CN117790784A - Lithium ion battery, screening method, battery pack, energy storage device and electric equipment - Google Patents
Lithium ion battery, screening method, battery pack, energy storage device and electric equipment Download PDFInfo
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Abstract
The present invention relates to the field of battery technologies, and in particular, to a lithium ion battery, a screening method, a battery pack, and an energy storage deviceAnd electric equipment. The lithium ion battery comprises an anode plate, a cathode plate, a diaphragm and electrolyte. The negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, wherein the negative electrode active material layer contains a negative electrode active material. The diaphragm is arranged between the positive pole piece and the negative pole piece, and the diaphragm, the positive pole piece and the negative pole piece form an electric core. Electrolyte is injected into the battery cell. Wherein the gram capacity of the negative electrode active material is C 0 And the unit is mAh/g, and the voltage change rate of the lithium ion battery is K 0 The lithium ion battery satisfies the following relation of 6 to K 0 ×C 0 /1000≤12。
Description
Technical Field
The invention relates to the technical field of batteries, in particular to a lithium ion battery, a screening method, a battery pack, an energy storage device and electric equipment.
Background
For lithium ion batteries, energy density and rate capability are two important performance indicators, but often it is difficult to combine both. If a fast-kinetics anode active material is used, it may result in excellent rate performance but reduced energy density, and if a high-energy-density anode active material is used, the rate performance of the battery may be reduced, making it difficult for the lithium ion battery to have both high energy density and high rate characteristics.
Disclosure of Invention
In order to solve the technical problems, the application discloses a lithium ion battery, a screening method, a battery pack, an energy storage device and electric equipment, wherein the lithium ion battery has good multiplying power performance and higher energy density.
In a first aspect, embodiments of the present application provide a lithium ion battery, including:
a positive electrode sheet;
the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, wherein the negative electrode active material layer contains a negative electrode active material;
the diaphragm is arranged between the positive pole piece and the negative pole piece, and the diaphragm, the positive pole piece and the negative pole piece form an electrode assembly; and
electrolysisA liquid, the electrolyte at least partially infiltrating the electrode assembly; wherein the gram capacity of the negative electrode active material is C 0 And the unit is mAh/g, and the voltage change rate of the lithium ion battery is K 0 ，S 1 ＝58.4％，S 2 ＝19％，S 0 ＝0，V 1 、V 2 、V 0 The voltages of the lithium ion battery at 58.4% SOC, 19% SOC and 0% SOC are respectively shown as V 0 2.5V; the lithium ion battery satisfies the following relation: k is not less than 6 0 ×C 0 /1000≤12。
Optionally, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode plate, the positive electrode active material layer contains a positive electrode active material, and the voltage change rate of the button cell having the positive electrode active material is K c ，S 3 ＝50％，S 4 ＝7％，S 0 ＝0，V 3 、V 4 、V 0 Respectively represent the voltage of the button cell at 50% SOC, 7% SOC and 0% SOC, and V 0 2.5V; k (K) c Satisfies K of 35 to less than or equal to c ≤90。
Alternatively, K c And K is equal to 0 The following relationship is also satisfied: k (K) c -K 0 ≥18。
Alternatively, the positive electrode active material layer has an areal density CW 1 The following relationship is satisfied: 13g/mm 2 ≤CW 1 ≤27g/mm 2 ；
And/or the gram capacity of the positive electrode active material is 140 mAh/g-160 mAh/g;
and/or the mass ratio of the positive electrode active material in the positive electrode active material layer is 90.0-99.5%;
and/or, the positive electrode active material comprises a lithium iron phosphate material.
Optionally, the negative electrode is activeGram volume C of sex substance 0 320 mAh/g-370 mAh/g.
Alternatively, the surface density CW of the anode active material layer 2 The following relationship is satisfied: 5.2g/mm 2 ≤CW 2 ≤15.2g/mm 2 ；
And/or the mass ratio of the negative electrode active material in the negative electrode active material layer is 90.0-99.5%;
and/or the negative electrode active material is at least one selected from graphite, soft carbon, hard carbon, silicon-based material and lithium titanate.
Optionally, the anode active material layer further includes a conductive agent;
the mass ratio of the conductive agent in the anode active material layer is 0.2-3%;
the conductive agent is at least one selected from Super-P, ketjen black, conductive graphite, carbon nanotubes or carbon nanofibers.
In a second aspect, embodiments of the present application provide a screening method for screening a lithium ion battery, where the lithium ion battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, wherein the negative electrode active material layer contains a negative electrode active material; the diaphragm is arranged between the positive pole piece and the negative pole piece, and the diaphragm, the positive pole piece and the negative pole piece form an electrode assembly; at least partially infiltrating the electrode assembly with the electrolyte;
the screening method comprises the following steps:
obtaining gram Capacity C of the negative electrode active Material 0 The method comprises the steps of carrying out a first treatment on the surface of the Wherein C is 0 Is mAh/g;
obtaining the voltage V of the lithium ion battery at 58.4% SOC 1 ；
Obtaining the voltage V of the lithium ion battery at 19% SOC 2 ；
According to the voltage V 1 And the voltage V 2 Obtaining the voltage change rate K of the lithium ion battery 0 The method comprises the steps of carrying out a first treatment on the surface of the Wherein,S 1 ＝58.4％，S 2 ＝19％，S 0 ＝0，V 0 2.5V;
according to the following relation: k is not less than 6 0 ×C 0 And (3) screening the lithium ion battery, wherein/1000 is less than or equal to 12.
Optionally, the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer arranged on the positive electrode plate, wherein the positive electrode active material layer contains a positive electrode active material;
the screening method further comprises the steps of:
obtaining a button cell having the positive electrode active material;
obtaining the voltage V of the button cell at 50% SOC 3 ；
Obtaining the voltage V of the button cell at 7% SOC 4 ；
According to the voltage V 3 And the voltage V 4 Obtaining the voltage change rate K of the button cell c The method comprises the steps of carrying out a first treatment on the surface of the Wherein,S 3 ＝50％，S 4 ＝7％，S 0 ＝0，V 0 2.5V;
according to the following relation: k is not less than 35 c And (3) screening the positive electrode active material less than or equal to 90.
Optionally, the screening method further comprises:
according to the following relation: k (K) c -K 0 And (3) not less than 18, and screening the lithium ion battery.
In a third aspect, embodiments of the present application provide a battery pack having a lithium ion battery as described in the first aspect or a lithium ion battery screened by a screening method as described in the second aspect.
In a fourth aspect, embodiments of the present application provide an energy storage device comprising a battery pack as in the third aspect.
In a fifth aspect, embodiments of the present application provide a powered device, including an energy storage device as described in the fourth aspect.
Compared with the prior art, the invention has the beneficial effects that:
the embodiment of the application provides a lithium ion battery, wherein the gram capacity of a negative electrode active material of the lithium ion battery and the voltage change rate of the lithium ion battery meet the following relational expression: k is not less than 6 0 ×C 0 1000 is less than or equal to 12; the lithium ion battery meeting the relation formula has good multiplying power performance and higher energy density, namely the lithium ion battery can simultaneously take the two characteristics of energy density and multiplying power performance which are difficult to balance into consideration, and the lithium ion battery also has the advantages of small polarization and excellent overdischarge resistance.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a method flow diagram of a screening method of the present application;
FIG. 2 is another method flow diagram of a screening method of the present application;
fig. 3 is a flow chart of yet another method of screening according to the present application.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
For lithium ion batteries, energy density and rate capability are two important performance indicators. The simple realization of high rate performance or high energy density of lithium ion batteries is not difficult, and has the difficulty that the rate performance and the energy density are simultaneously considered, and in general, the rate performance and the energy density are mutually contradictory, and the balance between the rate performance and the energy density is very difficult to find. One of the reasons is that variations in the properties of the individual materials can lead to improvements in one of energy density and rate capability while the other is reduced. For example, the energy density of the battery is improved at present, the improvement of the compaction density and gram capacity of the material is mainly realized, the volume energy density of the battery can be obviously improved, but the problems of poor conduction of positive and negative active substances, difficult infiltration of electrolyte and the like are also brought, and the rate capability of the battery is further influenced.
On the other hand, the energy density and rate performance are affected by various material properties in the battery, for example, the ratio of the positive electrode active material, the ratio of the negative electrode active material, the gram capacity of the positive electrode active material, the gram capacity of the negative electrode active material, and the like have an influence on the energy density of the battery. The design of lithium ion batteries that compromise energy density and rate capability involves a variety of material property changes.
The above causes difficulty in designing a lithium ion battery having both high energy density and high rate performance.
Based on the above analysis, the present application provides a lithium ion battery whose gram capacity of a negative electrode active material and its voltage change rate satisfy the following relational expression: k is not less than 6 0 ×C 0 1000 is less than or equal to 12; the inventor researches and discovers that the lithium ion battery meeting the relation formula has good multiplying power performance and higher energy density.
The technical scheme of the present invention will be described below with reference to examples and drawings.
In a first aspect, embodiments of the present application provide a lithium ion battery, including a positive electrode tab, a negative electrode tab, a separator, and an electrolyte.
The negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, wherein the negative electrode active material layer contains a negative electrode active material. The diaphragm is arranged between the positive pole piece and the negative pole piece, and the diaphragm, the positive pole piece and the negative pole piece form an electrode assembly. The electrolyte wets at least a portion of the electrode assembly.
Wherein the gram capacity of the negative electrode active material is C 0 And the unit is mAh/g, and the voltage change rate of the lithium ion battery is K 0 ，S 1 ＝58.4％，S 2 ＝19％，S 0 ＝0，V 1 、V 2 、V 0 The voltages of the lithium ion battery at 58.4% SOC, 19% SOC and 0% SOC are shown as V 0 2.5V; the lithium ion battery satisfies the following relation: k is not less than 6 0 ×C 0 /1000≤12。
When K is more than or equal to 6 0 ×C 0 When the ratio of the lithium ion battery to the lithium ion battery is less than or equal to 12, the lithium ion battery has good multiplying power performance, higher energy density and better safety performance. The specific analysis is as follows:
rate of change of voltage K of lithium ion battery 0 The lithium ion battery has a great relation with the anode active material, and on one hand, when the multiplying power performance of the anode active material is poor, the lithium ion battery has larger polarization under the discharge of the corresponding multiplying power. When the polarization of the lithium ion battery is larger, the voltage of the lithium ion battery deviates from the discharge voltage of the material system, thereby leading to the voltage change rate K of the lithium ion battery 0 The larger will be. In other words, K 0 Can reflect the polarization degree, K of the lithium ion battery to a certain extent 0 And if the lithium ion battery is larger, the lithium ion battery has larger polarization and poor rate capability. K (K) 0 Is too large to cause K 0 ×C 0 Larger/1000, and thus at K 0 ×C 0 A larger/1000 may indicate poor rate performance of the battery. And the inventors found through extensive studies that when K 0 ×C 0 When the ratio of the lithium ion battery to the lithium ion battery is more than 1000, the charge and discharge curves of the lithium ion battery are not smooth, the voltage change is quick, the capacity of the lithium ion battery is difficult to release completely, and the multiplying power performance of the lithium ion battery is reduced.
On the other hand, when the voltage change of the battery is gentle, the voltage change rate of the battery is small, the negative electrode active material tends to have a larger interlayer spacing, and cause compaction thereofThe density and gram capacity decrease, and the lithium ion battery energy density is finally caused to decrease due to the fact that the lithium ion battery energy density is in direct proportion to the compacted density and gram capacity of the negative electrode active material. And the inventors found through extensive studies that when K 0 ×C 0 At/1000 < 6, the compacted density and gram capacity of the negative electrode active material are low, and thus the energy density of the lithium ion battery is lowered.
To sum up, K 0 ×C 0 If/1000 is larger, the multiplying power performance of the battery is poor, K 0 ×C 0 If/1000 is smaller, the energy density of the battery is poorer, and only when the lithium ion battery meets K which is less than or equal to 6 0 ×C 0 And when the ratio of the energy density to the multiplying power is less than or equal to 12, the lithium ion battery can achieve both the energy density and the multiplying power performance.
The rate performance of a lithium ion battery has a great relationship with the properties of the anode active material, while the gram capacity of the anode active material directly relates to the energy density of the battery, so that the selection of an appropriate anode active material is greatly helpful for improving the energy density and rate performance of the battery. More specifically, the higher the gram capacity of the anode active material means that more lithium ions can be accommodated with less anode material by mass, thereby improving energy density. Preferably, gram capacity C of the anode active material 0 Any point in the gram capacity range is included between 320mAh/g and 370mAh/g, such as 320mAh/g, 350mAh/g, or 370mAh/g.
Further, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on the positive electrode sheet, wherein the positive electrode active material layer contains a positive electrode active material, and the voltage change rate of the button cell with the positive electrode active material is K c ，S 3 ＝50％，S 4 ＝7％，S 0 ＝0，V 3 、V 4 、V 0 Respectively represent the voltage of the button cell at 50% SOC, 7% SOC and 0% SOC, and V 0 2.5V; k (K) c Satisfies K of 35 to less than or equal to c ≤90。
Since the full cell voltage is determined by the positive and negative electrodesThe voltage change rate K of the half cell is determined relative to the voltage change rate of the full cell c The characteristics of the positive electrode active material can be reacted alone. Further, the voltage change rate K of a half cell made of the positive electrode active material c The polarization properties of the positive electrode active material were evaluated alone.
When K is c When the voltage is more than 90, the polarization of the reactive positive electrode active material is larger, the voltage change in the discharging process is large, and the corresponding rate performance is poor. When K is c At less than 35, the density and gram-capacity of the positive electrode active material decrease, the battery energy is directly proportional to the density and gram-capacity of the positive electrode active material, and eventually the battery energy density decreases.
In conclusion, only K c In the appropriate numerical interval, i.e. K c Satisfies K of 35 to less than or equal to c When the energy density is less than or equal to 90, the lithium ion battery can further give consideration to the characteristics of difficult balance of multiplying power performance and energy density.
Further, K c And K is equal to 0 The following relationship is also satisfied: k (K) c -K 0 And (3) when the relational expression is satisfied, the anode active material releases more capacity in a slope area at the ending stage of the voltage platform, and absorbs lithium correspondingly with more defects, so that the anode active material has better low-temperature charge-discharge performance.
Further, the surface density CW of the positive electrode active material layer 1 The following relationship is satisfied: 13g/mm 2 ≤CW 1 ≤27g/mm 2 ；
And/or the gram capacity of the positive electrode active material is 140mAh/g to 160mAh/g, including any point value within the gram capacity range, for example 140mAh/g, 150mAh/g or 160mAh/g;
and/or the positive electrode active material having a mass ratio of 90.0% to 99.5% in the positive electrode active material layer includes any point value within the mass ratio range, for example, 90.0%, 95% or 99.5%.
Positive electrode capacity per unit area = gram capacity of positive electrode active material x areal density of positive electrode active material layer x mass ratio of positive electrode active material. In other words, by selecting the above numerical range, a positive electrode capacity per unit area that is stable within a certain numerical range can be obtained.
Preferably, the positive electrode active material comprises a lithium iron phosphate material, also known as LFP (Lithium Iron Phosphate) or LiFePO 4 . The lithium iron phosphate battery can be used in the temperature range of-20 ℃ to 60 ℃ and has strong adaptability. Due to its stable chemical properties, lithium iron phosphate batteries generally have a long cycle life of over 2000 times.
Further, the surface density CW of the anode active material layer 2 The following relationship is satisfied: 5.2g/mm 2 ≤CW 2 ≤15.2g/mm 2 ；
And/or the mass ratio of the anode active material in the anode active material layer is 90.0% to 99.5%, including any point value in the mass ratio range, for example, 90.0%, 95.0% or 99.5%.
Unit area anode capacity=gram capacity of anode active material×area density of anode active material layer×mass ratio of anode active material. In other words, by selecting the above-mentioned numerical ranges, a negative electrode capacity per unit area that is stable within a certain numerical range can be obtained, and a positive electrode capacity per unit area that is also stable within a certain numerical range can be obtained, and since the lithium ion battery N/P ratio=negative electrode capacity per unit area/positive electrode capacity per unit area, an N/P ratio that is stable within a certain numerical range can be obtained. The proper N/P ratio is beneficial to improving the multiplying power performance and the cycle performance of the lithium ion battery.
Alternatively, the negative electrode active material is selected from at least one of graphite, soft carbon, hard carbon, a silicon-based negative electrode material, and a lithium titanate negative electrode material.
Further, the anode active material layer further includes a conductive agent. When the content of the conductive agent is too low, the internal resistance of the pole piece of the lithium ion battery is larger, and the polarization of the lithium ion battery is larger, so that the voltage of the lithium ion battery is quickly reduced to the discharge cut-off voltage; increasing the mass ratio of the conductive agent is advantageous for improving conductivity and thus improving rate performance, but an excessive mass ratio of the conductive agent may cause a decrease in the mass ratio of other components of the anode active material layer, for example, the anode active material, and thus affect properties such as energy density. Preferably, the mass ratio of the conductive agent in the anode active material layer is 0.2% to 3% including any point value in the mass ratio range, for example, 0.2%, 1% or 3%.
Optionally, the conductive agent is selected from at least one of Super-P (Super carbon black), ketjen black, conductive graphite, carbon nanotubes or carbon nanofibers.
In a second aspect, embodiments of the present application provide a screening method for screening a lithium ion battery including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, wherein the negative electrode active material layer contains a negative electrode active material. The diaphragm is arranged between the positive pole piece and the negative pole piece, and the diaphragm, the positive pole piece and the negative pole piece form an electrode assembly. The electrolyte wets at least a portion of the electrode assembly.
As shown in fig. 1, the screening method includes:
s1, obtaining gram volume C of the negative electrode active material 0 The method comprises the steps of carrying out a first treatment on the surface of the Wherein C is 0 Is mAh/g;
s2, obtaining voltage V of the lithium ion battery at 58.4% SOC 1 ；
S3, obtaining the voltage V of the lithium ion battery at 19% SOC 2 ；
S4, according to voltage V 1 And voltage V 2 Obtaining the voltage change rate K of the lithium ion battery 0 The method comprises the steps of carrying out a first treatment on the surface of the Wherein,S 1 ＝58.4％，S 2 ＝19％，S 0 ＝0，V 0 2.5V;
s5, according to the following relation: k is not less than 6 0 ×C 0 And (3) screening lithium ion batteries, wherein/1000 is less than or equal to 12.
As described above, K 0 ×C 0 If/1000 is larger, the multiplying power performance of the battery is poor, K 0 ×C 0 If/1000 is smaller, the energy density of the battery is poorer, and only when the lithium ion battery meets K which is less than or equal to 6 0 ×C 0 When the ratio of the lithium ion to the lithium ion is not more than 1000 and not more than 12The battery can give consideration to both energy density and rate capability.
Optionally, the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer arranged on the positive electrode plate, wherein the positive electrode active material layer contains a positive electrode active material;
further, as shown in fig. 2, the screening method further includes:
s6, obtaining a button cell with a positive electrode active material;
s7, obtaining the voltage V of the button cell at 50% SOC 3 ；
S8, obtaining the voltage V of the button cell at 7% SOC 4 ；
S9, according to voltage V 3 And voltage V 4 Obtaining the voltage change rate K of the button cell c The method comprises the steps of carrying out a first treatment on the surface of the Wherein,S 3 ＝50％，S 4 ＝7％，S 0 ＝0，V 0 2.5V;
s10, according to the following relation: k is not less than 35 c And (3) screening the positive electrode active material less than or equal to 90.
In step S10, when K c When the voltage is more than 90, the polarization of the reactive positive electrode active material is larger, the voltage change in the discharging process is large, and the corresponding rate performance is poor. When K is c At less than 35, the density and gram-capacity of the positive electrode active material decrease, the battery energy is directly proportional to the density and gram-capacity of the positive electrode active material, and eventually the battery energy density decreases. In conclusion, only K c In the appropriate numerical interval, i.e. K c Satisfies K of 35 to less than or equal to c When the energy density is less than or equal to 90 percent, the lithium ion battery can further consider the multiplying power performance and the energy density.
Further, as shown in fig. 3, the screening method further includes:
s11, according to the following relation: k (K) c -K 0 And (3) not less than 18, and screening the lithium ion battery.
In step S11, when the above relation is satisfied, the negative electrode active material will release more capacity in the slope region of the ending stage of the voltage plateau, and will absorb lithium correspondingly with more defects, so that it will have better low-temperature charge-discharge performance.
In a third aspect, embodiments of the present application provide a lithium ion battery having a lithium ion battery as described in the first aspect or a lithium ion battery screened by a screening method as described in the second aspect.
In a fourth aspect, embodiments of the present application provide an energy storage device comprising a battery pack as described in the third aspect.
In a fifth aspect, embodiments of the present application provide a powered device, including an energy storage device as described in the fourth aspect.
The technical scheme of the present invention will be described below with reference to examples and comparative examples.
The lithium ion batteries of each example and comparative example were prepared as follows, including the following steps:
1) Preparing a positive electrode plate: lithium iron phosphate (molecular formula is LiFePO) 4 ) Fully stirring and mixing the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) in a proper amount of N-methyl pyrrolidone (NMP) solvent according to a weight ratio of 96:2:2 so as to form uniform anode slurry; and (3) coating the slurry on an aluminum foil of the positive electrode current collector, and drying and cold pressing to obtain the positive electrode plate.
2) Preparing a negative electrode plate: mixing a negative electrode active material (graphite), a conductive agent (super P), a thickening agent (CMC) and a binder (SBR) according to the solid content ratio of 96 percent to 1 percent to 2 percent with a solvent to obtain a negative electrode active layer slurry; coating the negative electrode active layer slurry on a negative electrode current collector with a conductive coating by adopting a die head extrusion coater, drying to obtain an unrerolled negative electrode plate, and rolling the negative electrode plate according to a designed compaction density by a roller press to obtain the negative electrode plate with a negative electrode active material layer with a specific thickness; wherein, anode active material layer = area density of anode active material x compacted density of anode active material.
3) Selection of a diaphragm: the PE porous polymer film is used as a diaphragm.
4) Preparing an electrolyte:mixing Ethylene Carbonate (EC) with diethyl carbonate (DEC) in a volume ratio of 3:7, followed by a sufficiently dry lithium salt LiPF 6 Dissolving in a mixed organic solvent according to a proportion of 1mol/L, and finally adding 2wt% of fluoroethylene carbonate (FEC) based on the basic electrolyte to prepare the electrolyte.
5) Preparation of a lithium ion battery: sequentially stacking the positive electrode plate, the isolating membrane and the negative electrode plate, enabling the diaphragm to be positioned between the positive electrode plate and the negative electrode plate to play a role of isolation, and then winding to obtain a bare cell; and placing the bare cell in an outer packaging foil, injecting the electrolyte prepared by the method into the dried cell, and performing the procedures of vacuum packaging, standing, formation, shaping and the like to prepare the lithium ion cell.
The preparation method for manufacturing the button cell by using the negative electrode active materials in the lithium ion batteries of the examples and the comparative examples comprises the following steps:
(1) preparation of button cell negative pole piece
Taking 5 lithium ion batteries (discharged to 2.0V) in a full discharge state, disassembling the lithium ion batteries, and taking out a negative electrode plate; soaking 30g of negative electrode plate in 200mL of pure water, slightly stirring for 1 minute, taking out the copper foil after all active substances on the surface of the foil fall off, stirring the solution for 30 minutes, and ensuring that all active substances are dispersed, wherein no macroscopic agglomerated particles exist inside; standing for 6 hours to enable most of solid substances to be deposited at the bottom of the container, and pouring out the upper layer solution; 200mL of water was added again, stirred for 30 minutes and left to stand for 6 hours, the solution was poured out, the above steps were repeated 3 times, and the lower precipitate was placed in an oven at 60℃or higher for 6 hours until it was dried. The bulk precipitate was ground for 15 minutes or more until no significant agglomerates were present therein, to obtain a negative electrode active material as a uniform powder.
Mixing the anode active material, the conductive agent, the thickening agent and the binder which are obtained in the previous step with a solvent according to the solid content ratio of 94.5 percent to 1.5 percent to obtain slurry, uniformly coating the slurry on copper foil with the thickness of 8 mu m by using 200 mu m film scraping equipment, baking the copper foil in an oven with the temperature of above 60 ℃ for 6 hours, and using a roll squeezer according to the thickness of 1.2g/cm 3 ～1.7g/cm 3 And (3) rolling, and punching by using a punching machine with the diameter of 1.2cm to obtain the negative electrode plate of the button cell.
(2) Preparation of button cell
Assembling a button cell negative electrode plate and a diaphragm, a metal lithium wafer and electrolyte into a CR 2032 button cell, wherein the electrolyte is LiPF 6 Dissolving in a mixed organic solvent according to a ratio of 1mol/L, and finally adding 2wt% of fluoroethylene carbonate (FEC) based on the basic electrolyte to prepare the obtained electrolyte.
The preparation method for preparing the button cell by using the positive electrode active materials in the lithium ion batteries of the examples and the comparative examples comprises the following steps:
(1) preparation of button cell positive pole piece
And removing the positive electrode plate of the lithium ion battery in a full discharge state, taking 100g of positive electrode plate, soaking the positive electrode plate for 4 hours by using DMC solvent, and then baking the positive electrode plate for more than 6 hours in a baking oven at 60-90 ℃. And (3) dipping the dust-free paper into a 75% ethanol solution to scrub one surface of the pole piece until no obvious active substance residue exists on the corresponding surface, and then drying, and punching the pole piece into a 1.2 cm-diameter single-sided pole piece by using a 1.2 cm-diameter punching machine to obtain the button cell positive pole piece.
(2) Preparation of button cell
Assembling a button cell positive electrode plate and a diaphragm, a metal lithium wafer and electrolyte into a CR 2032 button cell, wherein the electrolyte is LiPF 6 Dissolving in a mixed organic solvent according to a ratio of 1mol/L, and finally adding 2wt% of fluoroethylene carbonate (FEC) based on the basic electrolyte to prepare the obtained electrolyte.
Gram Capacity C of negative electrode active Material in lithium ion batteries of examples and comparative examples 0 The procedure is as follows:
the assembled button cell was tested on a test system using the following test method:
after the battery was left to stand for 4 hours, constant current discharge was performed at a current of 0.1C to 0.005V and left to stand for 10 minutes; then discharged to 0.005V at a current of 0.05mA and left to stand for 10 minutes; then it was discharged to 0.005V at a current of 0.01mA and left to stand for 10 minutes; the battery was charged to 2V at a current density of 0.1C, and the gram capacity obtained by the final charging process was taken as the gram capacity of the negative electrode active material.
The gram capacity test of the positive electrode active material in the lithium ion batteries of each example and comparative example was performed as follows:
the assembled button cell was tested on a test system using the following test method: after the battery is kept stand for 4 hours, constant power charging is carried out to 3.75V at the power of 0.1P and the battery is kept stand for 10 minutes; then constant power discharge is carried out to 2.5V with the power of 0.1P and the mixture is kept stand for 10 minutes; the above steps were repeated once, with the gram-discharge capacity of the second cycle as the gram-discharge capacity of the positive electrode active material.
Voltage change Rate K of lithium ion batteries of examples and comparative examples 0 The procedure is as follows:
taking 5 batteries, charging the batteries to 3.65V at constant current of 0.33C, then charging the batteries at constant voltage of 3.65V until the current is less than or equal to 0.05C, then discharging the batteries to 2.5V at constant current of 0.33C, repeating the steps for two times, taking the discharge capacity of C for the second time 2 The discharge capacity is (100-X)%C during discharge 2 The state is the X% SOC state of the battery, X=58.4, 19, 0, and the battery has a relationship between voltage and capacity during discharging, so that the voltage of the battery in a certain SOC state, namely 58.4% SOC, 19% SOC and 0% SOC, can be determined 1 、V 2 、V 0 . According toObtaining the voltage change rate K 0 The method comprises the steps of carrying out a first treatment on the surface of the Wherein S is 1 ＝58.4％，S 2 ＝19％，S 0 ＝0，V 0 Is 2.5V.
Voltage change rate K of button cell made of positive electrode active material in lithium ion batteries of examples and comparative examples c The procedure is as follows:
the voltage-gram capacity data of the second circle is extracted from the gram capacity test of the positive electrode active material in the lithium ion battery and is used as the first circleThe discharge data of the two circles is used as SOC calculation logic, and the state of 2.5V is 0% SOC, and the state of 3.75V is 100% SOC, according to the following conditionsObtaining the voltage change rate K of the button cell c The method comprises the steps of carrying out a first treatment on the surface of the Wherein S is 3 ＝50％，S 4 ＝7％，S 0 ＝0；V 3 、V 4 、V 0 Respectively represent the voltage of the button cell at 50% SOC, 7% SOC and 0% SOC, and V 0 Is 2.5V.
The powder compaction density of the negative electrode active material in each of the lithium ion batteries of examples and comparative examples was tested as follows:
the powder was subjected to a powder compaction test using a compaction densitometer (force test LD 43.305) by placing 1g of the negative electrode active material into a grinding tool at a displacement speed of 10mm/min under a pressure of 49000N, and the compaction density in this state was taken as the powder compaction density for 30 seconds.
Surface Density CW of negative electrode active material of each example and comparative example 2 The procedure is as follows:
copper foil in preparation process of buckling electrode plate is taken, and die head area is 1540.25mm 2 The round sheet punching machine is used for punching sheets, 10 sheets are obtained by repeated sheet punching, and the unit area mass M1 of the copper foil is obtained by taking the average value.
Taking a fully discharged lithium ion battery negative electrode plate, soaking the lithium ion battery negative electrode plate in DMC (dimethyl carbonate) immersed negative electrode plate for 12h, placing the lithium ion battery negative electrode plate in a 60-90 ℃ oven for fully drying, and using a die head with the area of 1540.25mm 2 The round sheet punching machine is used for punching sheets, 10 sheets are obtained by repeated sheet punching, and the average value is taken to obtain the average mass M2 and the surface density CW of the sheet 2 ＝(M2-M1)/1540.25/2。
Surface Density CW of the cathode active materials of each example and comparative example 1 The procedure is as follows:
disassembling the positive pole piece after the battery is fully put, soaking for 30min by using pure water, removing positive active substances, scrubbing the two sides of the aluminum foil by using 75% ethanol and dust-free paper after the clean aluminum foil is obtained, and further removing the positive pole on the surface of the aluminum foilAnd (3) the polar active material is baked for 30min at 60 ℃ and the aluminum foil is dried. The die area was then used as 1540.25mm 2 The round sheet punching machine is used for punching sheets, 10 sheets are obtained by repeated sheet punching, and the unit area mass M3 of the aluminum foil is obtained by taking the average value.
Taking a fully charged positive electrode plate of a lithium ion battery, soaking the positive electrode plate in DMC (dimethyl carbonate) immersed positive electrode plate for 12 hours, putting the positive electrode plate in a 60-90 ℃ oven for complete drying, and using a die head with the area of 1540.25mm 2 The round sheet punching machine is used for punching sheets, 10 sheets are obtained by repeated sheet punching, and the average value is taken to obtain the average mass M4 and the surface density CW of the sheet 1 ＝(M4-M3)/1540.25/2。
The lithium ion batteries of each example and comparative example were measured for lithium separation rate, cycle performance (5000 cycles), capacity retention at-20 ℃ and battery energy density, and the test methods were as follows:
(1) lithium ion battery lithium-out power test
Ten lithium ion batteries prepared from the active materials of the comparative examples and the examples are taken, the batteries are placed at 25 ℃ for 1 hour, two batteries are taken as one group, and constant power charging of 0.8P,1P,1.2P,1.4P,1.6P,1.8P,2P and 2.2P to 3.65V is respectively carried out according to the groups; standing for 30min, discharging to 2.5V with constant power of 0.8P,1P,1.2P,1.4P,1.6P,1.8P,2P and 2.2P respectively, standing for 30min, charging to 3.65V with constant power of 0.8P,1P,1.2P,1.4P,1.6P,1.8P,2P and 2.2P respectively according to the groups after 10 times of charge-discharge cycles, and then disassembling the battery to observe the lithium precipitation condition of the surface of the negative electrode respectively.
And (3) judging the lithium precipitation degree: the negative electrode is judged according to the state of fully charged and disassembled, and when the whole negative electrode is displayed as golden yellow and the area of the negative electrode displayed as silver gray is less than 2 percent, the negative electrode is judged to be free from lithium precipitation; and when the whole negative electrode is golden yellow and the area of silver gray is more than or equal to 2%, judging that lithium is separated.
(2) And (3) testing the cycle performance of the lithium ion battery:
the lithium ion batteries prepared using all of the comparative examples and examples were each taken 5 and averaged. The lithium ion battery was repeatedly charged and discharged by the following steps, and the discharge capacity retention rate of the lithium ion battery was calculated.
Firstly, carrying out first charge and discharge in an environment of 25 ℃, carrying out constant power charge under the charge power of 1P until reaching an upper limit voltage of 3.65V, converting into constant voltage charge, then carrying out constant power discharge under the discharge power of 1P until reaching a final voltage of 2.5V, repeating twice, and recording the discharge capacity of a second cycle; then 5000 charge and discharge cycles were performed, and the discharge capacity at 5000 th cycle was recorded.
Cycle 5000 cycles capacity retention= (discharge capacity of 5000 th cycle/discharge capacity of second cycle) ×100%.
The lithium ion batteries of the examples and comparative examples were tested for lithium separation rate, cycle performance (5000 cycles), capacity retention at-20 ℃ and energy density of the lithium ion batteries, and the results are shown in table 1.
TABLE 1 test results for lithium ion batteries of examples and comparative examples
As can be seen from the data of comparative example 1 and comparative example 1, K in comparative example 1 0 ×C 0 1000 is 12.2, namely K 0 ×C 0 And/1000 > 12, the lithium ion battery of comparative example 1 has an uneven charge-discharge curve, a rapid voltage change, a difficult total discharge of battery capacity, and a decrease in rate capability of the battery, and the lithium separation rate of comparative example 1 is only 0.6C although the battery energy density of comparative example 1 is 164 Wh/kg. Whereas the lithium deposition rate of example 1 was as high as 2C, the energy density was also as high as 166Wh/kg. It is apparent that example 1 gives a compromise between energy density and rate capability relative to comparative example 1. Likewise, each of the embodiments satisfies K 0 ×C 0 The lithium precipitation rate of each example was also higher than that of comparative example 1 by 1000.ltoreq.12, which is enough to indicate K 0 ×C 0 And when the ratio of the ratio to the total power of the lithium ion battery is less than or equal to 12, the lithium ion battery has better multiplying power performance.
Further, in combination with the test results of example 3, K of example 3 0 ×C 0 And/1000 is11.6, the lithium ion separation rate of example 3 still remains 1.4C. While in comparative example 1K 0 ×C 0 The difference between/1000 and example 3 is only 0.6, however, the lithium separation rate of comparative example 1 had been reduced to 0.6C. Further shows that the lithium separation multiplying power and K 0 ×C 0 The magnitude of the value/1000 is not linear, when K 0 ×C 0 And when the ratio of the lithium to the anode is/1000 is more than 12, the lithium precipitation multiplying power is greatly changed. Further combining the test data of comparative example 3, K in comparative example 3 0 ×C 0 The lithium precipitation rate of comparative example 3 was reduced to 0.4C with a value of 13.4/1000, indicating that with K 0 ×C 0 And/1000 is further increased, and the lithium separation rate is further reduced.
As can be seen from the data of comparative example 1 and comparative example 2, K in comparative example 2 0 ×C 0 1000 is 5.9, K of comparative example 2 0 ×C 0 Rate of change of voltage K of comparative example 2 with/1000 < 6 0 The surface negative electrode active material has larger interlayer spacing and causes the reduction of the compacted density and gram capacity, and the energy density of the lithium ion battery is reduced by 153Wh/kg because the energy density of the lithium ion battery is in direct proportion to the compacted density and gram capacity of the negative electrode active material. In contrast, example 1 has an energy density as high as 166Wh/kg, and example 1 also has a higher lithium separation rate than comparative example 2.
From the test data of example 4 and comparative example 2, it is understood that the voltage change rates K of example 4 and comparative example 2 0 The difference is not large, but the K of example 4 c K greater than comparative example 2 c Example 4 satisfies 35.ltoreq.K c Is less than or equal to 90 and also meets the K c -K 0 And more than or equal to 18. Whereas comparative example 2 does not satisfy 35.ltoreq.K c Less than or equal to 90 and not meeting K c -K 0 And more than or equal to 18. The lithium-ion power and the battery energy density of example 4 were both superior to those of comparative example 2, which suggests that the positive electrode active material of example 4 was lower in polarization degree than that of comparative example 2, so that the lithium-ion power and the battery energy density could be further improved. The capacity retention at-20deg.C of example 4 is superior to comparative example 2, indicating that K is satisfied c -K 0 When the temperature is more than or equal to 18, the anode active material releases more capacity in a slope area at the ending stage of the voltage platform and absorbs lithium correspondingly with more defects, so thatThe battery has better low-temperature charge and discharge performance.
The above describes a lithium ion battery, a screening method, a battery pack, an energy storage device and electric equipment in detail, and specific examples are applied to describe the principle and implementation of the present invention, and the description of the above embodiment is only used to help understand the lithium ion battery, the screening method, the battery pack, the energy storage device and the electric equipment and the core ideas thereof. Meanwhile, as those skilled in the art will vary in the specific embodiments and application scope according to the idea of the present invention, the present disclosure should not be construed as limiting the present invention in summary.
Claims (13)
1. A lithium ion battery, comprising:
a positive electrode sheet;
the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, wherein the negative electrode active material layer contains a negative electrode active material;
the diaphragm is arranged between the positive pole piece and the negative pole piece, and the diaphragm, the positive pole piece and the negative pole piece form an electrode assembly; and
an electrolyte, the electrolyte wetting at least a portion of the electrode assembly; wherein the gram capacity of the negative electrode active material is C 0 And the unit is mAh/g, and the voltage change rate of the lithium ion battery is K 0 ，S 1 ＝58.4％，S 2 ＝19％，S 0 ＝0，V 1 、V 2 、V 0 The voltages of the lithium ion battery at 58.4% SOC, 19% SOC and 0% SOC are respectively shown as V 0 2.5V; the lithium ion battery satisfies the following relation: k is not less than 6 0 ×C 0 /1000≤12。
2. According toThe lithium ion battery of claim 1, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode sheet, the positive electrode active material layer comprising a positive electrode active material, the rate of change of voltage of the button cell having the positive electrode active material being K c ，S 3 ＝50％，S 4 ＝7％，S 0 ＝0，V 3 、V 4 、V 0 Respectively represent the voltage of the button cell at 50% SOC, 7% SOC and 0% SOC, and V 0 2.5V; k (K) c Satisfies K of 35 to less than or equal to c ≤90。
3. The lithium ion battery of claim 2, wherein K c And K is equal to 0 The following relationship is also satisfied: k (K) c -K 0 ≥18。
4. The lithium ion battery according to claim 2, wherein the positive electrode active material layer has an areal density CW 1 The following relationship is satisfied: 13g/mm 2 ≤CW 1 ≤27g/mm 2 ；
And/or the gram capacity of the positive electrode active material is 140 mAh/g-160 mAh/g;
and/or the mass ratio of the positive electrode active material in the positive electrode active material layer is 90.0-99.5%;
and/or, the positive electrode active material comprises a lithium iron phosphate material.
5. The lithium ion battery according to any one of claims 1 to 4, wherein the gram capacity C of the anode active material 0 320 mAh/g-370 mAh/g.
6. The lithium ion battery according to any one of claims 1 to 4, wherein the anode active material layer has an areal density CW 2 The following is satisfiedThe formula: 5.2g/mm 2 ≤CW 2 ≤15.2g/mm 2 ；
And/or the mass ratio of the negative electrode active material in the negative electrode active material layer is 90.0-99.5%;
and/or the negative electrode active material is at least one selected from graphite, soft carbon, hard carbon, silicon-based material and lithium titanate.
7. The lithium ion battery according to any one of claims 1 to 4, wherein the anode active material layer further includes a conductive agent;
the mass ratio of the conductive agent in the anode active material layer is 0.2-3%;
the conductive agent is at least one selected from Super-P, ketjen black, conductive graphite, carbon nanotubes or carbon nanofibers.
8. The screening method is characterized by being used for screening lithium ion batteries, wherein the lithium ion batteries comprise positive pole pieces, negative pole pieces, diaphragms and electrolyte; the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, wherein the negative electrode active material layer contains a negative electrode active material; the diaphragm is arranged between the positive pole piece and the negative pole piece, and the diaphragm, the positive pole piece and the negative pole piece form an electrode assembly; at least partially infiltrating the electrode assembly with the electrolyte;
the screening method comprises the following steps:
obtaining gram Capacity C of the negative electrode active Material 0 The method comprises the steps of carrying out a first treatment on the surface of the Wherein C is 0 Is mAh/g;
obtaining the voltage V of the lithium ion battery at 58.4% SOC 1 ；
Obtaining the voltage V of the lithium ion battery at 19% SOC 2 ；
According to the voltage V 1 And the voltage V 2 Obtaining the voltage change rate K of the lithium ion battery 0 The method comprises the steps of carrying out a first treatment on the surface of the Wherein,S 1 ＝58.4％，S 2 ＝19％，S 0 ＝0，V 0 2.5V;
according to the following relation: k is not less than 6 0 ×C 0 And (3) screening the lithium ion battery, wherein/1000 is less than or equal to 12.
9. The screening method according to claim 8, wherein the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode sheet, the positive electrode active material layer containing a positive electrode active material;
the screening method further comprises the steps of:
obtaining a button cell having the positive electrode active material;
obtaining the voltage V of the button cell at 50% SOC 3 ；
Obtaining the voltage V of the button cell at 7% SOC 4 ；
According to the voltage V 3 And the voltage V 4 Obtaining the voltage change rate K of the button cell c The method comprises the steps of carrying out a first treatment on the surface of the Wherein,S 3 ＝50％，S 4 ＝7％，S 0 ＝0，V 0 2.5V;
according to the following relation: k is not less than 35 c And (3) screening the positive electrode active material less than or equal to 90.
10. The screening method of claim 9, further comprising:
according to the following relation: k (K) c -K 0 And (3) not less than 18, and screening the lithium ion battery.
11. A battery pack characterized by having the lithium ion battery according to any one of claims 1 to 7 or the lithium ion battery screened by the screening method according to any one of claims 8 to 10.
12. An energy storage device comprising the battery pack of claim 11.
13. A powered device comprising the energy storage device of claim 12.
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