Secondary battery

Abstract

The invention discloses a secondary battery which comprises core packages A and core packages B. The core packages A and the core packages B are alternately arranged, and the adjacent core packages A and the adjacent core packages B are connected in parallel. The core package A and the core package B meet the following conditions: (1) the maximum charge-discharge rate of the core package A is greater than the maximum charge-discharge rate of the core package B; (2) the energy density of the core package A is smaller than that of the core package B; (3) the capacity of the core package A is consistent with that of the core package B; and (4) the voltage windows of the core package A and the core package B are consistent. According to the invention, the high-rate core packages and the high-energy-density core packages are connected in parallel in a specific arrangement mode to assemble the secondary battery, so that the battery has high-rate performance and high energy density; particularly, when the core packages on the outermost sides are all the core packages A, the constructed secondary battery has high rate performance and capacity retention ratio under a low-temperature condition.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a secondary battery. Background Art

[0002] Lithium-ion batteries have the advantages of large specific capacity, high operating voltage, long cycle life, portability, safety, environmental protection, and low environmental pollution, and are widely used in various products. With the increasing requirements for battery performance in electric vehicles, energy storage systems, medical equipment and other fields, batteries are required to have high energy density and fast charging capabilities to meet the needs of efficient operation and long-term use of equipment. And as the complexity of the product use environment increases, batteries as energy sources need to have better environmental applicability, such as low-temperature performance.

[0003] However, it is currently difficult for lithium-ion batteries to achieve both high rate and high energy density. This is because the principles of increasing the rate and increasing the energy density are contradictory. For example, a high rate requires smaller positive and negative electrode particles, while a high energy density requires larger particles. Therefore, it is difficult to achieve high rate and high energy density in the same battery cell; and the charging speed and actual available capacity of secondary batteries will be greatly reduced under low temperature conditions.

[0004] Based on this, there is an urgent need for a secondary battery that can effectively improve the low-temperature performance of the battery and take into account both rate performance and energy density. Summary of the invention

[0005] To solve the above problems, the present invention provides a secondary battery. By arranging a high-rate core package and a high-energy density core package to form a secondary battery through a specific arrangement, the secondary battery can not only have both high-rate and high-energy density performance, but also effectively improve the low-temperature performance of the secondary battery.

[0006] Specifically, the following technical solutions are provided:

[0007] A first aspect of the present invention provides a secondary battery, the secondary battery comprising a core pack A and a core pack B, the core pack A and the core pack B are arranged alternately, and adjacent core packs A and B are connected in parallel;

[0008] The core package A and the core package B meet the following conditions:

[0009] (1) The maximum charge and discharge rate of the core package A is greater than the maximum charge and discharge rate of the core package B;

[0010] (2) The energy density of the core package A is less than the energy density of the core package B;

[0011] (3) The capacity of the core package A is consistent with that of the core package B;

[0012] (4) The voltage windows of the core package A and the core package B are consistent.

[0013] Further, the core package A comprises a first positive electrode sheet, a first separator and a first negative electrode sheet, and the core package B comprises a second positive electrode sheet, a second separator and a second negative electrode sheet; wherein the first positive electrode sheet comprises a current collector and a first positive electrode active layer arranged on at least one side of the current collector along the thickness direction, and the first positive electrode active layer comprises a first positive electrode active material; the first negative electrode sheet comprises a current collector and a first negative electrode active layer arranged on at least one side of the current collector along the thickness direction, and the first negative electrode active layer comprises a first negative electrode active material; the second positive electrode sheet comprises a current collector and a second positive electrode active layer arranged on at least one side of the current collector along the thickness direction, and the second positive electrode active layer comprises a second positive electrode active material; the second negative electrode sheet comprises a current collector and a second negative electrode active layer arranged on at least one side of the current collector along the thickness direction, and the second negative electrode active layer comprises a second negative electrode active material.

[0014] Furthermore, the first positive electrode active material is the same as the second positive electrode active material and is selected from one or more of lithium iron phosphate and ternary lithium battery positive electrode materials; the first negative electrode active material and the second negative electrode active material are both graphite.

[0015] Furthermore, when the first positive electrode active material and the second positive electrode active material are both lithium iron phosphate, the compaction density of the first positive electrode active layer is preferably 2.0-2.55 g / cm 3 The compaction density of the second positive electrode active layer is preferably 2.6-2.7 g / cm 3 .

[0016] Furthermore, when the first positive electrode active material and the second positive electrode active material are both positive electrode materials for ternary lithium batteries, the compaction density of the first positive electrode active layer is preferably 3.4-3.6 g / cm 3 The compaction density of the second positive electrode active layer is preferably 3.65-3.7 g / cm 3 .

[0017] Furthermore, the porosity of the first diaphragm is preferably 60%-80%; the porosity of the second diaphragm is preferably 40%-50%.

[0018] Further, the graphite used as the first negative electrode active material is the first graphite, and the graphite used as the second negative electrode active material is the second graphite, and the first graphite and the second graphite satisfy at least one of the following characteristics:

[0019] (1) The graphitization degree of the first graphite is Aa, and the graphitization degree of the second graphite is Ab, satisfying 1.022≤Aa / Ab≤1.068; more preferably, Aa is 92%-94%, and Ab is 88%-90%;

[0020] (2) The particle size D50 of the first graphite is Ba, and the particle size D50 of the second graphite is Bb, satisfying 1.25≤Bb / Ba≤2.5; more preferably, Ba is 8-12 μm, and Bb is 15-20 μm;

[0021] (3) The specific surface area of ​​the first graphite is Ca, and the specific surface area of ​​the second graphite is Cb, satisfying 2.867≤Ca / Cb≤3.461; more preferably, the Ca is 4.3-4.5 m 2 / g, Cb is 1.3-1.5m 2 / g;

[0022] (4) At 25°C and 10% SOC, the lithium ion diffusion coefficient of the first graphite is Da, and the lithium ion diffusion coefficient of the second graphite is Db, satisfying 1.15≤Da / Db≤2.95; more preferably, Da is 2.3×10 -14 cm 2 / s-2.4×10 -12 cm 2 / s, Db is 1.2×10 -14 cm 2 / s-2.0×10 -12 cm 2 / s.

[0023] Furthermore, the compaction density of the first negative electrode active layer is Ea, and the compaction density of the second negative electrode active layer is Eb, which satisfies 1.032≤Eb / Ea≤1.133; more preferably, Ea is 1.5-1.55 g / cm 3 , Eb is 1.6-1.7 g / cm 3 .

[0024] Furthermore, the ratio of the negative electrode reversible surface capacity to the positive electrode reversible surface capacity of the core package A is a, and the ratio of the negative electrode reversible surface capacity to the positive electrode reversible surface capacity of the core package B is b, satisfying 1≤a / b≤1.1.

[0025] Furthermore, the length and height of the core package A and the core package B are consistent.

[0026] Furthermore, the secondary battery can be obtained by arranging the core pack A and the core pack B in AB, ABA, BAB, ABAB, ABABA, etc. More preferably, the secondary battery comprises n core packs A and n-1 core packs B, n≥2, and both sides of the core pack B are the core packs A, such as ABA.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention provides a secondary battery composed of a high-rate core package and a high-energy density core package. The secondary battery obtained by alternately arranging two different core packages can have both high rate performance and high energy density.

[0029] The present invention adjusts the graphitization degree, particle size, specific surface area, lithium ion diffusion coefficient and compaction density of the negative electrode active layer of the two core packages with high rate and high energy density so that the negative electrodes of the two core packages meet 1.04≤Aa / Ab≤1.1, 1.6≤Bb / Ba≤1.9, 3.3≤Ca / Cb≤3.5, 1.9≤Da / Db≤4.35 and 1.02≤Eb / Ea≤1.09, so that the secondary battery composed of the above two core packages has both high rate performance and high energy density.

[0030] In addition, the present invention combines the high-rate core package with the high-energy density core package in a specific arrangement (AB...A). In a low-temperature environment, the high-rate core package is used to provide heat for the high-energy density core package sandwiched in the middle to promote lithium ion migration, thereby enabling the secondary battery to exert high energy density at low temperatures. DETAILED DESCRIPTION

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items. The term "includes" or "comprising" described in the present invention means that it may include or contain other components in addition to the components described. The term "includes" or "comprising" described in the present invention may also be replaced by the closed form "for" or "consisting of..."

[0032] As described in the background art, it is difficult for lithium-ion batteries to achieve both high rate and high energy density at the same time, and the battery also has problems such as greatly reduced charging speed and actual available capacity under low temperature conditions.

[0033] To solve the above problems, the embodiments of the present invention provide a secondary battery, wherein the secondary battery comprises a core pack A and a core pack B, wherein the core pack A and the core pack B are alternately arranged, and adjacent core packs A and B are connected in parallel; and the core pack A and the core pack B meet the following conditions:

[0034] (1) The maximum charge and discharge rate of the core package A is greater than the maximum charge and discharge rate of the core package B; that is, the core package A is a high-rate core package;

[0035] (2) The energy density of the core package A is less than the energy density of the core package B; that is, the core package B is a core package with high energy density;

[0036] (3) The capacity of the core package A is consistent with that of the core package B; the core package A and the core package B are kept consistent during the charging and discharging process. If the capacity of the core package A is smaller than that of the core package B, during the discharge process, the capacity of the core package A is fully discharged but the capacity of the core package B is still not fully discharged, and the core package A will be over-discharged, causing safety hazards. If the capacity of the core package A is larger than that of the core package B, during the charging process, the core package B is full but the core package A is not full. Continuing to charge will cause the core package B to be overcharged, causing safety hazards. Therefore, the capacity of the core package A and the core package B needs to be controlled to be consistent;

[0037] (4) The voltage windows of the core pack A and the core pack B are consistent to ensure that the charge and discharge voltages of the core pack A and the core pack B are equal. If the two are inconsistent, when one core pack is fully charged and the other core pack is not fully charged, if charging continues, the fully charged core pack will be overcharged, causing safety hazards.

[0038] The present invention forms a secondary battery by alternately arranging a high-rate core package A and a high-energy density core package B with consistent capacity and voltage window, and utilizing the respective advantages of different types of core packages and their specific arrangement methods, so that the composed secondary battery can have both high-rate performance and high energy density; and the high-energy density core package can be heated by the high heat dissipation of the high-rate core package to promote the migration of lithium ions and the exertion of energy density of the high-energy density core package in the battery at low temperatures, so that the secondary battery can still maintain a relatively high discharge rate and discharge capacity retention rate at low temperatures.

[0039] In the present invention, core package A comprises a first positive electrode plate, a first separator and a first negative electrode plate, wherein the first positive electrode plate comprises a current collector and a first positive electrode active layer arranged on at least one side of the current collector along the thickness direction, and the first positive electrode active layer comprises a first positive electrode active material; the first negative electrode plate comprises a current collector and a first negative electrode active layer arranged on at least one side of the current collector along the thickness direction, and the first negative electrode active layer comprises a first negative electrode active material.

[0040] In the present invention, core package B comprises a second positive electrode plate, a second separator and a second negative electrode plate, wherein the second positive electrode plate comprises a current collector and a second positive electrode active layer arranged on at least one side of the current collector along the thickness direction, and the second positive electrode active layer comprises a second positive electrode active material; the second negative electrode plate comprises a current collector and a second negative electrode active layer arranged on at least one side of the current collector along the thickness direction, and the second negative electrode active layer comprises a second negative electrode active material.

[0041] In some preferred embodiments of the present invention, the first positive electrode active material is the same as the second positive electrode active material and is selected from one or more of lithium iron phosphate and ternary lithium battery positive electrode materials; the first negative electrode active material and the second negative electrode active material are both graphite.

[0042] In the present invention, the compaction density of the first positive electrode active layer is less than the compaction density of the second positive electrode active layer, so that the core package B has a high energy density. For example, when the first positive electrode active material and the second positive electrode active material are both lithium iron phosphate, the compaction density of the first positive electrode active layer is preferably 2.0-2.55 g / cm 3 The compaction density of the second positive electrode active layer is preferably 2.6-2.7 g / cm 3 In some preferred embodiments, the compaction density of the first positive electrode active layer is 2.4 g / cm 3 The compaction density of the second positive electrode active layer is 2.6 g / cm 3 When the first positive electrode active material and the second positive electrode active material are both ternary lithium battery positive electrode materials, the compaction density of the first positive electrode active layer is preferably 3.4-3.6 g / cm 3 The compaction density of the second positive electrode active layer is preferably 3.65-3.7 g / cm 3 .

[0043] In the present invention, the porosity of the first diaphragm is higher than the porosity of the second diaphragm. The higher the porosity, the easier it is for lithium ions to shuttle, thereby reducing the polarization of the high-rate core package A; preferably, the porosity of the first diaphragm is 60%-80%, for example, 60%, 65%, 70%, 75%, 80%, etc., and the porosity of the second diaphragm is 40%-50%, for example, 40%, 42%, 44%, 46%, 48%, 50%, etc., including but not limited to the porosities listed above.

[0044] In the present invention, the graphite used as the first negative electrode active material is the first graphite, and the graphite used as the second negative electrode active material is the second graphite. The first graphite and the second graphite satisfy at least one of the following characteristics:

[0045] (1) The degree of graphitization of the first graphite is Aa, and the degree of graphitization of the second graphite is Ab, satisfying 1.022≤Aa / Ab≤1.068; more preferably, Aa is 92%-94%, and Ab is 88%-90%; the ratio of the degree of graphitization of the first graphite to the degree of graphitization of the second graphite is controlled in the range of 1.022-1.068, so that the secondary battery has both high rate performance and high energy density; in addition, the higher the degree of graphitization, the smaller the interlayer spacing of the graphite, which is not conducive to the rapid insertion and extraction of lithium ions, but if the graphitization is too low, the conductivity is poor, which affects the rate performance and capacity of the battery, so it is preferred to control Aa in the range of 92%-94%, and Ab in the range of 88%-90%, so that the battery can have both high rate performance and high capacity.

[0046] (2) The particle size D50 of the first graphite is Ba, and the particle size D50 of the second graphite is Bb, satisfying 1.25≤Bb / Ba≤2.5; more preferably, Ba is 8-12 μm, and Bb is 15-20 μm; the size of the graphite particles will affect the specific surface area and compaction. If the particle size is too small, the compaction of the material is low, the specific surface area is large, the contact area with the electrolyte is large, the area of ​​the formed SEI film is also large, and the initial efficiency will become low. If the particle size is too large, the compaction of the material is high, but the rate performance is poor; the ratio of the particle size D50 of the first graphite to the particle size D50 of the second graphite is controlled in the range of 1.25-2.5, so that the core package A whose negative electrode active material is the first graphite has high rate performance, and the core package B whose negative electrode active material is the second graphite has high energy density and the rate performance is not too low, so that the battery assembled by the core package A and the core package B can exhibit high rate performance and high energy density.

[0047] (3) The specific surface area of ​​the first graphite is Ca, and the specific surface area of ​​the second graphite is Cb, which satisfies 2.867≤Ca / Cb≤3.461. If the specific surface area of ​​the first graphite is too large, the contact area with the electrolyte is large, and the area of ​​the SEI film formed is also large. During the first charging process, more lithium ions are consumed, which will lead to a lower initial efficiency of the battery. Controlling the specific surface area of ​​the first graphite and the second graphite within this range is beneficial to improving the initial efficiency of the battery. More preferably, Ca is 4.3-4.5 m 2 / g, Cb is 1.3-1.5m 2 / g.

[0048] (4) At 25°C and 10% SOC, the lithium ion diffusion coefficient of the first graphite is Da, and the lithium ion diffusion coefficient of the second graphite is Db, satisfying 1.15≤Da / Db≤2.95; more preferably, Da is 2.3×10 -14 cm 2 / s-2.4×10 - 12 cm 2 / s, Db is 1.2×10 -14 cm 2 / s-2.0×10 -12 cm 2 / s; the larger the lithium ion diffusion coefficient of graphite, the faster the lithium ions move in the graphite, which helps to improve the charge and discharge rate and efficiency of the battery and reduce the polarization phenomenon during the charge and discharge process. However, the lithium ion diffusion coefficient of graphite used as the negative electrode active material of the battery should not be too large. The excessively fast diffusion rate of lithium ions in graphite will cause the internal temperature of the battery to rise rapidly, affecting the electrochemical performance, safety performance and cycle life of the battery. The ratio of the lithium ion diffusion coefficients of the first graphite and the second graphite is controlled in the range of 1.15-2.95, and Da is controlled in the range of 2.3×10 -14 cm 2 / s-2.4×10 -12 cm 2 / s range, Db is controlled at 1.2×10 -14 cm 2 / s-2.0×10 -12 cm 2 / s range, so that the battery can have both high rate performance and high energy density while ensuring safety.

[0049] In the present invention, the compaction density of the first negative electrode active layer is Ea, the compaction density of the second negative electrode active layer is Eb, and the compaction density of the first negative electrode active layer and the second negative electrode active layer satisfies 1.032≤Eb / Ea≤1.133; more preferably, Ea is 1.5-1.55 g / cm 3 , Eb is 1.6-1.7 g / cm 3 By controlling the compaction density of the negative electrodes of core pack A and core pack B, core pack A can have high rate performance while avoiding too low energy density, so that the secondary battery assembled by high rate core pack A and high energy density core pack B has both high rate performance and high energy density.

[0050] In the present invention, the ratio of the negative electrode reversible surface capacity to the positive electrode reversible surface capacity of core package A is a, and the ratio of the negative electrode reversible surface capacity to the positive electrode reversible surface capacity of core package B is b, satisfying 1≤a / b≤1.1. a and b refer to the ratio of the negative electrode reversible surface capacity N to the positive electrode reversible surface capacity P at the same stage and under the same operation. In order to avoid lithium deposition on the negative electrode surface of core package A, resulting in rapid attenuation of battery life, while core package B has no attenuation, and thus causing safety problems caused by over-discharge of core package A, it is necessary to keep the N / P of core package A and core package B in the same range, preferably satisfying 1≤a / b≤1.1.

[0051] In the present invention, in order to facilitate the placement of the core package A and the core package B in the same housing, preferably, the length and height of the core package A and the core package B are controlled to be consistent.

[0052] In the present invention, the secondary battery can be obtained by arranging the core package A and the core package B in the manner of AB, ABA, BAB, ABAB, ABABA, etc.; more preferably, the secondary battery comprises n core packages A and n-1 core packages B, n≥2, wherein both sides of the core package B are core packages A, such as ABA. The high energy density core package B is heated by the heat emitted by the high rate core package A distributed above, below or on both sides of the high energy density core package B, thereby promoting the ion migration rate and energy density of the high energy density B under low temperature conditions, so that the secondary battery can also have both rate performance and energy under low temperature conditions.

[0053] The present invention is further described below in conjunction with specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0054] Example 1

[0055] This embodiment relates to the preparation of a lithium battery, which is obtained by connecting a high-rate core package A and a high-energy density core package B in parallel in an AB arrangement. The specific preparation process is as follows:

[0056] Preparation of high-rate core package A:

[0057] Positive electrode sheet: Add the positive electrode active material LFP and the conductive agent (composed of conductive carbon black and carbon nanotubes in a mass ratio of 1:1) into the agitator, mix and disperse, continuously add NMP solution containing 1.5% PVDF, and mix at high speed until the viscosity reaches 6000mPa.s to prepare a positive electrode active slurry, in which the weight ratio of the positive electrode active material, the positive electrode conductive agent and PVDF is 97.5:1:1.5.

[0058] The positive electrode active slurry was coated on aluminum foil, dried, rolled and die-cut to obtain a positive electrode sheet with a compaction density of 2.4 g / cm 3 .

[0059] Negative electrode sheet: Negative electrode active material (artificial graphite, graphitization degree 92%, lithium ion diffusion coefficient D of 2.3×10 -14 cm 2 / s, particle size D50 is 8μm, specific surface area is 4.32m 2 / g), negative electrode conductive agent (conductive carbon black) are added into a stirrer, mixed and dispersed, an appropriate amount of aqueous solution containing CMC is added, mixed at high speed until the viscosity reaches 5000mPa.s, and then SBR is added and stirred at low speed to obtain negative electrode active slurry. The weight ratio of negative electrode active material, negative electrode conductive agent and negative electrode binder is 96:1:3, and the negative electrode binder is composed of CMC and SBR at a mass ratio of 1:1.

[0060] The negative electrode active slurry was coated on the carbon-coated copper foil, and then rolled and die-cut after drying to obtain the positive electrode sheet with a compaction density of 1.5 g / cm 3 .

[0061] Diaphragm: polyethylene / polypropylene composite diaphragm;

[0062] Electrolyte: Ethylene carbonate (EC) and propylene carbonate (PC) were mixed evenly in a volume ratio of 40%:30%, and then 10% of lithium fluoroalkyl phosphate, 10% of lithium hexafluorophosphate, 5% of vinylene carbonate (VC) and 5% of dimethyl sulfite were slowly added to the mixed solution based on the total weight of the electrolyte;

[0063] Assembly of high-rate core package A: first stack the diaphragm, negative electrode sheet, diaphragm, and positive electrode sheet in sequence, then wind and hot-press to obtain high-rate core package A.

[0064] Preparation of high energy density core package B:

[0065] Positive electrode sheet: Add the positive electrode active material LFP and the conductive agent (composed of conductive carbon black and carbon nanotubes in a mass ratio of 1:1) into a stirrer, mix and disperse, continuously add NMP solution containing 1.5% PVDF, and mix at high speed until the viscosity reaches 6000mPa·s to prepare a positive electrode active slurry, in which the weight ratio of the positive electrode active material, the positive electrode conductive agent and PVDF is 97.5:1:1.5.

[0066] The positive electrode active slurry was coated on aluminum foil, dried, rolled and die-cut to obtain a positive electrode sheet with a compaction density of 2.6 g / cm 3 .

[0067] Negative electrode sheet: negative electrode active material (artificial graphite, graphitization degree 88%, lithium ion diffusion coefficient D of 1.2×10 -14 cm 2 / s, particle size D50 is 15μm, specific surface area is 1.3m 2 / g), negative electrode conductive agent (conductive carbon black) are added into a stirrer, mixed and dispersed, an appropriate amount of aqueous solution containing CMC is added, mixed at high speed until the viscosity reaches 5000mPa·s, and then SBR is added and stirred at low speed to obtain negative electrode active slurry. The weight ratio of negative electrode active material, negative electrode conductive agent and negative electrode binder is 96:1:3, and the negative electrode binder is composed of CMC and SBR at a mass ratio of 1:1.

[0068] The negative electrode active slurry was coated on the carbon-coated copper foil, and then rolled and die-cut after drying to obtain the positive electrode sheet with a compaction density of 1.65 g / cm 3 .

[0069] Diaphragm: polyethylene / polypropylene composite diaphragm;

[0070] Electrolyte: Ethylene carbonate (EC) and propylene carbonate (PC) were mixed evenly in a volume ratio of 40%:30%, and then 10% of lithium fluoroalkyl phosphate, 10% of lithium hexafluorophosphate, 5% of vinylene carbonate (VC) and 5% of dimethyl sulfite were slowly added to the mixed solution based on the total weight of the electrolyte;

[0071] Assembly of high energy density core package B: first stack the diaphragm, negative electrode sheet, diaphragm, and positive electrode sheet in sequence, then wind and hot press to obtain a high-rate core package B.

[0072] The capacity of core pack A and core pack B is the same.

[0073] Assembly of lithium battery: The core pack after hot pressing is assembled in AB arrangement (tied together with tape), and then the tabs are ultrasonically welded, the adapter and the top cover are laser welded, and the battery is put into the shell. The top cover is welded around, baked, liquid injected, formed, and divided at 25°C to obtain a lithium battery.

[0074] Example 2

[0075] This embodiment relates to the preparation of a lithium battery, and the only difference from the embodiment 1 is that the negative electrode compaction density in the high-rate core package A is 1.55 g / cm 3 The graphitization degree of the negative electrode graphite is 93%, the particle size is 12μm, and the specific surface area is 4.4m 2 / g; the specific surface area of ​​the negative electrode graphite in the high energy density core package B is 1.5m 2 / g. The rest are the same, and the corresponding lithium battery is prepared.

[0076] Example 3

[0077] This embodiment relates to the preparation of a lithium battery, which is different from the embodiment 1 only in that: the graphitization degree of the negative electrode graphite in the high-rate core package A is 94%; the negative electrode compaction density in the high-energy density core package B is 1.6 g / cm 3 The specific surface area of ​​negative electrode graphite is 1.4m 2 / g. The rest are the same, and the corresponding lithium battery is prepared.

[0078] Example 4

[0079] This embodiment relates to the preparation of a lithium battery, which is different from the embodiment 1 only in that the graphitization degree of the negative electrode graphite in the high-rate core package A is 80%. The rest is the same, and the corresponding lithium battery is prepared.

[0080] Example 5

[0081] This embodiment relates to the preparation of a lithium battery, and the only difference from the embodiment 1 is that the specific surface area of ​​the negative electrode graphite in the high-rate core package A is 4.5 m2 / g; the graphitization degree of the negative electrode graphite in the high energy density core package B is 89%. The rest are the same, and the corresponding lithium battery is prepared.

[0082] Example 6

[0083] This embodiment relates to the preparation of a lithium battery, which is different from the embodiment 1 only in that the graphitization degree of the negative electrode graphite in the high energy density core package B is 80%. The rest is the same, and the corresponding lithium battery is prepared.

[0084] Example 7

[0085] This embodiment relates to the preparation of a lithium battery, which is different from the embodiment 1 only in that the lithium ion diffusion coefficient D of the negative electrode graphite in the high-rate core package A at 25°C and 10% SOC is 1.2×10 -14 cm 2 / s. The rest are the same, and the corresponding lithium battery is prepared.

[0086] Example 8

[0087] This embodiment relates to the preparation of a lithium battery, which is different from the embodiment 1 only in that the lithium ion diffusion coefficient D of the negative electrode graphite in the high-rate core package A at 25°C and 10% SOC is 2.4×10 -14 cm 2 / s, the particle size is 11μm. The rest are the same, and the corresponding lithium battery is prepared.

[0088] Example 9

[0089] This embodiment relates to the preparation of a lithium battery, which is different from the embodiment 1 only in that the lithium ion diffusion coefficient D of the negative electrode graphite in the high energy density core package B at 25°C and 10% SOC is 0.9×10 -14 cm 2 / s. The rest are the same, and the corresponding lithium battery is prepared.

[0090] Example 10

[0091] This embodiment relates to the preparation of a lithium battery, which is different from the embodiment 1 only in that the negative electrode compaction density in the high energy density core package B is 1.7 g / cm 3 The lithium ion diffusion coefficient D of the negative electrode graphite at 25°C and 10% SOC is 2.0×10 -14 cm 2 / s. The rest are the same, and the corresponding lithium battery is prepared.

[0092] Embodiment 11

[0093] This embodiment relates to the preparation of a lithium battery, which is different from Embodiment 1 only in that a high-rate core package A and a high-energy-density core package B are connected in parallel in an ABA arrangement, and the rest are the same to prepare a corresponding lithium battery.

[0094] Example 12

[0095] This embodiment relates to the preparation of a lithium battery, which is different from Embodiment 1 only in that a high-rate core package A and a high-energy density core package B are connected in parallel in a BAB arrangement, and the rest are the same to prepare a corresponding lithium battery.

[0096] Comparative Example 1

[0097] This comparative example involves the preparation of a lithium battery, which differs from Example 1 only in the preparation of a high-rate core package A. The preparation of the core package A in this comparative example is consistent with the preparation of the high-energy-density core package B in Example 1. The remaining operations are consistent to prepare the corresponding lithium battery.

[0098] Comparative Example 2

[0099] This comparative example involves the preparation of a lithium battery, which differs from Example 1 only in the preparation of a high energy density core package B. The preparation of the core package B in this comparative example is consistent with the preparation of the high rate core package A in Example 1. The remaining operations are consistent to prepare the corresponding lithium battery.

[0100] The relevant parameters of the batteries prepared in the above embodiments and comparative examples are summarized in the following Table 1:

[0101] Table 1

[0102]

[0103] In the above table, the graphitization degree of the A core package is Aa, the particle size is Ba, the specific surface area is Ca, the diffusion coefficient is Da, and the negative electrode compaction is Ea, the graphitization degree of the B core package is Ab, the particle size is Bb, the specific surface area is Cb, the diffusion coefficient is Db, and the negative electrode compaction is Eb. The ratios of the parameters of the batteries prepared in the above embodiments and comparative examples are shown in Table 2 below:

[0104] Table 2

[0105] Battery Aa / Ab Bb / Ba Ca / Cb Da / Db Eb / Ea Example 1 1.045 1.875 3.323 1.917 1.1 Example 2 1.057 1.25 2.933 1.917 1.065 Example 3 1.068 1.875 3.086 1.917 1.067 Example 4 0.909 1.875 3.323 1.917 1.1 Example 5 1.033 1.875 3.462 1.917 1.1 Example 6 1.150 1.875 3.323 1.917 1.1 Example 7 1.045 1.875 3.323 1.000 1.1 Example 8 1.045 1.364 3.323 2.000 1.1 Example 9 1.045 1.875 3.323 2.556 1.1 Example 10 1.045 1.875 3.323 1.150 1.133 Embodiment 11 1.045 1.875 3.323 1.917 1.1 Example 12 1.045 1.875 3.323 1.917 1.1 Comparative Example 1 1 1 1 1 1 Comparative Example 2 1 1 1 1 1

[0106] Performance Testing

[0107] (1) The discharge capacity, energy density and rate performance of the lithium ion batteries prepared by arranging two core packages in the above-mentioned Examples 1-10 and Comparative Examples 1 and 2 were tested. The test method is as follows:

[0108] Discharge capacity test: When the battery cell is divided into different capacities, the battery is charged at 1C and discharged at 1C, and the discharged capacity is recorded.

[0109] Energy density test: When the battery cell is divided into different capacities, the battery is charged at 1C and discharged at 1C, and the discharged energy is recorded. Then energy / battery cell weight = energy density.

[0110] Rate performance test: Prepare part of the above-prepared battery cell into three electrodes, try different rates by direct charging at 25°C, and then monitor the negative electrode potential until the negative electrode potential reaches 0V. At this time, the maximum rate supported by 25°C is obtained.

[0111] The above performance test results are shown in Table 3:

[0112] Table 3

[0113]

[0114] As can be seen from Table 3, the secondary battery prepared with a single high-energy-density core package B (Comparative Example 1) has a high energy density, but the rate performance is extremely low and cannot meet the fast charging requirements; while the secondary battery prepared with a single high-rate core package A in Comparative Example 2 has a high rate, but the battery energy density is too low. The secondary battery composed of high-rate core package A and high-energy-density core package B (Example 1) can have both relatively high energy density and better rate performance, and can meet the requirements of fast charging and high capacity at the same time.

[0115] It can be seen from Examples 1, 4, and 6 that the degree of graphitization of the negative electrode active material graphite used in core package A and core package B will have a great impact on the energy density and rate performance of the battery. Compared with Example 1, the degree of graphitization of the negative electrode active material graphite used in core package A in Example 4 is only 80%, which does not meet the preferred range of Aa of 92%-94%, and the Aa / Ab in the secondary battery composed is 0.909, which does not meet the preferred range of 1.022-1.068, and the rate performance of the secondary battery composed of core package B is greatly reduced, and the energy density is also significantly reduced; in Example 6, the degree of graphitization of the negative electrode active material graphite used in core package B is only 80%, which does not meet the preferred range of Ab of 88%-90%, and the Aa / Ab in the secondary battery composed is 1.150, which does not meet the preferred range of 1.022-1.068, and the rate performance of the secondary battery composed of core package A is slightly improved, but the energy density is significantly reduced.

[0116] In Example 5, the specific surface area Ca of the negative electrode active material graphite used in core package A is 4.5, which is within the preferred range of 4.3-4.5, but the ratio Ca / Cb of the specific surface area Cb of the negative electrode active material graphite used in core package B is 3.462, slightly exceeding the preferred range of 2.867-3.461. Compared with Example 1, the energy density and rate performance are slightly reduced, but the overall performance is still better.

[0117] In addition, it can be seen from Examples 1, 7, and 9 that the diffusion coefficient of the negative electrode active material graphite used in core package A and core package B will also affect the energy density and rate performance of the battery. The diffusion coefficient of graphite will affect the diffusion rate of lithium ions in the negative electrode, thereby affecting the battery rate performance and energy performance. The diffusion coefficient Da of the negative electrode active material graphite used in core package A in Example 7 is consistent with that of core package B, which is only 1.2×10 -14 cm 2 / s, which does not meet the preferred range of Da of 2.3×10 -14 cm 2 / s-2.4×10 -12 cm 2 / s and the Da / Db of the secondary battery formed is 1, which is lower than the preferred range of 1.15-2.95. Compared with the secondary battery formed by core pack B in Example 1, the rate performance is greatly reduced, and the energy density is also slightly reduced. The diffusion coefficient ratio Da / Db of the negative electrode active material graphite used in the secondary battery core packs A and B prepared in Example 9 is 2.556, which meets the preferred range of 1.15-2.95, but the graphite coefficient of the negative electrode active material graphite used in core pack B is too low, only 0.9×10 -14 cm 2 / s, which does not meet the optimal range of Db 1.2×10 -14 cm 2 / s-2.0×10 -12 cm 2 / s, because the diffusion coefficient of graphite used in core package B is too low, the diffusion speed of lithium ions is too slow, which greatly affects the rate performance of the secondary battery composed of it and core package A. The maximum rate supported at 25℃ is only 1.8C, and the energy density of the battery is reduced.

[0118] (2) The following low temperature performance tests were performed on the lithium ion batteries prepared in different arrangements of the above-mentioned Examples 1, 11, 12 and Comparative Examples 1 (equivalent to the BB arrangement) and 2 (equivalent to the AA arrangement):

[0119] 10℃@1C discharge capacity retention rate test: the discharge capacity obtained by 1C discharge at 10℃ / the discharge capacity obtained by 1C discharge at 25℃×100% is the 10℃@1C discharge capacity retention rate;

[0120] 10℃ supported discharge rate test: Prepare part of the prepared battery cell into three electrodes, try different rates at 10℃ by direct charging and then monitor the negative electrode potential until the negative electrode potential reaches 0V, at which time the maximum rate supported at 10℃ is obtained.

[0121] Battery cell internal temperature test: embed a temperature sensing wire inside the battery cell to monitor the temperature.

[0122] The test results are shown in Table 4 below:

[0123] Table 4

[0124] Arrangement 10℃@1C discharge capacity retention rate 10℃ can support discharge rate Battery internal temperature Example 1 AB 80％ 1.3C 12℃ Embodiment 11 ABA 85％ 1.5C 20℃ Example 12 BAB 75％ 1.2C 15℃ Comparative Example 1 BB 65％ 0.33C 10℃ Comparative Example 2 AA 70％ 2C 20℃

[0125] It can be seen from Table 4 that, compared with the battery cells prepared by the high-rate core package A and the high-energy-density core package B in the AA and BB arrangement modes, the batteries prepared by Examples 1, 11, and 12 arranged in an interval arrangement of the two have a better discharge capacity retention rate under low temperature conditions; and compared with the battery prepared in the BB arrangement mode, the internal temperature of the battery cells in Examples 1, 11, and 12 is relatively high at low temperatures, thereby increasing the available power of the battery and the discharge rate that can be supported, wherein the battery prepared in the ABA arrangement mode can reach a discharge rate of 1.5C at 10°C, and the internal temperature of the battery cell can reach 20°C. It can be seen that the battery prepared in the ABA arrangement mode is more suitable for use in a low temperature environment.

[0126] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A secondary battery, characterized in that: The secondary battery comprises a core pack A and a core pack B, wherein the core pack A and the core pack B are arranged alternately, and adjacent core packs A and B are connected in parallel; The core package A and the core package B meet the following conditions: (1) The maximum charge and discharge rate of the core package A is greater than the maximum charge and discharge rate of the core package B; (2) The energy density of the core package A is less than the energy density of the core package B; (3) The capacity of the core package A is consistent with that of the core package B; (4) The voltage windows of the core package A and the core package B are consistent.

2. The secondary battery according to claim 1, characterized in that: The core package A comprises a first positive electrode sheet, a first separator and a first negative electrode sheet, and the core package B comprises a second positive electrode sheet, a second separator and a second negative electrode sheet; The first positive electrode plate comprises a current collector and a first positive electrode active layer disposed on at least one side of the current collector along a thickness direction, wherein the first positive electrode active layer comprises a first positive electrode active material; The first negative electrode plate comprises a current collector and a first negative electrode active layer disposed on at least one side of the current collector along a thickness direction, wherein the first negative electrode active layer comprises a first negative electrode active material; The second positive electrode plate comprises a current collector and a second positive electrode active layer disposed on at least one side of the current collector along a thickness direction, wherein the second positive electrode active layer comprises a second positive electrode active material; The second negative electrode plate comprises a current collector and a second negative electrode active layer disposed on at least one side of the current collector along a thickness direction, wherein the second negative electrode active layer comprises a second negative electrode active material; Preferably, the first positive electrode active material is the same as the second positive electrode active material and is selected from one or more of lithium iron phosphate and ternary lithium battery positive electrode materials; Preferably, the first negative electrode active material and the second negative electrode active material are both graphite.

3. The secondary battery according to claim 2, characterized in that: When the first positive electrode active material and the second positive electrode active material are both lithium iron phosphate, the compaction density of the first positive electrode active layer is 2.0-2.55 g / cm 3 The compaction density of the second positive electrode active layer is 2.6-2.7 g / cm 3 .

4. The secondary battery according to claim 2, characterized in that: When the first positive electrode active material and the second positive electrode active material are both ternary lithium battery positive electrode materials, the compaction density of the first positive electrode active layer is 3.4-3.6 g / cm 3 The compaction density of the second positive electrode active layer is 3.65-3.7 g / cm 3 .

5. The secondary battery according to claim 2, characterized in that: The porosity of the first diaphragm is 60%-80%; the porosity of the second diaphragm is 40%-50%.

6. The secondary battery according to claim 2, characterized in that: The graphite used as the first negative electrode active material is the first graphite, and the graphite used as the second negative electrode active material is the second graphite. The first graphite and the second graphite satisfy at least one of the following characteristics: (1) The graphitization degree of the first graphite is Aa, and the graphitization degree of the second graphite is Ab, satisfying 1.022≤Aa / Ab≤1.068; preferably, Aa is 92%-94%, and Ab is 88%-90%; (2) The particle size D50 of the first graphite is Ba, and the particle size D50 of the second graphite is Bb, satisfying 1.25≤Bb / Ba≤2.5; preferably, Ba is 8-12 μm, and Bb is 15-20 μm; (3) The specific surface area of ​​the first graphite is Ca, and the specific surface area of ​​the second graphite is Cb, satisfying 2.867≤Ca / Cb≤3.461; preferably, Ca is 4.3-4.5 m 2 / g, Cb is 1.3-1.5m 2 / g; (4) At 25°C and 10% SOC, the lithium ion diffusion coefficient of the first graphite is Da, and the lithium ion diffusion coefficient of the second graphite is Db, satisfying 1.15≤Da / Db≤2.95; preferably, Da is 2.3×10 -14 cm 2 / s-2.4×10 -12 cm 2 / s, Db is 1.2×10 -14 cm 2 / s-2.0×10 -12 cm 2 / s.

7. The secondary battery according to claim 6, characterized in that: The compaction density of the first negative electrode active layer is Ea, and the compaction density of the second negative electrode active layer is Eb, which satisfies 1.032≤Eb / Ea≤1.133; preferably, Ea is 1.5-1.55 g / cm 3 , Eb is 1.6-1.7 g / cm 3 .

8. The secondary battery according to claim 1, characterized in that: The ratio of the negative electrode reversible surface capacity to the positive electrode reversible surface capacity of the core package A is a, and the ratio of the negative electrode reversible surface capacity to the positive electrode reversible surface capacity of the core package B is b, satisfying 1≤a / b≤1.

1.

9. The secondary battery according to claim 1, characterized in that: The length and height of the core package A and the core package B are consistent.

10. The secondary battery according to claim 1, characterized in that: The secondary battery comprises n core packs A and n-1 core packs B, where n≥2, and both sides of the core pack B are the core packs A.

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