaterials in the material layer is gradually accumulated in order of length from shortest to longest, the length of the one-dimensional nanomaterial corresponds to the ratio of the accumulated number to the total number of one-dimensional nanomaterials in the material layer when it reaches the second target proportion. Correspondingly, the proportion of one-dimensional nanomaterials smaller than the corresponding length description value in the corresponding material layer can reach the target proportion. The above description shows the statistical significance of the length description value of one-dimensional nanomaterials. In practice, when determining this length description value, the actual calculation method can be handled according to common sense in the field.

[0064] In one example, the second target percentage is in the range of 5%-40%, or in the range of 60%-99%. For example, it can be 5%, 10%, 20%, 40%, 60%, 70%, 80%, 90%, 99%, etc.

[0065] In one embodiment, along the direction away from the base film, for the same second target proportion, the length description value of the one-dimensional nanomaterial in each material layer gradually decreases. Thus, a trend of decreasing length of the one-dimensional nanomaterial layer by layer can be formed.

[0066] Furthermore, while the length description values ​​for the corresponding material layers are defined above by accumulating and determining the length description value based on the accumulation result, this does not necessarily mean that this statistical process is included in the actual preparation and acceptance process. In practical solutions, for any product, as long as the length description values ​​obtained after statistically analyzing the one-dimensional nanomaterials in the material layer with values ​​of the same statistical significance satisfy the above description, it does not deviate from the protection scope of this embodiment. In some solutions, the above length rules can be ensured in advance by selecting the length of the one-dimensional nanomaterials or by preparing the one-dimensional nanomaterials with targeted lengths.

[0067] in:

[0068] For example, the length description value of a one-dimensional nanomaterial for a material layer can be:

[0069] The l10 of the one-dimensional nanomaterial in the material layer refers to the length of the one-dimensional nanomaterial when the ratio of the accumulated quantity to the total quantity of one-dimensional nanomaterials in the corresponding material layer reaches 10% when the quantity of one-dimensional nanomaterials of each length in the corresponding material layer is gradually accumulated in order from shortest to longest.

[0070] The l50 of the one-dimensional nanomaterial in the material layer refers to the length of the one-dimensional nanomaterial when the ratio of the accumulated quantity to the total quantity of one-dimensional nanomaterials in the corresponding material layer reaches 50% when the quantity of one-dimensional nanomaterials of each length in the corresponding material layer is gradually accumulated in order from shortest to longest. This l50 can also be understood as being able to characterize the average length of the corresponding material layer to a certain extent.

[0071] The l90 of the one-dimensional nanomaterial in the material layer refers to the length of the one-dimensional nanomaterial when the ratio of the accumulated quantity to the total quantity of one-dimensional nanomaterials in the corresponding material layer reaches 90% when the quantity of one-dimensional nanomaterials of each length in the corresponding material layer is gradually accumulated in order from shortest to longest.

[0072] While achieving a decrease in l50 (i.e., average length), it is also possible to achieve a decrease in one or more other length description values ​​(e.g., l90 and / or l10).

[0073] Furthermore, in the above scheme, the changing trend of the defined length description value can fully demonstrate that: under l50 and the proportion of each second objective, the one-dimensional nanomaterials all show a trend of decreasing layer by layer, ensuring the orderly distribution of the one-dimensional nanomaterials. In turn, the length gradient distribution of the one-dimensional nanomaterials is more concentrated and uniform, which is more conducive to reducing the number and size of voids, increasing the number of contact points, and further improving heat resistance.

[0074] In one implementation method

[0075] The length of L10 of the one-dimensional nanomaterial in the coating structure is between 100 and 300 nm.

[0076] The length of the L50 of the one-dimensional nanomaterial in the coating structure is between 250 and 400 nm.

[0077] The length of the L90 of the one-dimensional nanomaterial in the coating structure is between 350 and 900 nm.

[0078] in:

[0079] L10 of the one-dimensional nanomaterial in the coating structure is characterized by the length description value of the one-dimensional nanomaterial in the coating structure when 10% is the first target proportion.

[0080] The L50 of the one-dimensional nanomaterial in the coating structure is characterized by the length description value of the one-dimensional nanomaterial in the coating structure when 50% is taken as the first target proportion, which can also be understood as the average length of the one-dimensional nanomaterial in the coating structure.

[0081] L90 of the one-dimensional nanomaterial in the coating structure is characterized by the length description value of the one-dimensional nanomaterial in the coating structure when 90% is taken as the first target proportion.

[0082] The length description value of the one-dimensional nanomaterial in the coating structure indicates that:

[0083] When the number of one-dimensional nanomaterials in the coating structure is gradually accumulated in order of length from shortest to longest, the length of the one-dimensional nanomaterials corresponds to the length of the one-dimensional nanomaterials when the ratio of the accumulated number to the total number of one-dimensional nanomaterials in the coating structure reaches the first target proportion.

[0084] Furthermore, for the one-dimensional nanomaterials in the coating structure, the following conditions must be met: L50 / L10 > 1.3, L90 / L50 > 1.3;

[0085] L10 of the one-dimensional nanomaterial in the coating structure refers to the length description value of the one-dimensional nanomaterial in the coating structure when 10% is taken as the first target proportion.

[0086] L50 of the one-dimensional nanomaterial in the coating structure refers to the length description value of the one-dimensional nanomaterial in the coating structure when 50% is taken as the first target proportion.

[0087] L90 of the one-dimensional nanomaterial in the coating structure refers to the length description value of the one-dimensional nanomaterial in the coating structure when 90% is taken as the first target proportion.

[0088] The above description illustrates the statistical significance of the length description value of the coating structure. When determining this length description value in practice, the actual calculation method can be handled according to common sense in the field.

[0089] Furthermore, regarding the length description values ​​of the coating structure, although the above definition uses an accumulation method to determine the length description value based on the accumulation result, it does not imply that this statistical process must be included in the actual preparation and acceptance process. In practical solutions, for any product, as long as the length description values ​​obtained after statistically analyzing the one-dimensional nanomaterials in the material layer with values ​​of the same statistical significance satisfy the above description, it does not deviate from the protection scope of this embodiment. In some solutions, the above length rules can be ensured in advance by selecting the length of the one-dimensional nanomaterials or by preparing the one-dimensional nanomaterials with targeted lengths.

[0090] In one example, for the one-dimensional nanomaterial in the coating structure, L10 = 110 nm, L50 = 310 nm, and L90 = 850 nm.

[0091] In the direction away from the base film, the fitted results of the relationship between the length of the one-dimensional nanomaterial l50 in each material layer and the position of the material layer in the coating (position in the coating thickness direction) can be referred to Figure 3 Understanding curves 1, 2a, and 2b, we can see that as the thickness increases (i.e., as the distance between the coating layer and the base film increases), the length of l50 gradually decreases.

[0092] exist Figure 3 In the diagram, the horizontal axis represents the coating position, indicating the location of the material layer within the coating structure along the thickness direction. If expressed as a percentage, it represents the distance between the coating position and the base film relative to the overall thickness of the coating structure. For example, 10% indicates that the distance between the coating position and the base film accounts for 10% of the overall thickness of the coating structure.

[0093] For curve 1, as the distance between the coating position and the base film increases, the length value of l50 of the one-dimensional nanomaterial in the material layer can be understood as a linear change. At this time, the relationship between the length value x of l50 and the coating position Y can be presented as follows: Y = kx + b (k < 0, b > 0).

[0094] Regarding curve 2a, as the distance between the material layer and the base film increases, the length of l50 of the one-dimensional nanomaterial in the material layer can show a trend of rapid change followed by slow change.

[0095] Regarding curve 2b, as the distance between the material layer and the base film increases, the length of the one-dimensional nanomaterial l50 in the material layer can show a trend of slow change followed by fast change.

[0096] To achieve the above-mentioned linear, fast-then-slow, and slow-then-fast variation trends, this can be achieved through the length configuration of the one-dimensional nanomaterials in the coating structure. Furthermore, the length configuration of the one-dimensional nanomaterials in the coating structure can be selected according to the desired variation trend.

[0097] For example:

[0098] To achieve linear variation (as shown in curve 1), the length configuration of the one-dimensional nanomaterial in the coating structure must satisfy: 2≥L90 / L50>1.5;

[0099] To achieve a change from slow to fast (as shown in curve 2b), the length configuration of the one-dimensional nanomaterial in the coating structure must satisfy: L50 / L10 > 2; 1.5 ≥ L90 / L50 ≥ 1.3;

[0100] If a change from fast to slow is to be achieved (as shown in curve 2a), then the length configuration of the one-dimensional nanomaterial in the coating structure must satisfy: L90 / L50 > 2.

[0101] Since existing technologies do not focus on forming layered structures, they cannot disclose or reveal the length configurations for different changing trends in the above schemes.

[0102] The table below details some one-dimensional nanomaterials (whose length is represented as fiber length in the table) and their effects after application:

[0103]

[0104]

[0105] Where L represents the length of the one-dimensional nanomaterial.

[0106] As can be seen from Examples 1 to 6, when L is within a suitable range, the coated diaphragm has the best heat resistance. When L is too small (Examples 10, 11, 12) or too large (Examples 15, 16), the heat resistance of the coated diaphragm deteriorates.

[0107] Research and analysis have shown that the main reason for this result is:

[0108] When the length of one-dimensional nanomaterials is too small, the degree of stacking between them is insufficient to form an interwoven network structure, resulting in inadequate heat resistance. Only by increasing the thickness can the heat resistance of the coating be effectively improved. When the length of one-dimensional nanomaterials is too long, they (i.e., nanowires) will form a twisted structure. When these twisted nanomaterials are deposited on the membrane surface, they will self-fold, leading to insufficient contact with other nanowires and weakened interactions (as shown in Examples 10, 11, and 12).

[0109] In addition, when the one-dimensional nanomaterial is too long, the deposited coating has large voids and the distance between contact points is too far. When subjected to external forces (such as shrinkage of the base film caused by heating), these contact points cannot transmit forces to each other in time, which leads to the collapse and destruction of the entire coating structure, thus failing to suppress the thermal shrinkage of the coated diaphragm (as shown in Examples 15 and 16).

[0110] Therefore, when L is between 100 nm and 900 nm, the coating will achieve both a thinner coating structure (the thickness of the coating structure is less than 1 micrometer) and excellent heat resistance (180℃). That is, the layered structure characteristics allow the coating to achieve excellent heat resistance with a relatively thin thickness (less than 1 micrometer). When the length of the nanowires (i.e., one-dimensional nanomaterials) is between 100 nm and 900 nm, the nanowires (i.e., one-dimensional nanomaterials) are deposited on the surface of the base film to form a layered structure (i.e., layers of one-dimensional nanomaterials of different lengths). During the deposition process on the base film, due to surface energy, the longest one-dimensional nanomaterial (which has the largest surface energy and is the least stable, and is most likely to adhere when in contact with an interface with a smaller surface energy) is deposited first, followed by the longer ones, and the shortest nanowires are deposited last, thus forming a layered structure that gradually accumulates from long to short.

[0111] Furthermore, in adjacent material layers, the voids in the lower layer of one-dimensional nanomaterials are partially or completely filled by the upper layer of one-dimensional nanomaterials.

[0112] It is evident that, due to the large gaps in the stacking of long nanomaterials, the gaps become larger at the bottom layer. The shorter nanomaterials in the next layer can fill these gaps to some extent. After layer-by-layer deposition, the coating has no excessive gaps and has many contact points. Therefore, when heated, the tight structure of the coating can suppress thermal deformation of the diaphragm.

[0113] Example 4 was compared with Comparative Examples 3 and 4, Example 15 was compared with Comparative Example 1, and Example 16 was compared with Comparative Example 2.

[0114] It can be seen that the coated membrane exhibits optimal heat resistance when the length of the one-dimensional nanomaterial decreases layer by layer (reflected in the decrease of the descriptive value of the length of the one-dimensional nanomaterial in each material layer). For coatings where the length of the one-dimensional nanomaterial increases layer by layer or is randomly arranged, the heat resistance of the coated membrane is poor. The main reason for this phenomenon is that only the layer-by-layer decreasing stacking method of the one-dimensional nanofibers results in the maximum packing density of the coating, maximizing the contact between the nanofibers. Whether the stacking length increases layer by layer or the arrangement is random, the packing density of the coating is relatively low, thus offering very limited improvement in heat resistance.

[0115] Further solutions can incorporate additional techniques to ensure the layering of one-dimensional nanomaterials. For example, since the layering of one-dimensional nanomaterials is primarily achieved during the coating and drying process, a temperature-sensitive polymer, such as poly(N-isopropylacrylamide) (PNIPAM), can be added to achieve layering during heating. PNIPAM molecules contain a certain proportion of hydrophobic isopropyl groups and hydrophilic amide groups. At temperatures below 40 degrees Celsius, the hydrophilic amide groups exhibit strong hydrogen bonding with the hydroxyl groups on the one-dimensional nanomaterials, resulting in good affinity between the polymer chains, the one-dimensional nanomaterials, and the solvent. At this temperature, the PNIPAM polymer chains are in an extended state, exhibiting water absorption and swelling, and resulting in poor solution flowability. As the temperature rises above 40 degrees Celsius, the hydrophilic interaction between water molecules and amide groups weakens, while the hydrophobic interaction between isopropyl groups in the PNIPAM molecular chain strengthens. The hydrophobic interaction in the PNIPAM polymer chain gradually strengthens and becomes dominant, causing the polymer chains to aggregate through hydrophobic interactions to form a hydrophobic layer. This leads to the expulsion of water molecules and a phase transition. At this point, the polymer chain changes from a loose coil structure to a compact colloidal particle structure, increasing the fluidity of the solution. Since the longer the length of the one-dimensional nanomaterial, the more PNIPAM it carries, and the stronger its hydrophobicity, the easier it is to settle first. Therefore, introducing PNIPAM can help ensure the realization of stratification.

[0116] As can be seen, in the above schemes, since the length of the one-dimensional nanomaterial is related to its surface energy, and thus to the adhesion ability of the base film, compared with randomly distributed one-dimensional nanomaterials, the present invention achieves an ordered distribution based on adhesion ability by distributing it layer by layer. Because it is ordered, it avoids the formation of potentially large voids due to random and disordered distribution, and ensures a sufficient number of contact points. Furthermore, the voids in some layers of one-dimensional nanomaterials are partially or completely filled by the one-dimensional nanomaterials above them, thereby further reducing voids and increasing contact points while ensuring the orderliness of the one-dimensional nanomaterials.

[0117] In addition to the diaphragm and base membrane mentioned above, other material layers may also be introduced in specific examples.

[0118] This invention also provides a battery including the separator described in the above-mentioned optional solutions.

[0119] The battery can be, for example, a lithium-ion battery. Furthermore, a separator can be provided on the electrode surface of the battery. In addition, other existing or improved structural layers can also be provided inside and outside the separator.

[0120] Please refer to Figure 2 The present invention also provides a method for preparing a diaphragm, used to prepare the diaphragm involved in the first aspect and its alternative solutions, the preparation method comprising:

[0121] S21: Disperse the one-dimensional nanomaterials of different lengths in the same or different dispersants to obtain at least one dispersion;

[0122] S22: Based on the at least one dispersion, form at least one corresponding slurry;

[0123] S23: Coat the base film with the at least one slurry, and dry the base film and the slurry to obtain the diaphragm.

[0124] In one example of step S23, the coating may be applied only once and then dried once; in this case, the coated slurry may contain a variety of one-dimensional nanomaterials of different lengths.

[0125] In another example of step S23, multiple coatings can be applied, and each coating can be dried. In this case, the slurry used for each coating can be of different types, and different slurries can be applied sequentially according to the length of the one-dimensional nanomaterial from shortest to longest. Taking three coatings and three layers as an example, the slurry containing the longest one-dimensional nanomaterial can be coated on the base film first. After drying, the slurry containing the longer one-dimensional nanomaterial can be coated on top. After drying, the slurry containing the shortest one-dimensional nanomaterial can be coated on top.

[0126] In addition, each coating can be done using one type of slurry, or two or more types of slurries can be mixed before coating.

[0127] In one embodiment, at least some one-dimensional nanomaterials of different lengths can be achieved based on the selection of raw materials for one-dimensional nanomaterials. For example, when one-dimensional nanomaterials using different materials are selected, one-dimensional nanomaterials of different lengths may be formed.

[0128] In other examples, one-dimensional nanomaterials of different lengths can also be formed through corresponding technical means.

[0129] In one example, before step S21, the following steps are also included:

[0130] S24: Break the raw material or broken one-dimensional nanomaterial into pieces, and form at least some one-dimensional nanomaterials of different lengths through one or more breaking processes.

[0131] In this regard, by breaking down one-dimensional nanomaterials, shorter one-dimensional nanomaterials can be formed from raw materials of one-dimensional nanomaterials of a certain length. For example, one-dimensional nanomaterials can be broken down into half of the raw materials. In other examples, it is also possible to achieve this without breaking down the materials in half.

[0132] Any existing or improved method that can achieve the breaking of one-dimensional nanomaterials can be used as a specific example of the embodiments of the present invention. In a specific example, it can be achieved by etching the one-dimensional nanomaterial; for example, the one-dimensional nanomaterial can be etched to half the length of the original material.

[0133] Based on the required layering, the raw material can be broken in one step or multiple times. For example, one-dimensional nanomaterials can be etched to half the length of the raw material, then half the length of the one-dimensional nanomaterials can be retained, and then the other half of the length of the one-dimensional nanomaterials can be broken to obtain a quarter-length one-dimensional nanomaterial. At this time, a three-layer structure can be formed. In other examples, a quarter-length of the one-dimensional nanomaterials can be further broken. The number of breaks can be arbitrarily configured according to the requirements.

[0134] In one example, before step S21, the following steps are also included:

[0135] S25: Perform at least one of the joining processes a), b), and c), and form at least partially different lengths of one-dimensional nanomaterials through one or more joining processes:

[0136] a) Joining the raw material of a one-dimensional nanomaterial to one end of another raw material;

[0137] b) The joined one-dimensional nanomaterial is joined to one end of the raw material;

[0138] c) Join the joined one-dimensional nanomaterial to one end of another joined one-dimensional nanomaterial.

[0139] It can be seen that the objects to be joined can be one end of a raw material and one end of another raw material, one end of a raw material and one end of a joined one-dimensional nanomaterial, or one end of a joined one-dimensional nanomaterial and one end of another joined one-dimensional nanomaterial.

[0140] In this invention, only one of the joining processes a), b), or c) may be performed; at least two of the joining processes a), b), and c) may be performed; or all three joining processes a), b), and c) may be performed. Of course, this invention does not limit the number of joining processes in any of the above-mentioned joining processes.

[0141] When performing at least two of the joining processes a), b), and c), the present invention does not limit the number of joining processes a), b), and c, or the joining order. For example, joining processes a) and b) can be performed sequentially, joining processes a), a), and c) can be performed sequentially, joining processes a), b), and c) can be performed sequentially, joining processes a), a), a), b), and c) can be performed sequentially, or joining processes a), a), b), b), and c) can be performed sequentially, etc.

[0142] In this regard, by joining one-dimensional nanomaterials, a longer one-dimensional nanomaterial can be formed based on a raw material of one-dimensional nanomaterial of a certain length. For example, two raw materials can be joined to form a one-dimensional nanomaterial of twice the length. In other examples, raw materials (or joined one-dimensional nanomaterials) of different lengths can also be used.

[0143] Any existing or improved means that can achieve the bonding of one-dimensional nanomaterials can be used as a specific example of an embodiment of the present invention.

[0144] For example, the bonding of one-dimensional nanomaterials can be achieved based on materials rich in hydroxyl functional groups (such as polyethylene glycol PEG). Furthermore, the bonding mentioned above can include:

[0145] The one-dimensional nanomaterial to be bonded is mixed with a material rich in hydroxyl functional groups (such as PEG) in a solution;

[0146] Molecular sieve particles are added to the solution as a catalyst;

[0147] The solution is heated, then cooled, and filtered to remove the molecular sieve particles, yielding the bonded one-dimensional nanomaterial.

[0148] In a specific example, let's take nanocellulose. The hydroxyl content at the ends of nanocellulose is significantly higher than in the middle region. To increase the length of nanocellulose, the activity of the hydroxyl groups can be fully utilized, as follows:

[0149] (1) Mix nanocellulose with polyethylene glycol (PEG). The molecular weight of PEG is 50,000-1,000,000 g / mol. PEG accounts for 1% of nanocellulose. Stir the two thoroughly to form the corresponding solution.

[0150] (2) Add 13A molecular sieve particles with a particle size of 1mm-10mm to the above solution. The molecular sieve is a catalyst.

[0151] (3) Heat the water to 80 degrees Celsius for 1-2 hours;

[0152] (4) Cool to room temperature and filter to remove 13A molecular sieve particles to obtain conjugated nanocellulose.

[0153] In the above scheme, by adding materials rich in hydroxyl functional groups (such as PEG), bridging can be achieved between nanocellulose layers. Using molecular sieve particles (such as 13A molecular sieve) as a catalyst can accelerate the polymerization reaction between PEG and nanocellulose, ultimately forming a nanocellulose-PEG-nanocellulose structure. Based on the desired layering, one-time or multiple bonding of the raw materials can be achieved. For example, the raw material of one-dimensional nanomaterials can be bonded to twice its length, then a portion of one-dimensional nanomaterials of twice its length can be retained, and another portion of one-dimensional nanomaterials of twice its length can be bonded to the raw material or to one-dimensional nanomaterials of twice its length, resulting in one-dimensional nanomaterials of three or four times its length. At this point, a three-layer structure can be formed. In other examples, further bonding can be performed, and the number of bonding operations can be arbitrarily configured according to requirements.

[0154] In one embodiment of step S21, one-dimensional nanomaterials of various lengths can be dispersed in the same dispersant, and then layered based on the slurry corresponding to the same dispersant after coating. In another embodiment of step S21, different dispersants can be formed based on one-dimensional nanomaterials of different lengths (the length of the one-dimensional nanomaterials in different dispersants is different), and then different dispersions and slurries can be formed. During coating, various slurries can also be coated in layers based on the length of the one-dimensional nanomaterials.

[0155] In one example, in step S21, one-dimensional nanomaterials of various lengths can be fully dispersed in a dispersant, such as water, ethanol, or methanol. The dispersion method can be, for example, ultrasonic treatment, high-speed stirring, high-pressure homogenization, or sand milling to achieve uniform dispersion in the dispersant. The concentration of the one-dimensional nanomaterials in the dispersion can range from 0.01 to 50 wt%.

[0156] In one embodiment, step S22 may specifically include: adding an adhesive and an additive to the dispersion in sequence.

[0157] The adhesive can be any material that provides an adhesive effect, such as at least one of the following: polyacrylic acid, lithium polyacrylate, polyvinyl alcohol, polyvinylpyrrolidone, carboxymethyl cellulose; but it is not limited to the examples here. Depending on the size and material of the one-dimensional nanomaterial, a suitable adhesive can be selected, all without departing from the scope of the embodiments of the present invention.

[0158] The adjuvants may include, for example, at least one of the following: glycerol, fluoroalkyl ethoxylate, sodium butadiene naphthalene sulfonate, sodium hydroxyethyl sulfate, and sodium dodecyl sulfate.

[0159] In step S23, the slurry can be coated onto the base film by methods such as micro-grooving, spraying, dip coating, or extrusion coating, and then dried to obtain a one-dimensional nanomaterial composite diaphragm. The slurry coating can be applied to one side (i.e., one side of the base film) or both sides (i.e., both sides of the base film).

[0160] In one embodiment, as mentioned above, poly-N-isopropylacrylamide (PNIPAM) can also be added. That is, the preparation method further includes adding poly-N-isopropylacrylamide to the dispersion or the slurry. Furthermore, the longer the length of the one-dimensional nanomaterial, the more PNIPAM it carries, and the stronger its hydrophobicity, making it easier to settle first. It can be seen that by introducing PNIPAM, it can help ensure the realization of stratification.

[0161] In the description of this specification, the references to terms such as "an embodiment," "an example," "a specific implementation process," and "an example" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0162] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A separator for a battery, characterized by include: A base film and a coating structure disposed on the base film, wherein the coating structure contains multiple material layers, each material layer contains a one-dimensional nanomaterial, and the average length of the one-dimensional nanomaterial in each material layer decreases layer by layer along the direction away from the base film. The one-dimensional nanomaterial includes at least one of the following: nanocellulose, aramid nanofibers, and polyimide nanofibers; For the one-dimensional nanomaterial in the coating structure, the following conditions must be met: 5≥L50 / L10≥1.3, 4≥L90 / L50≥1.3; the length value of L50 of the one-dimensional nanomaterial in the coating structure is between 250 and 400 nm. in: L10 represents the length description value of the one-dimensional nanomaterial in the coating structure when 10% is the first target percentage. The L50 characterizes the length description value of the one-dimensional nanomaterial in the coating structure when 50% is the first target percentage. L90 represents the length description value of the one-dimensional nanomaterial in the coating structure when 90% is taken as the first target proportion. The length description value of the one-dimensional nanomaterial in the coating structure indicates that when the number of one-dimensional nanomaterials in the coating structure is gradually accumulated in order from shortest to longest, the length of the one-dimensional nanomaterial corresponds to the ratio of the accumulated number to the total number of one-dimensional nanomaterials in the coating structure when the ratio reaches the first target proportion.

2. The diaphragm according to claim 1, characterized in that, The length of L10 of the one-dimensional nanomaterial in the coating structure is between 100 and 300 nm; the length of L90 of the one-dimensional nanomaterial in the coating structure is between 350 and 900 nm.

3. The diaphragm according to claim 1, characterized in that, The proportions of one-dimensional nanomaterials in different material layers relative to the same secondary target result in different length description values; The length description value of the one-dimensional nanomaterial in the material layer indicates that: When the number of one-dimensional nanomaterials in the corresponding material layer is gradually accumulated in order of length from shortest to longest, the length of the corresponding one-dimensional nanomaterial is such that the ratio of the accumulated number to the total number of one-dimensional nanomaterials in the corresponding material layer reaches the second target percentage. The second target percentage is not 50%. Along the direction away from the base film, for the same second target proportion, the length description value of the one-dimensional nanomaterial of each material layer gradually decreases.

4. The diaphragm according to claim 3, characterized in that, The second target percentage is in the range of 5%-40%, or in the range of 60%-99%.

5. The diaphragm according to claim 1, characterized in that, In the adjacent first material layer and second material layer, the voids of the one-dimensional nanomaterial in the first material layer are partially or completely filled by the one-dimensional nanomaterial in the second material layer. The first material layer is located on the side of the second material layer facing the base film.

6. A battery, characterized in that, Includes the diaphragm as described in any one of claims 1 to 5.

7. A method for preparing a diaphragm, characterized in that, The method for preparing the diaphragm according to any one of claims 1 to 5 includes: Dispersing one-dimensional nanomaterials of different lengths in the same or different dispersants yields at least one dispersion. Based on the at least one dispersion, at least one corresponding slurry is formed; The at least one slurry is coated onto the base film, and the base film and the slurry are dried to obtain the diaphragm.

8. The preparation method according to claim 7, characterized in that, Before dispersing the one-dimensional nanomaterials of different lengths in the same or different dispersants to obtain at least one dispersion, the process further includes: The raw material or the broken one-dimensional nanomaterial is broken apart, and one-dimensional nanomaterials of at least some different lengths are formed by breaking them apart once or multiple times.

9. The preparation method according to claim 7, characterized in that, Before dispersing one-dimensional nanomaterials of different lengths in the same or different dispersants to obtain at least one dispersion, the process further includes: Perform at least one of the following bonding processes, and form one-dimensional nanomaterials of at least partially different lengths through one or more bonding processes: The raw material of a one-dimensional nanomaterial is bonded to one end of another raw material; The joined one-dimensional nanomaterial is joined to one end of the raw material; The joined one-dimensional nanomaterial is joined to one end of another joined one-dimensional nanomaterial.

10. The preparation method according to claim 9, characterized in that, The joining includes: The one-dimensional nanomaterial to be bonded is mixed with a material rich in hydroxyl functional groups in a solution; Molecular sieve particles are added to the solution as a catalyst; The solution is heated, then cooled, and the molecular sieve is removed by filtration to obtain the bonded one-dimensional nanomaterial.

11. The preparation method according to any one of claims 7 to 10, characterized in that, Based on the at least one dispersion, at least one corresponding slurry is formed, including: Adhesive and additives are added to the dispersion in sequence.

12. The preparation method according to claim 11, characterized in that, The adhesive comprises at least one of the following: polyacrylic acid, lithium polyacrylate, polyvinyl alcohol, polyvinylpyrrolidone, and carboxymethyl cellulose; The adjuvants include at least one of the following: glycerol, fluoroalkyl ethoxylate, sodium butadiene naphthalene sulfonate, sodium hydroxyethyl sulfate, and sodium dodecyl sulfate.

13. The preparation method according to any one of claims 7 to 10, characterized in that, Also includes: Poly-N-isopropylacrylamide is added to the dispersion or the slurry.

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